Document NGEXE4O7zBN5QQKNrjgGRGyMR

REPRINTED FROM COPOLYMERIZATION Edited bj GEORGE E. HAM Spencer Chemical Company ' Merriam, Kansas INTERSCIENCE PUBLISHERS a division ofJohn Wiley & Sons NEW YORK * LONDON SYDNEY Copyright 1964 by John Wiley & Sofia, Inc. <9 AP00055697 CHARTER X. COPOLYMERIZATIONS EMPLOYING VINYL CHLORIDE OR VINYLIDENE CHLORIDE AS PRINCIPAL COMPONENTS James F. Gawjktt and W. Mayo Smith, Escambia Chemical Corporation, Wilton, Connecticut I. Copolymers Predominantly Vinyl Chloride The eopolyinerization of vinyl chloride with other monomers obtained its original impetus because of the belief that the iutractible nature and thermal instability of polyvinyl chloride provided a severe limitation to large scale exploitation of the hmnopolymer. The introduction of plasticizing side chains by eopolymerizuliun miiiimized these problems by decreasing the softening [joint of the poly mer. In more recent years the emergence of easy processing homupolymers of vinyl chloride was made possible through improved tech niques of molecular weight regulation and the development of im proved stabilizers and plasticizers. This has eliminated much of the original need for internally plasticized resins, but copolymers are still important in applications where superior melt flow characterisitics are desirable and little or no external plasticizer can be tolerated. II. Copolymers of Vinyl Chloride and Vinyl Acetate The copolymer of vinyl chloride and vinyl acetate is by far the most important of tire commercially available class of copolymers comprised principally of vinyl chloride. Copolymers containing from 3-4l)% vinyl acetate are offered for sale. Many of these resins are also available over a range of molecular weight to suit the particular needs of the consumer. In general, however, the vinyl acetate content of the copolymer is the more important cud use cuu- 5H7 AP00055698 I MS COPOI.VMliKIZA'JION- siderulion. Polymers containing 13% or more vinyl acetate are used in protective coatings, vinyl asbestos floor tile, flexible films, and compression molding where exceptional melt flow characteristics are important. Higher molecular weight copolymers with lower amounts of copolyiucrized vinyl acetate aTe useful for the prepara tion of a wide range of products including rigid sheeting, extruded rods and shapes, and calendered articles. In addition to the wide range of copolymers of this class available to the plastics industry, a number of modified vinyl chloride-vinyl acetate resins are used in protective coatings and decorative finishes where special properties are desired. Two of the more important resins of this class are modified by incorporation of a small amount of interpolymerized carboxyl compound such as maleic anhydride or by hydrolysis of a fraction of the acetate groups to provide hy droxyl groups along the polymer chain. The manufacture arid ap plication of these copolymers will be treated in the general discussion of chloride-acetate copolymers except for areas where specific dif ferences are important. 1. Preparation Vinyl chloride ami vinyl acetate copolyjnerize at moderate tem peratures to high conversions. Polymerization is usually initiated by a free-radical mechanism and the reactions may be carried out in mass, solution, suspension, or emulsion systems. Initiators most commonly employed are monomer soluble dialkyl or diaryl peroxides and diu/.r> compounds such as azobisisobutyronitrile. The choice of catalyst usually dejxmds on the polymerization temperature cho sen and determines to a large extent the duration of the reaction cycle. The use of acetyl benzoyl peroxide has been specified for polymerizations conducted at temperatures of 3(1--H)C. (25(i). while lauroyl or benzoyl peroxide is usually employed for ]>olymerizalions conducted at 5()-7(>C. Most producers use either aqueous suspension or continuous solu tion techniques. Emulsion systems are not commercially employed in the United States because of difficulties inherent in the removal of relatively large quantities of emulsifying agents and buffering salts which have a marked uffevt on the color um! clarity of the end prod ucts. Mass or bulk polymerizations, although capable of providing high purity resin, present a dillicult engineering problem due to j X. VIIVYJ. CHLORIDE OR VINYI.JliRNU CHLORIDE 1589 the highly exothermic nature of the reaction (30,(MX) BTU/lb./mol. of monomer) in polymerizing an undiluted mass of monomers. Solution Polymerization. Early development of vinyl chloride - vinyl acetate copolymers by the solution technique was initialed by the Union Carbide Chemicals Co. in about 192K. The earliest patent in the field was issued to Reid (239) in 1933. It described a copolymer of 22 parts vinyl chloride and 23 parts vinyl acetate prepared in the presence of 3 parts acetaldehyde and 50 parts sol vent. A later patent issued to Douglas in 1937 (78) described the preparation of copolymers of vinyl chloride and vinyl acetate in the ratio of about 4:1 by a continuous polymerization in a hydrocarbon which was a solvent for the monomers and a nonsolvent for the poly mer. The monomers were charged to a lead-Hued autoclave containing 4 parts butane to 1 part combined monomer and fitted with a pump capable of circulating the reaction mass through parallel filter presses. Polymerization was initiated with 0.5% benzoyl peroxide at a tem perature of 40C. As the copolymer formed in the system it was contained on one of the filter presses while additional monomers and initiator were added at a rate equivalent to monomer consumption. Filter presses were changed as they became loaded with polymer permitting uninterrupted continuation of the reaction. The fin ished polymer was dried by allowing residual butane to evaporate. The copolymer produced by this procedure was said to have unu sually good color because washing with water with subsequent lengthy drying at elevated temperature was avoided and thermal degrada tion was minimized. In theory it is possible to carry out solution copolymerization in diluents which are solvents for both the monomer and polymer, as well as in solvents which dissolve the monomer but precipitate the polymer. Polymerization in polymer solvents is not generally prac tical because of the very slow polymerization rates due to solvent activity. Preparation of most production solution resins is believed to be made in diluents which are nonsolvents for the copolymer. Copolymers prepared by the solution precipitation method are more generally homogeneous in composition than copolymers prepared in batch systems and because of this they are more suitable for solu tion applications. The copolymers arc free from residual quantities of suspending agents and emulsifiers and Ibis advantage along with AP00055699 AP00055700 500 COPOLYMERIZATION lower production and finishing temperatures provides resins with good color and clarity. The diluent solvents desirably control molecular weights because polymer chain growth is essentially terminated when precipitation occurs and because the solvent provides some solvent to radical chain transfer. Perhaps the most important advantage of the solution process is its ease of adaptability to con venient continuous polymerization techniques. Solution polymerization has several disadvantages and these may have limited adoption of the technique by more manufacturers al though the original Carbide patents expired about 1954. The resins arc somewhat more expensive than those prepared in aqueous suspension because of generally slower reaction rates and costs in volved in recovering and purifying the usually flammable diluent. The choice of monomer solvents is also limited by the tendency of many otherwise desirable compounds to act as polymerization in hibitors. In order to minimize such solvent effects it is often neces sary to conduct the polymerizations at low reaction temperatures. This lengthens reaction cycles, or in the case of continuous polymer ization decreases the overall production rate. Suspension Polymerisation. All aqueous suspension oopolymerizations of vinyl chloride and vinyl acetate are probably carried out batchwise, although several patents describe continuous suspension processes (122,307). Suspension of the monomer droplets present in the water as a disperse phase is maintained by the use of vigorous agitation and suspension stabilizers or protective colloids. The water-soluble suspending agents are usually polymers such as gela tin, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, and any number of other naturally occurring or synthetic macromoleciilar materials. Frequently, surface-active agents are used in minor quantities as secondary emulsifiers to assist in uniform dis persion of the suspension stabilizer and provide some control over the particle size of the finished product. During the reaction some dehydrohalogenation of vinyl chloride and hydrolysis of vinyl ace tate generates hydrochloric and acetic acids so buffering agents are usually added to maintain a near neutral pH. In a typical suspension polymerization the suspension stabilizers, buffering agents, anti initiator are dissolved in water and charged to a glass-lined autoclave, the largest of which is thought to be about 3,700 gallons. The reactor is closed and purged with an inert gas X. VINYL CHLORIDE OR VINYL1UBNR CHLORIDE 5Ul or monomer and then evacuated. The monomers are bled into the evacuated system from weigh tanks, and the reaction started by quickly raising the temperature of the system to the desired operat ing level. Because of the highly exothermic nature of the reaction, precautions must be exercised by control of the reaction rate and water to monomer ratio so that the cooling capacity of the reactor jacket cooling water is not exceeded. After a period of between K and 21 hr. and about 90% conversion of monomer to po/ymer, the reactor pressure starts to drop quickly and the reaction is usually terminated. Excess monomer is stripped off under vacuum and the product is transferred to blending tanks. Finishing is accomplished by washing the polymer and removing excess water on a continuous centrifuge altd then drying in a votary dryer. HI. Copolymer Composition Copolymers of the same average composition and the same average molecular weight are commercially available from several manufac turers but the physical properties ul some resins make them more suit able in certain applications than other apparently identical resins. Pig. 1. Copolyjiierization of vinyl chloride with vinyl acetate. Itisuuiluucuiis relation of feed ly copolymer eutujiosiliun. 5H2 COVOLYMKHUATION The difference between such cojjolyiners, assuming an equivalent degree of polymerization, is largely a difference in the degree of eopolymeric homogeneity attained during the manufacturing process. During any eopolyiuerization of two vinyl monomers different de grees of reactivity exist between the radical chain ends and the two monomers. Mayo et al. showed that in the copolymerization of vinyl chloride and vinyl acetate, the vinyl chloride monomer is more reac tive toward the growing chain regardless of whether the radical end X. VINVL CMJ-OKIUS OH VJNY1.IDBNB CULOHIOB 5`Kl In many copolymer applications, uniform chemical composition is important. A resin with a very wide spectrum of compositions from molecules very low in vinyl acetate to others very rich in vinyl ace tate may be difficult to process. It may also be insufficiently solu ble for use in solution applications. Relatively homogeneous copoly mers may be readily prepared by solution polymerization. In this system, the monomer composition of the reaction solution is held constant by continual addition of fresh monomer and removal of finished polymer. When steady-state conditions are attained all polymer molecules are initiated, propagated, arid terminated in an environment of nearly constant composition. Molecular weights also tend to be distributed over a narrower range because of limits im posed on the solution or dissolution of polymer molecules by the solvent and because termination occurs in a system nearly constant with regard to chain transfer. Homogeneity of composition may be improved in batch eopolyinerization by continuous addition of one, or a mixture, of both of the monomers. The "proportioning" is regulated at a given temperature by maintaining reactor pressures consistent with the vapor pressure of the desired monomer mixture. Thomas and Hinds calculated (2`J-i) the initial monomer charge and the amount of vinyl chloride to be proportioned to give a chemically uniform copolymer of several compositions. Their data, are repro duced bere: Fig. 2. CoimJyuii'mution of vinyl chloride with vinyl acetate. Instantaneous cimi|)<rsUioi) of the copolymer vs. conversion for a batch system charged with MO parts vinyl chloride and 15 parts vinyl acetate, was derived from vinyl chloride or vinyl acetate (201). Therefore, in copolymerization of these two monomers, the polymer is always Theoretical Monomer Loading and Operating Cundjtiuns fur Funning Chemically Homogeneous Copolymers at 00C. Desired copolymer composition, % Vinyl chloride Vinyl acetate Initial monomer charge parts/wt. Vinyl chloride Vinyl acetate Vinyl chloride to be proportioned Equi librium pressure lb./in* richer in vinyl chloride up to lUll% conversion of hath monomers. This relationship is shown in Figure I. As polymerization proceeds in a batch reaction, the composition of the copolymer molecules being > formed undergoes a progressive change. This effect is illustrated TJ in Figure 2 calculated from reactivity data and an integral form of the o o o copolymerizaticiu equation. The charge composition employed was No vinyl chloride/1,1 vinyl acetate. cn m --d o 97 3 57 3 40 142 94 6 54 6 40 136 91 9 51 9 40 131 88 12 48 12 40 125 85 15 4G 15 39 120 82 18 44 18 38 115 HO 20 43 20 37 112 AP00055702 594 COFOLYMIiKJZATIUN i. Physical Properties The physical projwrties of vinyl chSoride/vinyt acetate copolymers depend mainly on the composition of the copolymer. Molecular weight also contributes to the processing characteristics of the resins, although separation of the two effects is difficult to assess. Homo geneity, already discussed, also affects resin processibility. Copolymers have a lower softening fX/int and a lower melt viscosity titan homopolyiners of equivalent molecular weight. They are also more subject to chemical attach by ketones. Both of these proper ties are directly dependent on the vinyl acetate content and its plas ticizing effect on the molecule. The hofiiopo/ynicr of vinyl chloride is described as pseudo-crystalline because of its tendency to contain stcrcorcgular sequences of appreciable length. The close chain pack ing made possible by such molecular regularity raises the fusion point and decreases the solubility of the resin. Copolyrnerization with vinyl acetate introduces side chains which prevent such tight chain packing therefore decreasing inter- and intra molecular bonding forces. In this way, the comonomer acts as an internal plasticizer and the copolymer may be processed at lower temperatures. Copolymers also have slightly higher tensile strength, lower rigidity and heat distortion temperature, and poorer abrasion resistance than homopolymers of nearly the same molecular weight. These de ficiencies increase in proportion to the vinyl acetate content. The greater solubility of vinyl chloride-acetate copolymers in ketones has made the copolymers useful in a wide range of coating applica tions. Typical physical properties of a copolymer composed of 85% vinyl chloride and 25% vinyl acetate are compared in the following table with the physical properties of a copolymer containing only 3% vinyl acetate. Properties of Rigid Pruss-Pulished Sheet. Vinyl Chloride-Vinyl Acetate Copolymers Acetate content Mill roll temp., CF. Rockwell hardness M scale Notched impact, ft.-lb./in. Abrasion Jess % m 2000 cycles Heat distortion. "C, 66 jisi Tensile strength, psi Stress of yield, flex, psi 3% 340 60 .65 .02 67 8,200 32,800 16% 8,50(1 12,200 X. VINYL CHI.ORIDK OR VINVUDKNR CHLORIDR OUD 2. Applications Reliable consumption figures for chloride-acetate copolymers are difficult to obtain. The U.S. Tariff Commission does nut distin guish between vinyl chloride homopolymer uses and chloride--ace tate copolymers, and in many instances, companies jrroducing eo polymers do not know what the resin is being used for. The following table, however, represents a reasonable estimate of the consumption and applications of chloride-acetate copolymers during 19GI and 1962. Consumption (Millions of Pounds) 1961 1962 85 106 60 68 25 19 30 40 25 27 25 25 2(50 295 Application Flooring Records Calendered slicet Protective coatings Films, sheeting. and 1 Export Of the total consumption, approximately one-half is thought to be of copolymers containing 1ft to 15% bound vinyl acetate. Most of the remaining volume is made up of copolymers with lower amounts of vinyl acetate. flooring. In 1961 and 1962, the flooring industry was the largest consumer of chloride--acetate copolymers. Approximately 85 mil lion pounds of copolymer was used mainly in the production of vinyl asbestos flooring in 19GI and a somewhat higher volume was con sumed in 19G2. Growth is expected to continue in this application, mostly at the expense of asphalt flooring, due to the greater consumer appeal of the more decorative vinyl asbestos flooring. In addition to decorative superiority, vinyl asbestos tiles have greater flexural strength making possible the production of thin tiles (1/16 in.) which are generally easier to work with and, therefore, appealing to the do-it-yourself home owner. Cost has also been an important factor in the growth of vinyl asbestos flooring, The price of the copolymer to the flooring industry is about lll^/lb. and the consumer can pur chase the tiling through retail outlets for less than 22^/it.z in 1 /lt> in. i f>!H) COFOl.YMRRTZAiluN gage (ahout 12 per 0 in. X 0 in. tile). Asphalt tiles retail at prices ranging from 12.4j!:/ft.* for dark materials to about 23^/ft.* for the lighter tiles. The copolymer content of a typical vinyl asbestos floor tile is gen erally less than oi>% blended with asbestos and clay filler and a small amount of plasticizer and stabilizer. Copolymers are used rather than homopolymers, because their low melt viscosity permits easier and more rapid wetting of the highly filled stock. The following is a typical basic flooring recipe: Vinyl copolymer Clay Asbestos DOP Bpoxidized oil Barium-zinc stabilizer 100 115 115 20 15 6 Production techniques vary considerably from one manufacturer to the other, but the recipe components are usually blended in an intensive mixer such as a Banbury, and then dropped onto a heated mill. Some manufacturers use more than one milling operation, but the final step in the procedure is usually made on a 3-roll calender, followed by a cutting step to reduce the calendered sheet to the desired tile size. Pigments and colorants may be added during the milling or calendering steps to provide the desired decorative effect. Phonograph Records. The phonograph record industry was second only to the flooring industry in volume consumption of copolymer in 1001 and lf)G2, with a total volume of 6Q-G& million pounds. Nearly all of this was copolymer containing 13% vinyl acetate and 87% vinyl chloride. Virgin resin is used for the production of 12 in. high fidelity records, while scrap generated in the production is sometimes used to prepare the smaller 33 r.p.m. records. No other commercial application makes such exacting demands on the mold fidelity of a polymer. Compression molding of phono graph records with over 1000 highly complex grooves to fill demands a resin with a very low melt viscosity as well as one which has ex cellent resistance to shrinkage on cooling. These demands are well met by vinyl chloride-acetate copolymers. Such records are also highly resistant to water and changes in humidity and temperature. They are also essentially nonhreuknbli- and have reasonably good scratch resistance X. VtNYl. CHLORIUK Ok VlNYUOkNli eilLORlUtt A typical phonograph record formulation contains: 5U7 Vinyl copolymer retail (5/15) Black pigment Lead stabilizer 97.5(1 t .00 1.50 Several procedures are used in preparing compounds for phonograph records. Usually the resin, pigment, and stabilizer are dry-blciulcd and Banbury-mixed at some temperature lower than 3G0F. The mixed compound is fed to a calender and then scored into biscuits. The biscuits are preheated on steam tables and molded at 300350F. at a pressure of about 1500 psi. After molding, the discs are quickly cooled and removed from the presses to prevent warping and distortion. Protective Coatings. Vinyl copolymer surface coatings consume large quantities of resin. The coatings are resistant to most chem icals, including acids, alkalies, greases, oils, alcohols, and hydrocar bons. They arc, of course, attacked by solvents such as ketones and esters. The coatings are odorless, tasteless, nonteme, and nonflam mable and have excellent resistance to weathering. Because the polymer films are colorless, they can be pigmented in a wide variety of colors including the lightest pastel shades. The coatings are also tough, flexible, and have good wearing qualities. Nearly all of the resins used in the preparation of vinyl coatings are chloride-acetate copolymers with vinyl acetate contents varying from 5 to 40%. The acetate content of the copolymer and its degree of polymerization or molecular weight are important to the toughness, strength, and chemical resistance of the deposited coating and to the solubility of the polymer. In most applications copolymers con taining about 15% vinyl acetate with a medium average molecular weight are satisfactory. Such copolymers represent the largest volume of vinyls used in surface coatings. Copolymers with a lower molecular weight or a higher acetate content are used when low solu tion viscosity or higher diluent tolerance is desired. The coatings have consequently less toughness and strength and are softer and more subject to chemical attack. In many applications, such as metal coating, vinyl copolymers suffer from poor adhesion. To overcome this problem, special primers must be used, or the copolymer must be modified to contain a built-in AP00055703 AP00055704 5!J CUPoLYMIikIZATlON anchoring agent. The most commonly used anchoring agents are monomers containing carboxylic acid groups such as maleic anhy dride, methaerylie acid, or itacouie acid. A typical copolymer de scribed as having improved adhesion to metal has the composition vinyl chloride (85%), vinyl acetate (13%), and maieic anhydride (2%). Other copolymers are commercially available containing hydroxyl groups obtained by partial hydrolysis of the acetate groups in the cojxilymer. Such resins as these are usually not used as the primary coating but are more often mixed with conventional copoly mer solution resins in amounts sufficient to give the desired degree of adhesion. The most common and best solvents for vinyl chloride-acetate cojxjlyrucrs are ketones; and the most commonly used ketones are ace tone, methyl ethyl ketone, and methyl isobutyl ketone. The co polymers also have appreciable solubility in certain alkyl acetates, uitroparatTins, and chlorinated hydrocarbons. Ketones arc prefer red, however, because of their ability to solvate greater amounts of polymer. The solutions have low viscosities, are more stable to aging and can tolerate larger quantities of diluent. Ketones are also noncorrosive and relatively nontoxie. Chlorinated hydrocarbons are used in special nonflammable lacquers, but the toxicity oS these solvents makes extensive ventilation necessary. Diluents, such as toluene or xylene, are added to coating formulations to retard evaporation rates, reduce cost, thin the lacquers, improve brushability, and to simplify solution of the resin. Copolymer solutions are readily prepared by careful addition of the polymer to the solvent system. High shear agitation is desirable to prevent clumping of the resin, It also reduces the solution vis cosity because the resins are "shear thinning." When diluents are used it is often desirable to disperse the polymer in them first, and then add the solvent. This procedure usually makes solution times shorter. In certain applications where penetration of the coating into porous materials is desirable, or where higher solids contents are desired, chloride-acetate copolymers may be applied as oil-in-water emulsions. The emulsions are prepared by dispersing a dissolved resin in water with agitation and then passing the emulsion through a colloid mill to reduce the size of the lacquer droplets. Small amounts of surface active agents arc added to reduce coalescence i X. VINYL CITI.ORIJJR OK VlNYLIDRNft CilLORIOR HO!) and stabilize the emulsion. On application of the emulsion the water evaporates and the suspended droplets coalesce and become the continuous phase. Emulsion coatings offer the advantages of low cost, high solids content, low surface penetration, improved brush- jog characteristics, and low flammability. The coatings, however, are difficult to pigment, slow-drying, and cannot be used on surfaces that are corroded by or undergo dimensional changes on contact with water. Vinyl copolymers are used as surface coatings in a wide variety of applications, as: metal finishes, cement finishes, coatings for aluminum house siding, paper coating, wood finishes, artificial leather finishes, and textile sizing. The gradual acceptance of synthetic materials by the building in dustry provides an area for continued growth of vinyl surface coat ings. In 1959 an estimated 275,001) homes were covered with vinyl- coated aluminum siding. Vinyl coatings are also used on gutters, downspouts, and ducting. Application to traditional structural materials such as cement, interior panels, and wood flooring is used for protection against weathering, decorative effects, sound (leadening qualities, insulation, and waterproofing. In the food packaging industry vinyl surface coatings are used on the inside of cans, frequently over other resinous materials, to protect the product from flavor-contaminating impurities. Film and Sheeting. The increasing demand for unplasticixed sheeting and film has created a growing market for polyvinyl chloride acetate copolymers with an ester content generally lower than 13%. Converters prefer to use copolymers containing the least amount of vinyl acetate consistent with satisfactory product processing in order to approach the higher heat distortion temperature and superior heat stability of homopolymers. Copolymers containing as little as H% vinyl acetate are used in applications where rigidity, chemical resist ance, and hardness are important. Copolymers with higher acetate contents are used when flexibility and easy thermal processing are necessary. Impressive g-rowth occurred during 1001-1992 in the use of copoly mer for the preparation of calendered rigid sheeting. The material is used for playing cards, identification cards, templates, graphic urts. ring binders, ducts, and pipes. One manufacturer supplies copolymeric sheeting for use in the curved plate structure* of printing AP00055705 KOU OJPOLYMjtRtz.vnuN TABLE I Physical Empties of Viiiynn HH ami Dy.id Filers Composition Molecular structure Transition temperature Fiber cross section Dry tensile, psi Dry and wet tenacity, f./den. Dry and wet elungatlon Initial stiffness, g./<)ou. Elastic recovery Specific gravity Moisture regain, % at 70R, 05% RH Shrinkage, % in boiling water Shrinkage, % in 300"F. air Moth and mildew resistance Chemical resistance Solvents Vinyon HH 88% Vinyl chloride/ 12% vinyl acetate Amorphous Round 12,000-17,000 0.7-i-O 100-120% 1.33-1.35 Less than 0.1 00-70 Dynel fiO% Vinyl chliwide/ 40% acrylonitrile Slightly crystalline T, - I95'F. Irregular 40,000-57,000 2.5-33 42-30% 30 94% from 2% extension 1.30 0.4 2.0 45.0 Unattacked Unattacked Excellent to acids, 30% Good to acids and caustic, alcohols and alkalies--poor to aliphatic hydro ketones carbons Chloroform, acetone, methylene chloride Acetone, higher ketones, cyclic ethers presses. Other uses of rigid extruded stock are expected to develop h the building industry. Fibers. The production of staple fibers is a relatively small, bu interesting, application for polyvinyl chloride-acetate copolymers Since 1939 such fibers have been produced by American Viscose a: Avisco Vinyon (Vinyon HH). The copolymer is spun from acetont solution and is believed to be 88% vinyl chloride and 12% viny acetate. Vinyon fibers have similar physical properties (Table I] to polyvinyl chloride homopolymers made in Europe (RhovyI, Fibro vyl, Isovyl) except for a slightly lower softening point. This property is used to advantage in the preparation of bonded fiber batting, felts, and heat scalable wet strength papers. i X. VINYL CHLORIDE OR VINYUDENE CHLORIDE (jOL IV, Copolymers of Vinyl Chloride and Acrylonitrile 1. Copolymerization Vinyl chloride copolymerizes with acrylonitrile but the much faster polymerization rate of acrylonitrile with radicals of its own type or radicals derived of vinyl chloride, makes homogeneous copolymerization difficult. The instantaneous copotymer composition curve (Fig. 3) for vinyl chloride and acrylonitrile was calculated using reactivity ratios determined by Lewis et al. (186). The curve shows that any mixture of the two monomers results in a copolymer rela tively richer in acrylonitrile. If the monomers are charged batchwise, the composition distribution of polymer molecules will vary over a wide range from chains high in acrylonitrile to chains containing very little acrylonitrile. To overcome this problem an initial mono mer charge is chosen to give a copolymer of the desired composition. The faster reacting monomer is then added continuously or portion wise during the polymerization. In 1947 a commercial process was revealed for the copolymerizatiyn of vinyl chloride and acrylonitrile (235). The polymerization was Wt-Jg vinyl chloride in feed Fig. 3. Copolymerization of vinyl chloride with acrylonitrile. relation of feed to copolymer composition. lustautniH-ons AP00055706 002 CQPOLYMERIZATION carried out in an emulsion system as follows: 00 parts vinyl chloride, 10 parts acrylonitrile, 5 parts acetaldehyde, and 1 part potassium persulfate were emulsified in 400 parts water containing: 1 part 2-ethylhexyl sulfosuccinate. The polymerization was conducted in an auto clave at 40C. and the icmuinuig acrylonitrile was added during the polymerization, A 53% yield of polymer was obtained after 33 hr. Improved rates were obtained in later polymerizations using redox catalyst systems (1U). 2. Preparation Fibers: Vinyon N and Dynel. Copolymers of vinyl chloride and acrylonitrile have rather unusual physical properties. At low con centrations of acrylonitrile (10% or less), the resins behave much like polyvinyl chloride with respect to their use in solution and in thermal processing operations. As the acrylonitrile content is increased to 40-45%, the polymer becomes difficult to process because of the poor melt flow characteristics typical of polyacrylonitrile. Compres sion-molded articles can be made but they are fibrous in nature and generally non-isotropic. Some processing improvement is obtained with plasticizers such as p-toluene ethyl sulfonamide, but the poly mer is generally incompatible with most other plasticizers. Heat treatment leads to considerable darkening in processed articles, but unlike polyvinyl chloride the vinyl chloride--acrylonitrile copolymer becomes lighter colored on aging. Although poor melt flow characteristics limited the use of these copolymers in thermoplastic processing, their solubility in acetone and their high molecular weight made them useful resins for the pre paration of synthetic fibers. In 194S Union Carbide Chemicals Co. introduced a continuous filament called Vinyon N prepared from a 00/40 vinyl chloride-acrylonitrile copolymer. In 1050 the continu ous filament was withdrawn in favor of staple fiber, and the name of the product was changed to Dynel. Vinyl chloride copolymers containing 40% acrylonitrile are suffi ciently soluble in acetone to permit fiber spinning from 25% polymer in solvent solutions. It is interesting, however, that on aging at ele vated temperature the solubility of tbe copolymer in acetone decreases, and its heat distortion temperature rises. Fibers spun from acetone solution may be heut-treated at 150C. for 1 to 2 hr. to reduce their acetone solubility from 1UIJ% to less than 10%. The heat distortion i X. VINYL CHLORIDE OR VTNYLIDENR CHLORIDE 603 temperature of molded articles rises from 85C. to 90C. with the same heat treatment. Fabrics prepared from Dynel have a warm pleasant hand, good drape, and the resiliency and wrinkle resistance characteristic of fibers containing high levels of acrylonitrile. They also develop a high luster on heating and, due to their thermoplastic nature, they can be heat formed to prepare shaped fabrics such as felts used in men's hats. The high luster of the fibers makes them useful for the preparation of synthetic fleeces and furs. The fibers do not sup port combustion making them useful in drapery materials and other articles where flame resistance is desired. The chemical resistance of the fibers, especially to acids and alkalies, is desirable for preparation of protective clothing, wet and dry filtration fabrics, anode bags, overlays for glass fiber laminates, and many other applications. The physical properties of Dynel fibers are shown in Table I. V. Copolymers of Vinyl Chloride and Viuylidene Chloride When small amounts of viuylidene chloride (less than 5%) are copolymerized with vinyl chloride the copolymer is somewhat more soluble and processes at a lower temperature than a PVC homopolyiner prepared under equivalent conditions. Viuylidene chloride poly merizes at a faster rate than vinyl chloride with radicals derived of either monomer and it is usually metered In the system continuously during polymerization in order to obtain copolymers of reasonable composition uniformity. A relatively small quantity of vinyl cldoride-vinylidene chloride copolymer is produced each year, The resin is used mainly as a plastisol extender, VI. Other Copolymers Predominantly Vinyl Chloride Vinyl chloride has been copolymerized with a large number of com pounds and combinations of compounds. The reasons for preparing such resins vary, but most of the copolymers reported in the literature were prepared to improve the processability of polyvinyl chloride by lowering its melt viscosity through internal plasticization, Copoly mers are also described which have improved solubility, adhesion ami a wide spectrum of other advantageous properties. In general, ail ideal copolymer of vinyl chloride would process without breakdown AP00055707 004 COPQLYMERTZATION TABLE IIA Copolymers of Vinyl Chloride* Type Kef, Aromatic Compounds Allyl carbonate derivatives of aromatic hydroxy esters Aromatic Ackl amides of aruinoalkyl vinyl ethers Styrene and substituted styrenes Tetruhydro-em/0-rocthylene phthalates Epoxy Compounds Allyl 3,4-epoxy-2-hydroxybutyrrtCe Allyl glycidyl ether 3,4-Iipuxycycloliexnne methanols Uiisaturatcd esters of epoxy fatty acids Vinyl 0,10-cpoxystcurute Heterocyclic Compounds fV-Isopropenyl derivatives of 2-oxazinoncs and 2-oxazolidinones /7-2-Norcamphanyl acrylamides Tetrahydrofuran AT-Vinyloxaxolidinoite N-Vinylpyrmlidiiione Acrylamides Acrylonitrile MISCELLANEOUS COMPOUNDS Ally], nicthallyl chloride Allyl sulfide Butadienes 2-ChloroalIylidine diaectatc Isopropenyl acetate Maleic anhydride Maleimide derivatives d-Methylene-(3-propiolactone Octafltioro-l,3-cydohexadiene Phosphorus derivatives Silicon derivatives Succinic anhydride Sulfutes and sulfonates Vinyl acetals Vinylcne carbonate 243 319 52.127,180,185, 299,300 2B0 154 90,102 123,155,150 157 258,300 14 36 181 23 173 190,334 1,108,117,113,216, 222,255,257 203 195 38,172 297,298 130 315 290 46 138 75,17! ,81(1 13,228,234,205,290 329 7,51,213,220 202 120,131,132 i X. VINVL CHLORIDE OR VINYLIDENE CHLORIDE 005 TABLE UA (continued) Type Ref. Chlorinated polyethyleue 1-Chloro-l-fluorocthyiene w-Chloro-l-olefins Chioroprene Cblorotrifluoroethyiene OuBWNiC CvMrOvrtCS 1, l-Dichli)rcj-2,2-difluuroethy lent Dichlorohexafluorobutcnes Ethylene Fluorohaloethylenes (general) Fluoroolefins (general) Fluoruprene Isobutylene Olefins (general) Tetrafluoroethylene Trichloroethylene 3,3,3-Trifluoropropene Vinyl bromide Vinyl fluoride UnSATURaTUD Acini AND KSTtiKS Acrylic derivatives (general) Alkyi aconitutes Alkyl acrylates Alkyl carbonates of 2-liydroxyethyl acrylate Alkyl citraconntes or mesaconates Alkyl fumarates Alkyl itaconates Alkyl malcates Alkyl methacrylates Allyl acrylate Ally] triduoroacetate 2-(2-Chloroacetaoiido) acrylates Cyano ether esters of acrylic ur nietlvacrylic ackl Diamidophosphuroaorylates Diethyl chlorouiuleate 3,3-Difluuroacry lutes Ill 37,332 183 47,158 93,134,167,174, 223,224,287,288, 205 251 188 32,33,105,242 245 4 139 15,31,85,119 100 128,141,193 40 22 253 204,293 95,248 60 2,(38,98,111),175, 176,184,301 Cl 49 9,83,84,90,241 27,04,210,21) 3,11,12,39,94, 163-1(55,279 68,69,187,302 201 53 55 205 50 121 76 {coiiliunal) I COPOLYMEKJZATIO N TABLE 11A (Continued) Type Ref. Ethylene dicarboxylic acids, esters, and derivatives Hydronopyl acrylate Methyl 2-cliJoroacrylute l-Propen-2-nl acetate Unsaturated carboxylic adds and esters (general) Vinyl Estbrs Methyl carboxylic vinyl esters Vinyl 3-alkoxybutyrates Vinyl benzoate Vinyl carboxylic esters (general) Vinyl levulifvate Vinyl pinoate Vinyl propionate Vinyl stearate Vinyl Ethurs Alkoxyiucllioxyallcyl vinyl ethers Butyl vinyl ether T>ecaljydro 2-naphtliyl vinyl ether Isobutyl vinyl ether Methyl vinyl ether Trifluoruethyl vinyl ether Vinyl ethers (general) 87,97 330 72,95.291 231 I5&-1G1,107,203 182 200 252 232 01 212,335 H.335 240,250 5,0,244 * Limited to those copolymers containing at least 50% vinyl chloride, and npt including copolymers with vinyl acetate and vinylidene chloride. at relatively Jew temperatures with tnelt flow characteristics suit! ciently fluid to minimize power requirements. The processed poly mer would, however, have the high heat distortion temperature, Uiughwcss, strength, and chemical resistance of the homopolymer. No such ideal copolymer of vinyl chloride has been prepared. Many attempts have been made to improve on the processing and physical characteristics of polyvinyl chloride-acetate copolymers but no copolymer has been developed commercially which provides sufficient superiority to offset the low cost and versatility of vinyl acetate. Among the copolymers offered over the years was the copolymer of vinyl chloride and vinyl formate developed by 1. G. Farbeu, but never cotumeroializeil (2K4). Copolymers of vinyl chloride with vinyl s lour.11 e (232) were developed and soli I as internally plasticized resins The si |**d\ niiTs Mill ''ft 11 ,i lendcm v to lilnmii. ami iu,\ in >1 have been x. VII*VL CKT.ORIDR OR VINYI.IWtNR CH1X>RT>F, 007 true copolymers. Alkyl esters of maleic and fumaric acid copoly merized with vinyl chloride (130,241) are said to be insolubilized and crosslinked by the addition of an organic peroxide and exposure to actinic light (05). Copolymers containing 1-20% 2-ethyl hexyl fumarate are said to be proccssable without plasticizer and possess greatly increased shock and impact resistance (81). Cyauo ether esters such as 2-(2-eyanoethoxy) ethyl acrylate may be copolyrnerized with vinyl chloride in emulsion and provide tough flexible films (205). Copolymenzation of vinyl chloride with a wide range of alkyl acry lates and methacrylates has been reported. Preparation of homo geneous copolymers of vinyl chloride with acrylates or methacrylates requires monomer proportioning due to the much higher reactivity of the acrylics (G9,247). The polymers are usually prepared by emul sion techniques using redox catalyst systems. Physical properties of copolymers containing methyl acrylate are similar to vinyl chlor ide-acetate copolymers with the same ester content. Copolymers of vinyl chloride with methyl methacrylate are reported to have a higher softening point than polyvinyl chloride alone (11)3), greater flexural strength and superior optical properties (247), Although no vinyl chloride-acrylic copolymers have industrial importance in the United States, copolymers with methyl acrylate were sold in Germany as Jgelit MP-A and Igelit MP-K. Igelit MP-A was fabricated into clear press polished sheets sold under the trade name Astralon and Igelit MP-K was used for wire and cable insulation. Among the more recent copolymers of interest is a graft copolymer of vinyl chloride onto polyvinyl alcohol develojied by Toyo Chemical Co, of Japan (41). The composition of the polymer has not been revealed, but it is expected to find applications in the fiber industry as a replacement for silk. Pilot plant production was expected early in 1903. Fibers prepared from the copolymer have elasticity, dyeability, moisture absorption, and heat resistance which compare well with established fibers, Other examples of polyvinyl chloride block and graft copolymers are polyvinyl chloride grafted with acrylonitrile (54), polyvinyl chloride grafted with methyl acrylate (237), and polyvinyl chloride block eopolymeriz.ed with vinyl acetate, acrylonitrile, or vinylidene chloride (GO). Other copolymers reported in Ctn-miru/ .-!//>/rods from 1027 tluougli June 1052 arc contained in Table II. AP00055708 AP00055709 TABLE HB. Terpolyroens of Vinyl Chloride* _____ Second monomer Acrylic acid Acrylic or methacrylic compounds Acrylic add Acrylonitrile Alkyl ucryloti-s Alkyl esters of uusaturatetl dicarbojcylic acids Alkyl maleates Ally! enters of hydcoxyalfcanoic acids Ally) glycidyl ether AllyI cnftleate or triallyl cyanurate Butadiene Diallyl nialeate Dibutyl nwleate Diethyl maleate 2-EthyJhescyl acrylate *F|uoroacetoxyacryloni trile derivatives Fmuaric acid Isopropyl vinyl ether Maleic acid esters Maleic anhydride Maleic esters of alcohols from soybean oil reduction Maleic acid Methacrylic acid Styrene Third monomer Methyl acrylate Vinyliriene halides Ref. 220 67 Methyl methacrylate Vinyl acetate or pyrrolidoue Vinyl cfrioroacetate Vinyl pyridine Acrylonitriles Dibasic acid monovinyl esters Divinyl aromatic hydrocarbons Hydroxyalkyl acrylates Isoolehns Ofefmic tricarboxylic acid dialkenyl esters Styrene Vinyl aromatic esters Vinylidene chloride Styrene 305 106 217 63 325 322 323 327 321 324 328 320 260 310 Vinyl esters of fatty acids Ally! glycidyl ethers 308,309 89 Allyloxallcanoie acids Vtnyl acetate Vinyl esters ol soybean acids Vinylidene chloride Diallyl fumarate Methyl acrylate Vinyl acetate Vinyl acetate Styrene Vinyl acetate Vinyl acetate Vinyl acetate Vinyl acetate Vinylidene chloride Vinyl acetate 42 269 194 221 136 328 77 21 313 215 20,214,2153 2)8 43 Tetrahydrophtlmhc half-esters 229 Vinyl acetate 189 Vinylidene chloride 10 Maleic acid TETtA.POl.VU&V. Methyl methacrylate-polyvinyl 145 acetate Limited to those U-rpuIymer.s eimtnming at host 50% vinyl chloride, X. VINYL CHLORTDR OR VINYI.TURNR CHLURIUR 001) VIL Copolymers Predominantly Vinylidene Chloride The polymerization of vinylidene chloride (I.J-cfichloroethylene) was first observed by Kegnault in Ih'.'ltf (23S), but no detailed investi gation was made until nearly 10/1 years later when the reaction was studied by Fcisst (102) and then by Staudinger et al. (277). The intraetibility and general instability of vinylidene chloride hoiuopolymers was quickly recognized, and copolymerization was investigated as a means to obtain a useful plastic material. Intensive research work in the United States, particularly at the Dow Chemical Co., led to the introduction, in 1940, of the family of copolymers of vii^'lidenc chloride and vinyl chloride now known as Saran. Vm. Copolymers of Vinylidene Chloride and Vinyl Chloride 1. Preparation Vinylidene chloride may be copolymerized with a variety of co monomers by suspension processes, batch and continuous emulsion, solution precipitation, and bulk, although it is doubtful that bulk techniques are ever used commercially. The various techniques of polymerization form the basis for a number of patents too numerous to detail here, but in general copolymers of vinylidene chloride with vinyl chloride may be prepared in the same type of equipment used for chloride-acetate copolymers. Copolymerization techniques are also similar. Vinyl chloride polymerizes at a slower rate than v'mylidene chloride in mixtures of the two monomers, and homogeneous copolymers may be made in batch processes by controlled monomer feeding or proportioning. Proportioning procedures to obtain homo geneity are also possible in emulsion systems. Emulsion resins may also be prepared quite readily by continuous polymerization, u tech nique which provides inherently uniform polymers by continuous proportioning of both monomers. 2. Suspension Polymerisation A typical preparation of a vinylidene chloride -vinyl chloride co polymer by the suspension method was described in a recent U.S. patent assigned to the Dow Chemical Co. <112). The reactor used was described as cylindrical with a capacity of :j,50U gallons. It was fitted with a coaxial agitator which turned at 4.r> r.p.m. fluring dm AP00055710 0 JO COPOl.YMRRIZATION polymerization. The temperature of the reaction was C()C. The following recipe was charged: Water Vinylidene chloride Lauroyi peroxide Vinyl chloride 400 cp, Methyl hydroxyl propyl cellulose 200 85 0.3 15 0.05 The finished resin, after filtration and drying had a particle size of 30-100 mesh and could be extruded to give haze-free film. An earlier patent to Heerema (133) disclosed a procedure for pre paration of more homogeneous resins. In this system, the more vola tile vinyl chloride was overcharged and then vented off during the run to maintain a predetermined pressure. A glass-lined reactor was charged with 78 parts vinylidene chloride and 22 parts vinyl chloride. The reaction temperature was maintained at 60C. =fc 0.5. After an induction period of about an hour the reactor pressure rose to 60 lb. psig. As the reaction proceeded the tendency of the gauge pressure to increase, due to the faster consumption rate of vinylidene chloride, was offset by venting vinyl chloride. After 32 hr, the reactor pressure dropped below 00 lb. indicating essential completion of the polymer ization. The resulting polymer was 90.8% vinylidene chloride and 9.2% vinyl chloride. Only 11.39% of the resin was soluble in acetone indicaring a homogeneous composition. A similar resin prepared in an unvented system was 5.9% soluble in acetone, Polymers prepared in this way crystallized at a faster rate than less homogeneous resins. >7. Emulsion Polymerisation ' An interesting variation of the above procedure was revealed in a U. S. patent assigned to W. R. Grace 8c Co. (142). Jn this disclosure a copolymer containing 78% vinylidene chloride and 22% vinyl chloride was obtained in an emulsion system by initially charging 00 parts vinylidene chloride (33% of the total vinylidene chloride) and 40 parts vinyl chloride (100% of total vinyl chloride) to a stirred and evacuated reactor at SO^C. Water, emulsifier, initiator, and buffer were charged before the monomers were added. The reactor pressure at this point was 28 psig. When it rose to 29 psig addition of the remaining 120 parts viuylidene chloride was started. A pro portioning pump maintained a feed of vinylidene chloride sufficient i X. ViNVL CIlLORiDtt OR VINVLiUtiNK CllLORlOli Oil to hold the pressure at 29 psig to within 0.2 psig. After 7 hr. a pressure drop occurred and the vinylidene chloride flow was stopped automatically. The latex containing 33% solids was then coagulated, washed and dried. Resins produced by this teehukjue were said to form films having improved tensiie strength, greater clarity and heat stability, and were less brittle than films prepared in a uonprojrortioned batch process on an otherwise identical recipe. The recipe used in this system is shown below and is reasonably typical for the preparation of vinylidene chloride copolymer latexes. Water Vinylidene chloride Vinyl chloride Potassium persulfate Sodium bisulfate Aerosol MA (80%) (Dihexyl sodium sulfu-succinate) Nitric add (09%) 180 78 22 U 22 Oil 3.58 U 07 4. Physical Characteristics The homopolymer of vinylidene chloride and copolymers cumpriseil principally of vinylidene chloride are thermoplastic in naLure, but differ from other thermoplastics in their strong tendency to crystal lize. The high softening temperatures and relatively sharp melting points of the crystalline resins markedly affects the processing charac teristics and physical properties of the polymers. The crystallinity of polyviuylidene chloride is due to its regular molecular structure, which coupled with chain linearity results in lattice-like chain packing. Staudinger concluded that polymcrtza- l 012 COWLYHBMZA TION ticm occurs exclusively in a head-to-tail manner (270). Later work ers (114,240) assigned the configuration shown in Figure 4 as the most probable chain structure and suggested a serpentine arrangement of the carbon atoms. In this arrangement, with a carbon valence bond angle of 120" and a carbon to carbon distance of 1.55 A., au identity period of 4.07 A. results and is in agreement with observed values. Other chain con formations such as the planar zigzag or the trough arrangement pro posed by German investigators (179) require orientation of the C-Cl dipoles in an energetically unstable configuration. Based on x-ray analysis, the unit cell of polyvinylidene chloride is described as monoclinie and has the following dimensions (240): a - 13.69 0.05 A. 6 =4.67 0.01 A. c = 6.296 0.010 A. sin fi = 0.S212 0.016 A. Volume of coll = 330.6 A. Polyvinylidene chloride and its copolymers are obtained in a par tially crystalline state in which the polymer chains in the amor phous regions are randomly distributed. Areas of crystallinity or lattice-like packings of molecular segments occur as poorly de fined centers, with the long-chain molecules traversing both crystal line and amorphous regions, The extent of crystallinity in such polymers is affected by the amount of comonomer and by the na ture of the comonomer, but even in the most highly crystalline samples the amorphous regions constitute the continuous phase. Small amounts of comonomer cause only minor discontinuity in crystalline areas, but as the amount is increased the reduced ability of the poly mer to exist in uniformly packed lattices decreases the number of crystalline centers and the polymer becomes more amorphous. The nature of the comonomer is also important. Copolymerization with monomers containing bulky side chains, such as butyl acrylate or styrene cause much more severe geometric limitations to the for mation of crystalline areas than more compact comonomers such as vinyl chloride. On application of heat the polymer softens, and a few degrees above the softening point a sharp reproducible crystalline melting point may be observed by the use of crossed pularoids. At this point suf- X. VINYL CHLORIDE OR VINYLIDENE CHLORIDE tn:i Fig. 5. The effect of temperature on the crystallization rale of a typical crystalline vinylidene chloride--vinyl chloride copolymer. ficient thermal energy has been supplied to the crystallites to de stroy the cohesive bonding forces and a totally amorphous, low vis cosity polymer melt develops. If this melt is quickly chilled it will remain amorphous for a period of time determined mainly by the temperature, and to a lesser extent, by copolymer composition and amount of plasticizer. The relation of temperature to the crystal lization induction period, or time that the polymer remains totally amorphous, was reported by Reinhardt (240) and is reproduced in Figure 5. It is interesting that a plasticized compound (curve R) has a shor ter induction period than the same compound without plasticizer, The effect is due to the increased chain mobility provided by the plas ticizer which allows the polymer chains to slip more readily into posi tions of alignment. Above 15U to Kid0 ur the crystalline moiling i AP00055711 AP00055712 014 COPOLYMERIZATION point of the particular copolymer, no recrystallization occurs because of high molecular activity. At temperatures of 30 or below, the poly mer mass is supercooled and crystallite growth is essentially stopped by high internal viscosity. The transition of poly vinylidene chloride and its copolymers from the amorphous suite to the crystalline modification causes marked changes in the physical properties of the polymer mass. The polymer becomes harder, more dense and much more resistant to plastic de formation. The chemical resistance of the material to solvents increases and a change is observed in electrical conductivity. The heat of crystallization for the transition has been measured as 3.5 cal./g. The ability of jiolyvinylidene chloride and its copolymers to be cold-worked while in an amorphous state makes them unique among thermoplastics and forms the basis for the production of many com mercially important products. Vinylidene chloride copolymers can be stretched and oriented somewhat while at temperatures higher than their crystalline melting points, but if the polymer is first super cooled and then worked, a high degree of orientation results. The effect of the orientation is to create molecular alignment parallel to the direction of force. The lateral order so created extends exist ing crystalline regions and places polymer chains in positions con ducive to the formation of new areas of crystallinity. The growth of crystallinity in specimens of polyvinylidene chloride oriented 200250% manifests itself by slight additional elongation without ap plication of additional load. Although this phenomenon attribut able to additional molecular alignment through Brownian movement can occur in all linear polymers containing lateral bonding capacity, the effect is most pronounced witli polymers of vinylidene chloride. Polyvinylidene chloride and copolymers which are predominantly vinylidene chloride exist in three distinctly different modifications. The polymer as prepared is seinicrystatline with a continuous amor phous phase indicated by an x-ray pattern of sharply defined con centric rings on a diffuse background. The supercooled amorphous modification has a poorly defined x-ray pattern, characteristic of randomly distributed systems, while the highly oriented and internally crystallized modification has the sharply defined spot pattern char acteristic of crystalline materials. The x-ray diffraction patterns of even the most crystalline modification show some background scat X. VINYL CHLORIDE OR VINYLIDENE CHLORIDE 015 tering. This is due to the fact that although in principle the poly meric chains have sufficient regularity to completely crystallize, they never do. Crystallization starts at many random points throughout the polymer mass and 'grows from these {joints rather than from a sin gle point. The crystalline areas grow against each other iu a random fashion, and arc connected by regions which must therefore remain nonerystalliiie for purely geometric reasons. 5. Heat Stability Polymers and copolymers of vinylidene chloride have remarkable stability to the degradalive effects of sunlight, but at temperatures above 1()UC. they are thermally unstable and turn yellow on aging. At higher temperatures thermal decomposition proceeds with the evolution of hydrogen chloride. This effect is accelerated by Lite influence of certain metals such as iron. Boyer (24) proposes that the random loss of a molecule of hydrogen chloride from the polymer chain causes the chlorine atom adjacent to the newly formed double bond to acquire the activity of an aKylic chlorine. This eases the departure of another molecule of hydrogen chloride from the chain with the formation of another double bond. Once started the process continues and a polyene sequence of alternating double bonds is formed. The length of the sequence determines the intensity of color formed. A completely satisfactory explanation of the initi ating mechanism for hydrogen chloride elimination has not been made. Possible sites of initiation exist at the unsaturated ends of chains terminated by chain transfer. Other potential sites of instability are the tertiary carbon atoms which may be present due to branching or oxygen bridging, or the double bonds present along the polymer chain due to hydrogen chloride elimination during fabrication (27S). Copolymerization with a stable comonomer is reported to be an ef fective means of increasing heal stability, ur at least minimizing color formation. A monomer, such as ethyl acrylate, present iu Lite vinylidene cldoride chain acts as a block, to autaeatalylie dchydruhalogenalion and effectively shortens the length of the color-con tributing polyene sequences. Such comonomers also lower the sof tening temperature of the polymer and contribute to heat stability by decreasing the working temperature. Nonpolymerizablc heat stabilizers may also be used effectively to minimize discoloration due to hydrogen chloride elimination re- I <l(i COPUI.VMliKIZAVKfN actions. Typical of the compounds used for this purpose are his alpha methyl benzyl ether and glycidyl phenyl ether. The former is thought to form styrene at elevated temperatures which stabilizes the polymer molecule by reacting with labile groups to prevent elim ination of hydrogen chloride. Compounds containing oxirane groupings such as glycidyl phenyl ether and many other basic organic compounds arc thought to act as HC1 acceptors. It is uncertain why hydrogen chloride acceptors stabilize these polymers. Hydrogen chloride has been thought by many workers to catalyze dehydroehJorination, while others have shown that thermal decomposition proceeds even when conditions are such that it cannot accumulate (123). Whatever the mechanism is, basic compounds are good heat stabilizers if they react irreversibly with hydrogen chloride, and if they arc not so strong that they strip hydrogen chloride from tire polymer chain. 6. Processing Many of the commercially available copolymers of vinylidene chlo ride may be processed in conventional equipment, with minor modi fications necessitated by their low melt viscosity, corrosive nature, and relatively poor thermal stability. Monofilaments, rods, tubes, and films may be prepared by extrusion. Injection molding and com pression molding are also used, although injection molding is of more commercial importance. Other fabrication techniques such as vacuum forming, transfer molding, calendering, and various coating procedures are also employed. Extrusion of vinylideue chloride copolymers should be made in equipment constructed of nonferrous metals in all heated areas con tacting the resin. Iron catalyzes dehydrohalogenation very quickly resulting in severe fouling and corrosion of heated parts. Nickel, Hastelloy D, Durauiekel, Xaloy 300, Stellite 10, magnesium alloys and nickel plate are recommended materials of construction for screws, dies, breaker plates, and cylinder liners. The rather narrow temperature range between the crystalline melt ing point and the decomposition temperature makes a careful tem perature program desirable in any type of thermal processing of this plastic. In extrusion and injection molding equipment, heating and cooling arc best >i11r<i]Ic-ri by oil nr steam jacketing. Electrical In-altTs iu.iv In- used, but tin- rcs|>[|v,<- <>i Mu h systems to temperature X. VTNYL ClU.ORtUE OR VINYJ.IHKNK CIII-ORIIH? (117 adjustments is relatively slow. The heat sensitivity of the polymer also makes a shorter titan usual screw design desirable, and the low thermal conductivity of the hot melt requires volumes to be kept small in the interest of uniform melting. Care should also be taken to de sign a highly streamlined fluid flow path to eliminate the formation of pockets where holdup can occur and result in thermal degradation of the polymer because of excessive residence time. Extruded articles which do not require orientation such as chemi cally resistant pipe or rods emerge in a soft, rubbery state from the ex truder, but may be quickly hardened by passing through a heated (tiU-HMJC.) crystallizing zone. The length ami temperature of heating necessary for recrystallizalirm depends primarily on the composition of the copolymer. Monofilaments, films, tapes, and other articles are frequently quenched after extrusion by immersion in cold water. This maintains the extrudate in an amorphous stale and permits subsequent coldworking. Withdrawal of the soft, flexible, amorphous filament or tape over take-up rolls moving at carefully controlled but different speeds partially aligns the crystallites along the axis of orientation and causes a sharp increase in the tensile strength of the object. Heat treatment during the stretching process or at some other time while the extrudate is under tension is frequently used to "heat set" or preshrink the product. The cross-sectional area of the extruded tape or filament is directly related to the extent of elongation and can be controlled by the amount of stretching applied. Biaxial orientation of films is necessary so that the product will have strength in all directions. Flat film extrudates may be oriented by a rolling operation applied after the quenching step, but only limited transverse orientation is obtained in this way. A more satis factory technique involves simultaneous mechanical stretching alongand transverse to the axis of withdiawal. A commercially important way to prepare biaxially oriented film was described by Stephenson (2N.r>}. The procedure involves extru sion of ihe copolymer in tubular form into a quenching bath where it is supercooled. Some control over wall thickness and diameter oi the extruded tube as well as lubrication of its interior surface, is obtained by maintaining a constant head of nil in the tubing between the die orifice and a set of pinch rolls located in the cooling bath below the extruder die. The flattened tubing is then passed from Hie bath AP00055713 018 COPOLYMCRlZATrON to two sets of pinch rolls arranged so that the first set of rolls is travel ing at a slower speed than the second set. Compressed air is intro duced into the tubing at some point between the two sets of rolls. The injection is made with a hollow needle connected to a compressed air supply, and enough air is injected to blow a bubble of Sufficient diameter to provide the desired degree of transverse orientation. It is important in this process that the extruded tubing be of uniform wall thickness and free of wall defects caused by poor die design. The bubble is flattened as it passes through the second pair of pinch rolls. The biaxially oriented film may then be passed through a programmed heat cycle to provide the film with the desired shrink characteristics. The final steps in the process are a slitting operation and winding of the finished film on rolls. A process of this type is used by Dow Chemical Co. to prepare "Saran Wrap," Copolymers of vinylidene chloride may be compression molded although injection molding is a much more frequently used process. As in extrusion equipment, nonferrous metals are recommended for all heated parts in contact with the melted resin and careful stream lining should be employed to avoid polymer hold up. Conventional metals can be used in the dies because they can be operated either cold or hot. If the polymer is extruded into cold dies, it remains amorphous and can be reworked after ejection. Injection into heated dies speeds crystallization and hardening of the object, making shorter operating cycles possible. The ejected finished objects are strain-and warp-free, and dimensionally stable. 7. Application!; , The literature reports a large and varied number of copolymers and terpolymers which are composed of more than 50% vinylidene chlo ride but only three basic types of copolymers have become commer cially important. These are the copolymers of vinylidene chloride and vinyl chloride, vinylidene chloride and acrylonitrile, and certain co polymers and terpolymers containing alkyl acrylates. The copoly mers containing vinyl chloride and those containing acrylonitrile are marketed by the Dow Chemical Co., while copolymers containing alkyl acrylates are manufacturer! by National Starch and sold as aqueous dispersions. The Dewey & Almy Division of W. R. Grace markets a latex which is thought to contain a high level of vinylidene chloride copolymerized with acrylonitrile ami an acrylic ester. X. VINVL CHLORtWi OR VlNVLlUltNli CJlLURlWi Vinylidene chloride copolymers are odorless, tasteless, nontoxic, and flame-Tesistant. Toughness and abrasion resistance contribute to excellent wear properties. Oriented filaments, fibers, and films have tensile strengths of between 8,000 and 60,000 psi, depending on composition and the degree of orientation. Films of Saran are noted fortheir sparkling clarity and excellent vapor barrier properties. 1 he molecular weight of commercial copolymers varies somewhat depend ing on composition but is generally thought to be around 20.0UU, with a maximum softening temperature in the range of 14UC. Filaments and Fibers. Vinylidene chloride-vinyl chloride copoly mers (Saran) are sold by Dow Chemical Co. for extrusion of mono filaments, multifilaments and fine fibers, and for extruded tubing, sheeting, and film. The resins are generally sold as compounds, containing plasticizer, heat and light stabilizer, and, in some cases, fillers and pigments. Filaments are used in the manufacture of highquality outdoor furniture, automobile scat covers, and in practically indestructible window screening. Monofilaments and multifilanienls are also used in carpeting, grill cloths, Venetian blind tapes, acidresistant filter cloths, dolls' hair, awnings, draperies, and bristles. Molded Products. Injection-molded Saran parts achieved some prominence during the war years as replacements for strategic metals. Spray-gun handles with excellent solvent resistance were used in place of aluminum. Valve seats of Saran had superior abrasion re sistance and seating qualities, Spinneret couplings and other parts for the rayon industry were chemically inert and replaced hard rub ber. Injection-molded parts still have certain specialty applications, but the total volume produced is small. Film. The film market represents the largest outlet for vinylidene chloride-vinyl chloride copolymers. Basically, two types of film are sold. The familiar "Saran Wrap" contains about 15% copolymerized vinyl chloride, while films used in applications where greater heat shrinkage is desired probably contain up to vinyl chloride. Both types of film are prepared by the blown film extrusion technique anil are biaxially oriented. Saran Wrap is offered by Dow Chemical Co. in several types, dif fering in transparency, surface, composition and shrinkage charac teristics. For example, Saran Wrap 5 has the greatest cling ami transparency, while Saran Wrap 17, with a rougher surface is intended AP00055714 i AP00055715 t)20 COPOLYMttfctlZATlON for machine overwrapping. The high vinylidene chloride content and crystalline nature of Saran Wrap makes the film highly resistant to oils and greases and useful for the packaging of a large variety of food products including cheese and other oleaginous products. The moisture and gas permeability of the film is lower than that of any other polymeric packaging film making it a superior overwrap where moisture retention is desired. IX. Copolymers of Vinylidene Chloride and Acrylonitrile Protective Coatings Copolymers of vinylidene chloride with acrylonitrile are used in protective coatings where moisture impermeability, chemical resist ance, and solubility are important. They are sometimes modified with lesser amounts of other monomers to provide special properties such as adhesion to the coated object. The coatings are applied by solvent evaporation. Dispersion resins used for protective coatings do not need to be highly soluble and are usually copolymers with vinyl chloride or acrylic esters. Aqueous dispersions, or emulsions, are supplied with a solids con tent of up to 50% by at least three manufacturers and are used mainly for paper coating, and to a lesser extent for cellopliane coating and specialty paint applications. Dispersion coatings may be ap plied to the desired substrate by spray, dip, roller, doctor blade, and brush. They may be lightly plasticized to ease particle coales cence during the drying step. Small amounts of surface active agents are sometimes added to aid in wetting the substrate to ensure a continuous coating and a good surface bond. Additives should be held to a low level to prevent spewing and to maintain the efficiency of the polymer as a vapor barrier. Unfilled and unpigmented coatings dry on application of heat to a clear, glossy, tough film. Opaque and colored finishes may be obtained by the incorporation of suitable fillers and colorants and applied by similar procedures. Vinylidene chloride-acrylonitrile copolymers arc soluble in a num ber of inexpensive organic solvents providing the vinylidene chloride content of the polymer is not too high. Resins comprising f)0% vinylidene chloride and 111% acrylonitrile are used in huge volume for cellophane coating uml in other applications where a very ellicient moisture vapor barrier is required. The copolymers are readily soluble in tetruliydrufurun at room temperature and may be dissolved X. VTNYI. CHLORIDE OR VINYL1DKNK CHLORIDE G21 in methyl ethyl ketone at higher temperatures. As the vinylidene chloride content of the copolymer is decreased the resins become more soluble in ketones and other solvents. The moisture impermeability of the resin also decreases due to the increasing morphological dis order of the deposited film. Solvent coatings may be applied in the same general way as the dispersion coatings. Preparation of the substrate material before the coating is applied is critical if satisfactory bonding is to be ob tained. Concrete should be pretreated with a polysulficle rubber to ensure the integrity of the polyvinylidene chloride coating (fid). Before steel items such as marine ballast and fuel tanks arc coated, the metal should be carefully sandblasted. The coatings should be applied in thin layers to minimize pinhole formation which can be a problem in heavy films due to the slow solvent release of the imperme able resin film. Additional layers of coating should then be applied until the desired coating weight is obtained. Polyvinylidene chloride coatings are costly because of their higli density and relatively low solids content when applied from solvents. Substrate pretreatinent and priming are also expensive. These prob lems are balanced by the high level of protection provided by rela tively thin coatings. X. Markets for Vinylidene Chloride Copolymers The present market picture for copolymers based on vinylidene chloride is not clear. Most of the commercially available resins arc produced by one manufacturer and consumption data are not in cluded in the figures of the U. S. Tariff Commission. The following table, however, is thought to represent a reasonable estimate of pro duction of such copolymers in 19(53. Production of vinylidene chloride copolymers Use Filament Film Shrinkable film Coatings Extrusions Other Production (Millions of lb.) 8 15 :)0 j.0 3 G K2 AP00055716 <122 COPOL y M RRT7, AT ION TABLE III A Copolymers of VinylLdcnc Chloride* (Excluding Vinyl Chloride) Type Ref. Ajcomatic Compounds Atlyl carbonate derivatives of aromatic hydroxy esters Diullyl phthalate Diesters of tetrahydro-Midomethykne phthalic acid 9-Methylene fluorene 3-Methylene phlhalide Styrene and derivatives Heterocyclic Compounds /V-Isopropenyl derivatives of 2-oxazinnnes and 2-oxazolidinones iY-2-Norcamphaayl acrylamides Vinylfuran Vinyl oxazolidintme Acrylonitrile Miscellaneous Compounds Aliphatic epoxides Alkenyl silanes Allyl-3,4-epcxy-2-hydroxy butyrate Allyl esters of dicarboxylic acids Butadienes 1,1-Dichloro-l,3-butadiene iV-Fluoroalkyl-TV-vinyl amides JV-Hydroxymethyl maleimide Isoprapenyl isocyanate 0-Methylena-0-propiolactone 2.4,6-TrialIyl-l,3,5-tricyclohexylborazine 2,4,6-Trivinyl-1,3,5-tricyclohexylbnrazine Unsaturated esters of halo derivutives of acetic add Unsaturated ketones Vinyl compounds (general) Vinyl isocyanate Vinylideue cyanide 318 202 280 74 57 29,35,101 14 36 44,151 129 17,18,26.82,118, 124,178,192.207209,230,303 275 234 153 28 137,254,304 62 50 290 143 40 125 227 30 140 286 144 109.117 Icnnlin iini) Best available data indicate tliat the filament market is declining because of competition from polypropylene, especially in outdoor furniture and automobile seat covers. Saran film marketed by Dow as "Saran Wrap" is believed to be X. VINYL CHLORIDE OR VtNYLlDENE CHLORIDE (32J TABLE 11IA (continued) Type Ref. Cldon>trifimoethylciic Olkfjnic Compounds Haloolefiiis (general; Olefins (general) Tetraduorocthy leiie 3,3,3-TrifliKiroprnpenc Alkyl acrylates Unsaturated Acids and Esters Alkyl methacrylates Allyl acrylate Diamidophosphoroacry Lutes Ethyl fumarate Methyl 2-chloroacrylate Sodium sulfoprupyl acrylate Trialkyl aconitates Viayl isothiocyanate 134,167,174 86 139 15,31,76,35,281, 282 169 135 128,141 79,88,104.148-150, 177,191,259,312, 317 19,79,10-1,317 261 56 313 331 80 198 147 Vinyl Esters Butyl vinyl sulfonate Vinyl acetate Vinyl 3-alkoxybutyrates Vinyl esters of carboxylic acids (general) 226 168,264 25 146,197 Dodecyl vinyl ether Trifluorocthyl vinyl ether Vinyl. Eninas 206 249 Limited to those copolymers continuing at least 60% vinylideue chloride. declining in volume because of competition from less expensive poly ethylene wrapping materials. These have inferior barrier properties but are apparently satisfactory in noncritical household applications. Industrial film is apparently growing in volume. Such film is used to overwrap cheese, meat, and candy. Shrinkable film which generally contains higher levels of vinyl AP00055717 1)21 CeOOll''OljJJ..VYMMKKKKll//''..AANI'JDl INN TABl.li 1UU Tw[HJ lyna-rs of Viiiylklene Chloride* Second Mimomer Third Monomer Ref. Acrylates or acrylonitrile Acrylic or iilellmerylic acid Acrylonitrile r-Alkyl acrylates Alkyl iiuileatcs Allyl cliloridc L.3-Hti(:tdicnc Ihit.-ulL-ue A-d-FnrmnmkliH'tliyliicryluii liile Isobmyleuc 1 -Cliliiro-l-bniiin*cthyleiic Glycidyl methacrylate Methyl aery Into Styrene Vinyl lialkles Isnpropenyl acetate Vinyl or acrylate esters Butadiene Methyl methacrylate a-Mcthylslyrene Vinylidene chloride &-VLuyl-2-|dcnline Vinyl chloride Vinyl esters niiillyl funiarutc Chloroprene bthyl acrylate Isobutylene Methyl metbucrylnlv u-Methylstyreue Styrene Vinyl acetate Vinyl chloride Vinyl compounds Vinyl chloride Polymerizable substances Vinylidene bromide (2-Mcthucryluy Inxyuthyl; diethyl ammonium methyl sulfate Trichloroethylene Vinyl chloride Vinyl cliloridc Acrylic or ntclltacrylic compounds Acrylic acid Tbtkapolymur Acrylonitrile Methyl methacrylate 58 225 272 17U 272 200 230 48 107 2KU 15 271 207 274 27U 333 208 200 100 73 2K3 31 1 31 i 152,210 202 10 07 90 " Limited to those copolymers containing at leust 50% vinylidcne chloride. chloride titan the Surau Wrap type shows good growth, especially for poultry packaging. This film is presently produced by the Dobeeknutn Division of Dow us .Saran S and by Dewey and Aliny Chemical C<>. us Cryoviic S. Tile films are usually supplied us bags and may be shrunk lightly around the packaged object by the application of heat. X. V1NYI. OILnWIldi UK VINVUlH-.NIi C1I l.i >KII 0-. Solution copolymers arc slowly continuing to grow in volume mainly due to their increasing use as u moisture vapor barrier on cellophane. Dispersion coating of paper used to manufacture milk cartons, drink ing cups, and other packaging materials which require protection from grease or oil is relatively new, and faced with the problem of penetrating the established market for polyethylene latexes. Some growth seems reasonable in applications where superior barrier properties are required. A new use for polyviiiylidcne chloride copolymer emulsions was recently revealed by the Dow Chemical Co. The product is called Sarabond and the material shows growth potential in high bond masonry mortars. Dow claims that use of the new product will permit construction of higli strength brick walls and other masonry assemblages of only half normal thickness thus more than offsetting the higher cost of the mortar over conventional cement lime sand mortars. XI. Other Copolymers Predominantly Vinylidene Chloride As mentioned above, the only commercially important copolymers uf vinylidcne chloride arc those containing vinyl chloride, acrylonitrile, and certain alkyl acrylates or methacrylates. .Many other copoly mers, terpolyiners, and even mure highly complex iiiUTpolymcrs arc described in the patent literature intended for highly specific applica tions. As an example, a patent assigned to li. 1. tin Pont (.21(1) de scribes a dispersion coating resin prepared by the conjoint polymeriza tion of vinylidene chloride, maleic anhydride, acrylonitrile, 2-clhyl hexyl acrylate, isopropenylaeetatc, acrylic acid, and methyl acrylate. The principal component of the resin was vinylidene chloride flMJ'lf.). It was intended as a dispersion coating for cellophane. Ternary interpolyiners of vinylidene chloride, butadiene, and ethyl acrylate are described in another patent (27d). The resins are vuleauizuble, rubberlike materials useful as abrasion-resistant and moisture-imperme able coatings. Still other patents describe alkyl acrylate mollified vinylidene chloride, vinyl chloride interpolymers which ure useful for the preparation of unsupported film (71). A list of copolymers and more complex interpolymers of vinylidene chloride is contained in Tabic 111. 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