Document gDXLMdL1xYXOoa1wVpMG83X8q

('A' Ucjrvs'Ucr *.< *> . o A!--* Uis'v a; V:T' ^'^ 'u -r"'. vvi: r--' <r- - v-. -!-v \t *7* ** i > / : r i TT f r 1 ? 1\f JL.\t.~ v e. "J F" iO fVl MOEJEnhS CHEMICAL TECHWQLCGV ' `I I. i' -`T S .3 `'] .- PART Suspension, emulsion, bulk and solvent techniques convert vinyl chloride mono mer into polyvinyl chlorides. Initiating the reaction and controlling polymer size, length arid molecular weight depend to a large extent on the chemistry and on the type of multiple-phase relations that occur during the course of polymerization. LYLE F. Al BRIGHT, Purdnc University Polytirnl chloride polymers (commonly railed PVC polymers) arc the second largest family of high poly mers in the U.o., based on `lie amount prodi'n_iJ. In 1PGG, production war- over 2 billion lb., or over 17'; of all plastics. The term ``PVC polymers" as used here will induce materials produced by polymerizing pure* vinyl chloride (VC), or mixtures of comonomers that are predominantly vinyl chloride. PVC polymers are by far the most important mem ber of the family of vinyl polymers,* which normally include: polyvinyl (blonde, polyvinyl acetate, polyvinyl alcohol, polyvinyl acetals and polyvinylidene chloride. Production of I'VC polymers since 19.">j has giuwn almost ]3Cc/yr. in the U.S.,l i: This rate is expected to remain at this level for the next five years. Iri many parts of the world, production has increased e\e.u more rapidly thru in the U.S. In 19 10, the U.S. produced SOU of all PVC. but it only makes about 2o'"f cur rently. The amount of PVC prodm ed in Common Mar ket countries non surpasses th.u in this country, and Japanese output is over half of that in the U.S. Part of the major increase for PVC production in the io.-.t of the world is caused by delays in petting adequate production of other thermoplastic polymers, includin'': polyethylene. When other polymers are pro duced abroad in larger quantities, they may displace PVC for certain uso-. Nevertheless, the average annual growth rale for PVC polymers is estimated to be sub stantia! in most coonti ics, and to vary between 12 and 14fr for the Common Market from 10do to 1070. Increased p'-oduei im of PVC during the last few years has been caused in part 1 > a steady and sig nificant decrease m the selling price. Present prices for To it i i ( the ('In m. I . iYI* 1 " J '`-`T. |i 1 I Norm .. r: I" -x i v, i Si-* l t *n \ to l l \ :i* I ost. * i. : 11 For i\iii(Jr, Jit'iii'i \ .-i *. it to i i*w r to .!l i * * 1 \ iiw r* in it . h t ! t < t. 11; * t ini .*1 t! d.ltbi.r li.t` lh. loimt.l.i | t T i. -( *t \ - - >. 1 : h > v*. \ ix .ci'. ..i<>iii f\v %-jii I.. i'i t< t * i: n s n, o; U i a ; i oup vf Cltcni'rc'j f M~lncci iig---May 8, 1967 the general-purpose grade PVC are loo/lb., or much lower for quantity purchases. Projections based on recent prccess improvements (particularly those foi vinyl chloride manufactui e) indicate that PVC 'W.l sell for less than ldc/lti. (based on 19Go dollars) by 1970.11 At least 23 companies in the U.S. presently litoduee and sell PVC resins. The uses for PVC are many and vai ied, as indicated in Tabic i.-r- Extremely wide variations in the physic.-.', properties arc possible because of several major modi fications that include plasticized puiymers or ccpr.;.. mors produced primarily from vinyl chloride. PVC pn dtiCCis are spending large amounts of money in ru ctYort to find new uses and to develop improved p, i j nets. They have high, hopes for: 1. I'eveloping clear PVC polymers that can be u.-'d End-uses for polyvinyl chloride polymers and copolymers during 1965 in the U.S.--Table I flexible polyvinyl chlcides Coatings lor cot.les....................................................................... Films and sheets............................................................................ IS", Flooring.............................................................................................. ] 7 "0 Coatings............................................................................................ i t> "j M.scciler pous extruded products........................................... l-t "j Miscelli.ieous uses....................................................................... 1-fi so;:, liigid p jlyviryl chlorides 1 un^s ,-nd fittings............................................................................. !>'"% EtruttO"., records, etc................. ....................................................... I ilms and sheets................................................................................ ? D.tt.i i.ikiil.n* d !u>m Olten'r.'1 l.'.l. CTL030832 ) ;i CE KEFfCSHER . . . f The Chemistry of Vinyl Chloride Polymerization Yiityl chlotide or mixtures of comononic.s tii.v. me predominantly vinyl chlwii.le aic |i"!; uimri-J cmiiraeiciaib. by frcc-rr.dicn! chain r< 'clu.nx that are finite similar in the basic steps to those of hivh-pi <.-an e >l\mciization of ethylene.* The basic s'.ep< nail kinetics for vinyl chloinle poiynierizulinr. felloe.. I n it in I mu is noimally accomplished with a compound that foinis five radicals at 1 datively lew tcmpei ati.i es. Imtiatois in larjre-scalc use for vincl chloride poly merization are laiiri.y! peroxide, isopropyl pel carbonate, and azo-bis-lsabuty 1 onitnle.1 About 32', of all poioxide initir.toi-, (for p.dymerizntion of vaiious polymoi-A are used for vinyl polymers, including polyvinyl ace tate. Consumption of peroxide imt.ator- totals about 13 to 1 ! million lb. yr. Ciicmieal steps that oc-ur dining initiation are: 1.4 I--?]:. n. + cu..=cnri -- n~cir;--enci (i) (?) where !! is r. free radical obtained from the initiator I, and A/ is the rate constant for Kq. (1). The initiator fragment P. becomes incorporated in the tree radical formed in Eq. (2). The rate of decomposition of I is: - c/(I )/-// = Anil (31 where the parentheses around I in Eq. f3) indicate concentration of I in the solution. [Parentheses will he used similarly in other kinetic equation? in this article.] Since two frce-radicals !! are fanned from each decomposition of an initiator molecule, and since only a flection / of 1> reacts via Eq. (2) : rf'M )/<(/ - 2A.,/Ui (-1) where M* is the free radical formed after the addition of a vine] chloride molecule to a tree radical such as R. I'rr/ngrtinii involves addition of vinyl chloride to free nulical at the end of a ftrowinj chain. quiicJ, s nre two ftvc-rariicals arc destroyed by each teri`!jnnt;on i faction. The .stead)-slate appi o\imati<m is often nppIicaMo to tiee-iadna) polynu'i i7alnn>. includin': thr*c <>f vinyl chloiidc. Ti.is approximation sa\s that </(M*) ri* appioachos and remains equal to zero foi most of the pol\mcr.7atinn Therefore, tl*e >um of Eqs. (-1) mul (7) i> zero, and henee: Substituting Eq. (8) into Eq. (G) yields: -Sffirjass If / has a hw value, it is then essentially diicctly proportional to (M). In this case, the rate ol vinyl enloiide pol vmet ization is proportional to (CII. = CHC!)'--. Since (I) and (CI1. = CIIC1) vary with ti ne. Eq. (21 or its modifications has frequently been u.-od only for determining initial rates of polymerization--in which case, the quantities (I) anti (Cll.--CHCI) refer to tne initial convent) ations. Eq. (2) has been found to rep resent the kinetic data for some polymerizations of vinyl chlotide that occur in dilute solutions. Ti.is evi dence tends to substantiate the proposed model for the reaction, however, when concentrated solutions or un diluted vinyl chlorides are used, the equation does not fit the data. In suspension polymerization, which is of major industrial importance, vinyl chloride is present in an undiluted state. Chaut-iHuisicr slc/s are methods of terminating the jtiowt'n of a free-radical chain; but, in the inuccss, the isdica! is tian-ferred to another molecule. Tne net lesult is that there is no decrease in the concentration of free radicals. Chain transfer can occur with vinyl chloride as follows: --1;(--cih--enci),,--elf;--chci + nr.=--cuci--hr * R{--CH.--CIICl)^,--CH:--Clin (5) where >1 vaiies fiom zeto to a very laiqe number. The reaction-rate constant A> for the piopnp.ation stops is considered to be independent of chain length, i.e.. the value of a. Such an assumption has been verified for main types of frcc-i abb-al polyiuci iz.ation.T. The ktnoiic equation for Eq. (5) is then: -./iCII-CHCn/.// = A,(.\M (Cll..--CI1CI) where is, in this case, the concentration of: (0) 1:(--oi;-- nicib-- ar..--(Tit i Tcrmim'liuti stc/ns, in which the concentration of free radicals decrease?, often involve the leaeti'ii between two uiov.intr ehains M*. (Vunlincr is ess 111i:i11 y the com bination of and t M \. to form he'.M wheie and e1 refer to the imir.i.ei of I -- 01I.-011 (T - ) pi mips in eaeli chain. I b-pi >pn| non.'.t 1. m resit I is in two pnbnicr Hijleeii' -s, .t[,, and M. ; one uf the moleeulos 1- saturated, and li e otb.er ha? a double bond at one end. The late ipiatm.i is: -- r/(M >' '1 = 2A, i.M* i- (7) "bio I,, is the vote constant for tri initiation by both coupling and disproportionation. The .1.toper, 2, is re- Tin . w o: v !* i i!* I ui .* n u lift ; rl a l>: of I lti-< *-<- i"'*, < / in / ;t . i>. . r.. !.;. |, 11 i. R(--Cll;--C1ICK---Cir;--CHCI -f CHr---Cl Id--- It (--CTI.--CllC'l), --CTl.CHCI; + CII.-^CH Vinyl chioitde can add to the radical Cll. --CTI to form another ciowing- chain. Ilowovei, some of those iadicals act to terminate and destroy other fiee radi cals. ' For example: jcn--cn -- cn,--cii- cu=cn, (hiiladieiK ) Butadiene acts as a chain terminator. When it adds to a p-rowiim tham, an unrcaciivo resonance-stabilized aliyl i.ndic.d i- foimed. Chain tiansfer can also occur with the initiator or PYC polymer molecule. With the latter, a loim-eliai'i branch will form. Chain-tran.-fcr steps in which nno:her active i.idieal is formed do not alVovt the owr-nll late of polymerization. Usualiy, the molecular woiaht of the polymer i> devi eased when transfer is with vinyl chloride or with the initiator; but it is not do ne.im\I wln-i! tiansfer is with a polymer molecule. Opeiatine conditions dunmr polymerization alVocl li e charnctoi i.-tus of I'YC molecules. As a rule, mciea.cd teti'pc: aline and inei eased concent i at ions of initiator dovicn.-o the molcitilar weivilt of the I'YC P dymor. t'iii.in Inanchir.i; becomes of increased impotaiue win'n the mm cut rat ion of polxiuer buihi.-, up. i e. at l.iirii iio;;tee of polymerization, \ atioiis addi't'o. such as tha-.e ti-cil in mi .pensi at and eniuUioii poly merization in iy lesult in chniu-ti nnsfer steps. 1 1 ( I i ! j i I CTL030833 U2 Wry G, 1967--Clicniicol En<jincciinfj f for food packaging. At present, PVC film has found wide acceptance as a meat-wrap, and some believe that it v.-id dominate this field by 1008. Suitable plasticizers that can pet clearance from the Food and Drug Admin istration are nut always available for other types of film, or b]o\v-ninided bottles. Reynolds Metals has pub licized .-(line features of its prores- to form a heatshrinkable I'VC fdm that i.-, plasticized with an epoxidized soybean oil. or similar materia!.- This latter film is proposed for irregularly shaped articles such as fruits, vegetables or frankfurters. Recently Air Reduc tion Co. has announced a propylene-modified PVC that is cleai and has received FDA clearance.0 2. Increasing u.-o of PVC polymers in buildings.3,3 An effort is being made to develop suitable polymers for skimp, window frames, conduits, gutters and til ing. In many easts, it is necessary to have archaic building cedes changed to allow use of these plastics for building components. Polymerization Fundamentals More than one phase exists during polymerizations of vinyl chloride. This is particularly true in suspen sion or emulsion polymerization--presently the two most common commercial methods. In both methods, at least two phases are always present, namely the discontinuous organic phase and the continuous water phase. However, as polymerization progresses, there is belli a vinyl chloride phase and a PVC phase also present. Mass transfer is then of importance dining the polymerization reaction. Suspension Polymerization Window and Matreye!;-'7 have presented a schematic diagram of the states of dispersion of vinyl chloride for surpim.-Mn polymerization. This is shown in Fig. 1. The dispersed vinyl chloride droplets suspended throughout the water phase are subjected to shear by mean'; (,f mechanical agitation. As a result, the larger un.-tabiiized droplets are broken up into smallei ones that tend 10 coalesce and reform into larger droplets. A dynamic equilibrium between dispersion and coales cence then occurs. The degree and type of di-pershmconlescence is nnpoitanl in terms of the porosity and bulk den-:iy of the final polymer product. Protects-.o colloids such as -.larch, proteinaceous ma te; ;a!s or, frequently, polyvinyl alcohol (as indicated in Fig. li are added to stabilize the \inyl chloride' droplets and help prevent agglomeration of the PVC droplets. These colloids aie soluble m water but in soluble in vinyl chloride. One of their important prop erties is that they can increase the viscosity of the water layer, and hence delay the process of coales cence.-''- Inorganic materials are sometimes added to help prevent or regulate coalescence. Mater.als such as kaolin, barium sulfate, magnesium carbonate, talcum, neutral phosphates, and bentonite clay have been found effective. Those inorganic particles are quite insoluble in eithei phase, and concentrate at the interface be tween the water and organic phases. The initiator that starts polymerization is soluble in vinyl chloride. Viscosity of the organic phase in creases as polymerization occurs, and polymer mole cules form throughout the droplets, which become syrupy. -Agglomeration of particles is a problem during this phase of polymerization. Since PVC is quite insoluble in vinyl chloride, a "PVC phase1' is produced in the dispersed organic droplets. When this phase occurs, auto-acceleration is noted by an increase in the rate of polymerization instead of the decrease that is expected a? vinyl chloride concentration decreases. Autc-necc-Ioration has been explained by a decrease in the rate of termination steps for the over-ail reac tion. Evidence has been obtained to indicate that polvmeriz..:>n occurs in both the vinyl chloric a and PVC phases. Tul;. rncrization in the PVC phase occurs as vinyl chloride diffuses to the active sites of that phase.1' Those active sites tend to he located close to the surface of the semisolid PVC phase. Due to their limited mobility in the PVC phase, the active sitecannot easily react with each other to cause coupling or disproportionation reactions that destroy free rad icals. When nuto-acecleration occurs, the degree of pulymci i ..lion also increases--thus supporting the SUb'THSION POI.YMCmZATION OCems with a sud.it le stabilizer in a series rl steps, as ill.isbntril schemat ically. The type and deqtce of coales cence is imppitar.t idative to the bulk density and poiosity Of the final poly vinyl rlilnt nlc pa.iticlcs.--fig. 1 (1 ciT'ii.i.1 t'a.aii- i tiraj---V.ay 8, <967 /- Vinyl chloride bulk monomer / Ad sorbed inoieri'l ir film of polyvip.yl alcohol Agitation (Shear) Coalescence | liitrrfacial tension *' O O oo O O I Stabilizer sue h as polyvinyl V alcohol o o ^ o o o o o O O0 O CTL030834 153 C REffiES.MER . . . hypothvsis that there is a decrea-e,l possib'iity of chain-ler:r.ti.otin/ -lep-. Emulsion Polymerization The theory of emulsion polymerization is r.nt yet completely understood. Althoii'.rh the genera! concept ns outlined by H.-rkins14 is widely accepted, the mech anism may not be entirely applicable to till tv;>c-s of emulsion polymerization of vinyl chloride. Tor example, Peggion and others1:1 report data for some polymeriza tions, which do not agree with the earlier mechanism. At least four components are involved in emulsion polymerization--water, vinyi chloride, initiators, and an emulsifying agent. Water is the continuous phase: vinyl chloride, is the discontinuous phase. The initi ators arc water soluble, and the emulsifying agent stabilizes the emulsion f nmed when the system is agitated. Emulsifiers, either anionic or cationic, behave as essentially normal electrolytes at low concentra tions. When the cnr.ilsi.'ier concentration is increased, surface tension decreases between phases, and conduc tivity of the mixture increases. Eventually a critical concentration is achieved. Above this concentration, surface tension and conductivity change less rapidly. The emulsifier that was previously distributed uni formly begins to agglomerate into groups (called micelles) that contain 20 to 30 molecules.1,1 The initiator in the water phase forms a free radical that migrates to the micelle. Here the radical reacts with vinyl chloride to initiate the polymer chain, as shown in Eg. (2). Propagation reactions occur as additional vinyl chlo ride molecules combine with the growing free radical, as shown in Eq. (51. A polymer particle starts to foim. ar.d the emulsifier collects at the surface. Vinyl chloride m 'l eulcs then diffuse from the dispersed droplets of vinyl chloride through the water phase and through the e/r.uisifier to the growing chain. As polym erization progresses, and as the other polymer par ticles grow in size, more emulsifier is needed at the surface of the particles. In some cases when 12 to 20Cl conversion is reached during emulsion polymeri zation, the emulsifier micelles have disappeared and the emulsifier is all located at the surface of the par ticles.14 At higher conversions (perhaps (lOfc), all of the monomer is in the polymer phase. The number of polymer particles formed and hence their size seems to be controlled in the early stages of polymerization. Initially, there is competition be tween growing polymer pnrticic-s and micelles for each vinyl chloride molecule that is transferred. If a grow ing polymer chain forms in most micelles, there will then be many particles, but each will bo small because the molecules of vinyl chloride will be limited. In some cases, the i .minor of polymer particles remains almost constant afmr the miiellos disappear.111 Evidently, poly merizations c.iimot easily ue initiated in dispersed vinyl chloi ide droplets. Auto-accelei at ion sometimes occurs in emulsion po lymerization.1'' and apparently both monomer and poly mer phases I'M-! m the polymer particles. .After all of f' the emulsifier ha.- boen ti.msfoii I t<> ihe poiyn.-r pha-i. and as the ;n!\ m,"' particle-! grow, a lesser n"d lesser amount of emulsifier is available for a given surface area. The amount of cmuUifier affects the stability of the emulsion-'": the number of micelles, and hence the number of polymer pui tick's prodm.ed; and. in some cases, the rate of pVv nicrizatwm. The results of l\ggioii1'-' differ from tbo-e of Harkius14 i dative to the effect of some of the operating variables. Peggion sug gests that in the early stages of polymerization some vinyl chloride is pok merized while it is dissolved in the water. He points out that a rather appreciable amount tOOd by weight) of vinyl chlm ide is soluble in water at 50 C. After the polymer groups formed by initiation in the miceiie grow, and after tne mieo.les disappear, polymer formed in solution coagulates and precipitates on other polymer particles. Peggion indi cates that the mechanism for polymerizing vinyl chlo ride may be quite different than that for loss-soltib'e monomers. Termination steps involving coupling ,.r dispropor tionation are rare in emulsion polymerization because the number of PVC polymer chains for each particle is small. Hence, PYC polymers produced by emulsion polymerization tend to have high molecular weights. Occasionally, a second free radical enters the polymer particle and causes termination, or initiates another polymer chain. There is still a need for considerably more investi gation of emulsion polymerization. Many operating variables are of importance, and each has complex effect* on the final reaction and on the character of the emulsion. There is evidence that no sharp line of differ ence exists between emulsion and suspension polym erization. Bulk Polymerization The characteristics of bulk polymerization are essen tially identical to those of suspension polymerization if the temperature can be adequately controlled. Meth ods of temperature control are quite different, and will be discussed in a later article that will describe a commercial bulk-polymerization process. Solvent Polymerization The kinetics and mechanism of solvent polymeriza tion have been thoroughly discussed by Mickley. Mi chaels and Moore.1'' A solid PVC plia-e often forms as polymerization progresses, and some solvents are bet tor for solubilizing l'v'C than others. When a solid PYC phase ovcms, auto-acceleration also occurs. The reaction mechanism is in many respects similar to that of suspension polymerization. Characteristics of PVC Molecules Vinyl chloride monomers can unnbine in several ways during propagation. In most cases, vmyl chloride molecules react to form a head-lo-tail arrangement of 1S4 CTL030835 Moy f., 1V67--Clumicol Engineerin'? Effect of molecular weight on unplasticizcd PVC ond blends of PVC and ALS polymers--Table I! Vygen G5' Molecular weight of PVC.............................. Scluhon viscosity............................................ Tensile strength. ;-si...................................... Flexural strength, psi....................................... Flexural modulus, psi.................................... Notched Izod at 7 7 r., ft.-lb./in................. Heat distortion (204 psi.) ter: 10-rr.il deflect.on.`C................................... 60-mil defection, *C................................... 02,000 0.70 7,750 11,750 420,000 0.44 69 75 Product of Ccncn-.l Tir.;- A Ituhbrr Co. t Bif ii'1 c onl nt`, / . i '.'is V , - rn S.r and 30 rutrts A *3S j Cl unci cor,`.urns / o , . 'IS V>pen 120. a no 30 rafts ACS. Vygen 85* 74,COO 0.00 7,775 12,000 420,000 0.50 69 76 Vygen 120" 107,000 1.18 7.650 12,500 440,000 0.80 75 80 Vygcr, C5/ABSt Vygen 120/ABS; 74,000 107,000 6,150 9,225 330,000 14.0 6,250 9,600 3GC.000 18.0 66 72 74 78 Effect of molecular weight on plasticized PVC--Table lit Vygen 85* Vygen 105* Vygen 110* Vygen 120* Molecular v.eight.................................................................. ............ Solution viscosity................................................................. ............ Tensile strength, psi............................................................ ............ Ultimate elonpation, "5....................................................... ............ Tensi'e strength at 10Cpo elongation, psi.................... 74,000 O.CO 2.100 230 83,000 0.93 2,490 300 1,400 93,000 1.03 2,730 340 1,420 107,2C0 1.18 2,890 350 1,460 Prcdurt of Genera! 'T,.r* & Rubber Co. The formulation for the plasticized PVC (Vygen) is: 100 parts resin, 50 parts plasticizer (d oetyl phlha'ate;. rue 2 p2*': c' Lz. Cd st.-i'tiizer. the repealing units ( -- CII- -- CHC1 --) in the chain12: tail ./ \ (--OH---Cl Id-- CII;--CH Cl--) \/ head Occasionally, a few tail-tc-lail and head-to-head ar rangements occur: (--Cllf.'l--CH.---C.'lls--CI1C1--) (--C1I---CilCI--C1ICI--CH;--) Crystallinity Factors The cai'bcn atom to which tlic chlorine atom is at tached is asymmetric. As a result. I'\ C polymers can occur in various sterco-pecihc arrangements*-- namely, atactic, syr.diotact:c and isolactic.1'J4-Com mercial PYC lias been reported to be primarily ryndio- T *'V him' t*f (. r .* 1`tvrie mi .tr-t trout* *f t!io r'| U itti.r r i| jo|\ tn t t- '. nr iti .*<!%* t,.*mn-I r.i t* <1 !> I'-ii'J U ' Alt.:., pi* \ j ! *" i" nif li.mii.ii't Ihtt tt ts in. -i.t.tl n ;>>..rn.- .*s .i |.:.tv;i, I t 11* jvA !v- |..k i l.tt .-*' t. I* .,v ,i (.I i-'.u* .tli.l .i '\ t-i 1.< (i. i !m i | i< 11 .u 11. i< ri*t i! t!.' i\ rt*. r I i a f t !..* r.iM-l- /- ..ill ? ,t, .< ii. . i rt . . ! 11. l >]>. lin:' in .t * <*f t !. j. * \ : i'.ii % 11. * t c .tv w,.t . i it r i1 f ,.;i ci .ill / ii i.ii... iiii'iit ci i' t.tu* i-.-!smi \ i. \ til t.cii- tent (hit h.*v ,ir: ,i! i it. . 1111 _r i*l / ... i .i t . .Tit Ml * |<h stitii tlil\ Milt r- j..rth .*o if* I*., i i <:' .! :1> !* li*t. .'l.t'lh ."id I lit/ fours tactic in nature hut is said to have considerable amounts of atactic regions.1-'1 Some polymer experts believe that PVC is primarily atactic. In any case, commercial PVC is only slightly crystalline--perhaps being as high as 10 to 13T ,-'4 Crystallinity vnric-s with the method of polymerization. The polymer macromolecule is thought to be screw-shaped. Attempts have been made to produce isotactic PVC, and partial success seems to have been realized. The following points must be considered to determine whether isotactic PVC would have important commer cial interest: 1. The unplasticizcd product would presumably be quite crystalline, having increased density and tensile strength. These improved properties would be of defi nite interest. 2. The unplasticizcd product would presumably have a higher softening temperature.-'1 A problem with presently available PVC is a high softenin'.: tempera ture that is almost as high as its decomposition icmperalurc. This is especially true of high-molecularvvoight PVC. The decomposition problem with ismactic PVC would likely he accentuated, perhaps to an unrea sonable c-xteni. If so, conventional methods of extru sion and injection molding might not be applicable with tiie unplasticizcd product. Further, modification of these molding methods would liboly be expen.-dve. (liCmicu! ri.'iinc0.I.u--Mny ", 1157 CTL030836 155 i c5 RtiKCi-Hm . .. r' 4 3. If i'otactic PVC wee pla-.liK.v.l !.i de-'.rov its lions to occur on a given polvmur chain. Evidence sup improved packing :in>l rrv-tailmilv, it is mu slionablu porting these facts is: whether the material would have any -ienificar.lly im 1. The rate of dehydroehlonnatinn increases as proved properties as compared willi presently a\affable molecular weight decrease-, i.c. the i ate is essentially plasticized materials. proportional to the number of crni-gi mips. 2. Chlorination of the double bond- decreases the Molecular Weight of PVC Polymers rale of dehydrocldnnnalion. Initiator fragments on the end of PVC polymer Commercial PVC polymers have numbcr-aveiage molecules rrtnv also be the staiting point for decom molecular weights that \ .try flora about nO.OOO to position reactions. Chain branching, which occurs to 150,000.24 Pontine laboratory te-t-' for PVC gener only a relativelv small extent, ahn decrease- the sta ally involve the measurement of solution viscosity of bility of the polymer becau-e tertinrv carbon atoms the polymer rather than the direct measurement of exist with chlorine atoms attached. Such chlorine molecular weight. The relationship between solution atoms are much easier to abstract than tho-c attached viscosity q and molecular weight M for a specific poly to secondaiy carbon atoms. If any head-to-hoad ar mer is: t) = KM" where A" and a are constants for a rangement occurred, the polvniei nmlcuile would be given polymer-solvent combination. relatively unstable at the point where the two chlorine The higher-mole,,ii' ir-weight PVC icsins are plas atoms were adjacent. ticized and used for tloxible tubing, welting, electrical The exact mechanism for dehydrochlorination i? not components, garden hose and calendered film. These completely understood but depends on the presence or products are obtained by extrusion, and the resin is absence of oxygen. Inorganic stabilizers are added to subjected to elevated process conditions for only a short most PVC resins. period of time.9 Intcrmrdiate-molecular-wcight resins are used in film and sheer, coated fabrics and rigid Quality Control Tests products. Low-molecular-weight resins are used in fluidized-bed coatings, phonograph records and injec The following tests are generally made on batches tion-molded parts. of the finished polymer before shipment to the con Tables II and III indicate the effect of molecular sumer: (a) solution viscosity in older to determine weight on the physical properties of unplasticized and average molecular weight, (b) bulk density, (c) plas plasticized PVC polymer?/' Molecular weight has a sig ticizer takcup, (d) irreversible plasticizer takcup. (e) nificant effect on the impict resistance of unplasticb.cd moisture content, (f) mill stability, (g) clarity, (h) polymers, and on th V':g.''.inn and. (ensile strength at "fish eyes" or gel particles, (;) foreign particles such lOOCc elongation of plasthized products. Even better as dirt, (j) particle-size distribution, and (k) press impact strength is obtained for rigid polymers (con stability. For electrical-grade PVC, the following addi taining little or no pl.-sticizersl by blending nitrile tional tests are made: conductivity and pH. Plasticizer rubber or AES polymers* with PVC polymers. As in takeup is of interest since it inci: ates the rate at dicated in Table II. a blond of 70',' PVC and 30re which the plasticizer and PVC resin mix. and hence APS produces impact strengths up to 20 times greater the rate at which extrusion or injection molding can than pure PVC. Tens;;.' and flexural strengths of the be done. Careful control of quality is therefore essen blends are somewhat lower. tial in order to produce suitable polymers. Chemical Factors Affecting Stability Compounding of PVC Polymers PVC polymers are rcl.itivelv unstable with regard to temperature (especially 200 C.. or higher) and light.* Hydrogen chloride is then evolved. Some of the double bonds thus formed are attacked by oxygen or enter into cross-linking reactions. Severe dcgrad.ition of physical properties and appearance may result, de pending on the plasticizer. Although all factors affect ing stability are not known, several features of tlie polymer molecule contribute to this instability, (lienee, variation.' in the tcclmiuui-s of po'v mcrization that minimize these feature-, arc impoitant.) The end-groups of I'W iivA'culos are often the weak point at which decn:'>;io.. it io:i reactions begin. Such an end-group i-, -- CHCI-CH. Cl 1 .. A free-radical mechaui-in can easily begin a! the double bond. Ad.b- tion.il double bond, uic produced daring dehydto- ehlorination. allowing additional decomposition rear- Tvi n.cry t'f a* r\lu.ult tl-* (A), )ni!wiituc (H), nil.I *.!>ro.E (S). The polymers of vinyl chloride are often compounded (i.e.. blended) with plasticizers and stabilizers. Lubri cants and pigments are sometimes added. Hard, hornlike PVC is converted to a softer and rather flexible material by compounding it with a plasticizer. Generally, plasticizers decrease the tensile strength of the polymer, decrease the processing time for extrusion or molding operations, increase the allow able elongation of the polymer, and increase the im pact strength and the low-temperature flexibility ,s The exact role of the plastu jzer in PVC is not known, hut it act- to partially solv.i'c the polymer chains. As a result, separation of the chain is increased and, heme, the otherwise strong iutcrnioleeiilar forces be tween the chains are de.uea-eil. Any erv stallmity originally present in l'VC palymeis i- destroyed by the plasticizer. Table IV gives one example of the relationship among the various degrees of plasticization and im- CTL030837 May 8, 1967--Clno-.iical Coyinuci iny t f ]i< i-' !!' j ! i \ ' ..: 1 !hm-.or". I'v-ind j >) ;. i - i < ^ for Kpox.'di/'-d oils and ester-, pi.lynietn c-':s 11;c \ i .- 4 ji -i -t in o r iiii oil1'1*:* 4 * m di't ular we.gld- ranging front about J.fm.i to 1. Adequate eoinpal ibility with tin* 1'YC rosin -- rl.lorinalvd polyethylene, and otlier im'um'i < such as that i>. the degree to which I'YC rosin i- solvated by AI1S resins (see Table 11 i have been used commer the plasticizer. Witli hiy!) e"i:ipatib.!;:y. a nuue or ie-; cially as pkisticiz.ers or as special blending materials'1 true Milution is formed. With lower i ompatibihlv, theie may be a phase separation. J'or example, at Stabilizers higher 'omp< ratures <mh as are w"'d >, cxtn.-inn or molding, a single phase mav he tin'-eiit. As ;he nil.xtme Certain stabilizers have been found u-rft;l in min is cooled, n P\'C-eontimious phase forms and a plas- imizing decomposition reactions caused by lieat, light ticizer-di'eontiiiinnis phase is also pn -enl. The decree or ultraviolet radiation. Heat is always a factor in the of eompatibilitv has nil imprrtnnt effect on the pnqier- extrusion or molding operations of the nolynci. Mn-t t .c s of -.in li: ,i! prod'.ut. In .ohi.` and especial'.;, stabilizcf-a are metal salts. Copi c c iptt.ctc >1 barium and with low compatibility, the plasticizer may slowly dif cadmium hiuratcs. sometimes with zinc laurnte. are fuse old <d' the final product, llct.co the physical prop u-ed in most PYC resins as stabilizers up.mis; lira; erties (sudd di.-.nge significantly wit:; time. oxidation.-' By making an opaip.ie plastic. biUz.itinn 2. Low volatility, in order to mtriml/e loss of plas against ultraviolet or visible light is accomplished ticizer from the product and to m:'.mi.-c odor. With trail-parent PYC. seceral stabilizers have now 8. Good stability--particu'ariy in regard to lieat and been found to be quite sticcessful. In general, toe sta light. or other forms of radiation. bilizers are used in relatively low conce''tr:.t'o:i;. fre I. Xoidlammtibiiity. quently less than 1 to 2<~r in the final po`\men :c mate 5. Xoi'i'.oxieity. rial. A detailed analysis of the complicated problem of G. Satisfactory hiw-temperature properties. stabilization, and available stabilizers is given by 7. Reasonable cost. Chevassus and deBroulelles.1' No plasticizer meets all of these characteristics, and selection of the plasticizer or mixture of plasticizers Other Additives involves a compromise. Several classifications have been given to plasti Fil'ors. pigments or dyes, lubricants, end fungicides cizers. Externa! plasticizers are those additives that or pesticides are sometimes added, depending on the are mixed physically with the PYC resin, whereas final use of the plastic. The fillers arc generally cite; p internal pla'ticlzeis react chemically and ate incor extenders such as clays used foi certain clsc'trical- porated into the polymer chain The folio,vinp discus grade PYC re-ins. The days absorb free raid and other sion jie'tains to exterra! plasticitiers that tire divided polar compounds. Asbestos fdleis u.-t.l in certain into primary and secondary ones. Primary plasticizers floor-tile products. are highly compatible with the rc-iti. but secondary ones aie only of into: mediate compatibility. Copolymers Plasticizers are commonly organic esters with a liipli molecular weight. about 200 to 1..100. In 10G>. Copolymers prepared from a mixture of comnnon-.er-- phthalic anhydride esters amounting to 079 million containiiig GO'f, or more, of vinyl chloride, with the lb. were produced as plasticizers, of which di-f2-olhyl- remainder being primarily vinyl acetate, arc of com Jiex.vl i pJithal.itc was the major one.7 Other plithalate mercial importance.Copolymers accr tint for perhaps esters include various Ci to Cu. alkyl phihahates. Esters 25`lc of the production capacity of vinyl chloride poly of sebacic. adipic, azelaic tmd phosphoric acids are also mers. Copolymers tend to improve two important phys pood plasticizers. .Alcohols for lho?e esters are fre ical properties of the homopolymcr of vinyl chloride, <iuently obtained by nsinp the Oxo process. Straight- namely flexibility, and limited solubility in solvents. cliain alcoliols such as produced by Continental Oil External plasticizers may provide one method for in Co.'s Alfol process may have certain advantages as creasing flexibility, but such plasticizers are not always compared with branchod-chain alcohols.'" adequate for solubility requirements. Effect of pltsficizing with clioctyl phfhalole--Table IV Harts ot dioctyl phthzlate per 100 parts o! Vygen 120* 0 30 40 50 CO 70 Tens te strength, psi......................................................................... f loiigation. ...................................................................................... FI-O'C A iu-dnor . 10 rce.............................................................. 7,750 5 to 25) 115 3.550 205 98 3,200 295 92 2,850 345 86 2,500 370 79 4 V \ rt'n 1 TO (a p4"ltict of 1 * A f*ul'tior Co ) tuis .in mtnnsic vt;couitv of \ J .**! . n < -''i ol.n \m*i l t ! i . ' ,t >"' t I SktMYMtod fn*m I unties I lOj'i-ttu'i Ch tl "Uctlt in I litstics I.ncyelupc-ou ) Hut. How York. 2,100 410 77 < II p C ( . I' r* CTL030838 ir CE REfPfcSMcR . . . Propoflic-s of ri^'d p: csi-poliih.. ci 'JtCi'tS of vinyl cliloride/vir.yl acetate copoly iners--Table V Vinyl Acetate Content Property Mill roll temperature tor softening, * F. Hardness. Rockwell M................................ 3% 340 CO 15% 250 50 Notched impact, tt -lb./in.......................... Abrasion loss in 2.000 cycles. %............ 0 65 0.02 0.20 0.13 Heat distortion (Cb psi.), C.................... Tensile strength, psi.................................... Yield stress in flexure, psi......................... 67 8.200 12,800 57 8.500 12,200 f' dmod bv b.uch p, >! v mcr i/at ionHence, the relative ratios of V'uv! ill', ride and vinyl acetate that react lend to vniv with trie lime of the run, unle-< v mv 1 chloride (the more reactive comonomer) is added in order to maintain a constant ratio of comonomer.-, for the reaction 11 Vinyl chloride is also copolymerized commercially in .-ignifiiant. amount- with acrv lomti ile and vinvlidene chloride.--' Other types of copolymers have been reported, but their commercial importance is small. A copolymer of vinyl ihlornle and propylene lias recently been announced by Air Reduction Co. The properties annoumed for this copolymer are such that it will lihely find important uses--especially since it has received clearance from the Food and Drug Ad ministration for "clear" food containers.0 In one sense, copolymers are internal plasticizers. Certain comonomers such ns vinyl stearate or longchain esters of maleic anhydride are sometimes co polymerized into the final product. In such a case, the plasticizer is chemically bonded into the polymer chain and hence is. a true internal plasticizer. Vinyl Chloride/Vinyl Acetate Copolymers The properties of copolymers of vinyl chloride and vinyl acetate are dependent on the relative ratio of the two comonomers that have leaded, assuming that the final polymer molecules have the same molec ular weights. Copolymers containing less than 10'i vinyl acetate have physical properties quite similar to those of the homopcilymer of vinyl chloride, except for the lower teinpei aiurcs lequired for compound ing. Differences in mechanical properties lend to in crease lapidlv as concentrations of vinyl acetate in crease above 10rr. Table V gives the properties of two copolymers containing and 15% vinyl acetate.1'1 Copolymers containing lfiT. or more, of vinyl ace tate and having relatively low molecular weights are used for protective am! decorative coatings, flexible film, tloor tiies. and compre-.-ion moldings where ex ceptionally good llow characteristics are required.1'1 Phonograph records arc one example in which precise duplication, and hence excellent llow chu'-acterKtics. arc needed. A vinyl chloride'vinyl acetate ratio of 87/]:? for the copolymer has been used. If the heat stability problem can be solved, relatively low molecu lar weight hnmopolvmers can be used as an alterna tive solution.-1 Copolymers containing less than 13'..' vinyl acetalc and having relatively high molecular weights are used for rigid sheeting, extruded rods and calendered articles. When the copolymer is to be used for prole. ti\e or decorative ioutings, a. small amount of maleic anhy dride or other polymerizable carboxyl hydiu c.trhon is sometimes eopnlymorized with the vinyl chloride and vinyl acetate.11 Carboxyl groups improve the adhesion properties of the coatings. In other c.-ww. a poitum of the nictate groups on the polymer chain i; tctmivcil by hydiolws to piodtue hydroxy! gioups tb.it aUo improve adhesion. Vinyl chloride/vinyl acetate copolyniei s arc pro- References I nillmoyer. T' \\\. "Textbook of Polymer Suenec," Inter s' tenc o. N*\\ York. 1`*.2 2. Kcvn*dbt 11\| imK PVC Film Plant. CWinn. Eikj .Yrirs. Jan 1. ] 4*. 3. Pieid PVC l> Set for Sole*'* Growth, Chrm. Etui. .Yn-.v Julv 21k 1. i 34. I. Cnmiulitive Ctmvih for Peroxide Catalyst**. Chrm F.ny. .Yru*. Ft-h 24 |t Vinyl Si'lmt: M.ker Gear for Hattie. Chrm. Entj. .Yrirj, 0*t. tf*. 1 'ilj. p ! i, * Pr-*i'lcni*-M*difi d r..ttle** Could 12ns. Problems* of PVC T.otth-v ior V'omiv //* iti Hut/. ,V/'u x. Mar 7. !***.. p ;i. 7. Pb.stit :/er ?*.il*s P.o** t ne Pillion Pounds. Chrm. Eufi. .Yfir.v, ,\uir l. ru'.i,, p *jo * Phe\a-mi** F and d'-Pmuirlb-**. Ti . "The Stahlli/.itk.n of ]\d'\ir'l Chhn1e.' truri**!.iU*d l> (* .) P llirlikorn a ml 10 12. Snrmhnto. St. Marcus Pn Ww Yrk. 1 !*.*; !`. noiiL-in*. \V. C. ihfruv .1 M. Harkim. G an*! Hnnlev, A J.. PVP I'.i ont'.i t i.Mt'* .uni A|*ph< .itnms, AICIW'2 Seminar h.v toi.ei.P . in Pul>hi C.. . i><*t. 1Fcd*r W S. n.iMh izet P'M. pp. 1 1 Y-l ^^ Chrm.Eui. .Yrit.t. Nov. 13, II rVi'd \\` S.. C.inimmiitv Foret asline. Chrm Fun. .Vt S* ; *, 2. po.7. pp 1J. Flry. P. J Principle** of Polxmer Chcnuslrv.*' Cornell Vn,\trirx IT* S' lihat ,i .\ Y. l`P.\ 1'' Mam. G II. ` Ctp*d> mori/atmii." pp SS7-C17. Intvrtwionoe. New \ork P**H 14 ll.-.rkm**. W T A General Theorv of the M**rhani**m of r.innkci..n P.*:\io.ti/.ii M.rt, / .l/'S, i:*. 142<-HI1 M'*47) 1 .Ml( lv!c\ , If S. M < h.n K, A. S and M*oiv. A P . I\i:i*Ahs >f Pi npitat *on P<:> in*-rs/.aiion <-f Vm\I Chloride. J. /'o/ih-mt Sri . an. 1 lM ( 1 `'ik: > la MilVnxuh. K of pcdymeri/atlon, AIChH Seminar h\ GeiMT.t! Tin* Uiik'n r Co, (n-t. t ! -t. 17 'Mimim, G. Wli.tt ** the Future for PVC. II nilr irarhon {`x i s > . y.-pt ......... it 2M . Is* Park P ^l . 1 '! i-tici/c-r--Versatile, Net i.***. rv Ile**:n I'tor //*/./; or/I/ box Cr.x; w, M.,r 1'M`- V 1 2*1 1 ** Peui:in II. Te*ta. F anti Taknnln, G.. A Kuwdh' Sind'' <f the IIiihiImoii P-dMb rr/atn*n of Ymvl Chloride, ,l/i/.; .**hkxlxtr Cht ,.ii. . 7|. 17*. (1f*;4) I**1 I'ewt r*. .1 P i: P. F Goodri.-h Co.), **pd\inert/.it .*n f Yintl t*o.up miiiN t* h. potent 2 *.*_,ti (Sept p*.*e 21. Itieli ird \Y K.. Si .i Ini i/*> - -- Kt*v to A?vlei*s Pi.i*.lien, II 'tli tx urlxtr I'i.ii'i vt Mar po, j, p 1.5 JJ St hildkn*`ehi. C. 12. "Vn>f anti Printed Pohmern*' \Yilcv, N. u Yt*rk. P *il! '.*'* St hiltlknei h.t. C. 12.. "PtdymiT PrtK*essos." Intvr**uc nee, Ntw Voi k P.i.'ik 21. Smith \V. M ` Vuivl Pe*.in<." p. inhohl. New York. Snuth W. M.. * M.i niif tt ttire of Piastiej*.** Vol 1. pp 3P1;t!.i kei'i'mld. N w Yolk 1 2*;. Spent cr. P 1.. Pineros^ in Polymer** Today. Iltnh r*n //.>: /`i.q I'M .1 ii!\ l!*lll',. p S*t, 27. Winslow. I' mill M.tlrexek. \Y . Partiele Sr/* In Stis- 1 en'ion Po'ymeri/.iti.m, /f,d. /.,/, (/. m., 13, 110$ (11*31). Key Concepts for This At tide A et i r () Pt . i. \x in : I 'u > v i * (!I) Intuit'IVetlstot'k (I) Pi... i *.* *t* M - .|ir * Pin Miivtix V,n\ I I!. 11 It* Ptd\ i'll i .. t- Yin\ I an I ile* Holt* Pl.tMn o.-r-* Pol' imi'I v* St.thPi/t : *** <hit|Mif `I'roilurt (*2) Pl.i-tn Pol' .III I ** C * . d' re r*.* Pol' ' It*.' I t Idol Id0* (Word-* in ! dd ait* io*e indie, tt. >iw : imml r< oiirt'>t,<i'i|l to l'|P- Xlt'lill t *|. m i vi i ;! i of p i* V modi'n Cam A *' ri 1 ^ n:iii* k \ <>>. i p' *. vi;.. t. >1 | o| I tuii \ 111" 1 '* l i v .ii . .old. ! lo I'e.iu ox i \ol.ie-: i *. .in .*!*-- ul Iu-h \ tie* K tie*., rd* o :i. 1 t > Ion. <>i I II I "* *. |* I s 7 . or mu inn .**) t Pex ..............pt Ivplint. **0i*. u-i i.. Ile.oh i Servut Porii.inl.i CTL030839 158 Way 8, 1967--Chei.iiccil litgintfrirwi