Document 2qzLo7abM2rZNKr71OL9LoK8b

Gravimetric and Volumetric Study of the Sorption of Gases and Vapors in Poly(Vinyl Chloride) Powders A, R. UUHtiNS The BFCovdrich Company Research and Development Center Brechtville, Ohio 44141 The sorption of a variety of gases and organic vapors in poly(vinyl chloride) (PVC) powders has been studied gruviinetrieully with a recording iiiicnihuliuiec and volumetrie.dly will) a gas pycnometer utid an automatic surface area analyzer. For nitrogen, carbon dioxide, vinyl chloride, methanol, acetone, ii-lmtunc, ami benzene at low poiiclrunl activities and temperature* l>clow T,, sorption isotherms ex hibit the downward curvature characteristic ofdual-mode sorp tion. The solubility nf each of these penetrants is lower in heat-treated PVC samples than in samples recovered from the polymerization without additional heating. It has Iwen possi ble to estimate I Ik- parameters of I lie dual-mode sorption model loi carbon dioxide, vinyl chloride, and methanol. The results indicate that the history-dependence of gas or vapor solubility is associated only with the " hole-filling" term oftbe dual-mode model; the normal dissolntion or Henry's Law term is essen tially unaffected by tin- prior heat treatment of the PVC. INTRODUCTION previous study of the sorption of vinyl chloride monomer vapor (VCM) in PVC; resin powders (I) lias irated the i>e!iaviur id this system with variations of iperuture and va[Xir activity. Above the glass transiitemperature (T,, * --8SC), the Flory-Huggins r<jn- deweriia-s the sorption isotherms over the full age ofvapor uctivity. At low VCM activities Imlow?",. ! isotherms show a pimnumeed downward curvature, L-h was interpreted in terms of the dual-mode xorpi theory (2). The total sorption of VCM was ascribed contributions of Flory-Hugginx dissolution and agmuirian "hole-filling". as shown in Fig. I, The disearunce of the hole-filling contribution with increasjVCM pressure below 85*C was attributed to plastiuianofthe PVC by sorlx'd monomer. Values ofT,,, us a ftion of VCM concentration in PVC, huve been ol>- by a thermomechanicaJ method (3) and from the tpentture-dependenee of the limiting conversion of polymeri/iitinn (4). Tile temperatures and 011114tioHs .d winch the experimental sorption isotherms the Flory-Huggins curve (see Fig. 1) correspond ' well to the T vs composition data, as shown in Fig. Dual-mode sorption in the VCM/PVC system thus characteristic of the glassy state while simple y-Huggfns behavior occurs in the rubbery region of ^position and temperature, lu the glassy state, the apparent equilibrium so lubility of VCM in PVC was found to vary with the post-polymerization thermal history of the polymer sample (5). It was suggested that the content of holes or iiiK-rovoids in the PVC .sample is determined by (lie conditions prevailing when the sample wus brought from the rubbery to thoglassy state, and that the mi crovolt! eontent, in turn, determines the extent of Laiigmuiriun sorption in subsequent exposure to VCM vapor. Variations in |x>sl-[HilyMierizaliou history are il lustrated on pint ui'7'v v composition in Fig. d. At the 100- 50- Fig. i. Sorption isotherm* for ttnyl chitinde in PVC, from Htsf. U). iftat eNQiHteeiHG and scifsct, mid.janua*y, 1900, vi. 20, no. 1 95 AP000108I6 100 - so W A v s? N \ \* \x S* N -50 -100, 10 20 1T% VCM 30 I'm 3. '<*'vr.'Af WW.'. X, f/irrmiinu-WtfmC'ai Uatu [ii,' Itnttliiiii runt i-rsi<iu (-1J, 9, Uixappcaroiu'v of hobr-Jillhig /'ig. 3. Pml-jHiiytiiertuitiirti thermal hixiory vnrkiKou* of PVC wiui/ilr*. AHC, "iirirr.tu'iiiiut", ADC orAltCDC, Iti-tU-lrvulod. end <>f a typical polymerization (50*C, 60 percent con version), the PVC/VCM syiitum is in the rubbery state. Itrinoval of residual monomer without raising the totnjMTuture brings the polymer into the glassy state while it is .still swollen with monomer (Fig. 3, path ABC). This procedure seems In result mu higher microvoid content than il(x-s removal of monomer at T > T,, (piith ADC) or later heating aimvc- i'u ip.ilh t TI >< I). Variations mi the subsequent sorption ofYCM at low activity reflect thew history variations and seetn to provide u measure of tlw inicrovoid content of PVC samples. This earlier work clearly established the dual-mule and history-dependent nature of sorption in l1u< VCM/ PVC system. Other published studies of sorption m PVC seem limited to gaseous penetrants, as opposed to organic vapors. Tikhomirov, et ui. (6) studied (lie tramport of a number of permanent gases in PVC films, hut did not specifically investigate history effects or isotherm curvature. Burrer, Mallittder, and Wong i7) lound that the solubility of hydrogen and neon ua* affected by the thermal history of PVC films and suggested that pre-existing sorption sites, or "mien*, gaps'*, play u rule in sorption of these gases lieltiw Tt. The present study was undertaken tu determine whether the dual-mode, history-dependent liehavior observed for VCM sorption in PVC might lie generally characteristic of the sorption of other pcmUuuts is glassy PVC. A gravimetric method and two novel vd. umetric techniques were employed to determine the iiinounl of sorption and the form of sorption isotherms for several gases and organic vapors in PVC powders. lloMdl.s obtained with polymer samples ofvaried history were analyzed through the dual-mode model (2' to as certain whether history effects may be associated with i particular mode of sorption. A complementary study of sorption in PVC powders using the technique of inverse ggs chromatography will be reported separately (ft). ,, EXPERIMENTAL Materials . The PV<'. vuuple* studied include commercial and experimental polymers jiolymerized by suspension and emulsion techniques. These were used in the powder form obtained directly from the polymerization. Sam ples designated as "never-heated" were recovered and dried sit temperatures not exceedingthe 50*0 temperatore of polymerization. "lieut-trcatcd" samples, unless otherwise noted, were heated 1 h at 100*C and cooled slowly to room temperature. A sample of extruded, unplasticized PVC film, --50 /xm thick, was used in afew experiments. Cases and solvents were research grade, used without further purification. Equipment end Procedures CruvliiK-iric sorption experiments were [K-rformcd with the Cuhn recording micro)udunce, vucuum system, and procedures described previously (1). Volumetric gas sorption datu wen; obtained with a Beckman Model 930 Air Comparison Pycnometer (Beckman Instrument Corp.), This instrument, shows schematically in Fig. 4, consists essentially of two matchedcylinders withcrunk-drivcn pistons, connected through a differential pressure indicator; gas connrctions, valves, and a pressure gage permit evacuation, purging, and filling with a known pressure of selected gas. A weighed polymer sample is enclosed in the measuring cylinder. K, and cylinder A serves as arvfctenee volume. The total enclosed volume ul cylinder E V6 FOLVMM (NGJNfEXJNG AND SCItNCt, kUb-IAHUAXY, 1990. vw. 20. N I t< MAC AOWf I N* C Fm. 4. Sdtcm. can be meas and scale we its enclosed \ of the eyiind then closed a differential p both eylinde closed velum the polymer (hen in cyliti and m evlind where VA is t! mg Eqx I an< For a gas w at F, the wuij and at P, where M is the and T the tenr gas sorbed by from P| to Pi. Aif U)i - i . K A sorption cot weight of gas s increase in prt Pi - Pt. Bycoi M ` zRI Pycnometer n iilit.im Vs, arid Vj .uni ( f ),, i< AClYMf* NGIN AP00010817 r \ Cmuim-tn. (i 111/ Vo/tomdrit Study oj the Sorption uj (Jaw* and Vapor* in Faly(Vintjl Chloride) foivdfr.% aui lie measured with a built-in counter, and a pointer and scale were added to cylinder A to permit reading of itiencloscd volume, Inopcmtion, thcencioscdvolumes of the cylinders. VAl and VB|, are noted; the valves are then doted and the pistons advanced, while keeping the differentia! pressure ut zero. increasing the pressure in both cylinders to l\ ~2 P,. and decreasing the en closed volumes andV/*,, li the gas is not sorbed iiy the polymiT sample, and ideal gus licluivior is assumed, then in cylinder A, P,VAt-PtVAt (|) <uid in eyliuder B P, (V*t - V,} - P* (Vfl,-V.v> (2) whereV,, is tin- volume of the jadymer sample, Conduitmg Eif* I and 2 and solving lor V* gives vZ - V,',-- w For a gas winch is appreciably sorlx-d by the polymer, dt Pi the weight of free gas in cylinder 6, u?t, is and at Px " ' = 'lTTiV` ~ V'J fkjp <* -7ir(V**~ v*> W w where M is the gas molecular weight. ft the gas constant, andr the temperature of measurement. The weight of 4* sorbed by the polvmer upon increasing pressure from Pi to P*. Arc, Is therefore m tCi ~ Wf " - [P, (V, - V) - Pt (V,, - V,-U (6) A sorption coefficient, AwtgAp, may be defined as the weight ofgas sorbed by a unit weight ofpolymer per unit (ncrruM* in pressure. wilhg the sample weight und Ap liycomhitiingl-afs' / andti, it can Im-shown (lull Ato/gAP - VJ - V4l(V*t - VO V'dx * V*. Pycnometer measurements with helium were used to i>l>Uin VA. and E.if 7 was applied In pycnometer data for Nr and CO* lo yield sorption encilic ient.s. Art,-/gA/\ for these gases in PVC powders. The assumption ofidcal gas behavior in these calculations introduces an error of <2 percent in the worst case (C0f at 4 atm pressure). Additional volumetric gas sorption data were oh* tained with u Digisorb 2500 automatic surface area analyzer (Miernioerlties Instrument <lorp.). This eomptit<*r-oonlmlb*d instrument is designed for unto* malic determination of sorption isotherms ami ordinarily is used U> determine li.ls.T. surface areas of solid samples by adsorption of gases at liquid nitrogen tem perature. By u simple inodificutiou of (he computer progrum, solubility isiilherins were obtained for N, and CO* up to atmospheric pressure in PVC samples at room temperature. RKSUI.TX AND DISCUSSION Cascuua penetrants Helium. 'Die solubility coefficient lor helium in PVC at 25*C reported by Tikhomirov, rt a/. (6) is 7,3 x Krsee STP/ce PVC cm llg. or 7 x |C>-4 mg/g PVC-utm. Since the useful sensitivity of the Cahn balance is alxmt 10"* mg/g. gravimetric sorption measurements with helium were not attempts). Helium sorption experiments with the Digisorh 2500 wore precluded by (be refjoireim'iit for calibration of the instrument "dead volume" with helium, because the solubility of*helium in PV( i is below the snisitivilyofthc Heckman jjycnouu'ter, gus pycnoinctry with helium may be employed to measure displacement volume-sand densities within the instrument accuracy of iilwiut vl iXTeeiil. In the course oi this work, measure ment ol helium displacement volumes indicated u den sity of 1.404 * 0.014 g/cma for nearly 80 PVC powder samples of widely varied history and particle strneture. This value agrees well with the density of molded l*V<'. s|x*cimeos. Within the accuracy limits of the helium pycnometric method, no effect of thermal history upon the density of PVC could be detected. Nitrogen. The solubility coefficient for N* in PVC at 2.5V: (3.1 x ID-4 oe STP/cc PVC cm Hg or 0.021 mg/gatm (6)) is too low for precise gravimetric sorption exper iments. Although the precision of the pycnometric method is insufficient for quantitative measurements of N* solubility, displacement volumes of PVC powders obtained through Eij 1 from pyenometry with Nt were invariably lower than those with helium, indicating a significant sorption of N*. These data indicate u gener ally higher N* solubility io "never-heated" thun in heattreated PVC samples. Use ofthe Digisorb 2500 instrument for NS/PVC sorp tion measurements provides a substantial improvement in privision over gas pyenometry. Ixidierm.s obtained at 2ii*C liir Ny in "ncvcr-hcutcd" and heat-treated samples ofa suspension-polymerized PVC powder are presented in Fig. 5. These results confirm the magnitude and history-dependence of the pyenmnelric sorption <iK`ffieieids. I he total sorption at atmospheric pressure for the heat-treated sample. 0.035 mg Nj/g PVC, agrees fairly well with the sorption coefficient given by Tikhomirov, ct ill. (ft), tml the "never-hcnled" Mimple sorbed alxmt twiv lies anioiiut of \- inidet llie same tOLYM* INGINiCBING AH0 SCItHC. MIO-JANUAftY. 19*0. Vcl. 20, Ho. I 97 APOOO10818 f .A, It. Mcrm-s Fifi. 5 .Sorption isotherms for N, in tuipention FVC at 2if*C; HiUisorh 2-VJO tlalu. conditions. Significantly, isotherms showing the downward curvature characteristic of dual-mode sorption are clearly defined |>y (he Digisorb 2500 data despite the low total sorption in these experiments. Carbon Dioxide. The relatively high solubility ofCO* in PVC allows precise sorption experiments on this sys tem with Imth volnmetrie and gravimetric (<-clmi<jnrs. Sorption isotherms determined gravitnetrically at 25*C on "never-heated" and heat-trented samples of an emu kino-] knlymeri/ed l'V< 1 |>owtlevai e shown in Fi[>. fi. and 2S(' isotherms obtained with the Digisnrh 2300 for u similarly treated pair of suspension-type PVC's an* shown in Fig. 7. The two techniques for mcasunnj; sorption are in excellent agreement, both clearly shott ing isotherm curvature ofdual-mode form and a reduc tion in CO, solubility following heat treatment. The apparent solubility coefficients corresponding la the total COt sorption at atmospheric pressure in thew experiments are appreciably larger than the coefficient* obtained by Tikhomirov, et id. (6) from Umc-Ljf permeation experiments. It seems likely that the coefficients of Tikhomirov, et td. are in error, since apparent, rather than true, dilTusivities wr presumably obtained fn>rn their measured time lags, and the solubility calculated from permeability and ap parent diiTuiivity ignores the contribution of im mobilised penetrant (Langrouirian sorption) to the total concentration of sorbed CO,. The equilibrium uptake of CO, by a rigid FVC film was very similar to that of the heat-treated powder (w Fig. 6); it therefore seems unlikely that surface adsorp tion plays a significant role in CO, sorption by these* PVC powders. Measurements with CO, in the Beckman pyennmeh-r have been performed using a rungt- of iiiilud pressure*. P>, from 25 to 200 kPa (0.25 to 2 aim). Values of obtained for 'm-vor-lM-iiled" und heat-treated pnrtiuiiv ofa suspension-type FVC powder are plotted as a func tion of Pi in Fifi- 8. Since Auil#&P correspond* to the si-cant slop** of the sorption isotherm between P\ und Pi a* 2 Pi, the pycnometer data can he compared with the gravimetric und Digisorb isotherms (Fig*. 6 and 7). Excellenl agreemeot is found aiiaaig lla-se three sets of data. All show the marked reduction nl (.`tt, sorption following huut treutment; the decrease of Au./^Ap with Fill. b. Surption isotherm* for CO, in nmuiaim PVC at 25C, liroviDn-tni data, Fin. 7. borptiun isotherms for CO, in suspension PVC at 25`C, Desorb 2500 dula. 4 3 $ i s* -T i. FiU- $ ion inert and the i T} estin wh it Her* norn conti rion afitni modi slope Ch, \ cept P). T the s comi <0.7 < Lang and . obtai dualplots to 5. magr repot ethyl cellu Cc heat< ; ! AP00010819 r (Ji-ji ii/irf/ii and Vit/u//j7ui' .Study oj the Sorption itf Uum-s mui Vupors in PolytVintjl Chloride) Powders I fig.&.S'ltfint \(irf/((un ctMt/jivienlv, fw>n&P,jorCQxin *u*pnlion PVC at 23*C, gas pycnometer data at varied P,. increasing P is consistent with the isotherm curvature; wd the values of AudgAp agree well with the slopes of tin isotherms at corresponding pressures. The composite CO* sorption data provide a moults of estimating the parameters of the dual-mode model, which is generally expressed (2} in the form p i Ln c - Cu + Cu - k,,p + (fi) Here C is the total sorption, Ca the contribution of Bormal dissolution, CH the hole-filling or Langmuirian contribution, k,, the Henry's Law constant, C',t the sorpbon capacity of the "holes'* at saturation, and b the hole affinity constant. The usual procedure* fur evaluating the Bodl parameters is to obtain k from the asymptotic dope ofC vs P at high P, subtract k,f from C to obtain C, then determine C and b from the slope and inter cept of "Langmuir plots" (either l/C vs 1/P or P!Ctt vs H The pycnometric daata shown in Fig. 8 suggest that the sorption coefficients for lioth samples uppniuch a common asymptotic value ofapproximately l mg/g-atm R.7cc STP/ee-atinJ. Using this figure as an estimated Langmuir plots were constructed from the gravimetric Digisnrb data of Figs. 6 and 7. Linear plots were 'ned in all cases, supporting the applicability of tb<* -inode model. "Hie slopes und intercept* of these yielded values ofCf* from 2.5 to 7.1 mg/g-atm (1.8 5.1 cc/cc-atm), and of b from 0.4 to 0.8 atm"l. The titude of these parameters is consistent with those ported for CO, in olher glassy polymers, o.g., poly thene terephthalate (2). polystyrene (9), and ethyl teHulose (10). Comparison of the CO, sorption results for "neverbated'' and heat-treated PVC samples suggests an in teresting relation between thermal history and sorption parameters. The apparent common asymptote of the Atii/gAp vs P curves (Fig. 8) indicates that which reflects the contribution of normal dissolution, is inde pendent of thermal history. A measure of the contribu tion nf Langmufriun sorption relative to normal dissolu tion, at very low CO, pressure, is given by the ratio Ci/JyJki,. For "nover-huatiHl" samples, the gravimetric data on emulsion PVC give C'nb/ki, * 4.3. and the Digisorb data on suspension PVC give C'tJ>lku * 3.8; the corresponding figures for the heat-treated samples arc 2.0 and 2.2. Thus the history-dependence ofCO, sorp tion appears related predominantly to the Langmuirian or hole-filling term in the dual-mode model. This rela tion, in turn, seem* to support the inference drawn from VCM sorption studio* (5) that post-polymerization thermal history controls the hole or microvoid content of PVC samples. Further data on the relation between sample history and inferred microvoid content have been obtained from gas pycnometer solubility measurements with CO, on PVC powders heat-treated at varied temperatures. Data were tukun at low P\ (0.25 atm) where history effects are most pronounced. Figured shows Au>/gAp us a function of annealing temperature for portions of a PVC previously not heated above 50*C, Annealing at temperatures up to T produced a significant reduction in inicrovoid content measured by CO, sorption. Organic Vapors The study of organic va[K>r sorption in glassy ja>lymers, as compared to that ofgases, is complicated by two significant factors; the much lower diffusivity of the larger vapor molecules greatly retards the attainment of diffusion equilibrium, and sorption exjicrimenls cun lie pcrlonncd on a convenient time scale only with fine tOLYtiU (NGIHiUtlHG AMD SOtHCl. MIQ-JAHUAAY, 19*0. V*J. 20, Ho. 1 99 1 V I f A. K. licrt'm powder s.tmpU-s ill). The occurrence of reluxutkm- ctmtvulli-d swelling, which may be responsible for a significant portion uf the total sorption when a glossy polymer is exposed to tin organic vapor. also e-omplieab'*. llieitoalyNisd I. 12). Ihvvmus study ofthri'llt'Cls of Uine .mil sample history on vapor sorption isotherms suggest that different levels of "equilibrium" should In- <-omid- rred m glassy pulynu-r/orguuie vupor systems {13). Tin* uttaimm-ol of a uniform penetrant concentration in the polymer represents ''diffusion equilibrium". which cun he approached in a few minutes, or less, in Hne powders. "Keluxuliim equilibrium" muy la* said to occur whim the soennd-stugo. relaxation sorption has ceased or slowed to an immciomruble rate; days or weeks may l>c required to reach this point, depuration of the contributions of relaxation and diffusion controlled sorption appears pewsililc in experiments with line powders, us diffusion equilibration may he approached before significant ( ). Srelaxation occurs 12 hurt-time sorption experiments have been used here to estimate the "qnasrii'(|iiiiiltriiuu" Milubility of urguuic vapors in glossy PVC before tlie occurrence of u significant relaxation* eontnill-d swelling. Vinyl Chloride. The previously published sorption "isotherms" for the Vi .system (I j were obtained from experiments in which the VCM pressure was in creased incremenlaHy over periods of many hours; tinsorption therefore uu iuded a substantial onutrihirifou hoin rehisation/eoiitrolled swelling. To miiiiniize this ellect, gravimetric sorption data have Ireen obtained for hrief(Sl min) exposures of PVC sample* to Vf.'M vapor .il :i soeeessiou oi pressures; between exposures, sam* pies were held under vacuum lor at least 30 min. The PVC used in these experiment* was a monodisperse emulsion polymer of 0.11 particle diameter; its cal culated half-sorption time for Fickiun diffusion of VCM .il (P 3 2 x }f) l* rmVn) (10) was less than one second. The amounts of VCM sorbed in 30t could thus be taken to represent "diffusion equilibrium" with a negligible contribution of relaxation. The 30 s VC.'M sorption data obtained ut 3U^C for "never-heated" and heat-treated portions of this PVC are plotted againft the relative pressure of VCM f, * <.M atm) in fig. 10. The isotherms defined by these short-time VCM sorption data again show "dual-mode" curvature and a marked dependence on sample history. Moreover, the data for both samples appear to approach an asymptotic sfojx- equal to the low-activity limiting slope* (88 mg/g l*,..i or 19.3 mg/g-atm) of the Flory-Huggins curve de termined from earlier work at higher VCM pressures (1). This value was taken as ki, in order to estimate the parameters of the dual-mode model from lbe lineur l-augmuir plots. For the "never-heated" sample, the values found were Ce * 3.6 mg/g, b * 29 atm'1, and for the heat-treated sample. Cl, " 1.8 mg/g, h * 43 uttn-'. These results yield values of5.3 ami 3.9. resjavlivdy. lor the ratio Ciih/ki, iii never-huuted and heat-treated samples, significantly higher than the corresponding values in CO* sorption. From the VCM results, as with <'0*. it appears that the effect of thermal history is fill, #/>. Sorf/lion i\nlh>`r)Mn fur VCM in It.11 fitu i`inniiunt PVC fit Uf'C, gfoi-Oiu-liir itutti, :ttt * surfiUtnt iittiv. ussnc-ntlcd Willi the lioli-filling term. ndliei llian the Henry's Law term, of the dual-mode model. Methanol. Short-time gruvimetrk' sorpiimi data far melhiinol vujkir with never-heated and heut-treuWd samples of a smpefiskoHyjle l*Vf.' powder at 40C on- shown in Fig. 11, plotted against the relative pressureof methanol (P,, m 260 min llg). For these PVC samples, the estimated half-sorption lime lor Fickian diffusion of methanol is approximately 5 s; the plotted 1 min sorp. tion values, therefore, represent estimates of the "equi librium" uptake Ih-fore uppreciuhle relaxation occurs. The data define isotherms of dual-inode form which approach a similar asymptotic slope for Imill samples. Tlie dual-mode parameters obtained from these data for the never-heated sample are k/, * 31.9 mg/g-atm, C}f * i .69 It * 22 aim'1, and for tin- lieut-treun-d sam ple. kf, * 27.2 mg/g-atiu, C 0.50 mg/g, h .Malm"1. Oitee again, the effect ofsample history appears princi pally associated with the hole-filling term of the dud- mode model. /*g. //. Sorption (rollutfmx fur mvthunul in mypenmm PVC at <trC, gravimetric Jala, I mm sorption (line. 100 K>LYM* CNGJMffftMG AND SC/fNCf, MfO-UWlMAV. 1990, Vri. 30, M. I 6 S I'm. 12. jot'. * OlH xureim differin vapors rxtensi tlie dut of thesi determ effects. U-hlltiU 18 h oft been oi -.ubstun tion. tb historytrants s The c porimei POLYMM AP00010821 C.irji mu ll n mill t iluiiu tn, Study </ l/ir Snr/Jlwm o/Cwni-v muj Vapor* iu Poly(Vinyl Chloride} Putvden k sorption ofa wide variety of gases and organic vapors in glassy PVC follows the dual-mode sorption theory and also depends upon the post-polymerization thermal his tory of tlte polymer sample. Generally similar Inihavior is observed for penetrant molecules differing widely in size, polarity, and affinity for PVC. In the cases where the data permit estimation of the individual parameters of tlu* dual-mode model, i.e., curium dioxide, vinyl chloride, and mcthunol, the history-dependence of sorption appears to he related to the holc-lilliiig term, rather than the normal dissolution term, of the model. This resull lends support to earlier inferences (5) dial the major effect ofpost-polymerization history variations an PVC is to alter the polymer's content offroxen-in holes or miernvfiidi. i ?r" ft 12. Siiifiliun t\'ifhcnn\ {or n-hiitutie in VC. rm imvhii iliiin. uujiliuii liuu-i. 'tk h, PVC ill Other Organic Vapors. Gravimetric sorption men- Mir<-iii<-iiK iJmi Imtii riirurd i iiit mi PVt I samples of differing Inslurv Midi .iccltuic. IhiIuuc, uud lcu/.cne Vapors ut low activities. Tin* data arc not sufficiently extensive. however. to allow quantitative estimation of the dual-mode pur.nnrlrrs. Moreover, (lu-dillusivittes oftlu'M1 lurgci molecules are too low (or unambiguous determination of sorption unconfounded by relaxation effects. The data shown in Fig. 12 wen- obtained for the js-hulaue/PVt! sysO ui ill W'iin experiments involving Uf It nfi'oiilai l .it r.ieli jncssiiie, .Similar results have also been obtained fer acetone and Ircnzonc. Despite the ailatantiul contribution of relaxation to the overall sorp tion, the general dual-mode eharaeter and pronounced kiilory-de|*rilcncr of the dala are elenr for all pent-- tiuts studied. CONCLUSIONS The* eonsistenl evidence from thrift- indc-pemient ex perimental (eflmiques presented' here shows that the -.ur- ACKNOWLEDGMENTS The author is grateful to Miss Konnu Gander for porforming most ofthe experiments and calculations in this study, to Miss Carolyn McKutcn for cooperation with "the Digl-sorh 2500 experiments, to Prof. 11. 11. Ilopfcu}x*rg for continued eonstruetive discussions, and to 'Hie UEGondrioh Company for permission to publish this work. KBFUHENCtiS 1. A. K. Kerens Angela. Makrumut. Chtm.. 47.4#7 (PI75). 2. A. S. Mk li.n-K. W. U. ViHli, .kii! J. A. Hume. J. Apfil. Phys.. :u, I MOO.;/. 3. !. Y llir.igmmv. D. S. Hirt, and V. .N. tlreniova, Vjj>- okottuil. Stiedin. Ser. B., 16, 17SUM7AI. 4. X. Frlisiinif A. K. llatmeli-t,M.'S.Sipfijm<tiu?i Swies No, 24. . K2(l70). r,. A. It. hen-ns, y. Mrn'miiml. .S>.-/Vy., H14, 4K.'H|1j77j. <). It. I'.'liklmmirnv, It. ii. Ilujilenlwfg. V.T. Stuinacti, mid J, L. William*, Mukmnuil. Cfiem., UK. 177 U9KH). 7. It. M. Hurrer, II. Mullinder, and P. Jj.-L- Wong,Polymer, 8, .121 (l`*7). K. A. IV llrfi-nv to In- jMililtslicil. 0. W, tt. Vu-tli, I*. M. Tam, and A. 2. Michaels, j. Colloid Interface Sti., 23. 360 (1968). 10. A. H. dutn.W. J. Kro,uudD. H. PuullJ.Mcm/mtnrKcH.,3, 117 (IW7K). 11. A. H. Kerens, Polymer. IK, ttj7 < W77). 12. A. H. Ken......mil II. li. llopiei.lwra.Po/ymer, 10,4KU(IU7K>. 13. A. K Kerens.J. Membrane Set.. 3,247(197H). \ tOtVMM fNC/NfUONC AMO SCICHCi. MiO-JANtTAJtY, 1940. Vol. 20. M. 1 101 AP00010822