Stabilization of polyvinyl chloride using epoxide compounds

Stabilization of polyvinyl chloride using epoxide compounds

1056 S . R . IVA_~OVAe2 a/. 18. V. S. SHTEINBAK, V. V. AMERIK, F. I. YAKOBSON, Yu. V. KISSIN, D. B. IVANYUKOV and B. A. KRENTSEL', Europ. Polymer J...

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1056

S . R . IVA_~OVAe2 a/.

18. V. S. SHTEINBAK, V. V. AMERIK, F. I. YAKOBSON, Yu. V. KISSIN, D. B. IVANYUKOV and B. A. KRENTSEL', Europ. Polymer J. 11: 457, 1975 19. S. Ye. BRESLER, A. A. KOROTKOV, I. I. MOSEVITSKII and I. Ya. P O D D U B N ~ , Zh. tekhn, fiziki 28: 114, 1958 20. N. M. CHIRKOV, Kinetika i kataliz 11: 821, 1970

Polymer Science U.S.S.R. Vol. 20, pp. 1056-10{}2. {~) Pergamon Press Ltd. 1979. Printed in Poland

0032-3950/78]0401-1055507.50]0

STABILIZATION OF POLYVINYL CHLORIDE USING EPOXIDE COMPOUNDS* S. R. IVANOVA A. G. ZAR~OVX and K. S. Ma~SKER 40th Anniversary of October Bashkir State University

(Received I 1 July 1977) I t was shown t h a t the addition of epoxide compounds (EC) to PVC containing a n inert heat stabilizer (Ba, Ca or Na stearates) reduces the rate of separation of HCI from PVC macromolecules. Dehydrochlorination of PVC in the presence of EC is only inhibited as a result of the formation of polyconjugated systems, the rate ot statistical separation of HC1 remaining constant. During the breakdown of PVC by the action of heat in a mixture with EC the oxyrano ring reacts with ketochlorallyl groups (KCAG) of polymer macromolecules with the formation of a 1,3-dioxalano group, which does not affect the heat stability of the polymer. A reduction in the rate of HCI liberation during the breakdown of PVC stabilized b y EC in solid phase in the presence of Ba, Ca or Na stcarates is due to complex formation between EC and KCAG of polymer macrochains.

EC ~ E normally relatively weak stabilizers of thermal decomposition of PV(3, however, their effect suddenly increases in the presence of metal carboxylates -stabilizers and accepters of ttCl. For this reason EC are normally used in the form of synergic mixtures with some metal carboxylates. Irrespective of the wide use of EC in the practice of stabilizing PVC [1] the chemistry of their action, including that in the presence of metal carboxylates so far remains obscure and debatable to a large extent. EC mixed with PVC in the presence of metal carboxylates (e.g. Ba stearate) markedly reduces the rate of dehydrochlorination of PVC (Table 1). A study of kinetics of gross dehydrochlorination of PVC veal, bearing in mind the statistical elimination of ]-IC1 Vs and the extension of polyene sequences Vp [2, 3], enabled us to show experimentally t h a t the presence of EC in the polymer corn* Vysokomol. soyed. A20: No. 4, 936-941, 1978.

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position (e.g. butylepoxy stearate (BES) or 2-ethylhexylepoxys~earate (0ES)) does not influence the rate of formation of single bonds ~C----C_~ in a n y point of macromolecules b y the random law Vr, b u t markedly inhibits the formation of polyenes Vp (Table 1). This is also confirmed indirectly b y another fact: PVC T A B L E l . K I / ~ E T I C P A R A M E T E R S OF I ) E H Y D R O C H L O R n g A T I O N OF P V C

AT 175 ° U24"DER VACUUM

( ] 0 - 4 TORR) I N T H E P R E S E N C E OF E P O X I D E S T A B I L I Z E R S

[EC], mmole mole PVC 0 5 10 20 30 50

VHCI×10 8

V8×10 7

Vp×10 8

Vp/Vs BEC 0.80 0.80 0.80 0.80 0.80 0-80

0"70 0"44 0'38 0"39 0"39 0.40

Up/V8 (mole HOl/mole PVO).soe-1

(mole HC1/molePVC).see-* 0-78 0.52 0.46 0.47 0.47 0-48

VHCl×I0e[ Vg×107 vpxl0 s

8"0 5"5 4"7 4-8 4"8 5"0

0"78 0'56 0'54 0"40 0-40 0-40

OEC 0-80 0.70 0-80 0.48 0-80 0.46 0.80 0-32 0.80 0.32 0.80 [ 0"32

8.8 6.0 5.7 4.0 4.0 4.0

subjected to breakdown in the presence of EC and Ba stearate (175 °, 10 -4 torr) is coloured to a much slighter extent than the polymer decomposed under the same conditions b u t without EC. On increasing EC content in the P V C - B a stearate mixture, the effect of the statistical elimination of HC1 during dehydrochlorination of PVC increases, compared with the extension of polyenes (the ratio of Vp/Vs decreases). As a consequence, the initial colour of PVC is retained for a longer period of time. Stabilizers or other active additives which slow down the extension of polyenes vp, of course, usually impart a lighter colour to the polymer during decomposition as a result of the reduction of the average length of polyene sequences. There are basically three hypotheses described in the literature, which explain the stabilizing action of EC in relation to PVC: a) interaction of EC with ]=IC1 separated during the decomposition of PVC [1, 4] HC2--Ctt--R + C1H2C--CH(OH)--R \ / (1) 0 b) reaction of EC with a chlorine atom of the fl-chlorallyl group which, as proposed previously [1], activates the decomposition of PVC and results in the replacement of the labile chlorine atom by a more stable ether group [5, 6] 0 ------CH=CIt--CH-.CII~ . . . . . . I

Cl

( ~/1 . . . . . \/

CI{ ::CII~--C[I--CII,. . . . . . . . (')-. ~ cI

~,

(2)

1058

S . R . IVANOVA ~ d.

ad tion of EC to >c:e

bonds contained in PVC macromolecules [7] ....

- - ~ C H = CI-I--~-~-- -~- H2C\/CII--R

CH--CH--~--

--, 0/\

0

(s)

[

CII~--CIIR

In spite of the apparent obviousness in the practice of stabilization of PVC b y epoxide compounds, reaction (1) need not be taken into account because t h e formation of fl-ehlorohydrin is only observed during the decomposition of

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15

17

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18 2! 23 V,IO -z cm-!

Fro. 2

Fro. 1. Relation between the number of internal double bonds (I) and KCAG (II) in PVC macromolecules containing Ba stearate and EC and the time of thermal decomposition of the polymer at 175°: 1 -- BEC, 2 -- OEC. Fzo. 2. IR spectra of the initial PVC (1) and that heated for 20 (2) and 40 min (3) in a mixture with BEC (30 mmole/mole PVC); 175°, vacuum. t h e polymer in a closed volume. In the presence of inert stabilizers aeceptors o f HC1 (Ba, Ca or Na stearates in our experiments) chlorohydrin was not formed a s long as metal carboxylates were present in the system. The use of epoxide oxygen during the thermal decomposition of PVC in a mixture with EC is not accompanied b y the formation in I R spectra of an absorption band in the region o f 3400 em-1, typical of the HO group of chlorohydrin, which was observed during the interaction of a binary mixture of PVC with EC. However, this could be expected bearing in mind t h a t the rate constant of the reaction of HCI with metal carboxylate at 175 ° was of the order of 103 mole/mole PVC-sec -x [8]; this explains the much higher reaction rate of HCI with a HCI stabilizer acceptor, compared with the rate of interaction of HCI with EC. I t is important to note that it is :precisely the prevention of the formation of chlorohydrin catalyzing dehydro-

Stabilization of polyvinyl chloride

105~

chlorination of PVC, which produces a well known increase in the effect of EC' as stabilizers of PVC. Reactions (2) and (3) cannot have a marked effect either because the rate~ of dehydrochlorination of PVC, at least at the initial stages which are sufficient for the polymer to lose (irreversibly) a number of requisite operational properties, is not determined b y the contents of fl-chlorallyl groups in the PVC macromolecules; this is the flmction of the contents of ketochlorallyl - - ~ , - - C - - C H = 0 =CH--CHCI--CH~. (KCAG) or conjugated (>C--C<),, groups when n~>2 [9, 10]. The stabilizing effect of EC in relation to PVC should therefore be linked with the interaction of epoxides precisely with these active centres of polymer decomposition and first of all KCAG. For KCAG EC do not react by system (3) since the contents of KCAG in macromolecules during the decomposition of PVC in the presence of EC and Ba, Ca or Na stearate (175 °, purified nitrogen), determined by alkaline hydrolysis of PVC [9] do not decrease in the course of thermal dehydrochlorination, although the overall contents of internal >C=:C< bonds formed at random during the elimination of HC! from PVC (fl-chlorallyl groups), increase (Fig. 1). Since rates of statistical dehydrochlorination of PVC Vs are the same in the presence or absence of EC (Table 1), it is obvious that the epoxide stabilizer together with the metal carboxylate does not affect the > C = C < bonds of labile KCAG. Formally, the effect of EC on rates of reactions Vs and v, correlates with results of experiments carried out with model compounds [5, 6] and enables us to aa~ume that a reduction in the rate of dchydrochlorination of PVC is due to the reaction of EC with labile structural macromoleeules of PVC with active centrcs of polymer decomposition. A new, possible trend in the interaction of EC with PVC -- tlm reaction of EC with carbonyl oxygen of KCAG -- should be pointed out to form a 1,3-dioxMane group ....

C--CI-I=- CtI--CIIC[--Cll,., O

i It2(:

CIt--(CH.)nCOOR

(J - - ~--(.'.--.-C 1i = C I t - - C I [CI--CI I.,-- ~ - -

/\

O

I

II2C-

(4~

0

I

CIt--(C112),,COOl/

Dioxalane with a yield of the order of 10 w t . % was formed while heating in the presence of catalytic quantities of HC1 (50-60 °, 4 hr) methylvinyl ketone -a compound simulating KCAG with epiehlorohydrin. Similar reactions are also known from the literature [11]. Although the acetal group is not clearly shown. I R spectra of PVC a f a r interaction with e.g. butyl ester of epoxystearic a c i d as a consequence of low (of the order of 10 -4 mole/mole PVC) concentration o f

1060

S . R . IvA_~ovA et a/.

KCAG, typical absorption of carbonyl oxygen in the region of 1710-1720 cm -1 of the ester group of EC suddenly increases with exposure time (Fig. 2). This effect may, in our view, be explained by the reaction of EC with the ester group graft to PVC of an epoxide stabilizer molecule and the well known reaction [12] taking place during the catalytic action of proton acids /

\

c

cH.~ o

I

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I t should be noted t h a t on using polyep0xides reactions (4) and (5) m a y result in crosslinking of macrochains. T A B L E 2. GROSS D E H Y I ) R O C H L O R I N A T I O N OF P V C - ~ - K E A T S T A B I L I Z E R

(Ba STEA_*~T~)AT 175 ° r~r V A C U U ~ PREDATED

T~ ° C

100 100 100 175 175 175

COMPOSITION OF

A F T E R T H E REMOVAL OF E C FROM A

PVC-kEC-b~.EAT

Time hr

ramole [EC]'mole PVC

3 6 14 0.3

30 30 30 30 30 30

0.5 0.7

STABILIZER*

VHm× 106, [ mole HC1 [m~oleP-V-cJ"soc0"80 0"98

0.97 0"85 0"87 0"85

* v nct o f t h e Initial PVC was 0"78 × I0-*, of preheated PVC (175 °, vacuum 10-* tort) - 0 . 8 5 × x 10 -a (mole HCl/mole PVC).sec -l.

PVC, exposed to 100 ° for 3-4 hr or to 175 ° for 0.3-0-7 hr in the presence o f EC and, according to results of Table 1, characterized by a reduced rate of dehydrochlorination after the removal of EC by extraction with diethyl ether in a Soxhlet apparatus and three fold reprecipitation from cyclohexanone solutions in alcohol, reverts to the heat stability of the initial PVC (Table 2). This fact is satisfactorily reproducible experimentally and several major conclusions m a y therefore be drawn. Although EC interact with carbonyl oxygen of KCAG, this does not affect the heat stability of PVC. The rate of dehydrochlorination of PVC only decreases in the presence of EC, this however, is not due to the chemical interaction of macromoleeules, including t h a t taking place according

Stabilization of polyvinyl chloride

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t o s y s t e m (2). T h e well k n o w n r e a c t i o n b e t w e e n 4 - e h l o r o h e x - 2 - e n e a n d e.g. e y e l o h e x e n e o x i d e b y s y s t e m (2) o n l y t a k e s p l a c e in s t r o n g p o l a r m e d i a (aeetonitrile, m e t h y l e t h y l k e t o n e ) , or in t h e p r e s e n c e o f salts o f c o o r d i n a t i o n u n s a t u r a t e d m e t a l s [5, 6]. S t a b i l i z a t i o n o f P V C u n d e r c o n d i t i o n s w h e n e h l o r o h y d r i n is n o t f o r m e d ( c o m b i n a t i o n o f H C I w i t h B a s t e a r a t e ) is t h e r e f o r e p r o b a b l y d u e t o c o m p l e x f o r m a t i o n b e t w e e n E C a n d labile g r o u p s c o n t a i n e d or f o r m e d in P V C - K C A G m a e r o m o l e e u l e s or c o n j u g a t e d ( ) C -C~x)n b o n d s . C o m p l e x f o r m a t i o n r e d u c e s t h e r e a c t i v i t y o f a c t i v e e e n t r e s o f t h e b r e a k d o w n o f P V C a n d t h u s lowers t h e rate of dehydroehlorination of the polymer. c-70 P v c was examined having the following properties: density 1.41 g/em3; intrinsic viscosity in eyclohexanoae at 25 ° Jr/l----1"43; l~w= 157,000; content of KCAG ~o=0.91 X × 10 -4 mole/mole PVC. Butylepoxystearate and 2-ethylhexylepoxystearate contairfing ~3o;o epoxido oxygen were used as epoxide stabilizers. Decomposition of PVC compositions was carried out in sealed ampoules at a residual pressure 10 -* tort. Ba, Ca or Na stearates were used as HCI accepters isolated during the decomposition of the polymer; these were used in a quantity of 2.5 mmolc/mole PVC. Identical results were obtained in every ease. The mixture of the polymer with the heat stabilizer was prepared by pulverizing initial components in a porcelain beater for 1 hr. The cpoxido compolmd was introduced in solution form in diethyl ether. The anmunt of HC1 combined with a he,it stabilizer was determined mercurimetrically in the presence of a diphenyl earbazone indicator. ~C = C~ internal bonds were determined and kinetic paratneters of statistical dchydrochlorination of PVC and the formation of polyconjugated sequences were calculated and ketochl<)rallyl groups determined by a previous deseriptioll [10, 13] by hydrolysis and oxidafive ozonolysis. I R spectra of PVC films were obtained in a UPs-20 device. Films were cast from ,5°~/ polymer solutions m purified THF. PVC decomposed in the presence of EC was freed from cpoxido stabilizer by extraction with diothyl ether using a Soxhlet apparatus, followed by three fohl fractional reprecipiration in pur~ nitrogen with alcohol from 5(,)o PVC solution in cyclohexanoae. 1,3-Di~xalane was synthesized from methylvinyl ketone and epichlorohydrin by the followin~ method: a mixture of equimolar quantities of methylvinyl ketone and epoxido was heated at 50-60 ° for 4 hr in the presence of 6 ml ]ICl and then left for 48 hr at room temperature. Eeactioa products were analysed by GLC using an LKhM-69 device with a heat conductivity detector. Analytical conditions were: carrier gas--hydrogen, stationary phase Apiez(m-~, column length 5 m, column diameter, 3 rum temperature of the evaporator, 200 °, c<)hmm temperature, 150 °, velocity of hydrogen supply 66 ml/miu. The 1,3-dioxolano peak was identified by comparing the retention time of the product c)f synthesis with the retention time of 1,3-dioxolano, synthesized using BFsO (C2H5)2 as catalyst by conventional methods [ 14].

Translated by E. S~.~[FRE REFERENCES 1. K. S. MINSKER and G. T. FEDOSEYEVA, Dcstruktsiya i stabilizatsiya polivinilkhlorida (Breakdown and Stabilization of PVC). Khimiya, 1972 2. K. S. MINSKER, Al. Al. BERLIN, D. V. KAZACHENKO and R. C,. ABDULLINA, Dokl. A N SSSR 203: 881, 1972

1062

V.P.

YEPIFANOV

3. K. S. MINSKER, AI. AI. BERLIN, M. I. ABDULLIN, S. R. IVANOVA, D. V. K A Z A CHENKO and V. P. MALINSKAYA, Dokl. AN SSSR 241: 1117, 1974 4. J. WYPYCH, J. Appl. Polymer Sci. 19: 3387, 1975 5. D. F. ANDERSON and D. A. MCKENZIE, J. Polymer Sei. 8, A - l : 2905, 1970 6. T. V. HOANG, A. bHCHEL and A. GUYOT, Europ. Polymer J. 12: 347, 1976 7. R. R. HOPF, Materialy Mezhdunarodnogo simpoziuma po vysokomolekulyarnoi khimii (Proceedings of an I n t e r n a t i o n a l Symposium on High Molecular Weight Chemistry). Moscow, 1960 8. K. S. MINSKER, V. P. MALINSKAYA and V. V. SAYAPINA, Vysokomol. soyed. A I 4 : 560, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 3, 628, 1972) 9. K. S. MINSKER, AI. A1. BERLIN, V. V. LISITSKII, S. V. KOLESOV and A. S. KORNEVA, Dokl. AN SSSR 232: 93, 1977 10. K. S. MINSKER, AI. AI. BERLIN and V. V. LISITSKII, Vysekomol. soycd. BIS: 54, 1976 (Not translated in Polymer Sei. U.S.S.R.) 11. F. G. PONOMAREV, N. I. CHERNOUSOVA and G. N. YASHCHENKO, Zh. obshch, khimii 5: 1156, 1969 12. D. L. RAKHMANKULOV, I. L. LAKILMANKULOVA, V. S. MARTEIMIANOV a n d E. A. KANTOR, React. kinet. Catal. Lett. 6: 181, 1977 13. K. S. MINSKER, V. V. LISITSKII, Z. VYMAZAL, M. KOLINSKII, Ya. KALAL, Ye. N. SHVAREV, I. B. KOTLYAR, I. I. GORBACHEVSKAYA and I. G. SAMOILOVA, Plast. massy, No. 1, 19, 1976 14. F. G. PONOMAREV, Dokl. AN SSSR 108: 648, 1956

Polymer Science U.S.S.R. Vol. 20, pp. 1062-1068. ~) PergamonPre~s Ltd. 1979.Printed in Poland

0082-395017810401-1062507.5010

ACOUSTIC STUDIES OF DILUTE POLYETHYLENE OXIDE SOLUTIONS* V. P. YEPIFAI~OV I n s t i t u t e of Mechanical Problems, U.S.S.R. Academy of Seiences

(Received 25 July 1977) Experiments were carried out with two systems: with a P E O solution in w a t e r and a model PS suspension of the same density which are characterized by a frequency dependence of absorption. For a PEO solution of 5 × 10 -6 concentration a relaxation process is observed, which may be presented by the relaxation time spectrum. When comparing the modulus of viscosity loss G"(eo), calculated from experimental results and the Zimm theory, it was found that the theoretical value is lower by two orders of magnitude than the experimental value. I t is assumed t h a t this discrepancy is due to the cooperative motion of macrbmolecular segments of PEO~ which corresponds to chains that had not been considered theoretically. The characteristic time of relaxation dependent on temperature and having a n order of 10 - t - * Vysokomol. soyed. A20: No. 4, 942-946, 1978.

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