Elastomers and Rubber Elasticity - American Chemical Society

10 Quasi-living Carbocationic Polymerization of Alkyl Vinyl Ethers and Block Copolymer Synthesis 1

MITSUO SAWAMOTO and JOSEPH P. KENNEDY Downloaded by UNIV OF NEW ENGLAND on February 9, 2017 | http://pubs.acs.org Publication Date: July 19, 1982 | doi: 10.1021/bk-1982-0193.ch010

The University of Akron, Institute of Polymer Science, Akron, OH 44325

Quasiliving carbocationic polymerizations of isobut y l vinyl ether (IBVE) and methyl vinyl ether (MVE) were achieved with the bifunctional p-dicumyl chlo ride (p-DCC)/AgSbF i n i t i a t i n g system in CH Cl2 solvent at -70 or -90°C. The quasiliving polymer izations were effected by slow and continuous mon omer addition to a premixed i n i t i a t o r solution (quasiliving technique). The number-average mol ecular weight (M ) of polymers increased linearly with the cumulative weight of added monomer (W), and linear M versus W plots passing through the origin have been obtained. The polymers exhibited narrow molecular weight distributions with M /M = 1.4 - 1.7. Polar solvents (CH Cl ) and lower tem peratures (-70 or -90°C) were optimum for these quasiliving polymerizations. Blocking MVE and αmethylstyrene (αMeSt) from quasiliving polymer (IBVE) dications led to novel triblock copolymers: poly(MVE-b-IBVE-b-MVE) and poly(αMeSt-b-IBVE-bαMeSt), respectively. 6

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"Living carbocationic polymerizations are most difficult to achieve mainly because of chain transfer to monomer and termi nation processes both of which frequently occur i n carbocationic polymerizations. I t has recently been demonstrated (1) that " q u a s i l i v i n g " polymerization ofα-methylstyrene(aMeSt) can be achieved by slow and continuous monomer addition and that the number-average molecular weight (M ) of PaMeSt increases l i n e a r l y with the weight of added monomer. A theory for q u a s i l i v i n g poly merizations has been developed (2). n

1

Current address: Kyoto University, Department of Polymer Chemistry, Kyoto 606, Japan.

0097-6156/82/0193-0213$07.25/0 © 1982 American Chemical Society

Mark and Lal; Elastomers and Rubber Elasticity ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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This paper concerns the quasiliving cationic polymeriza tions of isobutyl v i n y l ether (IBVE) OA) and methyl v i n y l ether (MVE) induced by the bifunctional jp-dicumyl chloride (p-DCC)/ s i l v e r hexafluoroantimonate (AgSbF ) i n i t i a t i n g system. This b i functional i n i t i a t i n g system was selected because our intention was to generate two-headed quasiliving growing species that i n turn was expected to lead to t r i b l o c k polymers. I n i t i a t i o n and propagation i n the p-DCC/AgSbF /IBVE system, for example, i s v i s ualized to occur as follows: 6

Downloaded by UNIV OF NEW ENGLAND on February 9, 2017 | http://pubs.acs.org Publication Date: July 19, 1982 | doi: 10.1021/bk-1982-0193.ch010

6

(1)

To f a c i l i t a t e ionization of _p-DCC, i t was premixed with AgSbF6 prior £o monomer introduction. The p-dicumyl cation [(CH3)2C$CeH^-C (CH ) ] may also form during premixing. The polymerization behavior of polar a l k y l v i n y l ethers and nonpolar olefins (such as aMeSt) are quite different. The pro pagating carbocations derived from a l k y l v i n y l ethers are more stable than those of hydrocarbon o l e f i n s . The high s t a b i l i t y of growing v i n y l ether cations i s advantageous for quasiliving po lymerizations. Although previous studies on IBVE polymerization suggest the involvement of long-lived growing species (5,6) or the absence of termination (7 8»9) * " l i v i n g or "quasiliving" po lymerizations of a l k y l v i n y l ethers have not yet been achieved. Applying the slow and continuous monomer-addition (quasil i v i n g ) technique, we polymerized IBVE and MVE with the £-DCC/ AgSbF6 i n i t i a t i n g system and defined optimum reaction conditions for the quasiliving polymerization of these monomers. Subsequent block polymerization starting poly(IBVE) quasiliving dications led to novel t r i b l o c k polymers: poly(aMeSt-b-IBVE-b-aMeSt) and poly(MVE-b-IBVE-b-MVE). 3

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Experimental Section Materials. Commercial IBVE (GAF Corp.) and aMeSt (Aldrich) were washed with 10% aqueous sodium hydroxide and water, drived overnight over sodium sulfate, and freshly d i s t i l l e d twice over calcium hydride under dry nitrogen. MVE (Matheson, purity > 99.5%) and AgSbF (Cationics Inc. and Alfa) were used as received. The l a t t e r was protected from l i g h t during storage and handling. p-DCC was prepared as reported (10,11). η-Heptane (Aldrich), 6


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toluene (Fisher), and methylene chloride (Fisher) were p u r i f i e d by the usual methods. Polymerization by Slow and Continuous Monomer Addition. Polymerizations were carried out under dry nitrogen i n a 300-cm three-neck, round-bottom flask equipped with a s t i r r e r , a Teflon plug for monomer addition, and a serum cap for sampling. F i r s t p-DCC and AgSbF6 solutions (200 cm i n total) were mixed and s t i r r e d for one minute at the desired temperature. To t h i s premixed i n i t i a t o r charge the monomer was added slowly but continuously at a controlled addition rate: IBVE (mostly 25 v o l % solution) was introduced through a precision solvent-metering pump (Beckman Model 110A) and a glass c a p i l l a r y outlet; MVE was d i r e c t l y condensed into the reactor from a lecture bottle with a regul a t i n g valve through Tygon tubing. At desired times known amounts of aliquots were withdrawn with a syringe from the reaction mixture and were injected into capped v i a l s containing a fewcm methanol. After f i l t r a t i o n and evaporation of v o l a t i l e s yields were determined by gravimetry. 3


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Blocking from Quasiliving Poly(IBVE) Dication. The quasil i v i n g poly(IBVE) dication was prepared as described above. At a desired time IBVE addition to the reactor was discontinued, an aliquot sample was withdrawn with a syringe, and blocking was effected by introducing the second monomer (aMeSt or MVE) continuously to the reaction mixture. aMeSt (25 v o l % solution) was added through the precision pump; gaseous MVE was d i r e c t l y condensed into the reactor (see above). The reaction was quenched with prec h i l l e d methanol (30 cm ). After f i l t e r i n g off the s i l v e r chlor i d e , the reaction mixture was concentrated to ca. 30 cm by evaporation and fractionated with 2-propanol (700 cm ) for aMeStIBVE blocks or an n-heptane (500 cm )/water (200 cm ) mixture for MVE-IBVE blocks. 3

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Polymer Characterization. Molecular weight distributions (MWD) were determined by gel permeation chromatography (GPC) on a Waters 6000A chromatograph equipped with yStyragel columns. M and M /M were calculated from GPC traces using polystyrene c a l i bration. M s thus obtained were i n good agreement with the corresponding absolute values determined by GPC/low-angle laser l i g h t scattering technique (12). The composition of the blocking products was determined by '''H-NMR spectroscopy on a Varian T-60 spectrometer (ca. 20 wt% polymers i n CCli*). n

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Results and Discussion Quasiliving Polymerization of IBVE i n CH2CI2 at -70° and -90°C. IBVE was polymerized by introducing the monomer slowly and continuously into a premixed £-DCC/AgSbF6 charge i n CH2CI2 at -70 or -90°C. In a l l experiments polymer y i e l d s at any time


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were i n good agreement with the cumulative weight of added I B V E , indicating consistently quantitative monomer con versions. Figure 1 shows a t y p i c a l set of GPC traces for poly(IBVE) s obtained at -90°C. The MWD s are narrow (M^/Mn = 1.4 - 1.7; see Figure 2) and s h i f t i n g towards higher molecular weights with time; no significant broadening can be observed. M and M /M values calculated from these data were plotted against W J B V E (e.g., Figure 2). At both -70 and -90°C M i n creases with W J B V E - Importantly, M versus WjBVE plots are l i n ear over a wide range of W J B V E ' S and pass through the o r i g i n . At higher W J B V E ^ however, the plots tend to deviate from l i n e a r i t y . Figure 2 also shows " M Q - W J B V E relationships obtained at d i f ferent monomer-addition rates (0.35 to 1.68 g/min/200 cm ). The monomer-addition rate does not seem to affect the M -WxBVE re lationships, which give a single straight l i n e passing through the o r i g i n with W J B V E ^^β» provided the monomer i s added slowly and continuously. The effect of the i n i t i a l i n i t i a t o r concentration (Ij>DCC] ) on M was studied at -90°C (Figure 3). ^ increased at a l l [£-DCC] s and the versus W J B V E plots passed through the o r i gin. The slopes of the linear portions of these plots were i n versely proportional to [£-DCC] . Similar results were obtained with samples prepared at -70°C. These results demonstrate that quasiliving polymerization of IBVE can be achieved by the use of CH2CI2 solvent at -70 or -90°C. This novel quasiliving technique leads to poly(IBVE) s with controlled (and high) molecular weights and narrow MWD. ^IBVE> ^ I B V E f

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Number of Polymer Chains. The quasiliving character of IBVE polymerization i s further supported by quantitative analysis. Figure 4 i l l u s t r a t e s changes i n N, the number of poly(IBVE) chains produced per unit i n i t i a t o r (jp_-DCC), as a function of WjBVE* ϋ i s defined by eq. 2: W IBVE Ν -

M .I -DCC] n

£

(2) o

In ideal l i v i n g polymerizations Ni i s equal to unity throughout the experiment. At -70 and -90°C the obtained Ν values are close to unity and remain unchanged during the early stages of the po lymerizations, indicating the presence of quasiliving polymeri zations. During the l a t e r stages of the polymerization, however, Ν gradually increased with increasing WjBVE* probably because of chain transfer to monomer. Effect of Temperature. In experiments carried out at -30° using CH2CI2, M s increased with WjBVE but the absolute values were an order of magnitude smaller than expected and the M f

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Figure 1. MWD of poly(lBVE) obtained in CH Cl at -90°C: [p-DCC] is 0.50 mM; [AgSbF ] is 1.1 mM; IBVE addition rate is 0.76 g/min (3). 2

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Figure 2. M and M /M as junctions of monomer input W VE in CH Cl at —90°C: [p-DCC] is 0.50 mM; [AgSbF ] is 1.1 mM. IBVE addition rates are 0.38 (Φ), 0.76 (0),1.22 (θ), 1.68 (9). N

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Figure 3. Effect of [p-DCC] on M — W VE relationships in CH Cl at —90°C. [p-DCC]ο (mM) and 0.50 (O), 1.0 (Q), 1.8 (%). [AgSbF ] /[p-DCC] is 2.3; IBVE addition rate is 0.38 g/min (3). 0

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-50°C^=-

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Ρ -70°C, -90°C

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Figure 4. Relationships between monomer input WIBVE and N, the number of poly(IBVE) chains produced per unit p-DSS molecule, in CH Cl . [p-DCC] is 0.50 mM; [AgSbF ] is 1.1 mM; IBVE addition rate is 0.76-0.80 g/min. -30°C (·), -50°C (O), -70°C (Ah -90°C (7U (3). 2

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versus WiBVE plots could no longer be back-extrapolated to the o r i g i n . M versus WjBVE plots for -50°C increased continuously but non-linearly. In Figure 4 the number of polymer chains (N) obtained at these higher temperatures are compared with those f o r -70 o r -90°C. In contrast to Ν values obtained at -70 or -90°C which are close to unity and nearly constant, those for -30 or -50°C are much higher than unity and increase steeply with WiBVE. These trends indicate increasing interference of chain transfer at higher temperatures, i . e . , these conditions are not suitable for quasiliving polymerizations.


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Effect of Solvent P o l a r i t y . Quasiliving polymerization of IBVE was also attempted i n a nonpolar solvent, η-heptane, ajt -50 and -70°C. Figure 5 gives results obtained at -70°C. The M versus WjBVE plots obtained at this temperature are strongly curved. Importantly, the Ν values were less than unity at the beginning of the reactions and they increased beyond unity with increasing WiBVE* Evidently i n i t i a t i o n i s slow i n nonpolar media due to incomplete ionization of the i n i t i a t o r ( i . e . , Ν >1). At -50°C M s remained unchan£ed_(M % 3 χ 10**, l£-DCC] = 0.50 mM) with increasing W J B V E * Mw/M % 2.0. The polymeriza tion i s no longer quasiliving but follows a conventional chaintransfer-dominated course. Nonpolar media are evidently unsuit able for quasiliving polymerization of isobutyl v i n y l ethers. n

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Quasiliving Polymerization of Methyl Vinyl Ether. Similar l y to IBVE polymerization, MVE was polymerized with premixed £DCC/AgSbF i n i t i a t i n g systems i n CH2CI2 solvent at -70°C by slow and continuous monomer addition. Polymer yields were ^100% at every reaction time. Figure 6 shows plots of M of poly(MVE) versus the cumula tive weight of added MVE, W^VE* M s increase l i n e a r l y with i n creasing W ^ V E l the l i n e s pass through the o r i g i n , M i s higher at a lower i n i t i a t o r concentration, [£-DCC] ; the slope of the plots i s nearly proportional to the r e c i p r o c a l of [p-DCC] . These results show that quasiliving polymerization oJE MVE has been achieved by the use of CH2CI2 solvent at -70°C. M^s obtained at different monomer-addition rates (0.50 to 1.13 g/min/ 200 cm ; Figure 6) lead to a single straight l i n e through the o r i gin, which indicates that quasiliving conditions can be maintained independent of the monomer-addition rate i n that range. The linear M versus W^^E plots imply that the number of poly(MVE) chains produced per unit i n i t i a t o r , Ν (cf. eq. 2), i s constant during the polymerization. The absolute values of Ν were greater than unity (2.50 and 2.79 at l£-DCC] = 1.0 and 2,0 mM, respectively), suggesting that chain transfer to monomer may bave occurred during the early stages of the polymerization. In the polymerization at a higher temperature (-30°C) i n CH C1 solvent, M s were much smaller than expected from [£-DCC] ; 6

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Figure 6. M as functions of monomer input W in CH Cl at —70°C. [p-DCC] (mM): A, 1.0; Β, 2.0. [AgSbF ] /[p-DCC] is 2.3. MVE addition rate (g/min) are 0.30 (Ah 0.50 (O), 0.87(D), 1.01 (m),1.13(Q).


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,

the M versus p l o t s showed an i n t e r c e p t , although M s i n creased l i n e a r l y with Polymerizations i n a nonpolar s o l v e n t (toluene) a t -7() C_gave s t r o n g l y curved M versus W p l o t s ; the MWD was broad (M /M = 2.4 t o 3.9). w η n

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Optimum Conditions f o r Q u a s i l i v i n g P o l y m e r i z a t i o n . Table I summarizes ^ " " r e l a t i o n s h i p s obtained under a v a r i e t y o f c o n d i t i o n s . The corresponding t a b l e f o r MVE i s almost i d e n t i c a l . The observed r e l a t i o n s h i p s are c l a s s i f i e d i n t o three c a t e g o r i e s : 1) (0) L i n e a r M^ versus j p l o t s passing through the o r i g i n , i n d i c a t i n g q u a s i l i v i n g p o l y m e r i z a t i o n s ; 2) (Χ) M independent o f w VE' i n d i c a t i n g conventional chain-transfer-dominant polymeri s a t i o n s ; and 3) (Δ) intermediate cases between (1 and 2), where M^ versus W p l o t s are s t r o n g l y curved o r have an i n t e r c e p t . w

n

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B

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TABLE I M

η

a ~ W „ R e l a t i o n s h i p s under a V a r i e t y o f C o n d i t i o n s IBVE T

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m

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-90

Temperature, °C -70 -50

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Inspection o f Table I shows t h a t optimum c o n d i t i o n s f o r q u a s i l i v i n g p o l y m e r i z a t i o n o f IBVE (and MVE) p r e v a i l i n p o l a r



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s o l v e n t s (CH2CI2) and a t lower temperatures (-70 o r -90°C). Apparently chain t r a n s f e r and t e r m i n a t i o n are "frozen out" a t low e r temperatures, and f a s t i n i t i a t i o n and/or r e - i o n i z a t i o n o f dor mant growing end a r e promoted i n p o l a r media. The presence o f the ether oxygen i n the monomer may o r may not be advantageous f o r q u a s i l i v i n g p o l y m e r i z a t i o n s o f a l k y l v i n y l ethers i n general and IBVE o r MVE i n p a r t i c u l a r . Vinyl ether growing c a t i o n s a r e r e l a t i v e l y s t a b l e and may undergo t e r m i n a t i o n l e s s p o l y m e r i z a t i o n (5-_9)/ however, these monomers are s t r o n g l y b a s i c and h i g h l y prone t o c h a i n t r a n s f e r t o monomer Ç7, 13, 14). The attainment o f q u a s i l i v i n g p o l y m e r i z a t i o n s o f IBVE and MVE, as demonstrated i n t h i s work, i m p l i e s t h a t the q u a s i l i v ing technique can overcome t h i s drawback by promoting the r e v e r s i b i l i t y o f chain t r a n s f e r t o monomer. B l o c k i n g aMeSt o r MVE from Q u a s i l i v i n g Poly(IBVE) D i c a t i o n . An important a p p l i c a t i o n o f q u a s i l i v i n g p o l y m e r i z a t i o n s may be f o r the s y n t h e s i s o f block copolymers. E f f o r t s have been made t o prepare novel block polymers s t a r t i n g from q u a s i l i v i n g poly(IBVE) d i c a t i o n by the a d d i t i o n o f aMeSt and/or MVE as the second mono mer. Eq. 3 o u t l i n e s the p r i n c i p l e o f the b l o c k i n g experiments: p-DCC/AgSbF IBVE

CH Cl f 2

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WArupoly (ΙΒνΈ)'νννυ

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p o l y (M ) 2

'WVpoly (IBVE) w o fooly (M )

(3)

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During the second stage o f these block p o l y m e r i z a t i o n s , aMeSt o r MVE was added slowly and continuously t o charges c o n t a i n i n g qua s i l i v i n g poly(IBVE) d i c a t i o n s . The products obtained i n IBVE-aMeSt block copolymerization were f r a c t i o n a t e d with 2-propanol, a good s o l v e n t f o r poly(IBVE) and a nonsolvent f o r poly(aMeSt). Table I I shows molecular weights and compositions o f t y p i c a l b l o c k i n g products. Figure 7 i l l u s t r a t e s examples o fH-NMR s p e c t r a o f the 2-propanol-soluble and - i n s o l u b l e f r a c t i o n s . In expt. C i n Table I I , f o r i n s t a n c e , the molecular weight of the 2-propanol-insoluble f r a c t i o n was much higher (M = 30,500) than t h a t o f the s t a r t i n g pol^(IBVE) (M = 7,100). The 2-propanols o l u b l e f r a c t i o n a l s o had an M (7,700) t h a t was c l e a r l y , though s l i g h t l y , higher than the s t a r t i n g polymer. The 2-propanol-in s o l u b l e f r a c t i o n s ranged from 73 t o 87 wt% o f the products. H-NMR s p e c t r a o f the 2-propanol-insoluble f r a c t i o n s (e.g., F i g u r e 7a) e x h i b i t e d s i g n a l s due t o both aMeSt and IBVE u n i t s (aMeSt, 6^ 0.1 and 6.9 ppm; IBVE, 6^ 0.9 and 2.8-3.6 ppm), i . e . , the s p e c t r a i n d i c a t e the presence o f both poly(aMeSt) and p o l y (IBVE) segments i n these f r a c t i o n s . As 2-propanol-insoluble f r a c t i o n s cannot c o n t a i n homopoly(IBVE), the existence o f IBVE 1

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Figure 7. H-NMR spectra of the 2-propanol-soluble and -insoluble fractions of IBVE-aMeSt block copolymerization products obtained in experiment A, Table II.


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TABLE I I B l o c k i n g aMeSt from Q u a s i l i v i n g PIBVE i n C H 2 C I 2 a t -90°C w i t h p-DCC/AgSbF6 I n i t i a t o r


_ ^ Expt.

b Feed, wt% IBVE/aMeSt

a

[p-DCC] , — 0

Fraction(wt%)

. . c Composition, wt% IBVE/aMeSt

— (GPC)

A

0.50

14/86

100/ 0 S t a r t i n g PIBVE 2-PrOH S o l . (13) 89/11 2-PrOH Insol.(87) 13/87

10600 11600 69100

Β

2.0

30/70

100/ 0 S t a r t i n g PIBVE 2-PrOH S o l . (22) 90/10 2-PrOH Insol.(78) 21/79

6600 7300 35700

C

2.0

36/64

100/ 0 S t a r t i n g PIBVE 2-PrOH S o l (27) 90/10 2-PrOH Insol.(73) 29/71

7100 7700 30500

a)[AgSbF ] = b) Expt. A? Expt. B: Expt. C: c) Determined 6

2.3; i n i t i a l volume o f p-DCC/AgSbF 6 charge, 200 IBVE , 0.76 g/min, 2 min; aMeSt, 0.91 g/min, 10 IBVE , 0.37 g/min, 10 min; aMeSt, 0.44 g/min, 20 IBVE , 0.37 g/min, 10 min; aMeSt, 0.44 g/min, 15 by H NMR.

3

cm . min. min. min.

1

u n i t s i n these f r a c t i o n s i s strong evidence f o r the formation o f IBVE-aMeSt b l o c k polymers, which are i n s o l u b l e i n 2-propanol be cause o f t h e i r high aMeSt contents (71 t o 87 wt%). Although homopoly(aMeSt) should be absent i n the 2-propanols o l u b l e f r a c t i o n s , H NMR spectra o f these f r a c t i o n s showed a r e sonance c h a r a c t e r i s t i c o f aMeSt u n i t s (δ 6.9 ppm) together with l a r g e s i g n a l s o f IBVE u n i t s (e.g., F i g u r e 76). E v i d e n t l y the 2p r o p a n o l - s o l u b l e f r a c t i o n s a l s o c o n t a i n IBVE-aMeSt b l o c k polymers t h a t most l i k e l y c a r r y short poly(aMeSt) segments p u l l e d i n t o 2propanol by the attached poly(IBVE) segments. The formation o f IBVE-aMeSt b l o c k polymers was f u r t h e r sup p o r t e d by r e s u l t s o f f i l m - c a s t i n g experiments (12). These data a l s o show t h a t the s t a r t i n g q u a s i l i v i n g poly(IBVE) d i c a t i o n i s s u f f i c i e n t l y r e a c t i v e t o i n i t i a t e e f f e c t i v e l y subsequent aMeSt polymerization. S i m i l a r l y , b l o c k i n g MVE from q u a s i l i v i n g poly(IBVE) d i c a t i o n s was accomplished. The products were f r a c t i o n a t e d with a hetero geneous mixture o f n-heptane and water (5/2, v / v ) ; the former i s a good s o l v e n t f o r poly(IBVE) o n l y , the l a t t e r a good s o l v e n t f o r poly(MVE) o n l y . The H NMR spectra o f the η-heptane-soluble f r a c t i o n s e x h i b i t e d a sharp resonance a t 6 3.3 ppm ( - O C H 3 ) , c h a r a c t e r i s t i c o f MVE u n i t s , and a doublet a t 6 0.9 ppm (-6 (CH3)2)# charac t e r i s t i c of IBVE u n i t s . The presence o f poly(MVE) segments i n these f r a c t i o n s i n d i c a t e s the formation o f IBVE-MVE b l o c k polymers. X

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Alkyl Vinyl Ethers

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A f u l l account o f the IBVE-MVE block c o p o l y m e r i z a t i o n w i l l be pub l i s h e d s e p a r a t e l y (12). Acknowledgment F i n a n c i a l support by the N a t i o n a l Science Foundation (Polymer Program, DMR-77-27618) and the F i r e s t o n e T i r e and Rubber Company i s g r a t e f u l l y acknowledged.


Literature

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Cited

Faust, R.; Fehérvári, Á.; Kennedy, J.P. to be published. Kennedy, J.P.; Kelen, T.; Tüdös, F. to be published. Sawamoto, M.; Kennedy, J.P. Polym. Prepr., Div. Polym. Chem., Am. Chem. Soc. 1981, 22 (2), 140. Sawamoto, M.; Kennedy, J.P. Polym. Prepr., Jpn. 1981, 30 (6), S2Cl5. Higashimura, T.; Mitsuhaski, M.; Sawamoto, M. Macromolecules 1979, 12, 178. Ohtori, T.; Hirokawa, Y.; Higashimura, T. Polym. J. 1979, 11, 471. Bawn, C.E.H.; Fitzsimmons, C.; Ledwith, Α.; Penfold, J.; Sherrington, D.C.; Weightman, J. A. Polymer 1971, 12, 119. Chung, Y.J.; Rooney, J.M.; Squire, D.R.; Stannett, V.T. Polymer 1975, 16, 527. Rooney, J.M.; Squire, D.R.; Stannett, V.T. J. Polym. Sci., Polym. Chem. Ed. 1976, 14, 1877. Kennedy, J.P.; Smith, R.A. J. Polym. Sci., Polym. Chem. Ed. 1980, 18, 1523. Chang, V.S.C.; Kennedy, J.P.; Iván, B. Polym. Bull. 1980, 3, 339. Sawamoto, M.; Kennedy, J.P. to be published. Imanishi, Y.; Higashimura, T.; Okamura, S. Kobunshi Kagaku 1962, 19, 154. Imanishi, Y.; Nakayama, H.; Higashimura, T.; Okamura, S. Kobunshi Kagaku, 1962, 19, 565.

RECEIVED

February 24, 1982.


Elastomers and Rubber Elasticity - American Chemical Society

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