Kinetics of the gamma‐induced graft copolymerization of vinyl acetate to Teflon

Abstract

AbstractThe gamma‐induced graft copolymerization of vinyl acetate to films of polytetrafluoroethylene is affected by hydroquinone. A study of the effect of polytetrafluoroethylene film thickness on the rate of grafting indicates that the weight of vinyl acetate grafted is independent of the film thickness. The rate of grafting is observed to be proportional to the three‐halves power of the monomer concentration from 2.0 to 10.8 molar vinyl acetate in ethyl acetate, and to the one‐half power of the intensity in the range investigated from 15,000 to 460,000 r/hr. After initial grafting there is an increase in the grafting rate. The addition of as much as 15 g./dl. of high molecular weight polyvinyl acetate to the copolymerization mixture has no effect on the initial rate of grafting. The activation energy is found to be 4.78 ± 0.32 kcal./mole (95% confidence limit). A mechanism consistent with these observations is presented. The addition of small quantities of carbon tetrachloride results in a decrease in the rate of grafting as well as a decrease in the molecular weight of the homopolymer formed. The decrease in grafting rate is attributed to a smaller G‐value for radical formation of carbon tetrachloride when compared to that for vinyl acetate and to the differential rate of chain transfer between carbon tetrachloride and grafted polyvinyl acetate with vinyl acetate radical. The chain transfer constant of carbon tetrachloride with vinyl acetate radical has been measured with the use of gamma‐rays to initiate polymerization. The value is 0.47.