The copolymerization of vinyl chloride with 1‐olefins. V. Heat stability of copolymers of vinyl chloride with propene, 1‐butene, and 1‐pentene

Abstract

SYNOPSISCopolymers of vinyl chloride with propene, 1-butene, and 1-pentene containing 2-15 mol % of 1-olefinic structural units were prepared. The copolymers were dehydrochlorinated at 18OoC in an inert atmosphere; the amount of hydrogen chloride split off was determined by continuous potentiometry. The results show that the heat stability of propene, 1-butene, and 1-pentene copolymers containing the same amount of 1-olefinic structural units does not differ significantly. Compared with the homopolymer of vinyl chloride, it is favorably affected by the presence of 1-olefinic structural units in poly (vinyl chloride) (PVC) chains. On the other hand, however, the heat stability of copolymers is impaired by the higher content of structural defects able to initiate the dehydrochlorination reaction. These structural defects, probably represented by chloroallyl groups, are formed in the copolymers during their synthesis. At the beginning of heating, structural defects produce intensive dehydrochlorination and, therefore, copolymers of vinyl chloride with 1-olefins if processed appear to be less thermally stable than does PVC. I NTRO DUCT10 NIn our earlier papers, we investigated the kinetic course of the copolymerization of vinyl chloride with propene, 1-butene, and l-pentene.2 Later, other samples of these copolymers were tailored so that their parameters allowed us to characterize the effect of the individual 1-olefins and of molecular weight of the copolymers on rheological and mechanical properties of these material^.^ A chosen assembly of such samples was investigated with respect to heat stability by using a continuous potentiometric determination of hydrogen chloride. The amount of hydrogen chloride released and the time dependencies thus derived were used to describe the dehydrochlorination process of the copolymers of vinyl chloride with 1 -olefins differing in the content and length of the comonomer and to compare this process with the behavior of the ho-* To whom correspondence should be addressed.