Head-to-head polymers: 19. Chlorination of cis-1,4-polybutadiene

Chlorination of cis-1,4-polybutadiene (PB) has been studied in detail. It was found that chlorination must be carried out in an oxygen free atmosphere at polymer concentrations below 0.5%, and at temperatures below room temperature in mixed solvents with dichloromethane as the major component. In the initial stage of chlorine addition to the double bonds of cis-1,4-polybutadiene, block structures of chlorinated segments are formed. The chlorine addition to the cis-butadiene units was not stereospecific and the final chlorination product had nearly a 1:1 ratio of the threo- and erythro structure of the CHCICHCI-units. Microphase separation in partially chlorinated PB was observed by d.s.c., dynamic-mechanical measurement, and transmission electron microscopy. It was concluded that partially chlorinated PB, whose degree of chlorination was lower than 65 mole %, was composed of almost pure cis-1,4-PB domains and a separate phase which consists ofCH₂CHCICHCICH₂units with perhaps as much as 10% of cis-1,4-PB units incorporated in this phase. If the degree of chlorination is more than 90 mole % one phase exists.