Effect of the local motions of chemical linkages on segmental mobility in poly(ester carbonate) block copolymers

A series of glassy bisphenol poly(ester carbonate) copolymers containing va rious linkage groups were synthesized, and the segmental motions were inves tigated by dynamic mechanical analysis (DMA). DMA results indicate that str ong coupling exists between the motion of the cyclohexylene ring and those of neighboring segments, and the segmental mobility of the resulting polyme rs is thus enhanced. In contrast to the cyclohexylene ring conformational t ransition, the motions of terephthalate, bicyclo[2.2.1]heptane-1,4-dicarbox ylate, and bicyclo[2.2.2]octane-1,4-dicarboxylate linkages are relatively i ndependent of their environments, and therefore their incorporation does no t cause much variation in polymer mobility. These results are consistent wi th those of a dipolar rotational spin-echo C-13 NMR study,(1) which show th at the cyclohexylene dicarboxylate linkage is most likely to undergo the ch air-boat-chair conformational transition, while the terephthalate, bicyclo[ 2.2.1]heptane-1,4-dicarboxylate, and bicyclo[2.2.2]octane-1,4-dicarboxylate linkages are mainly capable of rotational motions in these copolymers.