The novel synthesized OPCA compounds copolymerized readily with ST under freeradical conditions (Scheme 2) forming white flaky precipitates when their solutions were poured into methanol. The conversion of the copolymers was kept between 10 and 20% to minimize compositional drift (Table ). Nitrogen elemental analysis showed that between 23.3 and 41.1 mol% of OPCA is present in the copolymers prepared at ST/OPCA = 3 (mol), which is indicative of relatively high reactivity of the OPCA monomers towards ST radical which is typical of halogen ring-substituted OPCA. Since OPCA monomers do not homopolymerize, the most likely structure of the copolymers would be isolated OPCA monomer units alternating with short ST sequences (Scheme 2).