The novel synthesized OCPP 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 9.2 and 34.5 mol% of OCPP is present in the copolymers prepared at ST/ OCPP = 3 (mol), which is indicative of relatively high reactivity of the OCPP monomers towards ST radical which is typical of ring-substituted OCPP. Since OCPP monomers do not homopolymerize, the most likely structure of the copolymers would be isolated OCPP monomer units alternating with short ST sequences (Scheme 2).