N-oxyl mediated free radical donor-acceptor co- and terpolymerization of styrene, cyclic maleimide monomers and n-butyl methacrylate

The N-oxyl mediated donor-acceptor copolymerization of styrene as a donor a nd the maleimides N-phenylmaleimide (NPI), N-benzylmaleimide (BMI), and N-c yclohexylmaleimide (CMI) as acceptor monomers is studied, using 2,2,6,6-tet ramethylpiperidine-N-oxyl (TEMPO) as reversible capping agent and benzoyl p eroxide (BPO) as initiator. These copolymerizations are characterized by hi gh polymerization rates and very short induction periods. In bulk, a contro l of the molecular weights and the polydispersity is only possible for the weakest acceptor CMI. For the stronger acceptors BMI and NPI the polymeriza tions have to be performed in solution(anisol) to realize a linear increase of the molecular weight with conversion and polydispersities below M-w/M-n 1.55. The polymerization rates (NPI > BMI > CMI), the induction periods (C MI > BMI > NPI) and the total number of polymer chains (NPI > BMI > CMI) of the TEMPO mediated free radical donor-acceptor copolymerization are a func tion of the acceptor strength of the maleimide monomers. As the main reason for the observed high reactivity, an "acceptor depending self-initiation", proceeding via a Diels-Alder reaction mechanisms, is discussed. Additional ly, the concept of the "acceptor depending self-initiation" is used for the rate of acceleration of S/BuMA copolymerizations leading to pol(S-co-BuMA- co-maleimide) terpolymers with well-controlled molecular weights and narrow molecular weight distributions.