Controlled radical copolymerization of styrene and 4-vinylpyridine

Full Paper: In this paper the copolymerization of styrene and 4-vinylpyridi ne at 125 degreesC in the presence of benzoyl peroxide (BPO) and 2,2,6,6-te tramethylpiperidine-N-oxyl (TEMPO) on the one hand and in the presence of a TEMPO-terminated polystyrene on the other is described. The molecular weig hts of the synthesized copolymers and block copolymers were found to increa se with increasing conversion. Various nitroxides were used to prepare poly [styrene-co-(4-vinylpyridine)] copolymers with BPO as the initiator. We fo und the use of 4-Oxo-TEMPO yielded high polymerization rates and high molec ular weights. However, the polymerization in the presence of 4-NH2-TEMPO ex hibits a slow rate and leads to copolymers with broad polydispersities. The influence of the other investigated nitroxides (4-OH- and 4-ACETAMIDO-TEMP O) on the copolymerization range between these both Limits. The TEMPO-media ted copolymerizations of styrene and 4-vinylpyridine are slower than the co mparable autopolymerization. However, the addition of an initiator which de composes at the reaction temperature, such as dicumyl peroxide, leads to a considerable acceleration. By means of the Kelen-Tudos method, the monomer reactivity ratios r(s) (styrene) and r(4-VPy) ( 4-vinylpyridine) were deter mined. The calculation for the TEMPO-mediated copolymerization at 125 degre esC results in r(s) = 0.73 +/- 0.09 and r(4-VPy) = 0.96 +/- 0.15. The value s for the spontaneous copolymerization at this temperatures are r(s) = 0.58 +/- 0.04 and r(4-VPy) = 0.91+/- 0.05.