Controlled radical copolymerization of styrene and 4-vinylpyridine

In this paper the copolymerization of styrene and 4-vinylpyridine at 125°C in the presence of benzoyl peroxide (BPO) and 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) on the one hand and in the presence of a TEMPO-terminated polystyrene on the other is described. The molecular weights of the synthesized copolymers and block copolymers were found to increase with increasing conversion. Various nitroxides were used to prepare poly-[styrene-co-(4-vinylpyridine)] copolymers with BPO as the initiator. We found the use of 4-Oxo-TEMPO yielded high polymerization rates and high molecular weights. However, the polymerization in the presence of 4-NH2-TEMPO exhibits a slow rate and leads to copolymers with broad polydispersities. The influence of the other investigated nitroxides (4-OH- and 4-ACETAMIDO-TEMPO) on the copolymerization range between these both limits. The TEMPO-mediated copolymerizations of styrene and 4-vinylpyridine are slower than the comparable autopolymerization. However, the addition of an initiator which decomposes at the reaction temperature, such as dicumyl peroxide, leads to a considerable acceleration. By means of the Kelen-Tüdös method, the monomer reactivity ratios rS (styrene) and r4-VPy (4-vinylpyridine) were determined. The calculation for the TEMPO-mediated copolymerization at 125°C results in rS = 0.73 ± 0.09 and r4-VPy = 0.96 ± 0.15. The values for the spontaneous copolymerization at this temperatures are rS = 0.58 ± 0.04 and r4-VPy = 0.91 ± 0.05.