Rate acceleration of N-oxyl-mediated free radical random copolymerization of styrene and n-butyl methacrylate

The N-oxyl-mediated free radical bulk copolymerization of styrene and n-butyl methacrylate was studied at 130°C using dibenzoyl peroxide (BPO) and 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) as well as polystyrene-2,2,6,6-tetramethylpiperidine-N-oxyl adducts (PS-TEMPO). The main focus was to describe a rate acceleration by additionally added radical initiator dicumyl peroxide (DCP), since the polymerization rates become rather slow with increasing butyl methacrylate content. The effects of DCP on the polymerization rates and the molar masses were studied and compared with the accelerating effects of camphersulfonic acid (CSA) and acetic anhydride (Ac2O). It was demonstrated that for an equimolar composition of the monomers, DCP allows a significant rate acceleration up to a factor of 9, depending on the polymerization conditions, without causing any appreciable increase in the polydispersity of the copolymers. In comparison with not accelerated copolymerizations, even the relative portion of dead chains can be reduced. The accelerating effects of CSA (factor 4) and Ac2O (factor 2) are distinctly smaller.