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-but yl methacrylate was studied at 130 degrees 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 t o describe a rate acceleration by additionally added radical initiator dicu myl peroxide (DCP), since the polymerization rates become rather slow with increasing butyl methacrylate content. The effects of DCP on the polymeriza tion rates and the molar masses were studied and compared with the accelera ting effects of camphersulfonic acid (CSA) and acetic anhydride (Ac2O). It was demonstrated that for an equimolar composition of the monomers, DCP all ows a significant rate acceleration up to a factor of 9. depending on the p olymerization conditions, without causing any appreciable increase in the p olydispersity of the copolymers. In comparison with not accelerated copolym erizations, even the relative portion of dead chains can be reduced. The ac celerating effects of CSA (factor 4) and Ac2O (factor 2) are distinctly sma ller.