Synthesis of star-shaped polystyrenes via nitroxide-mediated stable free-radical polymerization

High molecular weight star-shaped polystyrenes were prepared via the coupling of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) terminated polystyrene oligomers with divinylbenzene (DVB) in m-xylene at 138°C. The optimum ratio of the coupling solvent (m-xylene) to divinylbenzene was determined to be 9 to 1 based on volume. Linear polystyrene oligomers (M_n = 19,300 g/mol, M_w/M_n = 1.10) were prepared in bulk styrene using benzoyl peroxide in the presence of TEMPO at approximately 130°C under an inert atmosphere. Coupling of the TEMPO-terminated oligomers under optimum conditions resulted in a product with a number average oligomers under optimum conditions resulted in a product with a number average molecular weight exceeding 300,000 g/mol (M_w/M_n = 3.03) after 24 h, suggesting the formation of relatively well-defined star-shaped polymers. Additionally, the intrinsic viscosities of the star-shaped products were lower than calculated values for linear analogs of equivalent molecular weight, which further supported the formation of a star-shaped architecture.