Synthesis of low polydispersity polybutadiene and polyethylene stars by convergent living anionic polymerization

Star-shaped polybutadiene stars were synthesized by a convergent coupling of polybutadienyllithium with 4-(chlorodimetliylsilyl)styrene (CDMSS). CDMSS was added slowly and continuously to the living anionic chains until a stoichiometric equivalent was reached. Gel permeation chromatography-multi-angle laser light scattering (GPC-MALLS) was used to determine the molecular weights and molecular weight distribution of the polybutadiene polymers. The number of arms incorporated into the star depended on the molecular weight of the initial chains and the. rate of addition of the CDMSS. Low molecular weight polybutadiene arms (M-n 640 g/mol) resulted in polybutadiene star polymers with an average of 12.6 arms, while higher molecular weight polybutadiene arms (M-n = 16,000 g/mol) resulted in polybutadiene star polymers with an average of 5.3 arms. The polybutadiene star polymers exhibited high 1,4-polybutadiene microstructure (88.3-93.1%), and narrow molecular weight distributions (M-w/M-n = 1.11-1.20). Polybutadiene stars were subsequently hydrogenated by two methods, heterogeneous catalysis (catalytic hydrogenation using Pd/CaCO3) or reaction with p-toluenesulfonhydrazide (TSH), to transform the polybutadiene stars into polyethylene stars. The hydrogenation of the polybutadiene Stars was found to be close to quantitative by H-1 NMR and FTIR spectroscopy. (c) 2005 Wiley Periodicals, Inc.