Polystyrene with dendritic branching by convergent living anionic polymerization

The synthesis of two types of polystyrene with dendritic branching was achi eved through the development of a novel method that combines living anionic polymerization with a convergent process in a one-pot reaction. The method is based on the slow addition of a reactant such as 4-(chlorodimethylsilyl )styrene (CDMSS), which contains a polymerizable vinyl group and a moiety c apable of undergoing quantitative S(N)2 reaction, to a solution of living p olystyryl anions. The sequence of reactions results in star-shaped polymers with the initial chains forming the arms and the residue from the CDMSS fo rming a hyperbranched core. Different amounts of styrene monomer were added along with the CDMSS in order to increase the molecular weight between bra nch points. The molecular weights and polydispersities of the dendritic pol ystyrenes were characterized by GPC coupled with MALLS. The molecular weigh ts of dendritic polystyrenes without added comonomer corresponded to dendri tic growth of the core of 3.1-3.4 average generations with polydispersities less than 1.5. The observed narrow molecular weight distributions were int erpreted using a kinetic model that relates increased steric hindrance arou nd the reactive site to the reaction rate constants of different size dendr itic polymers formed during the reaction. Adding a comonomer along with the coupling agent allowed for the synthesis of high molecular weight dendriti c polystyrene (up to M-n > 600 000 g/mol) and generational growth approachi ng an average of six generations. Intrinsic viscosities of all dendritic po lystyrenes produced were found to be much lower than that of linear polysty rene. Thermal analysis of the dendritic polystyrenes showed that T-g versus molecular weight corresponded well to that of linear polystyrene normalize d to the number of end groups, being slightly higher due to the effect of b ranching.