Controlling The Formation Of Long-Subchain Hyperbranched Polystyrene From Seesaw-Type Ab2 Macromonomers: Solvent Polarity And Solubility

Through atom transfer radical polymerization of styrene with 1,3-dibromomethyl-5-propargyloxy-benzene as initiator followed by the conversion of bromine end-groups into azide end-groups, well-defined seesaw-type polystyrene (PSt) macromonomers with two molecular weights (Mn = 8.0 and 28.0 k) were obtained. Thus, a series of long-subchain hyperbranched (lsc-hp) PSt with high overall molar masses and regular subchain lengths were obtained via copper-catalyzed azidealkyne cycloaddition click chemistry performed in THF and DMF, respectively. The polycondensation of seesaw-type macromonomers was monitored by gel permeation chromatography. Because DMF is the reaction medium with higher polarity, click reaction proceeds more easily in DMF. Therefore, the growth of lsc-hp PSt in DMF has faster rate than that in THF for the shorter seesaw-type macromonomer (Seesaw-8k). However, THF is the solvent with better solubility to PSt and leads to looser conformation of PSt chains. Thus, for the longer seesaw macromonomer (Seesaw-28k), lsc-hp PSt in THF has higher overall molar mass. As well, the self-cyclization of seesaw-type macromonomers also depends on both solvent and molar mass of macromonomer. The self-cyclization degrees of Seesaw-8k in DMF and THF are almost the same while that of Seesaw-28k macromonomer is obviously lower in THF. The experimental results suggest a physical consideration to control the growth of hyperbranched polymers. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012