Synthesis and characterization of hyperbranched polycarbonates
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Hyperbranched aromatic polycarbonates were prepared by the polymerization of an A2B monomer derived from 1,1,1-tris(4-hydroxyphenyl)ethane. Protection of one of the three phenols of the triphenol by a tert-butyldimethylsilyl group was followed by conversion of the remaining two phenolic groups to carbonylimidazolide functionalities to give the A2B monomer. Polymerization was accomplished via the anhydrous removal of the silicon protecting group and subsequent reaction of the phenoxide with a carbonylimidazolide moiety to yield the hyperbranched aryl polycarbonate bearing carbonylimidazolide chain ends. Subsequent cleavage of these end groups by reaction with methanol upon precipitation, yielded the phenol-terminated hyperbranched polycarbonate. Silylation of the phenol-terminated material with tert-butyldimethylsilyl chloride, followed by degradation of the carbonate linkages by reaction with lithium aluminum hydride and analysis of the products by HPLC allowed for the degree of branching to be determined as 53%. The molecular weights (Mw) of the carbonylimidazolide-, phenol-, and tert-butyldimethylsilyl ether-terminated hyperbranched polycarbonates were 16 000, 77 000, and 82 000 amu from GPC based on polystyrene standards. 23 000, 180 000, and 83 000 from GPC with LALLS, and 24 000, 160 000, and 88 000 from GPC with SEC,3 respectively.