Synthesis of Hyperbranched Aromatic Homo- and Copolyesters via the Slow Monomer Addition Method

Random bulk polycondensation and the slow monomer addition (SMA) strategy have been employed for the preparation of hyperbranched aromatic homo- and copolyesters, based on 3,5-bis-(trimethylsiloxy)benzoyl chloride (AB 2 monomer) and 3-(trimethylsiloxy)benzoyl chloride (AB comonomer). Whereas random copolycondensation in bulk yielded limited molecular weights (M n = 2900-8400; SEC-LALLS in DMF/GHC), considerably higher molecular weights and low polydispersities were obtained under slow monomer addition conditions (M n = 83 000-278 000; PD = 1.09-1.49). Copolymerization of the AB 2 and AB monomers resulted in polymers with controlled degrees of branching (DB) in the range 0-0.5. In the random copolycondensation the theoretical DB values could be confirmed by detailed analysis of the 13 C NMR data, demonstrating equal reactivity of the comonomers. Using the slow monomer addition strategy (SMA), the DB was significantly enhanced above the value of 0.5 for bulk AB 2 polycondensation to 0.61-0.66, in agreement with theoretical predictions (DB = 0.66), and also high molecular weight polymers were obtained. Also, for all copolymerizations enhanced DBs were obtained. A strictly linear dependence of the intrinsic viscosity [η] on molecular weight was observed for all copolymers, measured by online SEC viscosimetry. The Mark-Houwink exponents α MH clearly decreased with the DB and were in the range 0.18-0.55.