One-step synthesis of hyperbranched polyesters. Molecular weight control and chain end functionalization

A new procedure is described for the preparation of chloride ion free 3, 5-bis(trimethylsiloxy)benzoyl chloride, which allows the reproducible preparation of hyper-branched aromatic polyesters with controllable molecular weights. The pure monomer is thermally stable at temperatures of more than 200°C, but is readily polymerized when heated in the presence of catalytic amounts of dimethylformamide or trimethylamine hydrochloride. The molecular weight of the polymers increases with higher reaction temperatures, longer reaction times, and larger amounts of catalyst. Polymerizations in o-dichlorobenzene also afford similar results. The hyperbranched polyesters have degrees of branching of ca. 60% and contain a large number of free phenolic groups both at the chain-ends and in “linear” portions of the chains. Functionalization of these free phenolic hydroxyls is readily accomplished in homogeneous solution. However, reactions with solid Pd/C catalyst were not possible. The solubility and thermal properties of the resulting blocked hyperbranched aromatic polyesters reflect the choice of hydroxyl protecting group.