Tailoring the degree of branching: Preparation of poly(ether ester)s via copolymerization of poly(ethylene glycol) oligomers (A ₂) and 1,3,5-benzenetricarbonyl trichloride (B ₃)

A novel approach to tailor the degree of branching of poly(ether ester)s was developed based on the copolymerization of oligomeric A ₂ and B ₃ monomers. A dilute solution of polyethylene glycol) (PEG) (A ₂) was added slowly to a dilute solution of 1,3,5-benzenetricarbonyl trichloride (B ₃) at room temperature in the presence of triethylamine to prepare high molar mass gel-free products. PEG diols of various molar masses permitted the control of the degree of branching and an investigation of the effect of the distance between branch points. ¹H NMR spectroscopy indicated a classical degree of branching (DB) of 69% for a highly branched poly(ether ester) derived from 200 g/mol PEG diol. A revised definition of the degree of branching was proposed to accurately describe the branched poly(ether ester)s, and the degree of branching decreased as the molar mass of the PEG diole was increased. The effects of branching and the length of the PEG segments on the thermal properties of the highly branched polymers were investigated using differential scanning calorimetry (DSC). Amorphous branched poly(ether ester)s were obtained using PEG diols with number-average molar masses of either 200 or 600 g/mol. In-situ functionalization of the terminal acyl halide units with 2-hydroxylethyl acrylate provided novel photocross-linkable precursors.