No abstract

No abstract

This paper reports the first synthesis of A2 + B3 highly branched polyesters with the minimal formation of cyclics in the absence of a polymerization solvent. Highly branched poly(ether ester)s were synthesized in the melt phase using an oligomeric A2 + B3 polymerization strategy. Condensation of poly(propylene glycol) (M n ∼1060 g/mol) and trimethyl 1,3,5-benzenetricarboxylate in the presence of titanium tetraisopropoxide generated highly branched structures with high molar mass when the reaction was stopped immediately prior to the gel point. Size exclusion chromatography (SEC) and 1H NMR spectroscopy were used to monitor molar mass as a function of monomer conversion and to determine the gel point. Monomer conversions at both the theoretical and experimental gel points for an A2:B3 = 1:1 molar ratio agreed well. Thus, cyclization reactions, which are common in A2 + B3 polymerization in solution, were negligible in the melt phase. The degree of branching (DB) increased with an increase in monomer conversion and molar mass, and the final product contained 20% dendritic units. Monofunctional end-capping reagents were also used to avoid gelation in the melt phase, and high molar mass final products were obtained with nearly quantitative monomer conversion in the absence of gelation. The presence of a monofunctional comonomer did not affect the molar mass increase or the formation of branched structures due to desirable ester interchange reactions.

No abstract

No abstract

A novel approach to tailor the degree of branching of poly(ether ester)s was developed based on the copolymerization of oligomeric A2 and B3 monomers. A dilute solution of poly(ethylene glycol) (PEG) (A2) was added slowly to a dilute solution of 1,3,5-benzenetricarbonyl trichloride (B3) 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 diols 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 photo-cross-linkable precursors.

No abstract

No abstract