Synthesis, Structure, and Properties of Hyperbranched Polyesters Based on Dimethyl 5-(2-Hydroxyethoxy)isophthalate

The melt condensation polymerization of the AB₂ monomer dimethyl 5-(2-hydroxyethoxy)-isophthalate exhibits unusual molecular weight growth characteristics. The number-average molecular weight (M_n) reaches a plateau value after a relatively short polymerization time, whereas the weight-average molecular weight (M_w) continues to increase. The maximum in M_n is thought to be a consequence of intramolecular cyclization reactions, evidence of which is provided by MALDI-TOF MS. It is postulated that the continual increase in weight-average molecular weight, even after complete cyclization, is due to a redistribution of polymer chains by ester interchange reactions. The polymers are soluble in common organic solvents, and solutions have characteristically low intrinsic viscosities. The degree of branching, as determined by quantitative ¹³C NMR spectroscopy, is consistent with the theoretical value for a statistical distribution at high conversion. The physical characterization of these polymers is reported.