Heat-Induced Polycondensation Reaction with Self-Generated Blowing Agent Forming Aromatic Thermosetting Copolyester Foams

This work presents a unique chemical strategy and a facile fabrication scheme toward development of novel aromatic thermosetting copolyester foams. Designed aromatic-based acetoxy and carboxylic acid end-group oligomers carry out an endothermic condensation polymerization reaction, which self-generates acetic acid blowing agent forming macrocellular porous morphology within cross-linked ester backbone polymer matrix. Herein, we provide a visual insight into the foaming reaction between the constituent oligomer groups via optical micrographs captured at polymerization phase transformation stages; oligomer melt-compounding, bubble nucleation via release of gaseous acetic acid, and subsequently bubble growth at elevated temperatures. Furthermore, we show cure and postcure characteristics of the constituent oligomers in the course of the foaming reaction that the most favorable pair of cure temperature and cure time is determined. Then, combining these outcomes, we design an optimum cure cycle and fabrication process to develop physical products of aromatic thermosetting copolyester foams. Afterward, we assess thermomechanical properties with respect to cross-linking densities and molecular weights of the aromatic thermosetting copolyester foams. Aromatic thermosetting copolyester foams offer a unique thermoset polymer system that would address needs for emerging techonologies for development of lightweight, strong, and high temperature stable innovative materials.