Synthesis and characterization of a novel unsaturated polyester based on poly(trimethylene terephthalate)

Unsaturated aromatic polyesters were obtained by glycolysis of poly(trimethylene terephthalate) with cis-2-buten-1,4-diol followed by a solid-state polymerization. The glycolysis was performed in a batch mode as well as through a continuous process in a twin screw extruder. The degradation and subsequent rebuilding of the polymer chain during the course of reaction was followed by means of inherent and melt viscosity measurements, and ¹H NMR terminal group analysis of the intermediates and the final products. Structural investigations revealed that this new approach resulted in melt processible unsaturated polyesters with cross-linkable sites having similar characteristics to that of the virgin saturated polyester. Although the processing temperature for the different reaction steps was sufficiently high (180−260 °C), no thermally induced cross-linking of the incorporated unsaturated bonds could be evidenced indicating that the obtained products remained stable during the production stage. For comparison purposes, a commercial unsaturated polyester (Vestodur^©) was included in the investigations. UV irradiation of thin polyester films did not result in cross-linked products but in cis-trans isomerization of the incorporated bisoxybutenyl unit.