THERMAL DEGRADATION OF POLYESTERS. PART II. AROMATIC AND SEMIAROMATIC POLYMERS.

Polyhexamethylene terephthalate degrades by the mechanism observed for aliphatic polymers--random scission and subsequent reaction of the olefinic and acid end-groups. When the acid part is aliphatic as in poly1,4-phenylene succinate and poly1,4-phenylene sebacate, the polymers are less stable initially than comparable aliphatic polyesters. The degradation mechanism is more complex and involves cross-linking the cross-linked sebacate product breaks down by a second degradation reaction but the succinate forms a residue which does not undergo further breakdown. Fully aromatic systems studied, namely poly1,4-phenylene terephthalate, poly1,3-phenylene isophthalate, poly1,4-phenylene isophthalate-co-terephthalate and poly4,4-biphenylene isophthalate, were more thermally stable, especially the all para system, and 35 to 45 of the initial weight remained at 800C. Features such as initial low activation energy processes, complex rate curves with several components and char formation at high temperatures imposed difficulties in kinetic analysis of the degradations by programmed thermogravimetry. Author