Inherent flame retardation of semi-aromatic polyesters via binding small-molecule free radicals and charring

This paper was published in Polymer Chemistry  Journal, online 19 Jan 2016

Abstract

Inherent flame-retardant semi-aromatic polyesters, containing special aryl ether and/or ketone structure (“Ar-CO-Ar”, “Ar-O-Ar”, “Ar-O-Ar-O-Ar” or “Ar-O-Ar-CO-Ar-O-Ar”) were synthesized successfully. Interestingly, these polyesters show different flame retardance beyond our traditional knowledge that more benzene rings are beneficial to flame retardance. The polyester containing “Ar-O-Ar-O-Ar” shows excellent flame retardance, whose LOI value reaches 34.1 % and UL-94 rating is V-0. Meanwhile, the polyester with “Ar-O-Ar-CO-Ar-O-Ar” structure does not perform expectedly well (31.6 % and V-2 rating respectively). In order to make clear of the effect of aryl ether and/or ketone structure units on the flame retardance, the pyrolysis behaviours and the char residue are investigated by Py-GC/MS, TGA, and SEM. In TGA test, the char residues of polyesters containing “Ar-CO-Ar”, “Ar-O-Ar” “Ar-O-Ar-O-Ar” or “Ar-O-Ar-CO-Ar-O-Ar” are 31.6%, 22.5%, 30.6%, 38.7%, respectively. These values do not match with the calculated results, which indicate that some special reactions occur during the combustion. Furthermore, these polyesters show a common initial pyrolysis pathway and subsequent unique processes in Py-GC/MS test. Their pyrolysis intermediate products can bind small-molecule free radicals, and eventually form different conjugated aromatic structures. In this way, inherent flame-retardant polyesters are obtained even without any traditional flame-retardant elements. And their flame retardant performance has great relationship with the amount of char formation, the microstructure of char, and the chemical structure of pyrolysis products.

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