Polycondensation of saturated polyesters

This article describes the synthesis processes for saturated, semi-aromatic and aliphatic (co)polyesters. These polymers are thermoplastic; they are obtained by melt polycondensation (possibly followed by solid-phase postcondensation) of a major aromatic diacid (terephthalic or naphthalenedicarboxylic) or its dimethyl ester onto an aliphatic diol (ethylene glycol, propanediol or butanediol), or of an aliphatic hydroxyacid onto itself or its lactonic form (lactic acid and caprolactone).

The unitary units making up the macromolecular chain of the polyesters concerned therefore necessarily contain an aliphatic hydrocarbon sequence. This chapter therefore excludes aromatic polyesters, such as polyarylates or LCPs (Liquid Crystal Polymer), resulting from the polycondensation of aromatic diacids (or acid chloride) and diphenols, as well as polycarbonates obtained from phosgene and bisphenol A.

The synthesis processes are described in terms of their chemical (main and secondary reactions) and technological aspects. Mention is also made of a new family of polyesters, aliphatic hyperbranched polyesters, which have recently appeared on the market.

As regards polyethylene terephthalate in particular, readers are referred to the article which is specially dedicated to this polymer and describes current manufacturing processes and recycling techniques.

In this article, we focus on the secondary chemistry that accompanies the main polycondensation reactions leading to PET.

For further information, please refer to the recent two-volume work on thermoplastic polyesters .