Unsaturated polyesters glycolysis

The effect of incorporating p-hydroxybenzoic acid (I) into the structures of various unsaturated polyesters synthesised from polyethylene terephthalate (PET) waste depolymerised by glycolysis at three different diethylene glycol (DEG) ratios with Mn acetate as transesterification catalyst, was studied. Copolyesters of PET modified using various I mole ratios showed excellent mechanical and chemical properties because of their liquid crystalline behaviour. The oligoesters obtained from the twelve modified unsaturated polyesters (MUP) were reacted with I and maleic anhydride, with variation of the I ratio with a view to determining the effect on mechanical... 

A description is given of a comparative study of the glycolysis of PETP waste soft drinks bottles by various mixtures of EG and DEG with subsequent polyesterification of the glycolysed products by maleic anhydride in order to obtain unsaturated polyesters suitable for the production of varnishes. The processing characteristics such as viscosity, exotherm temperatures of curing, compatibility of resins with monomers was investigated with respect to the type and amount of reactive monomers. The mechanical properties of varnishes produced were analysed. 13 refs. 

Glycolysis is also conducted to create polyols for unsaturated polyester usage. The PET can be dissolved in DEG to create polyols with ether linkages [30], The reaction can be carried out with propylene glycol [31] or by reacting with an unsaturated dibasic acid [32] and needed additives and catalysts [33],... 

A wide range of chemical agents, catalysts and conditions for the glycolysis of unsaturated polyester resins, used in the manufacture of buttons, have been described in a recent patent.34 In addition to different metal acetates, the following compounds have been proposed to be catalytically active in PET glycolysis sodium methylate, sodium ethylate, sodium hydroxide, methane-sulfonic acid, magnesium oxide, barium oxide and calcium oxide. Different applications of the depolymerization products were described, e.g., preparation of fresh unsaturated polyesters by reaction with maleic acid, maleic acid/ phthalic anhydride or maleic anhydride/terephthalic acid or the synthesis of polyurethane resins by reaction with a diisocyanate. 

PET glycolysis, mainly by reaction with ethylene glycol, leads to the formation of BHET, which can be used as a monomer for the preparation of fresh PET or, alternatively, it can be utilized in the formulation of unsaturated polyesters and polyurethane and polyisocyanurate foams through the corresponding polyesterification reactions. 

In addition to the possible reuse of BHET in the preparation of fresh PET polymer, two other processes have been proposed starting from the PET glycolysis products preparation of unsaturated polyesters20-27 and synthesis of polyester polyols.28-32 The latter can be used in the formulation of polyurethanes and polyisocyanurate foams26-30 (see Figure 2.1). 

---