Cross-linked polyesters : investigation of commercial polymers based on terephthalic acid

The thesis describes the characterisation of the polymeric components of crosslinkedunsaturated polyesters; that is the saturated prepolymer synthesised from terephthalic acid and excess propylene glycol, the alkyd resulting from the condensation of this prepolymer with maleic anhydride and finally the styrene cured product. The poly (propylene terephthalate) prepolymer has been characterised qualitatively as well as quantitatively by high resolution nuclear magnetic resonance spectroscopy. A method has been developed which permits the determination of the molecular weight, free propylene glycol content and the amount of glycol lost during polyesterification, from the integrated nmr spectrum. The prepolymer, has also been resolved into its chain components by low pressure gel permeation chromatography. The species eluting from the chromatographic column were detected by an infrared spectrophotometer and displayed as sets of curves on a time-response recorder. The lowest molecular weight diol, dihydroxypropyl terephthalate, assumed to be a member of the distribution, was synthesised and used for the identification of the same compound present in the prepolymer. The isomeric forms of this component have been estimated statistically by nmr. Furthermore, a method, has been developed which enables the quantitative interpretation of the chromatograms and the subsequent determination of the prepolymer chain distribution. The effect of the concentration of the starting materials on. the distribution has also been studied. In addition the molecular weights as deduced by this method were in very good agreement with those estimated by nmr.This project also includes attempts of splitting the double bonds of unsaturated terpo1yesters; tbe aim being the determination of the sequence distribution of the saturated segments. However, ozonolysis, phase transfer catalysed oxidation as well as preferential hydrolysis of some ester bonds failed to give unambiguous results. Finally, the sequence distribution of the styrene crosslinks in the cured polyester has been studied by C nmr and infrared spectroscopy. The first method involves the degradation of the cross1inked polyester into a styrene-fumaric acid copolymer and the assignment of the styrene quaternary carbon atom absorptions to styrene sequences the length of which is determined from. the spectra of standard styrene-diethy1 fumarate copolymers. In the second method the whole cross1inking process is followed spectro~ photometrica11y. The styrene sequences are determined through the statistical treatment of the spectral changes occurring during curing.