The pyrolysis of an unsaturated cross-linked polyester resin

Unsaturated polyester resins are used in a large number of commercial products. They are formed by the copolymerisation of linear unsaturated polyester resins and unsaturated monomers; some of the unsaturated linkages in the polyester molecules copolymerise with the monomer to form a cross-linked resin. This thesis describes some aspects of the thermal decomposition of poly(ethylene fumarate - methyl a-methylacrylate), a typical unsaturated polyester resin. Since Grassic has made a comprehensive study of the pyrolysis of poly(methyl a-methylacrylate) itself, the work in this thesis deals mainly with poly(ethylene fumarate). To indicate the possible breakdown routes of this polyester, simple model compounds representing segments of the chain were first studied. These compounds were ethyl acrylate, ethylene diacrylate and methyl fumarate; their breakdown products and other simple compounds related to poly(ethylene fumarate) were separately pyrolysed. The pyrolysis of poly(ethylene fumarate) itself was then studied. Three major competitive reactions were found: further linear polycondencation, followed by crose-linkage and eventual carbonisation, decarboxylation to a non-fumarate polycater, alkyl-oxygen scicsion, yielding chain fregnents which undergo further breakdown to low molecular weight compounds, Thermal cross-linking of poly (ethylene fumorate) has provionely been observed. Decarboxylation and alkyl-oxygen sciesion are predictable from the work on simple enters. The mechanism of decarboxylation is not known, but is suspected to be free redical. The reaction appears to result in the removal of every second carboxyl group from the polyfumarate chain. Alkyl-oxygen scission is a molecular reaction in which migration of the hydrogen atom yields acid and vinyl ester end-group fragments. In two other linear polyosters lacking an available ?-hydrogen atom, alkyl oxygen scission was prevented and the polyester were found in some respects to be more thermostable than poly (ethylene fumarate). In pyrolysis of poly (ethylene fumerate-methyl a methlacrylate) the initial reaction is liberation of monomeric methyl a methylacrylate, This is thought to be a free redical chain reaction terminated at the inclusion of a polyester unit in the copolymer chain. The results of pyrolysis of other copolymers of methyl a methlaerylate support this theory. An apparatus was built for measuring the termpratures at which gasecus products of specifie breakdown routes are first detected. Under constant stardard conditions, comperative values of these temperatures were obtained for simple esters, poly (ethylene fumrate). Poly (ethylene fumarate - methyl a-methylacrylate) and other related polyesters and copolymers of methyl a-methylaerylate. In poly (otheylene fumorate) decorboxylation was detected at a lower temperature than alkyl-oxygen sciasion, while in poly (ethylene furarate methyl a methylacralate) monomeric methyl a mothylacrylate is liberated before any products dorived from breakdown of the polyester chain. It is suggested that this monomer liberation might be suppresaed by dispersion of a suitable free radical inhibitor in the resin. Decarboxylation of the polyester chain, if it is a free radical reaction, night simllarly be suppressed. The only apparent method of clisinating alkyl-oxygen scisaion is by modifzying the structure of the polyester to exclude the available hydrogen atom