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T. Pokropski, A. Balas

Modifications of epoxy resins and polyurethanes. Part I. Polymers with oxazolidone rings

Polimery 2003, No 6, 417


Summary

The methods of modification of epoxy resins (EP) and polyurethanes (PU) have been reviewed. Two main research areas could be noted. First one, which this paper describes, concerns the reaction between epoxy ring and isocyanurate group leading to oxazolidone ring formation. The reaction requires the presence of a catalyst, which usually is tertiary amine, quaternary ammonium salt, Lewis acid or imidazole. Different mechanisms of oxazolidone ring formation are proposed [equations (1)-(3)]. Side reactions taking place in the system depending on the temperature and stoichiometry of the process are observed. These are trimerization of NCO groups leading to isocyanurate rings [equation (4)], homopolymerization of epoxy rings and reaction between isocyanate groups and secondary hydroxyl groups of the epoxy resin backbone. The initial molar ratio of isocyanate and epoxy groups (I/E) greatly influences the structure of materials obtained. Epoxy excess leads to linear oxazolidone polymers, whereas isocyanate excess leads to formation of isocyanurate rings, thus crosslinked structure. This influences glass transition and thermal stability of the materials. The second group of research on epoxy resins and urethanes modification concerns the formation of epoxy-urethane IPNs and is presented in the second part of the paper, which will be published later.


Keywords: epoxy resins, polyurethanes, modifications, oxazolidone rings, isocyanurate rings, thermal properties


T. Pokropski, A. Balas

Modifications of epoxy resins and polyurethanes. Part I. Polymers with oxazolidone rings