Abstract
Unsaturated polyesters based on maleic and phthalic anhydrides have been modified by 1,3,4-oxadiazole derivatives, viz. 2,5-bis-( m- or p-carboxyphenyl)-1,3,4-oxadiazole and 5,5-bis-( m- or p-carboxyphenyl)-1,3,4-oxadiazolyl-2,2. A study has been made of the influence of the modifying additives on the formation of polyethylene glycol maleatophthalates and on curing of the latter by oligoester acrylates, as well as the effect of these additives on the properties of the cured products. It is shown that the additives have an accelerating influence on the polycondensation reaction. The modified polyesters have in the oxadiazole ring structure a tertiary nitrogen atom, which accelerates peroxide decay during copolymerization with the unsaturated monomers, and plays the role of an accelerator. The modifying additives enhance mechanical properties of the cured polyesters, giving better heat stability, increased hardness and higher breaking stress levels under compression. Changes in the foregoing properties stem from the influence of 1,3,4-oxadiazole derivatives on cis-trans-isomerization of the maleate units into fumarate ones. An 85% degree of isomerization is attained, mainly in the initial period of the reaction.
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