Abstract
The structure and dynamics of a network formed by radiation induced crosslinking of polyesters based on 1,6-hexane diol and 1,2-propylene glycol and maleic anhydride (HDF and PGF, respectively) with styrene is studied by proton pulsed n.m.r. spectroscopy. The dependence of spin-lattice, T 1, and spin-spin, T 2, relaxation times on the structure of polyester chain, molar ratios of styrene to polyester unsaturations and the radiation doses are analysed in terms of network formation and structure, and their effect on molecular motion. Above the gel point, at temperatures above the glass transition, the presence of two T 2 components reflects the heterogeneity of the network structure in both resins. The glass transition temperature, determined from the T 2 relaxation measurements for PGF resins having molar ratio of styrene to polyester unsaturation (RU) up to 1.67:1 continuously decreases with the increasing styrene content. Generally, all the PGF-styrene mixtures have a higher degree of conversion of diol component than the styrene component. The largest shift in the glass transition to higher temperatures for HDF-styrene resins, which indicate the less mobile network, is found for resins with RU about 1:1. Glass transition temperatures also increase with increasing fumarate content as a consequence of better reactivity of styrene with the trans form. The shift in glass transition and the conversion data suggest a formation of different network structure in PGF- and HDF-based networks, which is a consequence of different chain structure. Parallel with the n.m.r. relaxation measurements the crosslink density was determined from the extracted gel phase or double bonds (fumaric and styrene) participating in the crosslinking process. Although the degree of cis-trans isomerization in the HDF series has an influence on the network formation, samples of both series having 50 mass per cent of styrene after irradiation with 3kGy do not reach the gel point.
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