Abstract
Unsaturated resins crosslinked with styrene, have been investigated by magic angle spinning-cross polarization (MAS-CP) 13C n.m.r. and relaxation times in the rotating frame obtained. The relaxation times T 1 ϱ obtained ranged from 2 to 34 ms, and were found to change with cure temperature in the polyester resin with a maximum value observed for all carbons when curing proceeded in the temperature region 80°C–90°C. The relaxation times evaluated indicate that more complete crosslinking occurs at temperatures in this temperature region indicating that there was a correlation between T 1 ϱ and the cure temperature. There was also a common pattern for all carbon atoms and similarly a strong influence on relaxation time existed for all carbons in the cured polyester. The corresponding main-chain motions are mainly cooperative which, with a suggested spin-lattice relaxation mechanism will be a significant influence on the molecular mobility along with the cure temperature. This influence on the molecular mobility is dependent on the carbon chain polymer length and thereby on the number of endgroups in the carbon chain polymer.
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