Analysis of Crosslinked Structure of Unsaturated Polyester Resin

A method of analyzing the crosslinked structure of unsaturated polyester resin (UP) has been studied. Vinyldicarboxylic acid copolymer, obtained by the hydrolysis of a cured UP, includes components of crosslinks. Therefore, the “average length of crosslinking chains (Nv) ” was estimated from the vinyl/acid ratio of the copolymer. The “average length of the main-chains between crosslinks (NE) ” was estimated from the ratio and yield of the copolymers. To evaluate the ratio and yield accurately, conditions of hydrolysis were studied using the resins of known compositions. The results of the study indicated that the best condition was to heat the resin 2N KOH at 150°C for 20 h in a Teflon-sealed decomposition vessel. Under this condition, the crosslinked structure of the resin was evaluated with a precision better than 3%. This analytical method was also applied to the studies of relations between structures and cure conditions, and of structural changes by heat treatment. In both cases, the structural changes were evaluated exactly.