STRUCTURE PROPERTY RELATIONSHIPS FOR STYRENE CROSS-LINKED POLYESTERS .1. NETWORK STRUCTURE AND RUBBERY ELASTIC-MODULUS

Ten unsaturated polyester prepolymers differing by the nature of the diol, by the maleate/phthalate molar ratio, or by the chain length, were crosslinked by about 40% by weight of styrene and then analyzed by IR spectrophotometry, solid state NMR, and rubbery elasticity measurements. The spectrometric measurements revealed a practically complete conversion of the styrene/fumarate copolymerization. The rubbery elastic modulus varies in a complex way with the presumed network structure. A non-ideality factor f was defined from the current theories; f is a decreasing function of the average number of flexible bonds between crosslinks. The networks based on dimeric diols display a practically ideal behavior. The influence of dangling chains, corresponding essentially to polyester chain ends, is taken into account by the Graessley's formula in which trifunctional and tetrafunctional crosslinks are distinguished. A method for the estimation of the nature and weight fraction of dangling chains was proposed.