GLASS-TRANSITION IN POLY(PROPYLENE GLYCOL) NETWORKS

In the reported experiments, a series of well-characterized networks of poly(propylene glycol) having narrow network chain-length distributions and average molecular weight between crosslinks M//c in the range of 425-3000 has been prepared. The glass transition temperatures T//g of these networks were found to vary linearly with M//c** minus **1, consistent with several theoretical treatments. Both the physical crosslinking and the incorporation of crosslinking agent into the system (a 'copolymer' effect) are shown to be responsible for increase in T//g upon crosslinking in this system. Varying the network chain-length distribution without changing M//c did not affect the T//g of the system. The chemical nature of the crosslinking agent, however, does affect the T//g of the network, particularly at high crosslink densities.