THE ROLE OF NETWORK ARCHITECTURE ON THE GLASS-TRANSITION TEMPERATURE OF EPOXY-RESINS

A series of epoxy networks were synthesized in which the molecular wei ght between crosslinks (M-c) and crosslink functionality were controll ed independent of the network chain backbone composition. The glass tr ansition temperature (T-g) of these networks was found to increase as M-c decreased. However, the rate at which T-g increased depended on cr osslink functionality. The dependency of M-c on T-g is well described by two models, one based on the concept of network free Volume while t he other model is based on the principle of corresponding states. Init ially, neither model could quantitatively predict the effect of crossl ink functionality in our networks. However, our tests indicated that b oth the glass transition and the rubbery moduli of our networks were d ependent on M-c and crosslink functionality, while the glassy state mo duli were independent of these structural variables. The effect of cro sslink functionality on the rubbery modulus of a network has been addr essed by the front factor in rubber elasticity theory. Incorporation o f this factor into the glass transition temperature models allowed for a quantitative prediction of T-g as a function of M-c and crosslink f unctionality. (C) 1997 John Wiley & Sons, Inc.