The glass transition temperature for non-gaussian network polymers

The influence of crosslinking and copolymerization on the glass transition temperature, Tg, of a range of diepoxide-diamine network polymers is examined. It is established that existing theories relating Tg to the level of crosslinking are inexact above a crosslink concentration of approximately 0.5 mole dm−3. To account for this deviation, the thermodynamic treatment of the glass transition is modified to take into consideration a non-Gaussian spatial distribution of chain segments and the steric restrictions upon movement of segments in the vicinity of junctions. The resulting equation-involving two empirical parameters, and the number of rotatable bonds between junctions—is shown to adequately explain data for the diglycidylethers of bisphenol A and butanediol, crosslinked with benzidine/aniline and 1,8-oc-tanediamine/n-butylamine mixtures. The behavior of networks prepared from α, ω-alkyldiamines containing from 2 to 36 methylene units can be predicted provided it is assumed that