Synthesis and Swelling Behavior of Highly Porous Epoxy Polymers

Many advantageous properties of cross-linked polymers relate to their network structures. In this study, network structures of three DGEBA-based epoxy systems at various DGEBA monomer sizes were investigated via equilibrium swelling and glass transition behavior. Each system was cured with a tetra-functional diamine, 4,4'-methylenebiscyclohexanamine, in the presence of a nonreactive solvent, i.e., THF at a solvent-to-monomer volume fraction ranging from 0 to 92%. Experimental results revealed that the conventional swelling model (the Dušek model) accurately calculates M _c values of the cured gels prepared in moderate dilute environments, up to approximately 60% by volume of THF. For gels cured in extreme dilute environments, i.e., in the presence of above 60% by volume of THF, the calculated M _c values using the Dušek model were found to increase sharply as a function of the initial solvent content. The observed dramatic increase in M _c values was not supported by the dry T _g of the identical polymer systems. In fact, the dry T _g values of the polymer systems were found to be relatively insensitive to the initial solvent content. A modification was proposed to the Dušek model that incorporates an additional term, which accounts for the probability of finding elastic chains in a polymer network. Using the modified equation, M _c values were varied as expected with the molecular weight of DGEBA and insensitive to the amount of the solvent initially used during cure. Furthermore, the modified M _c values were shown to be consistent with the dry T _g values in view of the Fox and Loshaek model.