Synthesis and Swelling Behavior of Highly Porous Epoxy Polymers

[Image: see text] 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.