EFFECT OF THE MOLECULAR-WEIGHTS OF RAW EPOXY-RESINS ON THE PHYSICAL-PROPERTIES OF CURED EPOXY-RESINS

The relationship between cross-linking density and physical properties was investigated for cured epoxy resins. These resins were prepared by using poly(glycidyl ether) of o-cresol-formaldehyde novolacs having different molecular weights, a phenol-formaldehyde novolac hardener, and various accelerators. The cross-linking density of the cured resins is higher for raw epoxy resins of higher molecular weight. The density reached the highest value when 2-ethyl-4-methyl imidazole was used as an accelerator. The thermal expansion coefficient of the cured resins in rubbery state decreased with higher values of cross-linking density, while it increases in the glassy state. The elasticity values of highly cross-linked resins in glassy state are lower than those of low cross-linked resins. Furthermore, the saturated water content, water vapor permeability and diffusion coefficient and specific volume increase as the cross-Unking density becomes higher. Such relationships between cross-linking density and physical properties were observed in the cured resins which were prepared by using the raw epoxy resins having different molecular weights and in the cured resins prepared by using different accelerators. © 1990, The Society of Polymer Science, Japan. All rights reserved.