Rubber-modified glassy amorphous polymers prepared via chemically induced phase separation. 4. Comparison of properties of semi- and full-IPNs, and copolymers of acrylate-aliphatic epoxy systems

The introduction of rubbery particles can be applied to enhance shear yield ing and, consequently, the toughness of brittle amorphous polymers. The cri tical transition in these polymers from crazing to shear yielding requires a submicrometer- or even nanometer-sized rubbery phase. These can be obtain ed via coalescence suppression in processes involving chemically induced ph ase separation but are also obtained in interpenetrating polymer networks ( IPN) where cross-linking or gelation is responsible for the morphology cont rol. In all cases, the formation of a nanometer-sized morphology is accompa nied by an enhanced interphase mixing, i.e., incomplete demixing resulting in a broad interface in which the composition gradually changes from one ph ase to the other. In this study, the influence of interphase mixing on the mechanical properties has been investigated. Besides the standard semi-IPN system based on poly(methyl methacrylate) and aliphatic epoxy resins, two a dditional systems being composed of the same constituents but with an incre ased degree of interfacial mixing have been investigated: a full-IPN prepar ed by cross-linking the acrylate phase and a copolymer system in which the acrylate phase is chemically bonded to the epoxy phase. In situ small-angle X-ray scattering experiments during tensile deformation demonstrated that the microscopic deformation mechanism is clearly influenced by the degree o f demixing. Despite this, the macroscopic toughness is found to be rather s ystem independent since for all three systems, a comparable synergistic tou ghening effect is observed in both tensile and impact deformation.