ELECTRON-BEAM EFFECTS ON POLYMERS .5. SYMMETRICAL AND ASYMMETRIC MATERIALS BASED ON THE CONTROLLED DISTRIBUTION OF BIS-GMA INTO CROSS-LINKED NITRILE RUBBER FILMS PRIOR TO CURING BY ELECTRON-BEAM RADIATION

Two systems based on the controlled distribution of the methacrylic acid derivative of the diglycidyl ether of bisphenol-A (bis-GMA) into crosslinked acrylonitrile-butadiene copolymers, commonly called nitrile rubber (NBR), were prepared utilizing electron beam (EB) radiation. In the system called "symmetric," the EB crosslinked NBR was swollen to equilibrium in solutions containing different concentrations of bis-GMA. The swollen NBR film was then EB irradiated to different dosage levels. The other system, called "asymmetric" or "gradient," was prepared by applying the solutions containing bis-GMA to one surface of the EB crosslinked NBR film in a controlled time that was less than the time to achieve an equilibrium concentration across the thickness or "swelling" dimension. This asymmetrically swollen NBR film was then immediately EB irradiated using different dose levels. The prepared symmetric and asymmetric NBR systems were investigated by thermal and mechanical, as well as microscopic, analyses. The mechanical responses were shown to be strongly dependent on the bis-GMA content in the NBR film and the type of preparation history. The dynamic mechanical spectra showed the presence of two transitions, indicating some level of phase separation that was supported by scanning electron microscopy of fracture surfaces for symmetric and asymmetric systems. The asymmetric distribution of the imbibed (cured) monomer in the asymmetric system was confirmed by both FT-IR and optical microscopy analyses.