Electron beam effects on polymers. II. Surface modification of bis-GMA substrates by functionalized siloxane oligomers

Surface modification of polymer films via electron beam irradiation was studied using the methacrylic acid derivative of the diglycidyl ether of bisphenol A, commonly called bis‐GMA, as a curable substrate. Functionalized polydimethylsiloxane (PDMS) oligomers were utilized as surface modifiers. Considerable changes in the wetting characteristics were observed for the siloxane modified bis‐GMA surfaces by critical surface tension measurement. For dosages up to 5 Mrads, the dosage level strongly affects the critical surface tension of the polymer. This result implies differences in the concentration of the attached PDMS oligomers to the bis‐GMA substrate. The methacrylate‐terminated PDMS was observed to be more effective in lowering the critical surface tension than a similar vinyl‐terminated PDMS. Higher molecular weight and multifunctional PDMS coatings resulted in somewhat lower critical surface tensions in the dosage range applied in this study. The surface thickness of the functionalized PDMS coatings which were bonded to the substrate surface depended on the molecular weight of the surface modifiers as obtained by XPS analysis. Peel tests of the uncoated and PDMS coated bis‐GMA clearly resulted in agreement with the critical surface tension data. Chemical inertness and poor wettability of PDMS provided the PDMS coatings with enhanced resistance to chemical degradation caused by a 24‐h exposure to aqueous nitric and acetic acid.