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SynopsisStructure-property relationships were investigated for the diglycidyl methacrylate derivative of bisphenol-A crasslinked by electron beam irradiation. This material, commonly called bis-GMA, is a viscous liquid a t room temperature which crosslinks to form a glassy network. The major parameters which were systematically varied in this study were radiation dosage, dose rate, aging time after irradiation, and post-cure annealing at higher temperatures. Measurements were conducted to quantify the crasslinking reaction and to characterize the physical properties of the resulting networks. Solvent extraction was done to determine the relative degree of network formation through the equilibrium swelling and the gel weight fraction after drying. Another method utilized FTIR to monitor the disappearance of double bonds as the crosslinking reaction proceeded. To characterize the thermal and physical properties, differential scanning calorimetry (DSC) and dynamic mechanical spectroscopy were utilized. Network density was found proportional to the irradiation dosage, with an upper limit reached above some critical dosage. Over the range of dose rate studied, this variable was not found to influence the degree of cure greatly. The croslinking reaction became diffusion limited as vitrification occurred. These phenomena were discussed in terms of the well-known time-temperature-transformation diagram. Free radicals trapped in these reacting networks due to vitrification exhibited a finite lifetime. Post-curing could be achieved by annealing at a temperature above the Tg of the initially cured network, as shown by the increase of the glass transition temperature from both DSC and dynamic mechanical results. INTRODUCTIONCoating processes have gained prominence in industry for large scale application of adhesives or other formulations onto a substrate (e.g., polymeric, paper, metal, etc.). Formulations have historically consisted of polymeric "binders," surfactants, adhesives, and fillers suspended in solvents. Thermal ovens are widely used to evaporate carrier solvents as well as to initiate crosslinking in reactive systems.More recently, solventless coatings have emerged to significance in industry. Development of solventless coatings using radiation crosslinking was expedited during the 1970s to battle rising energy costs and stiffer pollution standards. This momentum has been carried into the 1980s, as more economical radiation sources are becoming available, and, in many cases, radiation crosslinked materials possess certain desirable physical properties. The purpose of the study was to investigate the structure-property relationships present in a diglycidyl methacrylate of bisphenol-A (bis-GMA) crosslinked by electron beam irradiation. Bis-GMA is a thermosetting resin with a viscosity at room temperature near lo4 P. Its chemical structure is shown in Figure 1 . This potential coating ingredient is one of several that we are investigating in terms of its response to EB radiation.Earlier studies were done by Yilgor et...

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SynopsisSurface 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. Functionalid 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 dects 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 methacrylateterminated 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 functionalid 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.