Structure-property relationships were investigated for the bis-glycidyl methacrylate deriva-tives of bisphenol-A crosslinked by electron beam irradiation. This material, commonly called bis-GMA, is a viscous liquid at room temperature which crosslinks to form a glassy network when a 3 to 5 mil coating is irradiated with sufficient energy. 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 first to quantify the crosslinking reaction, then to characterize the physical properties of the resulting networks. Extraction by a solvent was done to deter-mine the degree of network formation through the equilibrium swelling ratio and the gel weight fraction after drying. Another method utilized FTIR to monitor the disappearance of double bonds as the crosslinking reaction proceeded. In order to characterize the physical properties, differential scanning calorimetry (DSC) and dynamic mechanical spectroscopy were done to determine the glass transition temperature.
It was found that the network density or amount of cure is proportional to the irradiation dosage, with an upper limit reached above some critical dosage. Dose rate was not found to influence the degree of cure greatly. The crosslinking reaction often 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 networks exhibited a finite lifetime. Post-curing can be achieved by annealing at a temperature above the T₉ of the network, as shown by the increase of the glass transition temperature from DSC and dynamic mechanical results.
Bis-GMA was mixed with rubbery modifier materials with acrylate and methacrylate functional ends in order to toughen the bis-GMA networks. It was observed that the acrylate end groups were more reactive in EB cured systems than analogous methacrylates probably due to their higher polymerization enthalpy and less steric hindrance. Phase separation, which would provide rubber toughening without depressing the high glass transition temperature, was not achieved by irradiation with the modifying materials at the molecular weights used in this study, but the mixtures were toughened as shown by the dynamic mechanical data. / M.S.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/94482 |
| Date | January 1986 |
| Creators | Thompson, Danny C. |
| Contributors | Chemical Engineering |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Thesis, Text |
| Format | xii, 159 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 15255653 |
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