DPIHP exhibited little effect on the polymerization process. The results indicated that with CQ as the photoinitiator, 4E appeared to be the most efficient CI, whereas the CQ-DMAEMA combination led to very low radical generation efficiency (DC < 5%). The polymerization rate and the degree of conversion (DC) of the model adhesives with 5, 15, or 25% water content were determined using FTIR/ATR with a time-based spectrum analysis. The model adhesive contained two monomers: (bis phosphate) (2MP) and 2-hydroxyethyl methacrylate (HEMA) whose mass ratio was 1:1, thus representing an acidic and hydrophilic formulation. The concentrations of dye, CI, and DPIHP in model adhesives were all maintained at 0.022 mmol per gram monomer. The role of diphenyliodonium hexafluorophosphate (DPIHP) in the polymerization process was also studied. N-phenylglycine (NPG), ethyl 4-dimethylaminobenzoate (4E) or 2-(dimethylamino) ethyl methacrylate (DMAEMA) was used as the coinitiator (CI). This study evaluated different initiator systems in self-etching model adhesives, in which camphorquinone (CQ) or trimethylammonium chloride (QTX) was employed as a photoinitiator (dye).
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