Effect of polyacid aqueous solutions on photocuring of polymerizable
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Effect of polyacid aqueous solutions on
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ewa.andrzejewska@put.poznan.pl (E. Andrzejewska). covalent crosslinks to resin phase after curing. Like their self-curing counterparts, RMGI contain glasses of the calcium fluoro-aluminosilicate type. These glasses have two roles: they act as the source of crosslinking ions for the acid – base process, and as filler for the resin phase. Water is included in the formulation to promote the neutralization reaction, but is present at reduced levels compared with the self-curing cements. The curing of the resin part of RMGIs is mainly initiated photochemically using visible light and a camphorquinone-based photoinitiating system; it may be induced also chemically, by the use of benzoyl peroxide with amine accelerator. Setting chemistry is complicated for RMGIs because the photochemical polymerization and the acid – base reaction affect each other. The rate of the acid – base process will be reduced in the presence of organic components, and also by reduced diffusion coefficients of the reactants through the crosslinked network. On the other hand, the photochemical reaction will be affected by the polar nature of the acid – base medium. Thus, the presence of a polar polyacid molecule in water is likely to alter the rate of the polymerization reaction, though it is still not clear whether or not it is disadvantageous [1] . During polymerization at human body temperature, HEMA can reach conversions about 89 – 90% [4] , depending on other reaction conditions (initiator con- centration, initiating light intensity, presence of oxy- gen). Since HEMA concentration in RMGIs is 21 – 41% [2] , its polymerization rate may be lowered due to dilution effect; the degree of conversion may also be altered. The cured RMGIs were found to release measurable levels of HEMA [5] . This unreacted monomer could leach into the body, where various fates are possible. Thus, the important problem is, whether other organic components of RMGI, like polyacids used, will additionally retard HEMA polym- erization or will exert a positive effect on the curing process. Increasing the degree of conversion would be quite beneficial, since the amount of leachable monomer would be decreased. The aim of this work was to find the effect of aqueous solutions of polyacids on photochemically initiated polym- erization of HEMA and a multifunctional monomer under various polymerization conditions (atmosphere, photoini- tiating system), so the multifunctional monomer triethyle- neglycol dimethacrylate (TEGDMA), widely used in photocurable dental resins, was chosen. The acids investi- gated were PAA (45 wt% solution) and a liquid (acid- containing) component of a commercial glass ionomer cement. 2. Materials and methods 2.1. Materials HEMA (Merck-Suchard; purity . 97%) and TEGDMA, (Aldrich; purity . 90%) were purified from inhibitor before use by column chromatography on basic alumina. PAA (mol. weight 2000) was supplied by Aldrich. The liquid component of a commercial glass ionomer cement, which contained the mixture of poly(maleic anhydride) and PAA or a copolymer of the two starting monomers and water was from Adhesor Carbofine, Dental a.s. Praha, batch no. 220557. It has been abbreviated as AC. Camphorquinone (CQ) was from Aldrich and 2,2-dimethoxy-2-phenylaceto- phenone (DMPA) was from Ciba. As coinitiators for CQ, N ,N-dimethyl-p-toluidine (DMT, Aldrich) and 2-mercapto- benzoxazole (MBO, Aldrich) were used. 2.2. Methods The polymerizations were monitored by differential scanning calorimetry (DSC). DSC 605M (UNIPAN- TERMAL, Warsaw) instrument equipped with a lid Download 222.27 Kb. Do'stlaringiz bilan baham: |
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