Effect of polyacid aqueous solutions on photocuring of polymerizable
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Effect of polyacid aqueous solutions on
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m needed to reach R p max (peak maximum). This effect increases with the amount of polyacid added (up to 10%). Addition of PAA influences R p max only to a minor degree although in the presence of AC, R p max increases somewhat (it was found by Student t-test for comparison of mean values [9] , which indicated a statistically important difference between corresponding R p max ). E. Andrzejewska et al. / Dental Materials 19 (2003) 501–509 503 However, addition of polyacids slightly lowers the final conversion of double bonds. The effect of PAA and AC solutions on HEMA photopolymerization in air is shown in Fig. 3 . The shape of the kinetic curves obtained is different from that observed for polymerization in Ar: two autoacceleration peaks appear. Generally, polymerization proceeds with much lower rates than in an Ar atmosphere, indicating its high sensitivity to oxygen inhibition. Addition of polyacids affects the first polymerization peak similarly to that in Ar—the autoacceleration sets in earlier. The peak maximum substantially increases, especially in the presence of AC. The results obtained for TEGDMA photopolymeriza- tion in the presence of 3 wt% of PAA solution ( Fig. 4 ) Table 1 The parameters characterizing HEMA photopolymerization under Ar initiated by 0.02 M DMPA in the absence and presence of 5 and 10% of aqueous polyacid (PAA or AC) solutions with confidence intervals for R p max R p max (s 21 ) p R m t R m (s) p f No additive 0.00477 ^ 5.079 £ 10 27 0.421 249.6 0.900 5% PAA 0.00482 ^ 5.437 £ 10 27 0.412 233 0.856 5% AC 0.00513 ^ 9.358 £ 10 27 0.417 211.8 0.858 10% PAA 0.00508 ^ 4.074 £ 10 27 0.356 185 0.804 10% AC 0.00608 ^ 3.243 £ 10 27 0.390 159 0.823 R p max : maximum polymerization rate, p R m : conversion at the rate maximum, t R m : time to the rate maximum, p f : final conversion. Fig. 2. The effect of addition of 10 wt% of polyacid aqueous solution on HEMA photopolymerization in Ar initiated by DMPA. Description as in Fig. 1 . Fig. 1. The effect of addition of 5 wt% of polyacid aqueous solution on HEMA photopolymerization in Ar initiated by DMPA. The kinetic curves show the polymerization (1) in the absence of the additive and (2) in the presence of PAA and (3) AC: (a) polymerization rate vs. irradiation time curves, (b) double bond conversion vs. irradiation time curves, (c) polymerization rate vs. double bond conversion curves. E. Andrzejewska et al. / Dental Materials 19 (2003) 501–509 504 showed that at such low concentration PAA does not influence polymerization, neither in air nor in Ar (within the experimental error). Because in practice the curing of the resin component of RMGIs is induced by visible light, the second set of experiments involved visible light initiated photopolymerization. Fig. 5 shows the results obtained for polymerization carried out in Ar atmosphere. Photopolymerization of HEMA induced by CQ in the absence of any coinitiator occurs very slowly. Addition of a coinitiator accelerates the process substantially and it is clearly seen that photopolymerization initiated by the CQ/MBO system is much faster and more efficient than that initiated by the CQ/DMT couple. The addition of 5 wt% of PAA solution exerts a very advantageous effect: it additionally strongly accelerates polymerization and increases conversion in both cases. The main effect of the PAA solution on HEMA photopolymerization induced by CQ alone is an increase in conversion. When polymerization is carried out in air, the strong inhibitory effect of oxygen under the conditions used, causes HEMA not to polymerize in the absence of coinitiators. Although the addition of DMT enables the polymerization to occur, this coinitiator is poor and the polymerization proceeds with very low rates ( Fig. 6 ). Efficiency of MBO in radical formation is much better and the polymerization initiated by CQ/ MBO couple occurs with significantly higher rates and conversions. The addition of 5% of PAA solution has a similar effect on polymerization as in the absence of oxygen: the rate and the double bond conversion substantially increase. The effect of 3 wt% of PAA solution on TEGDMA photopolymerization initiated by CQ or to CQ/MBO system is shown in Figs. 7 (Ar) and 8 (air). Polymerization occurs much faster with the use of the coinitiator. Under Ar the polyacid solution retards the reaction somewhat and reduces its rate. The final conversion remains practically unaffected. For polym- erization under air no substantial difference was found Fig. 4. The effect of addition of 3 wt% of PAA aqueous solution on TEGDMA photopolymerization in Ar and air initiated by DMPA. The kinetic curves show the polymerization (1) in the absence of the additive and (2) in the presence of PAA: (a) polymerization rate vs. irradiation time curves, (b) double bond conversion vs. irradiation time curves. Fig. 3. The effect of addition of 10 wt% of polyacid aqueous solution on HEMA photopolymerization in air initiated by DMPA. Description as in Fig. 1 . Download 222.27 Kb. Do'stlaringiz bilan baham: |
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