Effect of polyacid aqueous solutions on photocuring of polymerizable
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Effect of polyacid aqueous solutions on
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E. Andrzejewska et al. / Dental Materials 19 (2003) 501–509
508 in the presence of CQ. Heteroaromatic thiols were found to be very effective in this reaction [7,14,15] ; the activity of the CQ/thiol system and the mechanism of the initiation of polymerization are the subject of our ongoing investigations. Taking into account the above discussion it is surprising why the addition of 3% of PAA solution a negative influence on TEGDMA photopolymerization in Ar ( Fig. 7 ). In this case, the most important effect seems to be phase separation (the polymerized PAA-containing TEGDMA samples were opaque). The retarding effect is more visible at low polymerization rates (without the coinitiator) when an increase in restriction of polymer chain diffusion occurs slowly and phase separation is easier. At higher polymerization rates the miscibility is kinetically favored, thus, the effect of polyacid solution is rather low (for CQ/MBO initiating system) or almost not observed (initiation by DMPA, Fig. 4 ). Because the addition of polyacid solution probably also counteracts oxygen inhibition, it exerts an opposing effect on the reaction rate to phase separation. As a result, the additive practically does not influence CQ-initiated TEGDMA photopolymerization in air ( Fig. 8 ). The results obtained show that the addition of aqueous solution of polyacids has a beneficial effect on HEMA photopolymerization both in air and in Ar atmosphere. When polymerization is induced by an efficient photo- fragmentating initiator (e.g. DMPA), the main effect is earlier onset of autoacceleration. However, under initiation conditions used in curing of commercial dental products (CQ-based two component initiating system) the addition of only 5% of PAA solution markedly increases the polymerization rate and the conversion both in Ar as well as in an air atmosphere. The photopolymerization of the crosslinking monomer, TEGDMA, is somewhat retarded by PAA solution, but only when carried out under anaerobic conditions. Because in commercial systems TEGDMA, if used, is dissolved in HEMA, we may expect that it will exert two effects on HEMA polymerization: an accelerating effect resulting from earlier onset of the gel effect due to network formation and a slight decrease in the accelerating effect caused by the addition of PAA solution. The results presented in this work contribute to a characterization of the setting process of RMGIs and may be important for application of RMGIs in dental practice. Acknowledgements This investigation was supported by Grant DS- 32/010/2001. Authors thank Dr John Nicholson for introduction to problems of resin-modified glass ionomer cements. References [1] Nicholson J, Anstince HM. The development of modified glass- ionomer cements for dentistry. Trends Polym Sci 1994;2:272– 6. [2] Braden M, Clarke RL, Nicholson J, Parker S. Polymeric dental materials. Berlin: Springer; 1997. Chapter 11, p. 1 – 50. [3] Pashley EL, Zhang Y, Lockwood PE, Rueggeberg FA, Pashley DH. Effects of HEMA on water evaporation from water – HEMA mixtures. Dent Mater 1998;14:6– 10. [4] Young JS, Bowman CN. Effect of polymerisation temperature and cross-linker concentration on reaction diffusion controlled termin- ation. Macromolecules 1999;32:6073– 81. [5] Palmer G, Anstice HM, Pearson GJ. The effect of curing regime on the release of hydroxyethyl methacrylate (HEMA) from resin-modified glass– ionomer cements. J Dent 1999;27:303 – 3111. [6] Odian G. Principles of polymerisation, 2nd ed. New York: Wiley; 1981. [7] Andrzejewska E, Andrzejewski M, Linde´n L-A ˚ , Rabek JF. Anomalie w przebiegu polimeryzacji monomero´w wielofunkcyjnych (Anom- alous polymerisation of multifunctional monomers). Polimery (War- saw) 1998;43:427– 36. [8] Braden M, Clarke RL, Nicholson J, Parker S. Polymeric dental materials. Berlin: Springer; 1997. Chapter 2, p. 51 – 90. [9] Petrucelli JD, Nandram B, Chen M. Applied statistics for engineers and scientists. Upper Saddle River, NJ: Prentice Hall; 1999. [10] Krakowsky I, Jelinkova M, Vacik J. Elastic and swelling behavior of 2-hydroxyethyl methacrylate, diethylene glycol methacrylate and methacrylic acid copolymers. J Appl Polym Sci 1997;64:2141 – 8. [11] Andrzejewska E, Andrzejewski M, Zych-Tomkowiak D. In prep- aration. [12] Davidson RS. The role of amines in UV curing. In: Fouassier JP, Rabek JF, editors. Radiation curing in polymer science and technology, vol. 3. London: Elsevier; 1993. p. 153 – 76. Chapter 5. [13] Andrzejewska E, Marciniak B, Zych-Tomkowiak D. In preparation. [14] Andrzejewska E, Zych-Tomkowiak D, Andrzejewski M. Photopoly- merisation of dimethacrylates in the presence of 2-mercaptoben- zothiazole (MBT) and 2,2 0 -benzothiazole disulfide (BTDS). Polimery (Warsaw) 2000;45:639 – 41. [15] Andrzejewska E, Zych-Tomkowiak D. Thiols in photopolymeriza- tion. VII International Symposium Chemistry Forum, Warszawa; 14 – 16 May 2001. p. 70 – 4. E. Andrzejewska et al. / Dental Materials 19 (2003) 501–509 509 Document Outline
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