Behavior comparison of PMMA-PTEGDMA copolymerized by two different methods
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Behavior comparison of PMMA-PTEGDMA copolymerized by two different methods. R. Velazquez, J. Reyes and V.M. Castaño. Instituto de Física, U.N.A.M. Apdo Postal 1-1010 Querétaro, Qro. México ABSTRACT. The acrylic system consisting of a casting syrup [made of polymethyl methacrylate (PMMA) dissolved in methyl methacrylate (MMA) monomer] and triethylene glycol dimethacrylate (TEGDMA) monomer was polymerized by two different methods. One of these methods was made by thermal decomposition of benzoil peroxide (BP) as initiator, and the other one, used the promoted decomposition of BP using dimethyl p-toluidine (DMT). Both types of polymerization were carried out by bulk polymerization in closed test tubes. Since the polymerization reactions were over, the polymer obtained from the two methods were very different each other in appearance and, when characterization analysis were performed those gave evidence of different behavior between the two types of polymers. The characterization study was carried out using Scanning Electron Microscopy (SEM) to observe the morphology and microstructure in the polymers. Fourier Transform Infrared (FTIR), Raman and micro-Raman to analyze differences on the chemical compositions in the polymer bulk. Differential Scanning Calorimetry (DSC) to evaluate the thermal behavior, Dilatometry to determine the final cure shrinkage after polymerization reaction in the two types of polymers. INTRODUCTION. Few years ago, Liu and Armeniades1 developed one method to control cure shrinkage in an acrylic system. That system was made of PMMA, MMA and TEGDMA, all of them mixed in different proportions. This system undergoes phase separation when BP and DMT were used to initiate the polymerization reaction. The phase separation produced microdomains and their corresponding interfacial volume compensates the polymer volume reduction after the cure reaction. In that work Liu and Armeniades based their conclusion on density determinations using a specific gravity balance and observations of the polymer microstructure by SEM. Those polymers, where the phase separations were more evident, had the same density value than that determined in their corresponding uncured resins. Besides, the authors also reported there was no evidence of pores or cracks on the polymer bulk in the SEM observations. Now in this work, cure reactions of the PMMA-MMA-TEGDMA system were carried out by bulk polymerization using two types of initiation. The first one employed the conventional thermal decomposition of BP to obtain the so-called “conventional polymers” (C.P.).The other type of initiation was the same use by Liu and Armeniades. The decomposition of BP was promoted at room temperature by DMT when both chemicals were mixed in proportion of 10:1 respectively. The polymers obtained from this method were called “phase-separated polymers” (P.P.). This last kind of reaction is very interesting for several reasons. It is possible to obtain from this reaction, polymers in a very short time and it is not necessary any energy inver
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