Influence of microwave heating on the polymerization kinetics and application properties of the PMMA dental materials

The effects of heating mode (conventional isothermal heating (CIH) and microwave isothermal heating (MWIH) on the kinetics of polymerization and the properties important for the application (residual monomer, hardness, and water absorption) of three commercial poly(methyl methacrylate) (PMMA) base dental materials were investigated. The degree of monomer conversion was determined by infrared spectrometry. The hardness of the polymerized samples was measured by shore D method, whereas the water absorption was measured gravimetrically. Kinetics models for polymerizations using different heating modes were determined by model fitting method. The rate of the MWIH polymerization was eight times higher compared with the CIH polymerization. The CIH polymerization is found to be the phase-boundary controlled reaction for which the rate of contracting volume is the rate limiting step, whereas MWIH polymerization is found to be the first-order reaction and the monomer concentration in the polymerization mixture is the rate limiting step. The samples of PMMA base dental materials synthesized by MWIH polymerization exhibit better application properties (hardness and water absorption).