Thermal and mechanical properties of microwave‐ and heat‐cured poly(methyl methacrylate) used as dental base material

The thermal and mechanical properties of dental base materials cured by microwave and conventional heat methods were studied. The commercial dental base poly(methyl metacrylate) (PMMA) powder and liquid were mixed in a 3/1 ratio. They were polymerized by a peroxy catalyst at 65°C, then cured with a boiling water temperature and microwave radiation for periods of 5, 10, 15, 20, 25, 30, and 35 min for heat curing and 1, 2, 3, 5, and 7 min for microwave radiation. The microwave radiation outputs used were 500 and 700 W. The products of 5‐min heat curing and 1‐, 2‐, and 7‐min microwave curing were soluble in chloroform. All the others were partially soluble. The viscosity‐average molecular weights of the soluble samples were about 1 × 10⁶. The thermal properties of the polymer samples were studied by differential scanning calorimetry (DSC). For the samples that were not cured completely, broad exothermic peaks at around 125°C were obtained in the DSC thermograms. The glass‐transition temperatures for completely cured samples were 110–120°C. The mechanical properties of the samples were determined from tensile and three‐point bending tests. The elastic modulus was highest for samples obtained by the conventional method with a 30‐min curing period. However, the bending modulus was highest for 7‐min cured samples in a 700‐W microwave. The mechanical strengths of the 700‐W output were higher than those at 500 W. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 251–256, 2003