The poly(methyl methacrylate) (PMMA)/nanometer-scaled calcium carbonate particulate nanocomposites prepared by means of the gas-synthesis was investigated. PMMA absorbed the saturated solvent mixture (the ratio of calcium chloride dehydrate and methanol at 1.5, 4.5, and 6.0 g/100 g) at 40-60 degrees and then desorbed the methanol completely and then CO2 gas diffused into the desorbed completely in specimens for 48 h at 60 degrees, approximately 30-nm calcium carbonate particulates were precipitated evenly to distribute in the PMMA matrix. The content of calcium carbonate particulates decreases with increasing concentration of the saturated solvent mixture. The transmittance of the nanocomposites decreases with the increasing content of calcium carbonate particulates and the cutoff wavelength of transmittance is shifted to the short wavelength side. Differential scanning calorimetry displayed the glass transition temperature of nanocomposites is much higher than the virgin PMMA. Compared with the original PMMA, with only 1.53 wt% calcium carbonate particulate loading, the PMMA-matrix nanocomposites exhibit higher glass transition temperature. (C) 2011 Wiley Periodicals, Inc. Adv Polym Techn 31: 280291, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20251