Carbon dioxide is an effective diluent for increasing the free volume of polymer. It has useful advantages with reductions of viscosity, surface tension and with an increase of diffusion into polymer. These properties are available in polymer processing and particle designing. We carried out free-radical polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) with AIBN as the initiator in carbon dioxide. This experiment was performed at fixed temperature (343 K), stirring speed and weight of monomer+initiator. Only weight ratios of carbon dioxide were changed. Molecular weight and T_g showed a minimum at 14.1 MPa and increased in the higher final pressure.