Present work gave a new method for preparing poly [methyl(3,3,3-trifluoropropyl)siloxane] (PMTFPS) in the mixing chamber of a torque rheometer using sodium silanolate as initiator, and ethyl acetate (EA) and dimethyl sulfoxide (DMSO) as promoters. The promoting effect of EA in the anionic bulk polymerization of 1,3,5-tris(trifluoropropylmethyl) cyclotrisiloxane (F-3) was investigated in comparison with DMSO, a common promoter. Results showed that EA exhibited an effective promoting effect as DMSO did. When the polymerization was carried out for 4.0 min at 120 degrees C in the presence of 0.30 mol L-1 EA, the maximum of number average molecular weight ((M) over bar (n) = 2.45 x 10(5) g mol(-1)) of PMTFPS was obtained with high yield (89.2 wt%). The back-biting reactions during the polymerization were almost suppressed and less than 0.75 wt% cyclic by-products were obtained by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for EA promoter system. Investigations of differential scanning calorimetry and thermogravimetic analysis showed that PMTFPS could be used in a wide range of operational temperatures. POLYM. ENG. SCI., 50:2440-2447, 2010. (C) 2010 Society of Plastics Engineers