Copolymerization of styrene (St) and methyl methacrylate (MMA) was carried out using 1,1,2,2-tetraphenyl-1,2-bis (trimethylsilyloxy) ethane (TPSE) as initiator; the copolymerization proceeded via a "living" radical mechanism and the polymer molecular weight (M-w) increased with the conversion and polymerization time. The reactivity ratios for TPSE and azobisisobutyronitrile (AIBN) systems calculated by Finemann-Ross method were r(St) = 0.216 +/- 0.003, r(mmA)= 0.403 +/- 0.01 for the former and r(St) 0.52 +/- 0.01, r(MMA)= 0.46 +/- 0.01 for the latter, respectively, and the difference between them and the effect of polymerization conditions on copolymerization are discussed. Thermal analysis proved that the copolymers obtained by TPSE system showed higher sequence regularity than that obtained by the AIBN system, and the sequence regularity increased with the content of styrene in copolymer chain segment.