A difunctional reversible addition-fragmentation transfer (RAFT) agent, S,S’-bis (α,α’-dimethylacetic acid) trithiocarbonate (BDAT) is synthesized and used as chain transfer agent (CTA) to mediate homopolymerization of methyl methacrylate (MMA) and random copolymerization of methyl methacrylate-styrene (St) system, respectively. Kinetic factors of these two polymerizations, which influence polymerization process and characteristics of polymers, are investigated. Experimental results show that molecular weights of polymers increase linearly with monomer conversions and these two polymerization kinetics behaviors exhibit “controlled/living” characteristics. For the homopolymerization of MMA, molecular weights increase gradually and are close to their theoretical values. Wherever, for the random copolymerization of MMA-St system, the presence of St has important influence on the kinetics of copolymerization. Addition of St to this system induces an induction period and this period increase with increasing content of St in monomer composition.