The homopolymerization of a polar monomer, 4-methylthiostyrene (MTS), was successfully achieved by a rare-earth metal based catalyst in the highest activity of 45.1 × 104 g molY–1 h–1and the excellent syndioselectivity (rrrr > 99%). The polymerization was rather controllable that the resultant poly(methylthiostyrene)s (PMTS) had molecular weights comparable to the theoretic ones reaching up to 1.7 × 105 while the molecular weight distributions were narrow (PDI = 1.3–1.9). Moreover, the copolymerization of this polar MTS with the nonpolar styrene (St) performed fluently under various MTS-to-St ratios in a quasi-living mode. The monomer reactivity ratios were rMTS = 1.08 and rSt = 0.77, following the first Markov statistics, and was close to the ideal random copolymerization. Therefore, a series of unprecedented statistical random copolymers, P(St-r-MTS)s, where the compositions were strictly closed to the monomer fed ratios, had been accessed. Strikingly, both monomer sequences remained highly syndiotactic as their homopolymers regardless of the compositions, thus endowing P(St-r-MTS)s variable glass transition temperatures and melting points. The shortest number-averaged sequence length for these copolymers P(St-r-MTS) crystallizing from the melts was n?St = 5.75 for PS sequences and n?MTS = 8.11 for PMTS