Chlorostyrene is difficult to polymerize due to its electron-withdrawing chlorine substituent. Herein, we report the polymerization of para-chlorostyrene (pCS) using rare-earth metal catalysts (Flu-CH2-Py)Ln(CH2SiMe3)(2) (THF)(n) (Ln = Y(1), Lu(2), and Sc(3)) performed fluently with high conversions to reach the highest activity at -25 degrees C and provide polymers with perfect syndiotacticity. The copolymerization of pCS with styrene is more facile and controllable to afford copolymers with narrow Chlorine-modified S' molecular weight distributions and variable pCS incorporations. Kinetics study reveals the monomer reactivity ratios of r(pCs) = 0.55 and r(St) = 2.87, indicating the random sequence distribution, which is further confirmed by a C-13 NMR spectrum analysis. Moreover, the terpolymerization of pCS with styrene and butadiene is realized with the highest pCS insertion rate of 9.3% and gives, for the first time, chlorine functionalized St-BD copolymers having high molecular weights, rrrr > 99% syndiotacticity for both PS and P(pCS) units, and high 1,4-regularity (73%) for polybutadiene units.