Polymerization of α-(halomethyl)acrylates and dithiols was achieved by the combination of S_N2′ (addition–elimination) and subsequent thiol–ene click reactions. A Bu₃P catalyst and an excess amount of a base that does not yield an acidic salt, e.g., 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or K₂CO₃, were key for achieving M_n > 10⁴.