Melting points (Tm's) and glass transition temperatures (Tg's) of stereoregular poly(methyl a-chlo­roacrylates), poly(ethyl a-chloroacrylates), and poly(isopropyl a-chloroacrylates) have been determined by differ­ential scanning calorimetry (DSC). Relaxation processes accompanying these Tg's and secondary relaxation phe­nomena have been studied by dynamic mechanical and dielectric relaxation. It was found that the extrapolated Tg values for high molecular weight syndiotactic poly(alkyl a-chloroacrylates) and high molecular weight isotactic po­ly(alkyl a-chloroacrylates) differed by the following amounts: 92° for the methyl esters; 83° for the ethyl esters; and 68° for the isopropyl esters. A secondary relaxation, labeled fl, and associated with motions of the ester side chains, occurs in the highly syndiotactic methyl and ethyl polymers and is absent in the isopropyl polymers regardless of their degrees of stereoregularity. Evidence was obtained for the formation of stereocomplexes of isotactic and syn­diotactic chains in the case of the poly(methyl a-chloroacrylates).