Polychloroalkane initiators in copper-catalyzed atom transfer radical polymerization of (meth)acrylates

A series of polychloroalkanes CClnR4-n (n = 2, 3, or 4) was tested as initiators for atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and methyl acrylate (MA) using CuCl/2,2′-bipyridine as the catalyst. 2,2-Dichloropropane and 2,2-dichloroethanol initiate the ATRP of MMA very slowly. 1,1,1-Trichloroalkanes, RCCl3, are good initiators. For all the R groups tested, the number-average molecular weight Mn increases with conversion and polydispersities are low (1.1 < Mw/Mn < 1.3). The initiator efficiency factor increases with electrophilicity of the initiating radical (0.7 < f < 1). CCl4 is a multifunctional initiator and the final Mn values are lower than targeted. This is explained by the generation of new polymer chains occurring once the third active site is created per chain. ATRP of MA initiated by CCl3CH2CF2Cl or CCl3C8H17 results in polymers with Mn values predetermined by the Δ [M]/[Initiator]0 ratio (f close to 1) and narrow molecular weight distributions (Mw/Mn < 1.3 at high conversion). The polymerization is much slower than that of MMA, but can be considerably accelerated by use of Cu(0) metal while maintaining an excellent control over molecular weights and polydispersities.