Polymerization of mono‐, Di‐, and trichloroethyl methacrylates: A study in chain transfer

Bulk free radical polymerization of the monomer series CH2 = C(CH3)C(O)OCH2CH3-nCln, n = 1, 2, 3, yields an unexpectedly crosslinked product with a crosslink density that increases with decreasing chlorine content of the respective monomer (n = 3 < n = 2 < n = 1). This chlorine substituent effect is investigated by correlation with chain transfer constant measurements for four homologous series of chloroalkyl compounds (chloroethyl acetates (CH3C(O)OCH2CH3-nCln, n = 1,2,3); chloromethanes (CH4-nCln, n = 2,3,4) and CD2Cl2 and CDCl3 analogs; butyl chloride isomers (n-, iso-, sec-, tert-) and tert-C4D9Cl analog; and nine chloroethanes (C2Hn−6Cln, n = 1–6)) in a methyl methacrylate polymerization. The pattern conveyed by the magnitude of chain transfer constants and deuterium isotope effects is consistent with a vicinal chlorine effect (i.e., chlorine activation of a vicinal hydrogen for abstraction) to account for the relative activities of the four series of model compounds and for the propensity of the chloroethyl methacrylates to crosslink in a bulk free radical polymerization. The chloroalkyl moiety's contribution to chain transfer is relatively modest (≤10−4), but, when incorporated as a monomer pendant group in free radical polymerizations, it is effective in broadening molecular weight to the extent of resulting in a crosslinked polymer. Published 2016.† J. Polym. Sci., Part A: Polym. Chem. 2016