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

Abstract

Bulk free radical polymerization of the monomer series CH 2 5 C(CH 3 )C(O)OCH 2 CH 3-n Cl n , n 5 1, 2, 3, yields an unexpectedly crosslinked product with a crosslink density that increases with decreasing chlorine content of the respective monomer (n 5 3 < n 5 2 < n 5 1). This chlorine substituent effect is investigated by correlation with chain transfer constant measurements for four homologous series of chloroalkyl compounds (chloroethyl acetates (CH 3 C(O)OCH 2 CH 3-n Cl n , n 5 1,2,3); chloromethanes (CH 4-n Cl n , n 5 2,3,4) and CD 2 Cl 2 and CDCl 3 analogs; butyl chloride isomers (n-, iso-, sec-, tert-) and tert-C 4 D 9 Cl analog; and nine chloroethanes (C 2 H n26 Cl n , n 5 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 24 ), 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. 2017, 55, 93-106