Application of thiol-ene click chemistry to preparation of functional polyethylene with high molecular weight and high polar group content: Influence of thiol structure and vinyl type on reactivity

A series of functional polyethylenes have been simply and efficiently synthesized via the combination of regioselective ethylene/5-vinyl-2-norbornene (VNB) copolymerization using [PhNC(CF3)CHCO(Ph)]2TiCl2 catalyst and following ultraviolet light initiated thiol-ene click reaction. On treatment of ethylene/VNB copolymer with different thiols including mercaptoethanol, 1-thioglycerol, methyl mercaptoacetate, methyl mercaptopropionate, 2-mercaptoethylamine, mercaptoacetic acid, and mercaptopropanoic acid, various polar groups have been successfully introduced into the polyethylene. Except 2-mercaptoethylamine, the functionalizations are quite efficient with the degree of functionalization higher than 94%, which is independent of thiol structure and double bond content. The content of polar group in functional polyethylene can be tuned in a wide range of 030 mol %. Gel permeation chromatography profiles indicate all functional polyethylenes that have very high molecular weights (160336 kg/mol) with homogeneous formation. Besides, systematic investigation of the influence of vinyl type and thiol structure on reactivity has been also carried out. By treatment of mercaptoethanol with different copolymers (ethylene/VNB, ethylene/5-ethylidene-2-norbornene, and ethylene/dicyclopentadiene copolymer), the order of vinyl reactivity can be summarized as terminal > internal > cyclic double bond. For different thiols, the reactivity has the sequence of SHCH2COOH > SHCH2COOCH3 > SHCH2CH2COOH > SHCH2CH2COOCH3 > SHCH2CH(OH)CH2OH > SHCH2CH2OH > SHCH2CH2NH2, which is depended on the solubility and the electron-withdrawing inductive effect of polar group. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012