Living Polymerization Of Polar Divinyl Monomers Mediated By Frustrated Lewis Pairs

The post-polymerization modification of polymers bearing reactive side-chain groups is a powerful synthetic strategy for introducing target functionalities into polymeric materials with improved physical and chemical properties.However,the reactivity difference between two types of C=C bonds could not safeguard that the anion or radical polymerization only occurred in one kind of vinyl group in the whole reaction process,and thus formed the cross-linking network until the reaction mixture turned to gelation at last.Recently,a completely regioselective polymerization of dissymmetric divinyl monomers at the methylacrylic C=C bond was achieved by the use of Lewis acid-base pairs as catalyst.Unfortunately,the polymerization system has a very low initiating efficiency of less than 10%.Also,the reported system could not apply to the synthesis of diblock copolymer,due to the complete chain-termination side reaction via intramolecular backbiting cyclization involving nucleophilic attack of the polymeric anion to the carboxyl carbon of the adjacent unit to generate a six-membered lactone-terminated polymer chain.As a consequence,the present thesis focuses on the completely regioselective and living polymerization of various polar divinyl monomers by adjusting the the fine balance of the Lewis acidity and the sufficient stereo-hindrance.1.Sterically hindered N-heterocyclic olefin?NHO?containing the same exocyclic methyl/ethyl group was synthesized and employed as the nucleophilic Lewis base in combination with A1?C₆F₅?₃,MeAl?BHT?₂,or EtAl?BHT?₂ for polymerizing 4-vinylbenzyl methacrylate?VBMA?under mild conditions,affording the polymers with controlled molecular weight and narrow molecular weight distribution.The reaction process exhibited high initiation efficiencies?I*?100%?.The living polymerization characteristic was confirmed by the following evidences:the predicted polymer molecular weight coupled with low dispersity,nearly quantitative initiation efficiencies,and the linear increase of polymer molecular weight vs.monomer conversion and monomer-to-catalysts ratio,as well as the perfect chain extensions2.MeAl?BHT?₂/NHO-Me Lewis pair consisting of was found to be efficient in regioselective polymerization of allyl methacrylate?AMA?and Vinyl methacrylate?VMA?.The MALDI-TOF MS spectrum of PAMA with low molecular weight proved the linear PAMA chains capped with NHO-Me/H chain ends and no evidence for"backbiting"side reaction.3.F-R computational method was applied to study the reactivity ratios of different monomers during the copolymerization of VBMA and MMA.The reactivity ratios for the two monomers are less than 1(r_MMA=0.859,r_VBMA=0.749),indicating that the resultant copolymer MMA-co-VBMA shows a random distribution.Moreover,Diblock and ABA type triblock polymers were prepared by the stepwise addition of different monomers after the complete conversion of the previously added monomer.