The Copolymers Prepared Via The Combination Of Free Radical Polymerization Of 1-octene And Ring-opening Polymerization Of Cyclic Ketene Acetal Monomer

Polyolefin has a huge annual output and can be used for many applications such as plastics,fibers and elastomers,and has always been the focus of attention.Copolymerization of olefin monomers and functional monomers is an important method to improve the performance of polyolefins.Free radical polymerization is an important method for preparing polyolefins.Controlled/"living" free radical copolymerization has already prepare low-dispersity,functionalized polyethylene.Compared with ethylene,chain transfer reactions generally occur during the free radical polymerization of α-olefins,and there are very few studies on free radical(co)polymerization of α-olefin.The free radical ring-opening polymerization of cyclic ketene acetal monomer can introduce a degradable ester bond in the polymer backbone.It is an important method for preparing biodegradable materials via the copolymerization of cyclic ketene acetal monomer with vinyl monomers.The problem of environmental pollution caused by non-degradable polyolefins has attracted great attention.The introduction of degradable groups onto the polyolefin backbone is expected to solve this problem.Recently,it has been reported that the preparation of biodegradable polyethylene can be realized through the controlled radical copolymerization of cyclic ketene acetal monomer and ethylene.Inspired by this,we prepared the copolymers of 1-octene with the cyclic ketene acetal monomer,2-methylene-1,3-dioxepane,via RAFT copolymerization.Brookhart-type α-diimine palladium(Ⅱ)catalysts are widely used in the olefins polymerization.The unique"chain walking" process in this polymerization system can reduce the branching density of poly-α-olefins.On the other hand,it has been reported that under blue light irradiation,the homolysis of the palladium-carbon bond of α-diimine palladium(Ⅱ)catalyst can generate free radicals to initiate free radical polymerization.Therefore we expected to combine the free radical ring opening process and palladium(Ⅱ)catalyzed polymerization of α-olefins to prepare the poly(1-hexene-b-ester)copolymer.(1)The copolymers of 1-octene with the 2-methylene-1,3-dioxepane were prepared by RAFT copolymerization for the first time.The results showed that,the proportion of 1-octene units in the copolymer increased with the increase of 1-octene in feed ratio,and the molecular weight decreased accordingly.We have synthesized some copolymers with the 1-octene unit ratio far exceeding 50%.We monitored the reaction process by nuclear magnetic resonance hydrogen spectroscopy and gel permeation chromatography.The result showed controlled polymerization features.(2)Due to the electron donation effect of the two oxygen atoms in the 2-methylene-1,3-dioxepane,the electron density of the double bond is high and the monomer is reactive to electrophiles.Spontaneous cationic polymerization occurs in the presence of the cationic α-diimine palladium(Ⅱ)catalyst and the free radical ring-opening polymerization of 2-methylene-1,3-dioxepane is suppressed.Therefore,we added chloride ion to the solution of cationic α-diimine palladium(Ⅱ)catalyst to transform it into a neutral α-diimine palladium(Ⅱ)complex.Experiments proved that the addition of chloride ion indeed converted the cationic α-diimine palladium(Ⅱ)complex into a neutral form,which can avoid the cationic polymerization of 2-methylene-1,3-dioxepane,but it was a very complicated process when 2-methylene-1,3-dioxepane reacted with neutral α-diimine palladium(Ⅱ)complex in the presence of blue light.