Photo-Induced Copolymerization of Chlorotrifluoroethylene and Methyl Isopropenyl Ether
Fluoropolymers exhibit unique properties,such as outstanding thermal stability and chemical inertness,ultralow surface energy,and have found broad applications in lots of areas.Many fluoropolymers show high crystallinity and low solubility,restricting their practical usage through melting and solution processing.To address such issues,copolymerization of fluoroalkenes and comonomers have been developed to prepare fluorinated copolymers that retain fluoroalkyl characteris-tics and good processibility,bringing many important commercial products,for example,copolymers of chlorotrifluoroeth-ylene(CTFE)and vinyl ethers.However,such copolymers could possess low glass transition temperature(Tg),which is a key property to influence the applicable scope.In this work,we report copolymerization of CTFE and methyl isopropenyl ether(MIE)for the first time,which have enabled the synthesis of novel fluorinated copolymers under LED(light emitting diode)light irradiation conditions by merging an organic thermally activated delayed fluorescence catalyst and a redox active organ-ic amine via a redox-relay catalysis.In comparison to conventional free radical(co)polymerization of fluoroalkenes,this method not only provides main-chain fluoropolymers of readily tunable molecular weights as evidenced by gel permeation chromatography(GPC)and multi-angle light scattering detection coupled with GPC(GPC-MALS),but also allows smooth transformation of fluoroalkene feedstock at ambient pressure using common Schlenk glassware without needing high-pressure metallic vessels.Although the obtained CTFE-MIE copolymers exhibited less controlled molecular weight distributions(MWDs)and limited chain-end fidelity as confirmed by chain-extension polymerization and GPC analysis,the chain-growth process presents first-order kinetics as validated by monitoring the monomer consumption,and follows alter-nating copolymerization as supported by the variation of degrees of polymerization(DPs)of both vinyl compounds along the light irradiation time,presenting improved chain-growth control as compared to conventional free radical transformation.Notably,as analyzed by differential scanning calorimetry(DSC),in contrast to copolymers of CTFE and ethyl vinyl ether(EVE),the CTFE-MIE copolymers with similar molecular weights exhibit clearly improved Tg of about 50 ℃ via simply introducing methyl substituents on the polymer backbone.Given the broad interests in fluoropolymers and established appli-cations of fluoroalkene-vinyl ether copolymers,we believe that this work should be informative to the rational design of nov-el fluoropolymers and attractive for material engineering with improved thermal stability.
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