Synthesis Of Functional Poly (Vinyl Acetate) Copolymers Via Photoinduced Controlled Radical Polymerization

Poly?vinyl acetate??PVAc?and its copolymer is an important polymer.Due to its unique physical and chemical properties,PVAc shows widely applications in coating,adhesive,paper layer,textile processing,resin adhesive,etc.In addition to homopolymerization,the vinyl acetate can also copolymerize with a variety of monomers such as vinyl chloride,ethylene,acrylonitrile,cyclic compound and so on.As we all know that the properties of polymers were decided by the structure.Thus,it has great theoretical and practical meaning to study basing on the structure of vinyl acetate.Living free radical polymerization is the most powerful tool for designing the structure of polymer.However,comparing with common vinyl monomers,the structure of vinyl acetate is special.Electronic donating oxygen of ester groups is adjacent to vinyl group in VAc,which showed non-effective for stabilizing the monomer derived free radicals.Such characteristic structure resulted in difficult of realizing living radical polymerization.After twenty years of development,some relatively mature methods can realize the polymerization of vinyl acetate currently.Reversible addition fragmentation chain transfer polymerization?RAFT?and cobalt-mediated radical polymerization?CMRP?are the most widely used methods.For these two methods,traditional free radical initiator was used.Relative high temperature is used,which evidently increasing the accumulating of side reaction.Alternatively,the way of photo-initiation has many advantages such as a wide temperature range,quickly switching,easy to implement,thus it has got a lot of attention among research in recent years.Herein,the photo-induced living radical polymerization of VAc under different conditions were investigated for extending the research area of both the photo-induced living radical polymerization and PVAc derived functional materials.Firstly,photoindued CMRP and radial ring opening polymerization was combined for the copolymerization of VAc and 2-methylene-1,3-dioxepane?MDO?under UV irradiation at 30 ^oC.The biodegradable polyester structure was introduced into the main chain of the PVAc successfully.Furthermore,taking advantage of temperature on the influence of hydrogen bonding which formed between fluorine alcohol and vinyl acetate.Three block polyvinyl acetate was successfully synthesized by photo-induced RAFT polymerization mechanism in the presence of ethoxy-?2-ethyl propionate?-disulfide generation carbonate?EXEP?under blue LED.The research contents are as follows:?1?The first example of photo-induced CMRP copolymerization of 2-methylene-1,3-dioxepane and vinyl acetate was successfully established using?2,4,6-trimethylbenzoyl?diphenylphosphine oxide as the initiator and Co?acac?₂ as the mediator under UV irradiation(450?W�cm^-2 at 365 nm)at 30�C in order to produce a functionalized degradable copolymer?poly?MDO-co-VAc??which based on broadly applicable PCL.This novel system showed typical features of�living�/controlled radical polymerization,such as linear kinetics,the molecular weight of the polymers linearly increasing with conversion and a narrow molecular weight distribution,furthermore,the obtained poly?MDO-co-VAc?can be used for further chain extension successfully.The reactivity ratio values of these two monomers(r_MDO=0.14,r _VAc=1.89)provided an alternative way for adjusting the composition in final copolymers by changing the weight ratio.Attractively,the final poly?VAc-co-MDO?can be degraded no matter in acid or alkali solution,confirming that the good degradability of the polymer.Finally,the influence of polymerization temperature on the reactivity ratio values of two monomers was investigated.The results showed that the temperature can significantly change the reactivity ratio.High temperature?60 ^oC?is easy to form�block copolymer�with MDO and VAc.However,these two monomers showed non-ideal copolymerization behavior?r₁*r₂<1 and r₁>1,r₂<1?under low temperature,which decreased the possibility of MDO cooperation into polymer chain.All of these results illustrated the great potential of the controlled on structure of polymer and vinyl monomers where a wide range of properties can be readily targeted.?2?Well-controlled tacticity tri-block copolymer based on poly?vinyl acetate?was synthesized using ethoxy-?2-ethyl propionate?-disulfide carbonate?EXEP?as the initiator and regulating agent by photo-induced controlled radical polymerization in HFIP under the irradiation of blue LED??max=450-460 nm?.The tacticity of polymers could be programmable controlled through the changing of reaction temperature based on the adjustalbe hydrogen bonding strength in the polymerization system.The structure and tacticity of obtained polymer was analyzed by GPC and ¹H NMR.The thermal performance?glass transition temperature,melting point,enthalpy change,the degree of crystallinity?of the polymer in each step was characterized by DSC.The results show that photo-initiation is a simple and efficient method to realize the precision controlling of stereoregularity-block-copolymer due to the wide temperature range.The current results extend the applicable area for synthesis structural controllable polymers through photo-induced living free radical polymerization methods.