Controlled Synthesis Of PVAc-b-PS And PBA-b-PNVP Through A Single Method

"Living"/Controlled radical polymerization(LRP)has attracted extensive attention from both academia and industry since its development.It has been widely applied to prepare polymers with various topological structures(such as block copolymers,graft copolyemrs and star copolymers,etc)because of its strong molecular designability.However,the preparation of well-defined copolymers from both more active monmers and low active monomers(P(MAM)-b-P(LAM))is still a great challenge.One of the main reasons is that the free radicals generated by the low active monomers are too active and easy to occur chain transfer and chain termination.It's a little difficult to realize LRP of such monomers.On the other hand,because the activity of these two kinds of monomers is quite different,it often needs to choose different polymerization methods or mediators to control their polymerization respectively.As a result,the preparation of P(MAM)-b-P(LAM)block copolymers usually requires the transformation of polymerization methods or polymer terminals.All of these reasons bring great inconvinence for the preparation of P(MAM)-b-P(LAM)block copolymers.The main purpose of this thesis is to realize LRP of MAMs and LAMs by the same polymerization methods(or mediators)simultanously,and to synthesize well-defined P(MAM)-b-P(LAM)block copolymers through a single method.The main research contents are as follows:(1)Controlled synthesis of poly(vinyl acetate)-b-polystyrene block copolymers(PVAc-b-PS)mediated by an Iniferter agent.A typical block copolymer PVAc-b-PS was successfully synthesized by using Iniferter agent as the regulator.Firstly,the synthetic Iniferter agent 1-cyano-l-methylethyldiethyldithiocarbamte(MANDC)or 2-(N,N-diethyldithiocarbamyl)isobutyric acid ethyl ester(EMADC)and appropriate amount of azo initiator 1,1'-azobis cyclohexanecarbonitrile(ACHN)were added to regulate the polymerization of VAc under 90?.PVAc with high end-group functionalities was obtained.Then,the resultant PVAc was directly used as macroiniferter agent to mediate the polymerization of styrene(St)under 110?,with the addition of appropriate amount of initiator ACHN as well.Finally,PVAc-b-PS block copolymer was successfully prepared by a single polymerization method.The kinetic studies of the chain extension experiment with St indicated the "living" features of the polymerization system,and the molecular weight distributions of the resultant block copolymers were narrow(Mw/Mn=1.33-1.52).Moreover,the obtained PVAc-b-PS copolymers could be easily converted into the amphiphilic block copolymers poly(vinyl alcohol)-block-polystyrene(PVA-b-PS)by methanolysis of the poly(vinylacetate)block.This method is simple and convenient to operate,which may be of great potential for industrial production.(2)Synthesis of block copolymers containing poly(n-butyl acrylate)and poly(N-vinyl pyrrolidone)(PBA-b-PNVP)by photo-induced RAFT polymerization.Poly(N-vinyl pyrrolidone)(PNVP)has been widely used in the field of biomedicine due to its low toxicity,good solubility in both aqueous and organic phases and biocompatibility.Therefore,it has certain practical value to prepare PNVP containing block copolyemrs.Light is a kind of efficient green energy,which has the advantages of low energy consumption and environment friendly.It is of great theoretical significance to develop LRP under irradiation of light.In this polymerization system,one kind of xanthate O-phenyl-S-[1-(phenylethyl)]dithiocarbonate(PXPE)was synthesized and used to mediate the polymerization of BA under UV or visible light,and then the received PBA with narrow molecular weight distribution(Mw/Mn? 1.20)acted as macroRAFT agent to mediate the polymerization of NVP under the same light.Finaly,PBA-b-PNVP block copolymer could be obtained.According to the experiment results,it could lead to the fragmentation of the PBA polymer chains when the chain extension reaction was carried out under irradiation of UV light with high energy at a certain time,which resulted in the generation of some dead polymer chains.So the GPC elution curves of the block copolymers were seriously trailing or bimodle.However,if the UV light was replaced by visible light with lower energy,this phenomenon could be improved,and well-defined PBA-b-PNVP block copolymer with controlled molecular weight and molecular weight distribution(Mw/Mn ?1.32)could be obtained.Kinetic studies indicated the "living" features of this polymerization system.The components in this polymerization system were simple and no extra initiators or catalysts were required,which brought convenience for the operation of the experiment.Moreover,it's the first time that PBA-b-PNVP block copolymer was synthesized through a single method under irradiation of light.