Green And Controlled Polymerization Inside Vesicle Membrane Nanoreactors

Structure determines the performance,and then the applications of polymers.As a result,the regulation of structure is vital for their performance and applications.Polymers have hierarchical structures including optical isomerism and branched topologies.Optical isomerism consists of isotactic,syndiotactic and atactic structures,which is generally controlled by stereoregular polymerization.Branched topologies of polymers are generally controlled by the degree of branching(DB).However,polymers with controllable stereoregularity or DB are generally synthesized in organic solvents and with heating,cooling or pressurization processes,which do not comply with the principles of green chemistry.Polymer vesicles are significant supramolecular structures featured with bilayer membranes and aqueous lumens.They can be self-assembled in water and are stable and controllable in size and structure.Most importantly,vesicle membranes generally exhibit a uniform and thin thickness of 5–20 nm.Currently,polymer vesicles have been widely used for the encapsulation of functional molecules including drug molecules,fluorescent molecules,nanoparticles,etc.,but there are few studies on the use of polymer vesicle membranes as nanoreactors for polymerization.This dissertation puts forward a new strategy for green and controllable synthesis of polymers using hyperbranched polymer vesicle membranes as nanoreactors.Hydrophobic monomers were spontaneously encapsulated into the hydrophobic vesicle membranes,where the confined polymerization of these monomers was carried out through photoinitiation.The configuration and reactivity of monomers were influenced by the confinement effect of vesicle membranes,thus realizing the control of optical isomerism and branched topologies of the synthesized polymers.The whole polymerization process took place in water without(or with very few)organic solvents,avoided heating or pressure,and was thereof completely in line with the concept of green chemistry.We believe the present work establishes a new method to control the stereoregularity and DB of polymers by using vesicle membranes as nanoreactors in water,which is called as the vesicular catalysis polymerization(VCP).Furthermore,it also expands the application of vesicles in green chemistry.The main results are shown as follows:1.Stereoregular polymerization of methyl methacrylate(MMA)in the vesicle membranes self-assembled from hyperbranched polymers HBPO-star-PEOsThe increase of isotacticity of poly(methyl methacrylate)(PMMA)can significantly enhance its physicochemical properties.Up to now,the isotacticity of PMMAs is generally controlled by anionic polymerization and coordination polymerization.Stereoregular polymerization of MMA in hyperbranched polymer vesicle membranes was realized in this work.The vesicle membranes with 5–10 nm in thickness self-assembled from HBPO-star-PEOs were used as nanoreactors for the photoinduced electron transfer-reversible addition–fragmentation chain transfer(PET-RAFT)polymerization of MMA at room temperature.The confined space of vesicle membranes improved the isotacticity of PMMA products.Furthermore,the isotacticity of the obtained PMMAs could be controlled by changing the size of vesicles.Isotacticity of the as-prepared PMMAs increased from 12%to 40%with the decrease of vesicle hydrodynamic diameter(D_h)from 840 nm to 85 nm as the hydrophilic fraction of HBPO-star-PEOs increased.Based on detailed characterizations of vesicle structure and the confinement effect on MMA inside vesicle membranes,the mechanism of stereoregular polymerization within vesicle membranes was studied.2.pH-controlled stereoregular polymerization of MMA in the vesicle membranes self-assembled from hyperbranched polymer H20-COOHIn order to expand the generality of VCP,the vesicle membranes of hyperbranched polymer H20-COOH were used as new nanoreactors to realize the stereoregular polymerization of MMA.Different from the previous work,on one hand,we adopted the traditional radical polymerization method.On the other hand,isotacticity of PMMA could be successfully controlled by simply regulating p H of the vesicle solution.Firstly,MMA and the initiator were encapsulated into H20-COOH vesicle membranes.Then,the photoinitiated radical polymerization of MMA was performed within it.H20-COOH vesicles with different D_h could be obtained by simply changing p H of the vesicle solution,which would provide different confinement effect on MMA,thus realizing the isotacticity control of PMMA products.The D_h decreased from 745 nm to214 nm with an increase of solution p H from 2.60 to 7.26,and the isotacticity of the obtained PMMAs was accordingly elevated from 9%to35%.The mechanism of the p H-controlled stereoregular polymerization was studied by in-situ Fourier Transform Infrared Spectrometry.3.pH-controlled hyperbranched polymerization within H20-COOH vesicle membranesDB is a significant structural parameter of hyperbranched polymers,which has an important influence on the rheological,thermal and mechanical properties of them.Generally,the control of DB is achieved by changing reaction conditions or adding additional reactants.In this dissertation,we proposed a new method to control DB and degree of crosslinking through VCP.Photoinitiated atom transfer radical polymerization(ATRP)of MMA together with 2-(2-bromoisobutoxy)ethyl methacrylate(BIBEM)was performed within H20-COOH vesicle membranes.The D_h of H20-COOH vesicles decreased from 726 nm to 225nm with an increase of solution p H from 2.60 to 7.26,the ratio of linear units to branched units of the generated polymers was regulated then.As a result,the DB of the hyperbranched P(BIBEM-co-MMA)polyesters could be successfully controlled,which declined with the decreasing of D_hof H20-COOH vesicles.Compared with control experiments performed in DMF solvent,under the same conditions,the DB of P(BIBEM-co-MMA)in H20-COOH vesicle membranes was significantly reduced 10%(from33%to 23%),which could effectively avoid cross-linking.The mechanism of confined hyperbranched polymerization within vesicle membranes was investigated by in-situ Fourier Transform Infrared Spectrometry.