Synthesis And Self-Assembly Of Novel Topological Functional Block Copolymers

At present,some scientists pay more attention to living control polymerization because this can overcome some shortage in the field of traditional radical polymerization,such as the polymerization possess the behavior of out of control which arose the results of lose of molecular weights, molecular distributions,molecular structure,molecular composing and end functions.As one of the living control polymerizations,Atom Transfer Radical Polymerization(ATRP)has become the hottest topic。More and more non-linear polymers such as block copolymer,star polymer,graft copolymer, and hyperbranched polymer with well-defined structure and narrow polydispersities have been synthesized and studied.Much attention has been paid due to their unique properties.ATRP was employed to control the macromolecular chain structure efficiently.In this paper we synthesized a series of living block copolymers, star polymers and graft copolymers with functional side groups.Functional multiblock copolymers with different structures were obtained,at the same time, the structure and properties of the resulting copolymers were investigated in detail.In addition,self-assembly behavior of copolymers in aqueous media was also studied by the numbers.There has been increasing interest in organic/inorganic hybrid materials for their unique and useful properties that can be applied to various fields,and polymeric materials hybridized with inorganic substances have been designed by a variety of techniques.Methacryloxypropyl trimethoxysilane(MPS),which possesses two reactive sites of vinyl and trimethoxysilane groups,is a highly useful monomer for the construction of polymeric hybrid materials.The structural control of polymers derived from MPS should be important to provide new hybrid materials with well-defined characteristics.The optimization of MPS polymerization should be useful for broadening its applicability.In chapter two,we have tried to carry out the random copolymerization of MPS and MMA in distilled DMF with Br-PEG-Br and Cu(I)C1/Bpy complex which afforded a block copolymer of the type P(MMA-r-MPS)-b-PEG(2000)-b-P(MMA-r-MPS).The kinetics results show that the copolymerization proceeds in a living fashion.To assess if the along-chain composition is uniform or gradient,we followed the conversions of MPS and MMA separately by NMR.These results indicate that no compositional gradient is present along the copolymer chain,and the copolymer is characterized by an ideal random structure.At the same time,The block copolymer P(4VP-r-MPS)-b-PEG(2000)-b-P(4VP-r-MPS)was synthesized by statistical copolymerization of 4-vinylpryridine(4-VP)and MPS using a PEG-based macro-initiator and a standard ATRP protocol.This route gave much lower polydispersities(M_w/M_n)1.21.We present a simple approach to organic/inorganic hybrid hollow particles based on hydrolysis and polycondensation reactions within the polymeric vesicles preformed in a selective solvent with P(4VP-r-MPS)-b-PEG(2000)-b-P(4VP-r-MPS)was used as the precursor of the hybrid vesicle.With a base catalyst,R-Si(OCH₃)₃ groups may be hydrolyzed easily into -Si(OH)₃,which are subsequently transferred into crosslinked polysilsesquioxane by polycondensation.Therefore a small amount of triethylamine(TEA)was added into the vesicle solution.TEM analysis shows that a hollow structure is clearly recognized and the contrast became much higher as compared with that without addition of TEA.DLS analysis shows essentially no change of the vesicle dimension was observed after addition of TEA.Owing to the reactivity of the precursor block copolymers and the convenient preparation of the robust hollow particles,this type of hybrid vesicle with a cross-linked wall may find applications for the encapsulation of dyes,catalysts,and other functional species as well as covalently binding guest molecules or other functional segments to be introduced to the vesicle wall.These vesicles can also be decorated with metal nanoparticles;this provides further structural insights and may offer some possibilities for vesicle-supported precious metal catalysts.In chapter three,trifunctional trimethyol propane(TMP)initiaited enzymatic Ring-opening Polymerization(eROP)of caprolactone(CL)to synthesize the hydroxyl group terminated star polyester TMP-(PCL-OH)₃. Theα-bromoester terminated star macroinitiator TMP-(PCL-Br)₃ was obtained in the subsequent modification of end hydroxyl groups and suitable for block-ATRP of N,N-dimethylamino-2-ethyl methacrylate(DMA)and glycidyl methacrylate(GMA).Diblock copolymers TMP-(PCL-PDMA)₃ and TMP-(PCL-PGMA)₃ were successfully synthesized.NMR,GPC and IR analysis testified the copolymers structure as expected.At first,we investigate novel biocompatible amphiphilic diblock copolymers combining PCL and PDMA.PCL is a kind of water-insoluble aliphatic polyester,which is known for its enzymatic biodegradability,its permeability,and the biocompatibility of its metabolites.PDMA is nontoxic and water-soluble in its protonated form, it can be absorbed by endocytosis and can be used as a nonviral DNA vector. When dispersed in aqueous media of appropriate pH,TMP-(PCL-PDMA)₃ copolymers are thus expected to associate into micelles,which could lay the basis for new drug delivery systems.The DLS results show that the size of the micelles increases with the relative amount of PCL.This is probably due to the fact that the longer PDMA segments are likely to improve the copolymer dispersion.In additon,we also studied self-assembly of the diblock star copolymer TMP-(PCL-PGMA)₃ into polymeric nanospheres in aquesous media.The AFM results show that nanascale micelles have a spherical shape and a mean diameter.In chapter four,we present a successful example of structurally well-defined, polystyrene(PS)-based graft copolymers through ATRP.PS could be partially brominated at the benzylic positions using N-bromosuccinimide(NBS)to form a "poly" benzyl bromide.At first,thermosensitive graft copolymer PS-g-PNIPAM was synthesized by ATRP using the brominated PS as initiator and CuCl combined with HMTETA as catalyst.The ¹H NMR spectrum and the unimodal and symmetrical shape of the trace obtained at GPC proved that the graft copolymer was obtained.Due to the fact that the carbonyl group derived from PNIPAM was introduced into PSt,the Tg value for the graft copolymer is higher than that of the starting PSt.On the other side,we prepared thermosensitive polymeric micelles in water with PS-g-PNIPAM and studied the conformational changes of PNIPAM blocks in their coronas using DLS.The study shows that PNIPAM brushes in coronas of the micelles exhibit a broaden collapse transition from 28 to 34℃with some second-order character relative to free PNIPAM chains and the lower critical solution temperature(LCST)is 31℃.The thermosensitive PS-g-PNIPAM micelles may find some applications. On the second,PS-graft-PGMA was synthesized by ATRP.A systematic study was performed in which the monomer conversion and the polymer molecular weight were correlated with the polymerization time.The polymerization is first order with respect to monomer concentration and the polymerization process is characteristic of a 'living' nature.PS-graft-PGMA samples are unable to crystallize regardless of the degrees of grafting.