| In the field of polymer science it has been of great interest to combine properties of useful functional group,;and polymers,especially well-defined block copolymers.The application of this approach provides a prospect of modifying polymer constitution to discovery new type of polymer which can be used as a pharmacological tool.Aminated polyelectrolytes have caused a great deal of attention because of their applications in drug delivery,immobilization matrices for enzymes and cells,and tissue engineering.As a matter of fact,the incorporation of primary amino groups onto the polymer backbone can tune both stabilization of polymer fragment and the useful biological activity of amino groups,which are among the most important classes of polyelectrolytes.Amino functionalized polymers aggregate to spherical,cylindrical,tubular and vesicular phases in selective solvent spontaneously.Such aggregations can be used as templates for making nano-materials,immobilization matrices for enzymes and cells,and tissue engineering,and applicated in drug delivery such as vesicles possessing nano-sized hollow cubages.We summarize the amino group properties;structures,synthesis and industrial applications of cationic polyelectrolyte;characteristics and aggregation of polyelectrolyte solution.In this paper,we study on the synthesis methods,conformation and self-assembly behavior of amino functional cationic homo- or block polyelectrolytes.We try to find out the relationship between the aggregation structures and self-assembly condition,by which to analyses the self-assembly mechanism and control the aggregation.(1)We synthesized unsaturated amino-monomer(4-vinyl benzyl amine hydrochloride salt)(4-VBAHS)by reduction reaction of azides,and prepared poly(4-vinyl benzyl amine hydrochloride salt)(PVBAHS)by free radical polymerization in aqueous solution.The homopolymer was characterized by 1H NMR,FT-IR,and acid-base titration.The conformations of narrow-distributed PVBAHS samples ranging in weight-average molecular weights from 1.1×103 to 2.6×105g/mol,prepared by free radical polymerization, followed by purification,were investigated in pure water and 0.15mol/L aqueous NaCl at 25℃.Weight-average molecular weights(Mw),root-mean-square radii of gyration(Rg), intrinsic viscosities[η]and conformational information obtained from gel permeation chromatography(GPC),viscosity(VIS)and multi-angle laser light-scattering(MALS) detection were examined for the amino functional polymers.Calculated conformational coefficients indicated a random coil configuration of the cationic PVBAHS in pure water, which exhibited a rod-like conformation in the NaCl aqueous solution.According to the Zimm plots,weight-averaged molecular weights(Mw),the root-mean-square radii of gyration(Rg),and the second virial coefficients(A2),of PVBAHS-11(the homopolymer with the highest molecular weight)in pure water and 0.15 mol/L NaCl aqueous solution were found to be 5.401×104g/mol,113.0nm,-3.655×10-4mol·cm3/g2 and 2.597×105g/mol, 131.7nm,1.012×10-4mol·cm3/g2,respectively.The conformation(folding or unfolding)and aggregation of PVBAHS in solution were studied.The polymer's conformation and aggregation were just like the secondary and tertiary structures of protein.We started with the unfolding or globule-to-coil transition of PVBAHS chains in pure water,and then studied the folding or coil-to-globule transition of PVBAHS in THF/H2O(v/v=1/3)binary solvent mixture with concentration increase by light scattering technology.On the other hand,PVBAHS in THF/H2O(v/v=1/3)binary solvent mixture formed concentration-dependent multiple morphologies including interpenetrating networks,tubular micelles,branched micelles,hexagonal phases,vesicles, and needle crystals observed by transmission electron microscopy(TEM).In addition,effect of cationic PVBAHS on the morphology and stability of anionic surfactant sodium bis(2-ethylhexyl)sulfosucciante(AOT)vesicles was detected using dynamic light scattering(DLS),zeta potential(ZP),surface tension,and percent transmission measurements by changing pH,storage temperature,and ion strength.The critical vesicle concentration(cvc)and critical micelle concentration(cmc)of the binary mixture system were determined by surface tension measurement,which were 0.72mmol/L and 4.01 mmol/L respectively.(2)To hinder amino-caused side reaction and interference of the amino groups with the catalyst system,the monomer 4-VBAHS was protected by di-tert-butyl dicarbonate(Boc2O) before use,and then polymerized via atom transfer radical polymerization(ATRP)to obtain poly(4-VBA-Boc)as the macroinitiator.Every chain of the poly(4-VBA-Boc)contained one halogen atom at its head group.The amino-containing homopolymer was introduced to initiate the ATRP of styrene.Deprotection of the Boc groups finally resulted in the desired block copolymer with aminated side-groups.Characterization data were reported from analysis by GPC,FT-IR and 1H NMR spectra,and element analysis.Well-defined amphiphilic diblock copolymers of 4-vinyl benzyl amine hydrochloride salt and styrene(PVBAHSn-b-PSm)were synthesized.We studied four specific homologous series(block1,2,3,4)with m=64,99,132,525 respectively and n=59.By measuring theπ-A isotherms for liquid expanded monolayers formed at air/water interface,differences of the copolymers in molecular area were of obvious relevance,where the largest PS block occupied the largest interfacial molar area than the other smaller ones.At the same time, this orderliness was invalid for block 1 to 2.A possible explanation for this non-trivial result was that the hydrophilic/hydrophobic balance for these copolymers with lower PS fractions shifted towards the hydrophilicity.Effect of bovine serum albumin(BSA) dissolved in the subphase was also discussed.Significant changes of films were observed formed by copolymers and BSA:with little contents of BSA in surface,new amphiphilic molecule was formed with multi-hydrophobic chains and large volume between PVBAHS-b-PS and BSA based on many to one by electrostatic interaction.The compressibility and stability of the film increased rapidly.During the compression process, the resultingπ-A isotherm existed "the liquid-expanded state","the liquid-condensed state" and "the intermediate state" in turn.With the higher contents of BSA in surface,new amphiphilic molecule was formed between PVBAHS-b-PS and BSA based on one to one by electrostatic interaction.Mixed film was formed by the new amphiphilic molecules and the superfluous BSA molecules.The curves demonstrated smooth surface pressure increase and the rapid decrease of collapse pressure(πmax),illustrating the rearrangement and even extrusion of the unassociated BSA molecules in the film.The presence of much more BSA molecules in the subphase was not favorable to the formation of compact accumulating compressing film.The different aggregated structures of the block copolymer PVBAHS59-b-PS132 containing pendant amino groups in THF/H2O(v/v=3)were formed with pH changes due to electrostatic interaction in PVBAHS segments with different protonization degrees.Observed by dynamic light scattering,the three block copolymers,PVBAHS59-b-PS64, PVBAHS59-b-PS132,and PVBAHS59-b-PS525formed core-shell micelles in DMSO/THF (w/w=3/2)binary solvent mixture,with PS in corona and PVBAHS in core.The core of micelle formed by some sort of hydrogen-bonded structure of special stability in response to the need to solvate the ion pairs of the salts.For primary amino groups in PVBAHS segment,an additional hydrogen of each group was available and a three dimensional structure could be envisioned,which would accommodate a higher aggregate.Water addition would make the interfacial energy increase,which induced the radii of aggregates increasing in response to the need to decrease the interfacial specific surface area. Single-chain exchanges occurred among different micelles,and the N-H…Cl hydrogen bonds in core were destroyed.With the increasing addition of water,the aggregate radius increased,the aggregate size distribution broadened,and the peak height of the light scattering intensity was descending,which showed the number of micelles decreasing.While longer corona chain made the micellar aggregation number decrease,the micelles formed by PVBAHS59-b-PS525were smaller than those self-assembled by PVBAHS59-b-PS64and PVBAHS59-b-PS132,though the former molecule was larger.(3)In this study,amphiphilic linear block copolymer with one block of polystyrene (PS)and another environmental-sensitive block of poly(dimethylaminoethyl methacrylate) (PDMAEMA)was successfully synthesized by ATRP.We reported on TEM based structural studies of the self-assembly behavior of PS-b-PDMAEMA.Indeed our experiments reported changes in the structures of aggregates formed by PS62-b-PDMAEMA3 resulting from changing in solvent and in charge density by adjusting solvent acidity.A rich variety in the image contrasts was observed.At the same time, PS62-b-PDMAEMA47copolymers were in the form of spherical micelle in different solvents.Besides simple,core-shell micelles,large compound reverse micelles(LCRMs), vesicles,reverse vesicles,hexagonal phases,reverse hexagonal phases and pearl necklace-like micellar aggregates were prepared from asymmetric diblock copolymers PS62-b-PDMAEMA3 in dilute solution(1 wt%).This study illustrated the chain architectures of block copolymers in the morphologies of molecular self-assembled nanostructures.Some of the aggregates might have potential applications in areas such as separations and drug delivery systems.When the PS block length was nearly equivalent to the PDMAEMA block length,most of the aggregates of semi-symmetric diblock copolymers PS62-b-PDMAEMA47in organic solvent(DMF)or binary solvent mixture (dioxane/water,v/v=94/6)were spherical,with a core-shell structure.We noted that the larger sizes of aggregates were due to their electrostatic repulsion of these positively charged PDMAEMA head-groups and their low surface curvature associated energy.The participation of polymers in aggregation enhanced the configuration stability caused by the viscosity between polymeric long chains.Moreover,their large surface-to-volume ratios made them sensitive to environmental condition,which was intimately linked to their structural reorganizations,including size,shape,bulk(interior),and surface bonding.All above structures were controlled by three components of the free energy of aggregation: core-chain stretching,interfacial energy and intercoronal chain interaction. (4)Novel double hydrophilic block copolymer methoxyl poly(ethylene glycol)-block-poly(4-vinyl benzylamine hydrochloride salt)(mPEG-b-PVBAHS)with amino pendant chains was synthesized by polymerization of 4-vinyl benzyl amine hydrochloride salt using 4,4'-azo-bis[4-cyanopentanoate methoxyl poly(ethylene glycol) ester]as macroazoinitiator.The structure of the copolymer was characterized by 1H NMR, FT-IR spectra,acid-base titration,GPC-MALS,TGA,DSC and fluorescence techniques.The fluorescence intensity of mPEG-b-PVBAHS in pure water and in NaCl aqueous solution decreased with increasing of polymer concentration and chain length of PVBAHS segment.The fluorescence intensity ratio between excimer and independent phenyl pendant group(IE/IM)in NaCl aqueous solution was larger than the value in pure water.For the double hydrophilic block copolymer(mPEG-b-PVBAHS),the water soluble property of mPEG segment decreased with the temperature increase,and the protonization degree of PVBAHS segment was influenced by pH and salt concentration.We studied the effects of pH,temperature and salt concentration on the conformation and hydrodynamic radii of aggregates in 5.000×10-3g/mL mPEG-b-PVBAHS aqueous solution.The results showed that,with temperature increasing,the conformation of mPEG-b-PVBAHS in aqueous solution underwent the transition from rigid rod to flexible chain.In dilute aqueous solution,the longer the PVBAHS segment was,the more flexible the block copolymer chain was.The radius of aggregate self-assembled by mPEG-b-PVBAHS-1 in aqueous solution decreased,and the size distribution became narrower with temperature increasing.For the higher proportion of mPEG segment in copolymer,the radius of aggregate self-assembled by mPEG-b-PVBAHS-2 or mPEG-b-PVBAHS-3 in aqueous solution increased,and the size distribution broadened with temperature increasing,which was effected by the reduced solubility of mPEG segment.Vesicles,spherical micelles,and mixtures of planar layers and closed layers (vesicles)were observed by TEM in 5×10-3g/mL aqueous solutions of mPEG-b-PVBAHS-1, mPEG-b-PVBAHS-2 and mPEG-b-PVBAHS-3,respectively.Under different pH(pH=4,5,6,7),all of the mPEG-b-PVBAHS copolymers in aqueous solution presented the rigid rod status.With pH increase,the radii of aggregates increased at first,and then decreased.Affected by hydrogen bond formed between free amino groups and protonated amino groups,the pH value at the turning point reduced with length of PVBAHS chain decreasing.In aqueous solution with different concentration of NaCl,all of the mPEG-b-PVBAHS copolymers presented the rigid rod status,with similar conformation exhibited by PVBAHS homopolymer in 0.15 mol/L NaCl aqueous solution,without significantly difference in polymer concentration for the two systems.PVBAHS segment played a decisive role in determining the conformation of mPEG-b-PVBAHS block copolymer.The existence of flexible mPEG segment could not change the rigid rod status of the whole macromolecular chain in salt solution.The radius of aggregate self-assembled by mPEG-b-PVBAHS decreased,and the size distribution became narrower with the concentration of NaCl in aqueous solution increasing.The changes of size and distribution of these aggregates were in correspondence with those of PVBAHS homopolymer in aqueous solutions with different concentrations of NaCl.The interaction between mPEG-b-PVBAHS and BSA was studied by fluorescence spectroscopy,TEM and LS techniques.The results showed that the addition of infinitesimal mPEG-b-PVBAHS could make the fluorescence intensity of BSA decrease.The quenching efficiency decreased with decrease of PVBAHS lengths in the three block copolymers.As the increase of block copolymer concentrations,the fluorescence intensity of BSA increased.Blue shift of BSA fluorescent line occurred by mPEG-b-PVBAHS addition, which indicated the more compacted globular structure of BSA molecule.If the polymer concentration was not very high,the size of the complex formed by mPEG-b-PVBAHS and BSA increased with increase of polymer concentration.The incremental rate of particle size sped up significantly with the increase of chain length of PVBAHS segment in block copolymer.The morphologies of the complexes formed by mPEG-b-PVBAHS-1/BSA, mPEG-b-PVBAHS-2/BSA,and mPEG-b-PVBAHS-3/BSA were homogeneous spherical, regular spherical and ellipsoidal shapes,respectively.Continuous increase of polymer concentration made the particle size of mPEG-b-PVBAHS/BSA complex decrease.Meanwhile,the fluorescence of mPEG-b-PVBAHS could be quenched with the addition of BSA.And the quenching efficiency for excimers formed by mPEG-b-PVBAHS in aqueous solution was higher than that for independent phenyl pendant groups.The results demonstrated that there existed interaction and energy transfer between mPEG-b-PVBAHS and BSA.
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