侧链含胺基的水溶性和两亲性阳离子聚电解质的合成及性质研究
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摘要
把胺基引入到聚合物(特别是结构规整的嵌段共聚物)中得到的聚胺型阳离子聚电解质,与小分子胺一样具有一系列的生物学性能,在生物生理过程中起着非常重要的作用,而且聚合物的链结构有利于胺基的稳定和功能基团的发挥。本文系统介绍了胺基的性质,阳离子聚电解质的结构、合成方法和工业应用,聚电解质溶液的特性和自组装结构。研究了聚胺型阳离子聚电解质均聚物或嵌段共聚物的合成方法,在不同溶液体系中的构象和在不同的选择性溶剂中形成的聚集体形态,并试图找出自组装聚集体形态结构与自组装条件的对应关系,实现聚集体结构的可控形成,分析自组装的机理。
(1)含有胺基的不饱和单体4-乙烯基苄胺盐酸盐(4-VBAHS)的自由基聚合得到了含有胺基的水溶性阳离子聚电解质PVBAHS;聚合物的组成,即一级结构,用~1H NMR、FT-IR和酸碱滴定进行了表征。
应用MALS-VIS-GPC联用技术,测得了分子量介于1.1×10~3-2.6×10~5g/mol的窄分布聚乙烯基苄胺盐酸盐样品在纯水和0.15mol/L氯化钠水溶液中的特性粘度和均方根旋转半径与重均分子量的依赖关系分别为[η]=1.874×10~(-2)M_w~(0.666),R_g=0.67 M_w~(0.465)和[η]=1.456×10~(-3)M_w~(0.971),R_g=6.772×10~(-4)M_w~(1.012)。方程指数表明聚合物两种溶剂体系中的二级结构分别呈柔顺性无规线团和棒状或刚性链构象。由18角度静态光散射数据作Zimm图,得到分子量最大的样品在纯水中的表观分子量(M_(w(app)))、均方根旋转半径(R_g)和第二维利系数(A_2)分别为5.401×10~4g/mol、113.0nm和-3.655×10~(-4)mol·cm~3/g~2;在0.15mol/L氯化钠水溶液中的M_(w(app))、R_g和A_2分别为2.597×10~5g/mol、131.7nm和1.012×10~(-4)mol.cm~3/g~2。
光散射结果显示,与常规的聚电解质溶液行为相比,PVBAHS在水中表现出了特殊的构象转变行为。随浓度增加,PVBAHS在纯水中的构象为球到无规线团的去折叠转变,在体积比为1/3的THF/H_2O中为无规线团到球的折叠转变。通过负染色透射电镜和动态光散射等手段观察,这种均聚物在四氢呋喃与水的体积比为1/3的二元混合溶剂中,受浓度控制,可组装成为交联互穿网络、管状胶束、支化胶束、六角相、囊泡和针状晶体等结构。我们对各种结构中的链的形态和链间相互作用进行了解释。阴离子表面活性剂二(2-乙基已基)琥珀酸酯磺酸钠(AOT)与阳离子聚电解质PVBAHS混合体系有囊泡形成。应用表面张力测定法,得到了临界囊泡浓度和临界胶束浓度分别为0.72mmol/L和4.01mmol/L。用负染色透射电镜技术研究了囊泡在pH、温度和离子强度影响下的形态和稳定性。(2)利用二叔丁基二碳酸酯(Boc_2O)保护胺基单体4-乙烯基苄胺盐酸盐得到4-乙烯基苄胺叔丁基碳酸酯(4-VBA-Boc),通过原子转移自由基聚合(ATRP)方法制备聚合物大分子引发剂聚(4-乙烯基苄胺叔丁基碳酸酯)(P(4-VBA-Boc)-Cl),加入第二单体苯乙烯后脱保护基得到了两亲嵌段共聚物PVBAHS-b-PS。原子转移自由基聚合中,氯端基的P(4-VBA-Boc)作为大分子引发剂,链段长度已经固定,而嵌段共聚物中聚苯乙烯的链段长度可以通过改变聚合时苯乙烯单体与大分子引发剂的比例进行调节。我们合成了PVBAHS_(59)-b-PS_(64)、PVBAHS_(59)-b-PS_(99)、PVBAHS_(59)-b-PS_(132)、PVBAHS_(59)-b-PS_(525)四种嵌段比例的两亲嵌段共聚物,通过GPC、~1H NMR、FT-IR等手段进行表征,通过热分析(TGA和DSC)等手段对聚合物的性质进行研究。
两亲嵌段共聚物PVBAHS-b-PS在纯水为亚相的气/液界面上可以铺展成为紧密堆积压缩型单分子膜。向亚相中加入牛血清白蛋白(BSA),观察两亲嵌段共聚物PVBAHS-b-PS表面压-分子面积曲线的变化。向亚相中加入少量BSA时,PVBAHS-b-PS分子与BSA通过静电作用形成多对一缔合的多尾链、大体积的两亲分子,使分子膜的可压缩性和稳定性迅速增加,分子膜在压缩过程中依次经历液态扩张膜状态、转变膜状态和液态凝聚膜状态。向亚相中加入大量BSA时,PVBAHS-b-PS分子与BSA形成一对一缔合的两亲分子,过量的BSA在气/液界面上和与之发生缔合的两亲分子一起组成混合分子膜,压缩过程中,由于未缔合的BSA分子重排甚至被挤出单分子膜,使π-A曲线表面压随面积减小而平滑上升,崩溃压π_(max)迅速下降,说明亚相中大量BSA的加入不利于紧密堆积压缩型分子膜的形成。
通过负染色透射电镜观察到了在混合溶剂THF/H_2O(v/v=3)中随溶液pH升高,PVBAHS链段质子化程度降低,PVBAHS_(59)-b-PS_(132)嵌段共聚物在溶液中的组装自由能受到PVBAHS链段间的静电排斥力、PS链段的伸展作用和核壳形态的界面张力三者的共同作用,组装形态依次为花样团簇核壳胶束、囊泡和球状反相胶束,经历了从胶束到反相胶束的转变。
由于伯胺基中N-H…Cl氢键作用,PVBAHS链间可以形成三维网状聚集体结构,PVBAHS_(59)-b-PS_(64)、PVBAHS_(59)-b-PS_(132)、PVBAHS_(59)-b-PS_(525)三种聚合物在质量比为3/2的DMSO/THF二元混合溶剂中形成PS为壳,PVBAHS为核的胶束。向体系中加入微量水,会增大聚合物胶束核壳间的界面能,体系趋于增加聚集体半径以减小界面比表面积,胶束间发生单链的链交换,同时核内N-H…Cl氢键受到水分子的破坏,聚集体的粒径随水的加入量的增大而增大,粒径分布逐渐加宽,胶束数量的减少使粒径分布的光散射强度峰值高度降低。
由于较长的壳层链段使形成胶束的嵌段共聚物聚集数减小,所以,尽管PVBAHS_(59)-b-PS_(525)比PVBAHS_(59)-b-PS_(64)和PVBAHS_(59)-b-PS_(132)分子量大,分子链更长,但前者形成的胶束粒径却远小于后者形成的胶束粒径。
(3)通过苯乙烯(S)的原子转移自由基聚合得到溴端基的聚苯乙烯(PS)作为大分子引发剂,在DMF中引发第二单体甲基丙烯酸二甲胺基乙酯(DMAEMA)聚合,合成了两亲嵌段共聚物PS-b-PDMAEMA。原子转移自由基聚合中,溴端基的PS大分子引发剂的链段长度已经固定,而嵌段共聚物中PDMAEMA的链段长度可以通过改变聚合时DMAEMA单体与大分子引发剂的比例进行调节。我们合成了不对称的PS_(62)-b-PDMAEMA_3和准对称的PS_(62)-b-PDMAEMA_(47),两种嵌段比例的两亲共聚物,通过GPC、~1H NMR等手段对聚合物的结构进行表征,通过TGA和DSC手段对聚合物的热稳定性进行研究,两亲分子PS_(62)-b-PDMAEMA_3和PS_(62)-b-PDMAEMA_(47)均能在气/液界面铺展成紧密堆积的液态扩张膜,成膜分子最小截面积随着亲水链段的增长而增大。
通过负染色透射电镜研究了溶液pH变化对PS-b-PDMAEMA自组装行为的影响。不同pH条件下的DMF稀溶液中,不对称结构的PS_(62)-b-PDMAEMA_3组装形态除了简单的球形核壳胶束外,还有六角相、囊泡、反相六角相和珍珠项链状反相胶束串;PS_(62)-b-PDMAEMA_3在极性较小的二氧六环/水(v/v=94/6)混合溶剂中组装为大复合反相胶束(LCRM)和反相囊泡。相比之下,相同条件的准对称PS_(62)-b-PDMAEMA_(47)的DMF溶液中的组装形态则简单得多,只有球形胶束和六角相存在。PS_(62)-b-PDMAEMA_(47)在二氧六环/水(v/v=94/6)混合溶剂中只能组装成球形的反相胶束。上述结构的形成都是在聚集自由能的控制下形成的,自由能由三个组分组成:核内链段的伸展,壳链段间的排斥和核/壳界面张力。
(4)以4,4'-偶氮双(4-氰基戊酸)经酰氯化后与单甲醚聚乙二醇反应生成的4,4'-偶氮双(4-氰基戊酸单甲醚聚乙二醇酯)作为大分子引发剂通过自由基聚合方法引发单体4-乙烯基苄胺盐酸盐聚合,合成出具有良好生物相容性的双亲水嵌段聚合物mPEG-b-PVBAHS。偶氮大分子引发剂合成过程中使用的单甲醚聚乙二醇分子量为1300,嵌段共聚物中PVBAHS的链段长度可以通过改变聚合时4-乙烯基苄胺盐酸盐单体与大分子引发剂的比例进行调节。我们合成了三种嵌段比例的双亲水嵌段共聚物mPEG-b-PVBAHS,通过GPC-MALS、~1H NMR、FT-IR等手段对聚合物的结构进行表征,通过热分析(TGA和DSC)、酸碱滴定和荧光手段对聚合物的性质进行研究。
mPEG-b-PVBAHS在纯水和氯化钠水溶液中的荧光强度均随浓度的增加和PVBAHS链段的增长而减弱,盐水中激基缔合物和独立苯环侧基的荧光强度比值(I_E/I_M)小于纯水体系的比值。
双亲水嵌段共聚物mPEG-b-PVBAHS中,mPEG链段的水溶性随温度的升高而降低,PVBAHS阳离子聚电解质链段的质子化程度受pH和盐浓度的影响。我们研究了pH值、温度和盐浓度对嵌段共聚物在溶液中的构象(二级结构)和聚集体粒径及粒径分布(三级结构)的影响。
结果表明,mPEG-b-PVBAHS共聚物的二级结构随温度升高由刚性链变为柔性链,PVBAHS链段越长,共聚物在纯水稀溶液中的刚性越大。mPEG-b-PVBAHS-1纯水溶液聚集体随温度的升高,粒径减小,粒径分布变窄。mPEG-b-PVBAHS-2和mPEG-b-PVBAHS-3共聚物中mPEG链段所占的比例增大,受到mPEG在水中的溶解度随着温度的升高而降低的影响,水溶液中聚集体流体动力学半径随温度的升高而增大,且粒径分布变宽。通过负染色透射电镜技术观察到,室温下5×10~(-3)g/mL的mPEG-b-PVBAHS-1、m#EG-b-PVBAHS-2和mPEG-b-PVBAHS-3水溶液中聚集体分别为囊泡、球形胶束和平面层状相与闭合层状相的混合体。
在不同pH下(pH=4、5、6、7),mPEG-b-PVBAHS溶液中共聚物的二级结构均为刚性链状态。mPEG-b-PVBAHS溶液中粒径及粒径分布随着pH升高先增大后减小,受到高分子链中游离胺基与质子化胺基之间的氢键作用影响,转折点的pH值随PVBAHS链段长度的减小而降低。
在不同浓度的氯化钠溶液中,mPEG-b-PVBAHS二级结构均为刚性链状态,与浓度相近的PVBAHS均聚物在0.15mol/L氯化钠溶液中的构象相似。PVBAHS链段对mPEG-b-PVBAHS共聚物在盐溶液中的构象起决定作用,柔性的mPEG链段的引入不能改变mPEG-b-PVBAHS共聚物在盐溶液中的刚性构象。盐浓度的不断增加导致mPEG-b-PVBAHS嵌段共聚物粒径不断减小,粒径分布变窄。这一结果与氯化钠的加入对PVBAHS均聚物水溶液中聚集体形态的影响一致。
用荧光光谱法、透射电镜和光散射技术研究了mPEG-b-PVBAHS与生物大分子牛血清白蛋白(BSA)之间的相互作用。结果表明,极微量的mPEG-b-PVBAHS便会使BSA水溶液的荧光产生可分辨的降低,但淬灭效率随着PVBAHS嵌段在三种共聚物中含量的减小而降低。继续增加聚合物的加入量使BSA的荧光强度增大。加入mPEG-b-PVBAHS会使BSA的荧光谱线发生一定程度的蓝移,说明BSA的球状结构变得更为紧密。当聚合物浓度不是很大时,溶液中形成的mPEG-b-PVBAHS/BSA复合物的平均粒径随聚合物浓度的增加而增大,粒径增大的速率随聚合物中PVBAHS链段含量的增加而显著加快,复合物的形态也随之呈椭球形、不规则球状和圆球状;聚合物浓度继续增大使复合物的粒径减小。BSA也可淬灭mPEG-b-PVBAHS的荧光,且BSA对聚合物在水溶液中形成的激基缔合物的荧光淬灭效率高于对其独立苯环结构的淬灭效率。说明聚合物与BSA之间存在相互作用,二者之间发生了荧光发射能量的转移。
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 1.1×10~3 to 2.6×10~5g/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(M_w),root-mean-square radii of gyration(R_g), 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(M_w),the root-mean-square radii of gyration(R_g),and the second virial coefficients(A_2),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 5.401×10~4g/mol,113.0nm,-3.655×10~(-4)mol·cm~3/g~2 and 2.597×10~5g/mol, 131.7nm,1.012×10~(-4)mol·cm~3/g~2,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/H_2O(v/v=1/3)binary solvent mixture with concentration increase by light scattering technology.On the other hand,PVBAHS in THF/H_2O(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(Boc_2O) 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(PVBAHS_n-b-PS_m)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(π_(max)),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 PVBAHS_(59)-b-PS_(132) containing pendant amino groups in THF/H_2O(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,PVBAHS_(59)-b-PS_(64), PVBAHS_(59)-b-PS_(132),and PVBAHS_(59)-b-PS_(525)formed 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 PVBAHS_(59)-b-PS_(525)were smaller than those self-assembled by PVBAHS_(59)-b-PS_(64)and PVBAHS_(59)-b-PS_(132),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 PS_(62)-b-PDMAEMA_3 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, PS_(62)-b-PDMAEMA_(47)copolymers 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 PS_(62)-b-PDMAEMA_3 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 PS_(62)-b-PDMAEMA_(47)in 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(I_E/I_M)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~(-3)g/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~(-3)g/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.
(1)含有胺基的不饱和单体4-乙烯基苄胺盐酸盐(4-VBAHS)的自由基聚合得到了含有胺基的水溶性阳离子聚电解质PVBAHS;聚合物的组成,即一级结构,用~1H NMR、FT-IR和酸碱滴定进行了表征。
应用MALS-VIS-GPC联用技术,测得了分子量介于1.1×10~3-2.6×10~5g/mol的窄分布聚乙烯基苄胺盐酸盐样品在纯水和0.15mol/L氯化钠水溶液中的特性粘度和均方根旋转半径与重均分子量的依赖关系分别为[η]=1.874×10~(-2)M_w~(0.666),R_g=0.67 M_w~(0.465)和[η]=1.456×10~(-3)M_w~(0.971),R_g=6.772×10~(-4)M_w~(1.012)。方程指数表明聚合物两种溶剂体系中的二级结构分别呈柔顺性无规线团和棒状或刚性链构象。由18角度静态光散射数据作Zimm图,得到分子量最大的样品在纯水中的表观分子量(M_(w(app)))、均方根旋转半径(R_g)和第二维利系数(A_2)分别为5.401×10~4g/mol、113.0nm和-3.655×10~(-4)mol·cm~3/g~2;在0.15mol/L氯化钠水溶液中的M_(w(app))、R_g和A_2分别为2.597×10~5g/mol、131.7nm和1.012×10~(-4)mol.cm~3/g~2。
光散射结果显示,与常规的聚电解质溶液行为相比,PVBAHS在水中表现出了特殊的构象转变行为。随浓度增加,PVBAHS在纯水中的构象为球到无规线团的去折叠转变,在体积比为1/3的THF/H_2O中为无规线团到球的折叠转变。通过负染色透射电镜和动态光散射等手段观察,这种均聚物在四氢呋喃与水的体积比为1/3的二元混合溶剂中,受浓度控制,可组装成为交联互穿网络、管状胶束、支化胶束、六角相、囊泡和针状晶体等结构。我们对各种结构中的链的形态和链间相互作用进行了解释。阴离子表面活性剂二(2-乙基已基)琥珀酸酯磺酸钠(AOT)与阳离子聚电解质PVBAHS混合体系有囊泡形成。应用表面张力测定法,得到了临界囊泡浓度和临界胶束浓度分别为0.72mmol/L和4.01mmol/L。用负染色透射电镜技术研究了囊泡在pH、温度和离子强度影响下的形态和稳定性。(2)利用二叔丁基二碳酸酯(Boc_2O)保护胺基单体4-乙烯基苄胺盐酸盐得到4-乙烯基苄胺叔丁基碳酸酯(4-VBA-Boc),通过原子转移自由基聚合(ATRP)方法制备聚合物大分子引发剂聚(4-乙烯基苄胺叔丁基碳酸酯)(P(4-VBA-Boc)-Cl),加入第二单体苯乙烯后脱保护基得到了两亲嵌段共聚物PVBAHS-b-PS。原子转移自由基聚合中,氯端基的P(4-VBA-Boc)作为大分子引发剂,链段长度已经固定,而嵌段共聚物中聚苯乙烯的链段长度可以通过改变聚合时苯乙烯单体与大分子引发剂的比例进行调节。我们合成了PVBAHS_(59)-b-PS_(64)、PVBAHS_(59)-b-PS_(99)、PVBAHS_(59)-b-PS_(132)、PVBAHS_(59)-b-PS_(525)四种嵌段比例的两亲嵌段共聚物,通过GPC、~1H NMR、FT-IR等手段进行表征,通过热分析(TGA和DSC)等手段对聚合物的性质进行研究。
两亲嵌段共聚物PVBAHS-b-PS在纯水为亚相的气/液界面上可以铺展成为紧密堆积压缩型单分子膜。向亚相中加入牛血清白蛋白(BSA),观察两亲嵌段共聚物PVBAHS-b-PS表面压-分子面积曲线的变化。向亚相中加入少量BSA时,PVBAHS-b-PS分子与BSA通过静电作用形成多对一缔合的多尾链、大体积的两亲分子,使分子膜的可压缩性和稳定性迅速增加,分子膜在压缩过程中依次经历液态扩张膜状态、转变膜状态和液态凝聚膜状态。向亚相中加入大量BSA时,PVBAHS-b-PS分子与BSA形成一对一缔合的两亲分子,过量的BSA在气/液界面上和与之发生缔合的两亲分子一起组成混合分子膜,压缩过程中,由于未缔合的BSA分子重排甚至被挤出单分子膜,使π-A曲线表面压随面积减小而平滑上升,崩溃压π_(max)迅速下降,说明亚相中大量BSA的加入不利于紧密堆积压缩型分子膜的形成。
通过负染色透射电镜观察到了在混合溶剂THF/H_2O(v/v=3)中随溶液pH升高,PVBAHS链段质子化程度降低,PVBAHS_(59)-b-PS_(132)嵌段共聚物在溶液中的组装自由能受到PVBAHS链段间的静电排斥力、PS链段的伸展作用和核壳形态的界面张力三者的共同作用,组装形态依次为花样团簇核壳胶束、囊泡和球状反相胶束,经历了从胶束到反相胶束的转变。
由于伯胺基中N-H…Cl氢键作用,PVBAHS链间可以形成三维网状聚集体结构,PVBAHS_(59)-b-PS_(64)、PVBAHS_(59)-b-PS_(132)、PVBAHS_(59)-b-PS_(525)三种聚合物在质量比为3/2的DMSO/THF二元混合溶剂中形成PS为壳,PVBAHS为核的胶束。向体系中加入微量水,会增大聚合物胶束核壳间的界面能,体系趋于增加聚集体半径以减小界面比表面积,胶束间发生单链的链交换,同时核内N-H…Cl氢键受到水分子的破坏,聚集体的粒径随水的加入量的增大而增大,粒径分布逐渐加宽,胶束数量的减少使粒径分布的光散射强度峰值高度降低。
由于较长的壳层链段使形成胶束的嵌段共聚物聚集数减小,所以,尽管PVBAHS_(59)-b-PS_(525)比PVBAHS_(59)-b-PS_(64)和PVBAHS_(59)-b-PS_(132)分子量大,分子链更长,但前者形成的胶束粒径却远小于后者形成的胶束粒径。
(3)通过苯乙烯(S)的原子转移自由基聚合得到溴端基的聚苯乙烯(PS)作为大分子引发剂,在DMF中引发第二单体甲基丙烯酸二甲胺基乙酯(DMAEMA)聚合,合成了两亲嵌段共聚物PS-b-PDMAEMA。原子转移自由基聚合中,溴端基的PS大分子引发剂的链段长度已经固定,而嵌段共聚物中PDMAEMA的链段长度可以通过改变聚合时DMAEMA单体与大分子引发剂的比例进行调节。我们合成了不对称的PS_(62)-b-PDMAEMA_3和准对称的PS_(62)-b-PDMAEMA_(47),两种嵌段比例的两亲共聚物,通过GPC、~1H NMR等手段对聚合物的结构进行表征,通过TGA和DSC手段对聚合物的热稳定性进行研究,两亲分子PS_(62)-b-PDMAEMA_3和PS_(62)-b-PDMAEMA_(47)均能在气/液界面铺展成紧密堆积的液态扩张膜,成膜分子最小截面积随着亲水链段的增长而增大。
通过负染色透射电镜研究了溶液pH变化对PS-b-PDMAEMA自组装行为的影响。不同pH条件下的DMF稀溶液中,不对称结构的PS_(62)-b-PDMAEMA_3组装形态除了简单的球形核壳胶束外,还有六角相、囊泡、反相六角相和珍珠项链状反相胶束串;PS_(62)-b-PDMAEMA_3在极性较小的二氧六环/水(v/v=94/6)混合溶剂中组装为大复合反相胶束(LCRM)和反相囊泡。相比之下,相同条件的准对称PS_(62)-b-PDMAEMA_(47)的DMF溶液中的组装形态则简单得多,只有球形胶束和六角相存在。PS_(62)-b-PDMAEMA_(47)在二氧六环/水(v/v=94/6)混合溶剂中只能组装成球形的反相胶束。上述结构的形成都是在聚集自由能的控制下形成的,自由能由三个组分组成:核内链段的伸展,壳链段间的排斥和核/壳界面张力。
(4)以4,4'-偶氮双(4-氰基戊酸)经酰氯化后与单甲醚聚乙二醇反应生成的4,4'-偶氮双(4-氰基戊酸单甲醚聚乙二醇酯)作为大分子引发剂通过自由基聚合方法引发单体4-乙烯基苄胺盐酸盐聚合,合成出具有良好生物相容性的双亲水嵌段聚合物mPEG-b-PVBAHS。偶氮大分子引发剂合成过程中使用的单甲醚聚乙二醇分子量为1300,嵌段共聚物中PVBAHS的链段长度可以通过改变聚合时4-乙烯基苄胺盐酸盐单体与大分子引发剂的比例进行调节。我们合成了三种嵌段比例的双亲水嵌段共聚物mPEG-b-PVBAHS,通过GPC-MALS、~1H NMR、FT-IR等手段对聚合物的结构进行表征,通过热分析(TGA和DSC)、酸碱滴定和荧光手段对聚合物的性质进行研究。
mPEG-b-PVBAHS在纯水和氯化钠水溶液中的荧光强度均随浓度的增加和PVBAHS链段的增长而减弱,盐水中激基缔合物和独立苯环侧基的荧光强度比值(I_E/I_M)小于纯水体系的比值。
双亲水嵌段共聚物mPEG-b-PVBAHS中,mPEG链段的水溶性随温度的升高而降低,PVBAHS阳离子聚电解质链段的质子化程度受pH和盐浓度的影响。我们研究了pH值、温度和盐浓度对嵌段共聚物在溶液中的构象(二级结构)和聚集体粒径及粒径分布(三级结构)的影响。
结果表明,mPEG-b-PVBAHS共聚物的二级结构随温度升高由刚性链变为柔性链,PVBAHS链段越长,共聚物在纯水稀溶液中的刚性越大。mPEG-b-PVBAHS-1纯水溶液聚集体随温度的升高,粒径减小,粒径分布变窄。mPEG-b-PVBAHS-2和mPEG-b-PVBAHS-3共聚物中mPEG链段所占的比例增大,受到mPEG在水中的溶解度随着温度的升高而降低的影响,水溶液中聚集体流体动力学半径随温度的升高而增大,且粒径分布变宽。通过负染色透射电镜技术观察到,室温下5×10~(-3)g/mL的mPEG-b-PVBAHS-1、m#EG-b-PVBAHS-2和mPEG-b-PVBAHS-3水溶液中聚集体分别为囊泡、球形胶束和平面层状相与闭合层状相的混合体。
在不同pH下(pH=4、5、6、7),mPEG-b-PVBAHS溶液中共聚物的二级结构均为刚性链状态。mPEG-b-PVBAHS溶液中粒径及粒径分布随着pH升高先增大后减小,受到高分子链中游离胺基与质子化胺基之间的氢键作用影响,转折点的pH值随PVBAHS链段长度的减小而降低。
在不同浓度的氯化钠溶液中,mPEG-b-PVBAHS二级结构均为刚性链状态,与浓度相近的PVBAHS均聚物在0.15mol/L氯化钠溶液中的构象相似。PVBAHS链段对mPEG-b-PVBAHS共聚物在盐溶液中的构象起决定作用,柔性的mPEG链段的引入不能改变mPEG-b-PVBAHS共聚物在盐溶液中的刚性构象。盐浓度的不断增加导致mPEG-b-PVBAHS嵌段共聚物粒径不断减小,粒径分布变窄。这一结果与氯化钠的加入对PVBAHS均聚物水溶液中聚集体形态的影响一致。
用荧光光谱法、透射电镜和光散射技术研究了mPEG-b-PVBAHS与生物大分子牛血清白蛋白(BSA)之间的相互作用。结果表明,极微量的mPEG-b-PVBAHS便会使BSA水溶液的荧光产生可分辨的降低,但淬灭效率随着PVBAHS嵌段在三种共聚物中含量的减小而降低。继续增加聚合物的加入量使BSA的荧光强度增大。加入mPEG-b-PVBAHS会使BSA的荧光谱线发生一定程度的蓝移,说明BSA的球状结构变得更为紧密。当聚合物浓度不是很大时,溶液中形成的mPEG-b-PVBAHS/BSA复合物的平均粒径随聚合物浓度的增加而增大,粒径增大的速率随聚合物中PVBAHS链段含量的增加而显著加快,复合物的形态也随之呈椭球形、不规则球状和圆球状;聚合物浓度继续增大使复合物的粒径减小。BSA也可淬灭mPEG-b-PVBAHS的荧光,且BSA对聚合物在水溶液中形成的激基缔合物的荧光淬灭效率高于对其独立苯环结构的淬灭效率。说明聚合物与BSA之间存在相互作用,二者之间发生了荧光发射能量的转移。
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 1.1×10~3 to 2.6×10~5g/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(M_w),root-mean-square radii of gyration(R_g), 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(M_w),the root-mean-square radii of gyration(R_g),and the second virial coefficients(A_2),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 5.401×10~4g/mol,113.0nm,-3.655×10~(-4)mol·cm~3/g~2 and 2.597×10~5g/mol, 131.7nm,1.012×10~(-4)mol·cm~3/g~2,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/H_2O(v/v=1/3)binary solvent mixture with concentration increase by light scattering technology.On the other hand,PVBAHS in THF/H_2O(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(Boc_2O) 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(PVBAHS_n-b-PS_m)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(π_(max)),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 PVBAHS_(59)-b-PS_(132) containing pendant amino groups in THF/H_2O(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,PVBAHS_(59)-b-PS_(64), PVBAHS_(59)-b-PS_(132),and PVBAHS_(59)-b-PS_(525)formed 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 PVBAHS_(59)-b-PS_(525)were smaller than those self-assembled by PVBAHS_(59)-b-PS_(64)and PVBAHS_(59)-b-PS_(132),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 PS_(62)-b-PDMAEMA_3 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, PS_(62)-b-PDMAEMA_(47)copolymers 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 PS_(62)-b-PDMAEMA_3 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 PS_(62)-b-PDMAEMA_(47)in 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(I_E/I_M)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~(-3)g/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~(-3)g/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.
引文
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