聚苯乙烯-b-聚丙烯酸/聚苯乙烯在水中的自组装及胶束尺寸的研究

利用动态光散射、透射电镜研究了嵌段共聚物聚苯乙烯 b 聚丙烯酸(PS b PAA)与均聚物聚苯乙烯(PS)在选择性溶剂水中的自组装行为.由于均聚物PS与PS嵌段具有相同的结构单元,均聚物PS参与胶束的形成,和嵌段共聚物的PS链段一同组成胶束的核;在适当的均聚物分子量和含量条件下,PS b PAA PS可以自组装形成单分散的纳米胶束;通过改变体系中均聚物PS的分子量和含量可在较大范围内调变胶束的尺寸.     

带有可调通道的嵌段共聚物胶束对药物的控制释放

用聚丙烯酸叔丁酯-b-聚乙二醇(PtBA45-b-PEG114)和聚丙烯酸叔丁酯-b-聚4-乙烯基吡啶(PtBA60-b-P4VP80)制备了复合胶束. 该胶束在pH=2.5的酸性水溶液中形成以PtBA为核, PEG和P4VP为壳的稳定球型结构. 在pH=12时, 壳层的P4VP链段变为疏水, 塌缩在PtBA的核上形成内壳, PEG链段继续保持溶解状态, 与成核的PtBA连接并穿过塌陷的P4VP内壳, 形成胶束的冠, 由于PEG处于溶解状态, 其分子链间有比较大的空隙, 可以控制一些小分子通过, 在胶束的表面形成通道. 该通道类似于生物膜的蛋白通道, 可以控制PtBA核与外界进行能量或物质交换的速度. 以布洛芬为模型分子, 负载在胶束内进行药物控制释放研究的结果表明, 胶束表面的通道可以起到明显控制布洛芬释放速度的作用, 并且药物的释放速度与通道在胶束表面的比例成正比.     

两亲性嵌段共聚物PS-b-PMAA的合成与胶束化行为研究

利用原子转移自由基聚合法(ATRP)得到了分子量可控、分子量分布接近1.1的聚苯乙烯-b-聚甲基丙烯酸叔丁酯(PS-b-PtBMA)嵌段共聚物, 进而在酸性条件下由水解反应得到了两亲性的聚苯乙烯-b-聚甲基丙烯酸 (PS-b-PMAA)嵌段共聚物．用GPC, FTIR和¹H-NMR等对产物的分子量和组成进行了表征．使PS-b-PMAA在选择性溶剂中进行自组装, 通过激光光散射和透射电子显微镜研究了影响其胶束化行为的因素与胶束形态, 并初步探讨了胶束形成的机理, 发现通过控制嵌段共聚物的链段长度之比可得到空心球形的高分子胶束．     

核中含有羧基官能团的聚合物胶束的高效制备

通过化学交联反应诱导胶束化以较高的效率制备了PMCC(聚合物的质量浓度高达50 g/L). 首先制备嵌段共聚物聚苯乙烯-b-聚丙烯酸(PS-b-PAA), 然后对PAA嵌段中的羧基实行酰氯化, 在酰氯化产物聚苯乙烯-b-聚丙烯酰氯(PS-b-PACl)的共同溶剂二氯甲烷中加入交联剂乙二醇交联PACl嵌段. 交联反应使得PACl嵌段聚集, 同时, PS嵌段的保护作用使得PACl嵌段的聚集在有限个分子链间发生, 从而生成以PS为壳, 以含有羧基官能团的聚丙烯酸酯交联网络为核的PMCC.     

柱状相聚苯乙烯-b-聚乳酸的合成及引导组装

设计并合成了2种柱状相结构的聚苯乙烯-b-聚乳酸(PS-b-PLA)两嵌段共聚物,并表征了它们在化学图案上的引导自组装行为。在辛酸亚锡(Sn(Oct)_2)催化下,采用羟基官能化的聚苯乙烯(PS-OH)大分子引发剂分别引发外消旋丙交酯(rac-LA)和左旋丙交酯(L-LA)开环聚合,制备了两个相对分子质量相近但构型不同的PS-b-PLA:PS-b-PDLLA和PS-b-PLLA。通过核磁共振波谱仪(NMR)、凝胶渗透色谱仪(GPC)、示差扫描量热仪(DSC)、热重分析仪(TGA)、小角X射线衍射仪(SAXS)等测试手段对两个嵌段共聚物的性质进行了表征。然后,将PS-b-PDLLA和PS-b-PLLA薄膜在六方点阵化学图案模板上加热引导自组装,得到长程有序排列的六方柱状相结构。相对于柱状相的PS-b-PLLA,柱状相的PS-b-PDLLA具有较大的拉伸比例,可以在更大的周期范围内组装出规整的六方结构。这一结果与层状相PS-b-PDLLA和PS-b-PLLA薄膜在线性化学图案上组装的结果相似。     

聚苯乙烯-b-聚右旋乳酸二嵌段共聚物的热性能和结晶行为研究

合成了系列聚右旋乳酸(PDLA)嵌段重量分率(fw=0～0.61)的窄分子量分布聚苯乙烯-b-聚右旋乳酸二嵌段共聚物(PS-b-PDLA).运用温度调制示差扫描热分析仪(TMDSC)和热台偏振光显微镜(POM)等研究手段,对制备所得的结晶性二嵌段共聚物的热性能、结晶速率与结晶形貌等进行了研究.研究结果表明,与聚右旋乳酸均聚物相比,随着PS-b-PDLA中结晶性PDLA嵌段重量分率fw减少,无定形聚苯乙烯嵌段(PS)对PDLA嵌段链段的结晶抑制作用增强,PS-b-PDLA的热结晶性能与结晶形貌发生显著变化;相对于PDLA均聚物,PS-b-PDLA的冷结晶温度(Tcc)和结晶平衡熔点(Tm0)分别下降14℃和38℃,球晶生长速率明显降低.在无定形PS嵌段链段的玻璃化温度(Tg)附近,二嵌段PS-b-PDLA的结晶行为出现拐点,揭示PS嵌段由于相分离所形成纳米微相空间对PS-b-PDLA中PDLA链段的结晶产生影响,并且该影响作用程度与PDLA嵌段的重量分率fw和结晶温度(Tc)相关。     

聚苯乙烯-b-聚丙烯酸模板剂成核段长度对聚苯胺尺寸及性能的影响

以两亲性嵌段共聚物为模板是构筑导电聚合物纳米结构并对其形貌尺寸进行调控的有效方法之一。 嵌段共聚物成核段长度的变化对其胶束化行为有显著影响,进而也会改变受限于其胶束形貌的导电聚合物的形貌尺寸。 形貌尺寸的变化必然导致导电聚合物电化学性能变化。 本文欲通过嵌段共聚物模板诱导实现对聚苯胺(PANI)形貌尺寸的调控并使其电化学性能得到优化,采用可逆加成-断裂链转移自由基聚合(RAFT)法成功合成了嵌段共聚物聚苯乙烯-b-聚丙烯酸PS_x-b-PAA₇₀(x=38、64、101)并以其胶束为“模板”制备了窄相对分子质量分布的PANI。 在成核段(PS)长度较短时,模板诱导形成的棒状PANI颗粒,直径为100~200 nm。当 x=101时PANI呈现空间网状结构,其放电比容量高于其它样品,在电流密度为1 A/g时,其放电比容量可达386.71 F/g。     

基于葡萄糖和苯硼酸基元之间的可逆共价键构筑多重响应性高分子复合物胶束

通过可逆加成-断裂链转移(RAFT)的聚合方法,合成了分别含有苯硼酸基元和葡萄糖基元的聚(N-异丙基丙烯酰胺)-b-聚(丙烯酰胺基苯硼酸)(PNIPAM-b-PAPBA)和聚(N-异丙基丙烯酰胺)-b-聚(丙烯酰葡萄糖胺)(PNIPAM-b-PAGA)二嵌段聚合物.由于苯硼酸和葡萄糖基元之间在弱碱性条件下(pH9.3)形成硼酸酯共价键,两种二嵌段聚合物的水溶液混合后能自发形成以PAPBA/PAGA络合物为核,PNIPAM为壳层的高分子复合物胶束.由于硼酸酯共价键在pH值和葡萄糖浓度改变时能可逆形成和断裂,以及胶束PNIPAM壳层的温敏性,所制备的基于苯硼酸/葡萄糖可逆共价键的高分子复合物胶束对pH、葡萄糖和温度具有多重响应性.     

双亲嵌段共聚物PSt-b-PAA在甲苯中的自聚集行为

以α-溴乙苯为引发剂,溴化亚铜为催化剂,2,2'-联吡啶为配体,用原子转移自由基聚合(ATRP)法合成了结构一定的嵌段共聚物聚苯乙烯-b-聚丙烯酸丁酯(PSt-b-PBA).经水解制备了双亲性嵌段共聚物聚苯乙烯-b-聚丙烯酸(PSt-b-PAA);采用单溶剂溶解法配制了PSt-b-PAA在甲苯中的反胶束溶液;以极性荧光化合物N-1-萘乙二胺盐酸盐(NEAH)为极性微区探针,用荧光光谱法并配合透射电镜观察探索了双亲嵌段共聚物PSt-b-PAA在甲苯溶液中的自聚集行为,考察了双亲性嵌段共聚物浓度、链结构及温度等因素对反胶束化行为的影响规律.结果表明,亲水链PAA短而亲油链PSt长的双亲嵌段共聚物PSt-b-PAA,用单溶剂溶解法可使其在甲苯中发生自聚集,形成以亲水段为核,疏水段为壳的星状反胶束结构;反胶束为10-20nm的球形聚集态结构;PSt-b-PAA的自聚集行为及临界胶束浓度与分子链的微结构和温度等因素相关,且随着共聚物浓度的增大,小胶束会逐渐结合形成大的纺垂状聚集体.     

聚苯乙烯-b-聚谷氨酸苄酯刚柔嵌段共聚物的合成及其层状形貌考察

以末端带胺基的聚苯乙烯(PS-NH2)为引发剂,利用N-羧酸内酸酐(N-carbonyl anhydride,NCA)法制备一种刚柔二嵌段共聚物聚苯乙烯-b-聚(γ-苄基-L-谷氨酸酯)(polystyrene-b-poly(γ-benzyl-L-glutamate),PS-b-PBLG)杂化聚肽,并研究该聚肽嵌段共聚物的分子结构、热性能、液晶性与自组装形貌的溶剂效应.以氢核磁共振波谱(1H-NMR)和凝胶渗透色谱仪(GPC)表征两嵌段的摩尔比、分子量及其分布.利用示差扫描量热分析仪(DSC)与光学显微镜(POM)考察材料的热性质与液晶性.由小角X射线散射(SAXS)分析得知,两嵌段组分呈交替分布层状结构,聚肽层中α螺旋链在不同溶剂中会发生不同程度折叠;通过透射扫描电镜(TEM)清楚观察到PS-b-PBLG在1,2-二氯乙烷(EDC)中α螺旋折叠形成了条纹式层状形貌,不同于1,1,2,2-四氯乙烷(TCE)中α螺旋完全伸展形成的锯齿式层状形貌.     

Dendrimer-influenced supramolecular structure formation of block copolymers

The water content-dependent supramolecular structure formation of polystyrene-block-poly(acrylic acid) (PS-b-PAA) copolymer in the presence of a fourth-generation amine-terminated poly(amido amine) dendrimer (PAMAM) is investigated by dynamic light scattering, turbidity measurements, and transmission electron microscopy. The solvent system for this study is a mixture of dioxane/THF and water. A very complex turbidity profile is observed with increasing water content in the system and is explained by the presence of various aggregated structures based on strong interactions between the amine-containing dendrimers and the poly(acrylic acid) blocks of the polymer. The onset of the self-assembly of single chains of PS-b-PAA (primary structure) into single and multiple dendrimer core inverse micelles (secondary structure) is detected as very low water contents of cw < 2% wt (cwc). These micelles consist of dendrimers coated with PAA blocks, which are connected to the corresponding PS chains that form the corona. Further addition of water leads to an association of these micelles into compound multiple dendrimer core inverse micelles (tertiary structure) in the range of cw = approximately 6 to approximately 10% wt. At still higher water content, some of the acrylic acid chains of the block copolymer move from the vicinity of the dendrimer to the outside of the aggregates, resulting in a decrease in the size of the formed structures and the acquisition of progressively increasing hydrophilic character of the aggregates. Multiple dendrimer core inverse onion micelles are formed, which agglomerate into compound multiple dendrimer core inverse onion micelles at cw = approximately 12 to approximately 18% wt. Above this water content, vesicular structures are formed. The complexity is unusual for block copolymer systems and illustrates the importance of strong interactions in structure formation.     

pH-Induced antireflection coatings derived from hydrogen-bonding-directed multilayer films

Hydrogen-bonding-directed layer-by-layer assembled films, based on polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles and poly(4-vinylpyridine) (P4VP), were successfully fabricated in methanol. Varying the PAA content in the PS-b-PAA micelles afforded control over the film growth properties, especially the multilayer film thickness. Interestingly, antireflection films with refractive indices that could be tuned between 1.58 and 1.28 were obtained by treatment with an aqueous HCl solution (pH 2.27), and the transmittance obtained was as high as 98.4%. In acid solution, the pyridine group was protonated, destroying the hydrogen bonding between P4VP and PAA. A concomitant pH-induced polymer reorganization in the multilayers resulted in a porous honeycomb-like texture on the substrate.     

Micelle-encapsulated carbon nanotubes: a route to nanotube composites

We report a general approach toward dispersing single-walled carbon nanotubes (SWNTs) in solvents and polymer materials, by encapsulating SWNTs within cross-linked micelles. Micelles made from polystyrene-block-poly(acrylic acid) (PS-b-PAA), an amphiphilic block copolymer, are first assembled around SWNTs by gradually adding H2O to a suspension of nanotubes in dimethylformamide. The hydrophilic, outer shells of these micelles are then chemically cross-linked with a difunctional linker molecule. Pure encapsulated SWNTs (e-SWNTs) can then be separated from empty cross-linked micelles by consecutive cycles of centrifugation and redispersion. Atomic force and transmission electron microscopies of the resulting nanostructures demonstrate that individual nanotubes (rather than bundles) have been completely encased in polymer shells whose thickness is slightly larger than that of empty micelles. e-SWNTs encapsulated in PS-b-PAA can be permanently redispersed in H2O, in organic solvents, and in both hydrophobic and hydrophilic polymer matrices with minimal sonication. Micelle encapsulation could improve the compositing of SWNTs in a wide variety of polymer materials for structural, electronic, and thermal applications.     

Plasmonic nanoparticle chains via a morphological, sphere-to-string transition

Au nanoparticles encapsulated within polystyrene-block-poly(acrylic acid) (PS-b-PAA) micelles assemble into regular, one-dimensional arrays when they are exposed to solvent conditions that relax interfacial curvature in the micellar shell. Nanoparticle chaining was induced by adding salt, acid, or cationic carbodiimide to the suspension of purified encapsulated Au nanoparticles (Au@PS-b-PAA). The resulting assemblies were characterized by scanning and transmission electron microscopies, by dark-field optical microscopy, and by visible absorption spectroscopy. The length of the chains was modulated by varying the concentration of additive. More importantly, the spacing between Au nanoparticles was dictated entirely by the shell thickness of the Au@PS-b-PAA starting material. Far-field polarization microspectroscopy demonstrated directional surface plasmon coupling in a straightened nanoparticle chain, which is a basic requirement for the use of these assemblies as plasmon waveguides.     

Hollow capsules prepared from all block copolymer micelle multilayers

We introduce a novel and versatile approach for preparing hollow multilayer capsules containing functional hydrophobic components. Protonated polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and anionic polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films onto polystyrene (PS) colloids. After removing the PS colloids, the stabilities of the formed BCM hollow capsules were found to be strongly dependent on the charge density of the hydrophilic corona segments (i.e., P4VP and PAA block segments) as well as the relative molecular weight ratio of hydrophobic core (i.e., PS segments) blocks and hydrophilic corona shells. Furthermore, in the case of incorporating hydrophobic fluorescent dyes into the PS core blocks of micelles, the hairy/hairy BCM multilayers showed well-defined fluorescent images after colloidal template removal process. These phenomena are mainly caused by the relatively high degree of electrostatic interdigitation between the protonated and anionic corona block shells.     

Formation of spindlelike aggregates and flowerlike arrays of polystyrene-b-poly(acrylic acid) micelles

In this letter we describe a simple physical method for the ordered aggregation of scattered single spherical polystyrene-b-poly(acrylic acid) (PS-b-PAA) micelles. First, narrow dispersed spindlelike aggregates, about 60 nm in diameter and 1.5 microm in length, are obtained from the aggregation of single spherical PS-b-PAA micelles at 0 degrees C on a glass slide. Then, the yielding spindlelike units can further aggregate into long-ranged, close-packed, flowerlike arrays after a given amount of freeze-thaw cycles. The formation of the interesting arrays is ascribed to the templated aggregation of micelles on the water polycrystal at the freezing point.     

Polymeric micelles formed by splitting of micellar cluster

Polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymer chains form aggregates with bimodal distribution in toluene. The introduction of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) chains leads to the formation of mixed micellar cluster due to the hydrogen-bonding complexation between PAA and PEO. By using laser light scattering and transmission electron microscopy, we have investigated the structural evolution of the mixed micellar cluster. As the standing time increases, the cluster split into regular complex micelles composed of PS-b-PAA and PS-b-PEO chains. Our results reveal that the hydrogen-bonding complexation between PAA and PEO in the core and the repulsion between PS chains in the corona as a function of the molar ratio (r) of PEO to PAA manipulate the evolution.     

"Clickable" polymersomes

Polymersomes, composed of amphiphilic polystyrene-block-poly(acrylic acid) (PS-b-PAA), with the periphery being covered with azide groups, were used for further functionalization using "click" chemistry.     

Mineralization of gold in block copolymer micelles

Ultrasmall gold particles have been prepared inside the micelles of polystyrene-block-poly(ethylene oxide) and polystyrene-block-poly(2-vinylpyridine) in toluene. Starting point was the formation of a thermodynamically stable dispersion of HAuCl₄ or LiAuCl₄ in the inverse micelles of the block copolymer which were treated with hydrazine or pyrrole. Analysis of the effect of the reduction agent on the stability of the micelles yielded a simple model for the transformation process involving coagulation of the swelling micelles. Kinetic control of the different steps, i.e., reduction, mineralization, coagulation, film formation, allowed to prepare thin films in which highly uniform gold particles were arranged in yet unknown order. When pyrrole was employed for the reduction, the gold monocrystals got embedded in a shell of polypyrrole.     

Reversible aggregation of polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) block copolymer micelles in acidic aqueous Solutions

Micelles of polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-PVP-PEO) were studied in acidic aqueous solutions by static and dynamic light scattering, alkalimetric titration, fluorescence correlation spectroscopy, and after deposition on a mica surface by atomic force microscopy. The PS-PVP-PEO micelles prepared by dialysis in ternary 1,4-dioxane-methanol-acidic water mixtures have a very low association number and show a strong tendency to form aggregates. The aggregation, which is promoted at low pH, seems to be fully reversible. Possible mechanisms of the aggregation are discussed. Atomic force microscopy scans of PS-PVP-PEO micelles deposited on a mica surface reveal the formation of micellar aggregates and support the general concept of aggregation upon changes in conditions and deterioration of the stability of small micelles.