聚苯乙烯-b-聚氧乙烯-b-聚苯乙烯三嵌段共聚物的自组装

小分子表面活性剂、磷脂、接枝及嵌段共聚物等两亲分子在选择性介质中能够自组装形成特定的分子聚集体 [1,2 ] .嵌段共聚物自组装的某些行为具有生物膜模拟性 ,如最近发现的嵌段共聚物自组装囊泡 [3～ 5] .诸多因素影响着嵌段共聚物在稀溶液中的自组装行为 [6] .对于 ABA型三嵌     

嵌段共聚物自组装的研究进展

自组装是分子间通过非共价键相互作用自发组合形成的一类结构明确、稳定,同时具有某种特定功能或性能的分子聚集体或超分子结构的现象.嵌段共聚物不仅可以在本体中自组装,还能在溶液中自组装.本文综述了嵌段共聚物在溶液中自组装的规律及其主要影响因素,包括嵌段共聚物链段长度、选择性溶剂的性质、嵌段共聚物的浓度、溶液的pH值等;并介绍...     

嵌段序列对聚合物囊泡形成过程影响的Monte Carlo模拟

采用Monte Carlo模拟方法研究了具有相同链长和组分比的不同嵌段序列的AB两嵌段共聚物与ABA三嵌段共聚物在选择性溶剂中形成囊泡的动力学过程. 模拟结果表明, AB两嵌段共聚物囊泡的形成与ABA三嵌段共聚物囊泡的形成的动力学过程不同. 在慢速退火条件下, ABA三嵌段共聚物囊泡是通过亲水链段向胶束的表面和中心扩散而形成的, 而AB两嵌段共聚物囊泡则由片层弯曲闭合而形成. 相对而言, 退火速度对AB两嵌段共聚物囊泡形成的动力学过程没有显著影响, 其改变仅影响亲水链段与疏水链段发生相分离的难易程度. 当退火速度较快时, 亲水链段和疏水链段发生相分离的速度较快且相分离发生在囊泡形成之前; 而当退火速度较慢时亲水链段和疏水链段之间的相分离在囊泡形成之后仍在进行.     

双刚性共轭嵌段共聚物体系的自组装

棒杆-棒杆(rod-rod)共轭嵌段共聚物体系是近几年发展起来的一类新型共轭聚合物材料,由于其特有的电学活性以及通过自组装实现纳米尺度结构可控等特性正逐渐成为人们研究的热点.构筑单元的刚性棒状结构使得rod-rod共轭嵌段共聚物体系倾向于自组装形成囊泡或层状结构等低曲率聚集体.本文总结了近年来关于rod-rod共轭嵌段共聚物体系自组装行为的研究,分别介绍了溶液中以及薄膜状态下双刚性共轭嵌段共聚物体系的自组装行为,在此基础上进一步讨论了rod-rod共轭嵌段共聚物薄膜结构与性能的关系.     

多分散性对两亲性两嵌段共聚物在选择性溶剂中自组装行为影响的Monte Carlo模拟

采用Monte Carlo模拟方法研究了多分散性AB两亲性两嵌段共聚物在选择性溶剂中的自组装行为.模拟结果表明,嵌段共聚物的多分散性对体系在选择性溶剂中自组装所形成的胶束形貌结构有很大影响.当AB两嵌段共聚物的多分散系数由1.0增加至1.4时,体系中自组装所形成的胶束将会发生由囊泡到片层直至球状的一系列形态转变.通过统...     

两亲嵌段共聚物溶液自组装新进展

综述了两亲嵌段共聚物在溶液中自组装的新进展，重点介绍了两亲嵌段共聚物自组装聚集体中棒状、蠕虫状、囊泡、洋葱和实心洋葱等几种新形态的特点和形成机理；另外对两亲嵌段共聚物溶液自组装在光电、药物释放、靶向以及作为基因工程载体方面的应用前景及两亲嵌段共聚物聚集体的制备方法作了详细的评述。     

PLGA-PEG共聚物负载多西紫杉醇的药物输运体系的计算机模拟

采用耗散粒子动力学模拟的方法研究了抗癌药物输运体系多西紫杉醇与聚乙丙交酯与聚乙二醇的共聚物(PLGA-PEG)的自组装形态, 考察了共聚物浓度、共聚物组成和药物含量等对自组装形态的影响. 模拟结果表明, 不同浓度的PLGA-PEG能够和多西紫杉醇自组装成球状、柱状、层状等结构; 一定的浓度下, 亲水的PEG嵌段将疏水的PLGA嵌段包裹起来形成核壳结构, 可用于疏水药物输运应用. 在比较低的浓度下, 不同组成的PLGA-PEG均会形成球状核壳结构, PEG嵌段较多时壳层较厚核尺寸较小, PLGA嵌段较多时核的尺寸较大但壳层较薄, 综合考虑载药量和稳定性, 模拟结果中PEG嵌段的摩尔分数为60%即PLGA₄₀-PEG₆₀作为载体时性能较佳. 药物的含量对自组装结构也有影响, 药物含量较小时形成球状结构, 药物含量较大时, 则会形成柱状结构. 对PLGA₄₀-PEG₆₀体系, 模拟结果显示药物、聚合物和水的最佳配比为5:10:90. 本工作可为共聚物载药体系的设计与开发提供参考.     

桥连对嵌段共聚物自组装的调控

通过嵌段共聚物自组装形成"桥连"是制备具有优异力学性能的网络结构的有效途经,具有重要的应用价值.但是,过去的研究工作很少讨论"桥连"对嵌段共聚物自组装行为本身的影响.该研究评论主要总结了最近几年利用"桥连"对嵌段自组装行为进行调控的工作进展.作者设计了BABCB三组分线性多嵌段共聚物,当其自组装形成二元"介观晶体"(球、柱)结构时,中间B嵌段连接A和C相区(嵌段聚集成的"大原子"),自然地形成桥连;减小中间桥连B嵌段的相对长度,就可以增加其拉伸程度,从而降低介观晶体的配位数;另外,两个末端B嵌段的相对长度可以直接调控A和C"大原子"之间的相对配位数.基于这两个机理,自洽场理论计算预测了各种配位数相等和不相等的二元介观晶体结构.进一步,将"拉伸桥连"概念拓展到AB型嵌段共聚物体系中,并且通过多臂星型嵌段共聚物分子结构中的"组合构型熵效应"在AB型嵌段共聚物中形成高比率的桥连构型,使传统的六角柱状结构转变为了四配位的四方柱状和三配位的石墨烯类柱状结构.未来,在ABC三组分嵌段共聚物体系的设计中引入拓扑结构以及使用共混等方法,有望在介观尺度重铸大多数已知的原子/离子二元晶体结构,甚至超越原子...     

四臂星型聚苯乙烯-聚4-乙烯基吡啶嵌段共聚物纤维状胶束及负载金纳米粒子的研究

通过两步原子转移自由基聚合,制备了4种不同嵌段长度的四臂星型嵌段共聚物苯乙烯-聚4-乙烯基吡啶嵌段共聚物(PS-b-P4VP)4.在选择性溶剂甲苯中,随着嵌段长度的变化,自组装胶束的形态从球型到短棒状和纤维状的转变,其中(PS25-b-P4VP90)4自组装形成的以P4VP为核,以PS为花瓣型壳的纤维状胶束.以这种纤维状胶束作为模板,制备了金纳米粒子均匀分布的一维纳米材料     

两亲性/双疏性嵌段共聚物共混体系的自组装行为研究

采用耗散粒子动力学方法,研究了两亲性嵌段共聚物和双疏性嵌段共聚物共混体系的自组装行为,探讨了双疏性嵌段共聚物的浓度以及双疏性嵌段共聚物的嵌段体积分数对聚集体结构的影响.结果表明,随着双疏性嵌段共聚物浓度的增加,聚集体发生自囊泡到棒状胶束再到同心圆多舱胶束的转变,且当浓度较高时,同心圆多舱胶束的同心圆层数量与浓度密切相关.当双疏性嵌段共聚物中的嵌段体积分数降低时,球形胶束由同心圆结构转变为非同心圆结构.此外,利用Minkowski泛函方法表征了多舱胶束的形成过程,发现这是一个先形成大尺度球形结构、再形成小尺度内核结构的分级组装过程.     

Micellization through complexation of oppositely charged diblock copolymers: Effects of composition,polymer architecture,salt of different valency,and thermoresponsive block

The structural and electrical characteristics of polyelectrolyte complex micelles (PCMs) formed by mixing of oppositely charged double hydrophilic copolymers are studied by means of molecular dynamics simulations. In mixtures of linear diblock copolymers we found that the preferential aggregation number N_p of PCMs is a universal function of the ratio γ_± of the total positive to total negative charges of the mixture. The addition of divalent salts ions induces a secondary micellization. In mixtures of copolymers bearing a common neutral thermoresponsive block, micelles with contracted corona consisting of thermoresponsive blocks and complex polyelectrolyte core are formed at low salt concentration and temperature far away the biphasic regime. At high salt concentration and temperature in the biphasic regime, reversed micelles are obtained. In equimolar mixtures of linear copolymers with miktoarm stars we found that N_p of PCMs decreases as the number of charged branches of miktoarm copolymer increases. The shape of micelles progressively changes from spherical to worm-like with the increase of number of branches of miktoarm copolymers. Our findings are in full agreement with existing experimental and theoretical predictions and provides new and additional insights.     

Multicompartment Micelles From π-Shaped ABC Block Copolymers

Dissipative particle dynamics simulations were performed on the morphology and structure of multicompartmerit micelles formed from n-shaped ABC block copolymers in water. The influences of chain architectures were studied in a systematic way, and a rich variety of morphologies were observed, such as spherical, wormlike, X-shaped, Y-shaped, ribbon-like, layered rod-like, layered disk-like, as well as network morphologies. The simulations show that the distance between the two grafts plays an important role in control of the morphology. Since n-shaped ABC block copolymers can be reduced to linear ABC and star ABC block copolymers, they are good model copolymers for studying the self-assembly of complex block copolymers into micelles. The knowledge obtained in this work as well as the new morphologies identified provide useful information for future rational design and synthesis of novel multicompartment micelles.     

Synthesis and self‐assembly of amphiphilic macrocyclic block copolymer topologies

We demonstrated the synthesis of miktoarm star block copolymers of AB, AB₂, and A₂B, in which block A consisted of linear poly(tert‐butyl acrylate) (P^tBA) and block B consisted of cyclic polystyrene. These structures were produced using the atom transfer radical polymerization to make telechelic polymers that, after modification, were further coupled together by copper‐catalyzed “click” reactions with high coupling efficiency. Deprotection of P^tBA to poly(acrylic acid) (PAA) afforded amphiphilic miktoarm structures that when micellized in water gave vesicle morphologies when the block length of PAA was 21 units. Increasing the PAA block length to 46 units produced spherical core‐shell micelles. AB₂ miktoarm stars packed more densely into the core compared to its linear counterpart (i.e., a four times greater aggregation number with approximately the same hydrodynamic diameter), resulting in the PAA arms being more compressed in the corona and extending into the water phase beyond its normal Gaussian chain conformation. These results show that the cyclic structure attached to an amphiphilic block has a significant influence on increasing the aggregation number through a greater packing density. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Brownian dynamics simulation study on the self-assembly of incompatible star-like block copolymers in dilute solution

We study the self-assembly of symmetric star-like block copolymers (A(x))(y)(B(x))(y)C in dilute solution by using Brownian dynamics simulations. In the star-like block copolymer, incompatible A and B components are both solvophobic, and connected to the center bead C of the polymer. Therefore, this star-like block copolymer can be taken as a representative of soft and deformable Janus particles. In our Brownian dynamics simulations, these "soft Janus particles" are found to self-assemble into worm-like lamellar structures, loose aggregates and so on. By systematically varying solvent conditions and temperature, we build up the phase diagram to illustrate the effects of polymer structure and temperature on the aggregate structures. At lower temperatures, we can observe large worm-like lamellar aggregates. Upon increasing the temperature, some block copolymers detach from the aggregate; this phenomenon is especially sensitive for the polymers with less arms. The aggregate structure will be quite disordered when the temperature is high. The incompatibility between the two parts in the star-like block copolymer also affects the self-assembled structures. We find that the worm-like structure is longer and narrower as the incompatibility between the two parts is stronger.     

Rod-sphere transition in polybutadiene-poly(L-lysine) block copolymer assemblies

This paper describes the synthesis and characterization of poly(butadiene)m-poly(L-lysine)n (m-n = 107-200, 107-100, and 60-50) block copolymers. The polymers are prepared in a two-step process whereby amine-terminated polybutadiene is used to initiate the ring-opening polymerization of the epsilon-benzyloxycarbonyl L-lysine N-carboxyanhydride. After deprotection, the self-assembly of the block copolymers in aqueous media were studied using dynamic light scattering, transmission electron microscopy, and circular dichroism spectroscopy. These block copolymers were found to form either spherical micelles or rod-like micelles at high pH depending on the composition of the block copolymer. As the pH is decreased, the micelles swell due to charge-charge repulsions between corona chains and from the helix-coil transition of the polypeptide block. The two systems that form rod-like micelles at high pH also exhibit a pH-induced rod-sphere transition at low pH. This transition was verified from Kratky analysis of the static light scattering data and via CONTIN analysis of the dynamic light scattering data, which shows a bimodal distribution in particle sizes.     

Self-assembly and responsiveness of polypeptide-based block copolymers: How “Smart” behavior and topological complexity yield unique assembly in aqueous media

Polypeptide-based amphiphilic block copolymers are an attractive class of materials given their ability to form well-defined aqueous nanoassemblies that respond to external stimulus through secondary structure transitions. This report will highlight recent literature in the area of polypeptide-based block copolymer self-assembly, with the major focus being on how the responsive nature and structural complexity of the polypeptide blocks can be incorporated into systems with complex topologies such as ABA/BAB/ABC triblock copolymers, AB₂ and A₂B star copolymers, and miktoarm μ-ABC star terpolymers. In particular, the role of interfacial curvature changes and how they result in morphology transitions will be discussed. The ‘smart’ assembly properties of peptides in complex block copolymer topologies can lead to enhanced responsiveness, morphological complexity, and unique morphological transitions with varying solution conditions. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

两亲性含糖三嵌段共聚物的合成与自组装研究

以二(2-溴异丁酸)4,4′-联苯酯(BiBBP)为引发剂,采用顺序加料的方法,用原子转移自由基聚合法(ATRP)合成了一系列窄分子量分布的甲基丙烯酸甲酯(MMA)和6-O-甲基丙烯酰基-1,2;3,4-双-O-亚异丙基-α-D-吡喃半乳糖苷(MAIPGal)的三嵌段共聚物.用GPC和1H-NMR表征了聚合物的相对分子量和链段组成.结果表明,通过改变投料顺序可以合成ABA和BAB型2种三嵌段共聚物,改变投料比和控制单体的转化率可以调控聚合物的链段组成.聚合物脱保护后得到两亲性含糖共聚物.用TEM考察了聚合物在水溶液中的自组装行为,表明具有不同链段组成的共聚物可以形成不同形态的聚集体,含糖段组成高的聚合物易于形成大尺寸的胶团,含糖段组成低的聚合物易于形成结构清晰的囊泡、胶束,其中,含糖段在两边的BAB型共聚物易于形成囊泡,含糖段在中央的ABA型共聚物易于形成胶束.     

Self-organization behavior of methacrylate-based amphiphilic di- and triblock copolymers

Amphiphilic di- and triblock copolymers having different hydrophilic-to-hydrophobic block length ratio were synthesized using ATRP. The self-assembly behavior of these AB and ABA block copolymers consisting of poly(n-butyl methacrylate) (B) and poly(2,2-(dimethylaminoethyl methacrylate) (A) was investigated using a combination of dynamic light scattering, negative-stain transmission electron microscopy, cryoelectron microscopy, and atomic force microscopy. Two populations of self-organized structures in aqueous solution, micelles and compound micelles, were detected for diblock copolymers. Triblock copolymers assembled into vesicular structures of uniform sizes. Furthermore it was found that these vesicles tended to compensate the high curvature by additional organization of the polymer chains outside of the membrane. The chain hydrophilicity of the polymers appeared to have a critical impact on the self-assembly response toward temperature change. The self-reorganization of the polymers at different temperatures is discussed.     

SELF-ASSEMBLY OF ROD-COIL DIBLOCK COPOLYMERS——INFLUENCE OF THE ROD LENGTH

The self-assembly of five narrowly distributed novel rod-coil diblock copolymers, poly(styrene-block-(2, 5-bis[4-methoxy-phenyl]oxycarbonyl) styrene) (PS-b-PMPCS), in p-xylene, a selective solvent at room temperature, was studied. Therod-coil copolymers, which have the same PS length but different PMPCS length, were synthesized by 2,2,6,6-tetramethyl-I-piperidinyloxy (TEMPO) mediated living free radical polymerization. The influence of the rod length on the self-assemblymorphology was studied by transmission electron microscopy (TEM). At a concentration of 2.0 mg/mL, those copolymerswith relatively shorter PMPCS length (copolymers 1 and 2) form individual spherical micelles; those with relatively longerPMPCS length (copolymer 3 and 4) form "pearl chains" coexisting with individual spherical micelles; the ones with longestPMPCS length form "pearl chains" coexisting with occasionally formed nanofibers. The diameter of all the morphologieswas controlled by the rod length. This gives us a way to govern the self-assembly morphology by altering the length of oneblock in the block copolymer.