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实验研究了剪切(搅拌)对ABC三嵌段共聚物PS720-b-P2VP200-b-PEO375在溶液中自组装形成的胶束形态的影响,研究结果表明剪切对多节状蠕虫胶束的生成和结构有着重要作用.在1500 r/min剪切速率时,嵌段共聚物自组装形成的球形胶束首先聚集形成蠕虫胶束的梭状轮廓,然后再经过不断地融合与调整形成蠕虫胶束节状部分的盘状结构,同时球的融合趋于沿着垂直于梭状结构的主轴方向(即流场方向).溶剂THF对PS嵌段充分的溶胀使得球形胶束进一步调整形成盘状结构,从而使梭状胶束聚集体顺利地向多节状蠕虫胶束过渡.通过透射电镜(TEM)和扫描电镜(SEM)对胶束形态进行表征,结果表明,多节状蠕虫胶束是剪切作用下球形胶束二次自组装的结果. 相似文献
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嵌段共聚物在选择性溶剂中能够自组装形成胶束,胶束的不同形状与嵌段共聚物的结构、溶剂和浓度有关.无定形嵌段共聚物通常形成球形胶束,在某些情况下也可以形成其它形状的胶束,关于结晶性嵌段共聚物在无定形链段选择性溶剂中的胶束结构和形状的报道非常少.由于结晶和相似相溶两种作用力的竞争,使得这类胶束的形状丰富多变.通常结晶作用较强时,结晶性嵌段共聚物形成片状的胶束,当结晶组分比较少时,可形成棒状胶束,尽管理论上已经指出存在球形胶束,但尚无关于这方面的报道。 相似文献
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利用核磁共振方法研究了AB型双嵌段共聚物(MPEG45-b-PA32)在选择性溶剂中的自组装行为及胶束化过程.嵌段共聚物在三氟乙酸中聚氨基酸和聚乙二醇链段均处于自由运动状态,聚丙氨酸链段为无规线团结构.在向该溶液中逐渐加入氘代水的过程中,聚丙氨酸链段又重新聚集形成规整的二级结构.结合1H-NMR和COSY谱分析,结果显示这一自组装过程伴随着聚(L-丙氨酸)链段由无规线团向α-螺旋结构的构象转变,同时嵌段共聚物逐渐形成核-壳型胶束结构.利用透射电镜观察了所形成胶束的形态,嵌段共聚物主要形成粒径150 nm到220 nm的球形胶束. 相似文献
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采用耗散粒子动力学方法(dissipative particle dynamics,DPD)研究了coil-rod-coil(CRC)三嵌段刚柔共聚物在选择性溶剂中的自组装.在链选择性溶剂中,刚性棒长Lr与柔性链长Lc都影响着CRC溶液的自组装及相转变.随Lr的增大,棒与溶剂的接触面变大界面能升高,为减小体系的自由能,棒嵌段趋向聚集以减少接触面与界面能.随Lc的增大,链的自由伸展构象熵增大,影响着棒嵌段聚集体结构的形成,使棒嵌段的分布更加分散.在研究溶剂性质aCS与棒长Lr对体系自组装影响的情况中,观察到两类有趣的相结构:球形相和胶束相.随着参数aCS从亲链变为中性再到亲棒,在球形相内部,不仅棒相区由球体内部移向球表面,而且棒相区与链相区的层次分布也发生了明显地变化.同样,Lr的改变也影响着球形相内部相区的分布,同时诱导了不同球形相间的构型转变.胶束相包括分段胶束和螺旋胶束两种,形成于棒长较长的情况,胶束相中棒嵌段的排列呈现出明显的液晶相结构. 相似文献
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以二重氢键为引导,二硫键连接疏水性聚乳酸(PLA)和亲水性β-环糊精(β-CD)合成了嵌段共聚物β-CD-PLA。采用1 H-NMR和GPC对嵌段共聚物β-CD-PLA的结构进行了表征,以芘作为荧光分子探针对嵌段共聚物β-CD-PLA自组装胶束的性质进行了表征,采用动态光散射纳米粒度仪(DLS)对自组装胶束的粒径进行了测试。结果表明:在二重氢键的引导作用力和碘的氧化作用下,中间体脱去保护基形成双二硫键,形成目标嵌段共聚物β-CD-PLA,该嵌段共聚物能够在水中自组装形成纳米胶束,临界胶束浓度(CMC)为0.089mg/mL,在稀溶液中具有良好的稳定性,自组装形成空白胶束的粒径为31nm,阿霉素盐酸盐(DOX)载药胶束的粒径为42nm。 相似文献
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以RAFT聚合制备了十二烷基末端聚乙二醇-b-聚(N-丙烯酰脯氨酸甲酯)两嵌段聚合物D12-EA,并用体积排除色谱和核磁氢谱表征了聚合物的结构。结合紫外-可见光(UV-Vis)、动态光散射(DLS)、静态光散射(LLS)、透射电镜(TEM)以及变温核磁氢谱(1 H NMR)研究了其在水溶液中的可逆再组装行为。不同于普通刺激响应性两嵌段在水溶液中由单分子链组装为纳米聚集体,在温度低于温敏性聚丙烯酰脯氨酸甲酯嵌段(A嵌段)浊点(CP)时,D12-EA两嵌段水溶液自组装形成粒径为20nm的球形胶束;而当温度高于CP时,球形胶束能够可逆地再组装为粒径约90nm的囊泡。变温1 H NMR揭示了当温度高于CP时,A嵌段由亲水壳层迁移至疏水核层,从而使体系再组装为自由能更低的结构。 相似文献
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Mikael Trollss Hans Claesson Bjrn Atthoff James L. Hedrick 《Angewandte Chemie (International ed. in English)》1998,37(22):3132-3136
A star-shaped molecule and a layered structure are displayed by the title compound, where the layers consist of high molecular weight polymers. A core molecule that is functionalized by six hydroxyl groups acts as the initiator for the ring-opening polymerization of ε-caprolactone, leading to a six-arm star polymer. The second layer of the dendritic block copolymer with 12, 24, or 48 hydroxyl groups (depending on the dendron generation in use) is obtained by the linkage of chain ends with functionalized dendrons. These macromoleculse act as “macroinitiators” for the construction of a further layer of poly(ε-caprolatone), the third generation of dendritic block copolymers. 相似文献
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Biodegradable polymers can be prepared by the incorporation of cellulose oligomeric blocks into the polymer backbone. Block copolymers prepared by reacting equimolar amounts of depolymerized cellulose triacetate (CTA) with MDI or TDI and block terpolymers prepared by reacting the CTA oligomer with poly (propylene glycol) capped with MDI or TDI were deacetylated and incubated with cellulysin at pH 5 and 50 °C. The intrinsic viscosity of each copolymer decreased substantially even after 10 hr incubation time. There was negligible acid hydrolysis. Cellulose showed a smaller decrease at the same incubation time-probably due to its lower accessibility. Methods for incorporating cellulose oligomeric blocks and other biodegradable blocks into different types of polymers are discussed. 相似文献
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Summary: Olefin block copolymers produced by chain shuttling catalysis exhibit crystallinity characteristics that are distinct from what would be expected for typical random olefin copolymers with comparable monomer compositions produced from either ‘single-site’ or heterogeneous catalysis. Olefin block copolymers produced by chain shuttling catalysis have a statistical multiblock architecture. A unique structural feature of olefin-based block copolymers is that the intra-chain distribution of comonomer is segmented (statistically non-random). Fractionating an olefin block copolymer by preparative temperature rising elution fractionation, TREF, results in fractions that have much higher comonomer content than comparable fractions of a random copolymer collected at an equivalent TREF elution temperature. We have developed a “block index” methodology which quantifies the deviation from the expected monomer composition versus the analytical temperature rising elution fractionation, ATREF, elution temperature. When interpreted properly, this index indicates the degree to which the intra-chain comonomer distribution is segmented or blocked. The unique crystallization behavior of block copolymers determine the magnitude of the block index values because the highly crystalline segments along an otherwise non-crystalline chain tend to dominate the ATREF (and DSC) temperature distributions. 相似文献
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Summary: The newly developed interactive separation of polyolefins by high temperature liquid chromatography (HTLC) provides new information about the chemical composition distribution of polyolefin elastomers. The technique has the advantage of being quantitative in its separation, and has high resolution for the separation of polyolefins by their chemical composition without influence by cocrystallization. Chemical composition distributions can be determined for individual polymers and blends which contain the full range of comonomer typically present in polyethylene and poylypropylene homopolymers, semi-crystalline copolymers, and amorphous copolymers. HTLC analysis in combination with the other fractionation techniques, such as DSC, TREF, NMR, and xylene fractionation, can be used to estimate the amount of olefin block copolymer present in a block composite produced by chain shuttling catalysis. 相似文献
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非线形嵌段共聚物的合成 总被引:1,自引:0,他引:1
主要介绍了非线形嵌段共聚物,如星型嵌段共聚物、杂臂星型共聚物、梳型聚合物等的合成方法,包括多官能团引发剂法、大分子引发剂法等。各种活性聚合方法,如阳离子开环聚合、原子转移自由基聚合(ATRP)和氮氧稳定自由基聚合等都可以用于合成非线形嵌段共聚物。 相似文献
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Igor Rychkov 《Macromolecular theory and simulations》2005,14(4):207-242
Summary: Microphase separation transition in block copolymer melts and solutions in equilibrium and under shear flow is reviewed. The non‐equilibrium molecular dynamics (NEMD) computer simulation methodology is presented in detail including the derivation of the SLLOD equations of motion, Gaussian thermostat, and operator‐splitting symplectic integrators. Results of our recent NEMD computer simulation studies of diblock copolymers in a selective solvent under shear flow are presented. Shear‐dependent structural, rheological, and microscopical properties are described. New phase transitions are discovered. The parallel‐perpendicular orientational transition in a weak‐strong flow is revealed. Theoretical approaches are reviewed including the Edwards Hamiltonian, Landau‐Ginzburg model, self‐consistent mean field theory, field‐theoretic simulation, as well as the time‐dependent Landau‐Ginzburg framework and its application to the studies of complex fluids.
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