pH响应壳聚糖衍生物的合成与自组装

以甲烷磺酸为反应溶剂,将己酰氯接枝到壳聚糖(CS)侧基上,得到可溶于常见有机溶剂的己酰化壳聚糖(HC);亲水性聚乙二醇单甲醚(mPEG)通过活泼酯法接枝到HC上,最终获得两亲性壳聚糖衍生物PEG-g-HC。用红外光谱(FT-IR)、核磁共振(1H-NMR)与紫外-可见光谱(UV-Vis)表征产物结构,用动态光散射、透射电镜与荧光光谱等方法研究了PEG-g-HC的自组装行为。结果表明:通过改变己酰氯与CS的投料比可调节HC的取代度;随着HC中己酰基取代度增大,HC在水介质中溶解的临界pH随之降低;PEG-g-HC可自组装为球形胶束,通过改变HC中己酰基的取代度可调控其pH响应行为。     

ABC型嵌段共聚物自组装理论研究进展

嵌段共聚物的自组装为功能性纳米材料的制备提供了一种重要途径. ABC型嵌段共聚物相比于AB型具有更大的参数空间,自组装行为也更加复杂.在实验所合成的三组分嵌段共聚物自组装体系中,已有多种复杂结构被发现,如螺旋超柱、编织图案等,但实验上比较难以直接阐明它们的形成机理.近年来,本课题组运用自洽场理论(SCFT)对ABC型嵌段共聚物自组装进行了系统的研究,聚焦探索其结构参数及拓扑结构对相行为的影响机制.本文介绍了本课题组关于“非受挫”和“受挫”两大类ABC型嵌段共聚物自组装的SCFT研究成果,揭示了一些非经典相的形成机理,并通过合理的分子设计预测了一系列新颖的有序结构.     

pH值响应性超支化多臂共聚物的合成及其自组装行为研究

以超支化双硫酯为链转移剂,偶氮二异丁腈（AIBN）为引发剂,采用可逆加成-断裂链转移（RAFT）活性自由基聚合方法,合成了以超支化聚酯（Boltorn H20）为核,聚丙烯酸为臂的两亲性超支化多臂共聚物（H20-star-PAA）,并通过紫外分光光度计、动态光散射（DLS）和透射电子显微镜（TEM）对它在水溶液中的pH响应的自组装行为进行了研究.结果表明,在稀溶液条件下,H20-star-PAA始终以单分子胶束的形式存在,随着溶液pH的降低,胶束的PAA壳层会逐步塌缩,导致胶束尺寸减小;而在浓溶液条件下,当溶液的pH较低时,单分子胶束会进一步聚集形成多分子胶束.     

光敏感三元共聚物的合成及溶液自组装

以一端为肉桂酸酯光交联基元、中间为聚己内酯长柔性链的甲基丙烯酸酯类大单体FM5C为第三单体,与马来酸酐(MAH)及苯乙烯(St)单体以AIBN引发共聚合,制备了光敏感三元共聚物P(FM5C-co-MAH-co-St).该三元共聚物可在选择性溶剂中形成纳米胶体粒子,并可先利用肉桂酸酯基元的光照交联作用使胶体粒子内聚合物交联,进而利用羧酸酐基元与2-氨基吡啶的室温氨解反应改变胶体粒子形态.用FTIR、GPC、1H-NMR等对该聚合物及其氨解产物进行了结构表征.用动态激光光散射（DLS）、透射电镜（TEM）、芘探针等技术研究了该聚合物胶体粒子微观形态、粒径与微环境在光照交联后及氨解后的变化.实验结果表明,P(FM5C-co-MAH-co-St)在选择性溶剂中可自组装成球形胶体粒子,肉桂酸酯光照交联作用使胶体粒子中的聚合物团聚得更加紧密,从而使其粒径更小、疏水区域更加集中;而进一步的室温氨解反应则使聚合物胶体粒子更松散、粒径变大.     

刺激响应性刚柔嵌段共聚物的自组装

刚柔嵌段共聚物是指刚性链段和柔性链段以共价键相连形成的共聚物。不仅由于刚性链段有序排列的特点使得其自组装行为更为丰富多样,而且刚性分子将优异的功能特性赋予到超分子组装体中,有望实现超分子材料的功能应用。这类嵌段共聚物在溶液中自组装形成的聚集体会对外界的刺激(例如pH、光、温度、化学添加剂等)敏感,产生聚集体形态的变化。本文选取了部分典型的具有刺激响应性的刚柔嵌段共聚物,介绍了其智能自组装行为,并对其良好的发展前景做了展望。     

环境响应性嵌段共聚物的合成、自组装及应用研究进展

近年来具有环境响应性的嵌段共聚物的研发受到了人们的广泛关注。该类型共聚物可以对外界环境刺激产生相应的结构、物理及化学性能的变化。根据外界环境刺激响应机理及类型的不同,可将其分为单一因素、双重因素以及三重因素刺激响应性嵌段共聚物三大类。针对每一类体系,本文重点综述了嵌段共聚物的设计合成、自组装以及应用等研究现状,并概括总结了各种有序聚集体(如胶束、囊泡等)随外界环境刺激(如pH、温度、光、CO_2、氧化还原剂等)所作出的响应性变化。最后,对智能型嵌段共聚物在药物控释、纳米容器制备、生物功能材料等方面潜在的应用价值和今后可能的发展方向进行了展望。     

ABA三嵌段离子型共聚物的合成及溶液自组装

以对二溴苄作引发剂,引发苯乙烯和甲基丙烯酸对硝基苯酚酯(NPMA) 相继进行原子转移自由基聚合(ATRP),合成了3个三嵌段聚合物PNPMA-b-PS-b-PNPMA,其中聚苯乙烯段含有146个单元,PNPMA段的结构单元数分别为8、20和36.对这3个三嵌段共聚物分别进行水解反应及与2-氨基吡啶的取代反应,得到了具有相反电荷的PMAA-b-PS-b-PMAA和PNPMAAm-b-PS-b-PNPMAAm两种6个三嵌段共聚物.用核磁、红外和GPC表征了聚合物的结构、分子量及分子量分布等.将这两种三嵌段共聚物以等摩尔混合,在水中可自组装成碗形聚集体结构,讨论了可能的形成机理.     

偶氮液晶嵌段共聚物自组装和光响应性研究进展

偶氮液晶嵌段共聚物是指分子中带有偶氮苯基团的液晶嵌段共聚物.偶氮液晶嵌段共聚物兼具偶氮聚合物的光响应性和液晶嵌段共聚物自组装形成多尺度有序结构的特性,是一类有重要应用前景的新材料.本文简要综述了近10年来偶氮液晶嵌段共聚物的研究进展,以几种典型的偶氮液晶嵌段共聚物为例,介绍嵌段共聚物在本体以及溶液状态下自组装,自组装形貌的光致变化,以及偶氮液晶嵌段共聚物在光全息存储领域等的研究进展.     

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。     

ABC三嵌段共聚物的聚合诱导自组装研究

聚合诱导自组装(PISA)是一种在高浓度溶液中可连续大量制备纳米材料的新技术,结合计算模拟方法,研究其动力学过程可强化对PISA的认识和调控.通过耗散粒子动力学(DPD)模拟,研究了ABC三嵌段共聚物的聚合诱导自组装过程.先利用亲溶剂A链段引发B单体聚合,随着疏溶剂B链段的增长,AB二嵌段共聚物可组装并发生聚集体结构的连续转变,由球形胶束→蠕虫状胶束→层状结构→囊泡.再将C单体逐步聚合到AB共聚物上,调控C链段的亲疏溶剂性,可聚合诱导组装或解组装形成不同的ABC三嵌段共聚物聚集体.     

Synthesis and Self-assembly of a Linear Coil-Coil-Rod ABC Triblock Copolymer

An interesting order-order transition between two different complex nanostructures was observed in a new liquid crystalline linear coil-coil-rod ABC triblock copolymer（tri BCP）. First, the ABC tri BCP, poly（dimethylsiloxane）-bpolystyrene-b-poly{2,5-bis[（4-methoxyphenyl）oxycarbonyl]styrene}（PDMS-b-PS-b-PMPCS）, was synthesized through sequential atom transfer radical polymerization. The degrees of polymerization of PDMS, PS, and PMPCS blocks are 58, 159, and 106, and the corresponding volume fractions of PDMS, PS, and PMPCS are 0.09, 0.29, and 0.62, respectively. The phase behaviors of the PDMS-b-PS diblock copolymer precursor and the final triblock copolymer were studied by smallangle X-ray scattering, one-dimensional wide-angle X-ray scattering, and transmission electron microscopy experiments. The PDMS-b-PS precursor self-assembles into hexagonally packed cylinders with a relatively small periodic size after thermal annealing. When the triblock copolymer is annealed at a relatively low temperature（120 ○C） at which the PMPCS block is in the amorphous state, the tri BCP forms core-shell hexagonally packed cylinders（CSH） with a relativly large periodic size. After the tri BCP is annealed above 140 ○C at which the PMPCS block transforms to the liquid crystalline（LC） phase, the nanophase-separated structure transforms to a three-phase four-layer lamellar structure（LAM-3P4L）. Thus, accompanied with the transition of the PMPCS blocks from the amorphous state to the LC phase, the order-order transition from CSH to LAM-3P4 L occurs in the PDMS-b-PS-b-PMPCS ABC tri BCP.     

Synthesis and Characterization of PS-PIB-PS Triblock Copolymers

Abstract

Poly(styrene-isobutylene-styrene) (PS-PIB-PS) block copolymers synthesized via living carbocationic polymerization using a di- or tricumyl chloride/TiCl₄/pyridine initiating system in 60/40 (v/v) hexane/methyl chloride cosolvents. The kinetics of formation of the PIB block at ? 80°C were found to be first order in isobutylene (IB) concentration, first order in the concentration of initiating sites, second order in TaiCl₄ concentration, and a negative fractional order with respect to the pyridine concentration. The rate of polymerization was found to decrease with increasing temperature, indicating an equilibrium between dormant, covalent and active, ionized chain ends, and chain-end concentration studies suggested that there was no contribution by free ions to the rate of propagation. Diagnosis of the livingness of the IB polymerization indicated that at high (≥90%) monomer conversion, β-proton elimination becomes important, causing the timing of addition of styrene to be critical. Addition of styrene at an IB reaction time significantly exceeding the time necessary for complete IB consumption resulted in contamination of the product with a substantial amount of homo-PS; conversely, addition at intermediate IB conversion resulted in slow copolymerization between IB and styrene and the formation of a tapered block copolymer. Addition of styrene at an IB conversion of about 90% resulted in well-defined block copolymers which displayed ordered, phase-separated morphologies consisting of cylinders of PS in a continuous phase of PIB. The block copolymers possessed properties consistent with those of physically crosslinked rubbers. Dynamic mechanical spectroscopy revealed two glass transitions with a broad rubbery plateau extending from about 0 to 100°C, and tensile strengths of up to 25 MPa and elongations to 1000% were observed for some samples.     

超强分凝含氟嵌段共聚物的RAFT合成及其自组装行为

单羟基聚乙二醇(mPEG)与端羧基链转移剂S-十二烷基-S-′(α,α′-二甲基-α″-乙酸)三硫代碳酸酯[DDMAT(1)]经酯化反应制得大分子链转移剂[mPEG-DDMAT(2)];以2为链转移剂,用AIBN引发1H,1H,2H,2H-全氟癸基丙烯酸酯(FA)的可逆加成-断裂链转移聚合(RAFT),合成了嵌段间强烈不相容的亲水/亲氟双亲嵌段共聚物[mPEG-b-PFA(3a~3k)。3在溶液中的自组装行为研究结果表明,3 f在D2O中PFA聚集形成核,mPEG形成冠层;3 j在正丙醇中自组装得到伸直状的珍珠项链状聚集体。     

官能化聚四氢呋喃-b-聚异丁烯-b-聚四氢呋喃三嵌段共聚物的合成与性能

采用2-氯-2,4,4-三甲基戊烷或对二枯基氯为引发剂和TiCl4或FeCl3为共引发剂,引发异丁烯(IB)可控/活性正离子聚合与官能端基转化,设计合成不同分子量及窄分子量分布的端基官能化聚异丁烯,如双端烯丙基溴官能化聚异丁烯(Br-PIB-Br)或双端烯丙基胺官能化聚异丁烯(H2N-PIB-NH2).采用烯丙基溴/高氯酸银体系引发四氢呋喃(THF)开环聚合,合成聚四氢呋喃活性链(PTHF+).进一步通过将IB可控/活性正离子聚合与THF可控/活性正离子开环聚合2种方法相结合,设计合成2种新型官能化聚四氢呋喃-b-聚异丁烯-b-聚四氢呋喃(PTHF-b-PIB-b-PTHF)三嵌段共聚物:(1)以上述Br-PIB-Br为大分子引发剂,在AgClO4作用下引发THF活性正离子开环聚合,采用水终止活性链端,设计合成双端为羟基的HO-PTHF-b-PIB-b-PTHF-OH三嵌段共聚物(简称:FIBF-OH);(2)以上述合成的PTHF+活性链与H2NPIB-NH2链端胺基发生高效亲核取代反应,设计合成中间链段连接点含―NH―官能基团的PTHF-b-HNPIB-NH-b-PTHF三嵌段共聚物(简称:FIBF-NH).在上述三嵌段共聚物中,极性PTHF链段与非极性PIB链段的热力学不相容,导致其呈现明显的微相分离,且微观形态与共聚组成相关.PTHF均聚物易结晶,在上述共聚物中由于PTHF链段单端受限致其结晶性减弱.三嵌段共聚物分子链的中间连接点含―NH―官能基团,具有更强的氢键作用,促进PTHF链段重排并结晶,易形成更紧密的超分子网络结构,导致即使在PTHF链段相对分子量为0.7 kg·mol^-1时仍具有较强的结晶性,且结晶熔融温度明显提高.此外,由于FIBF-NH中形成超分子网络结构,使材料具有优异的自修复性能,材料表面的切痕在常温下10 min后可以完全自愈合.本文设计合成的新型官能化PTHF-b-PIB-b-PTHF三嵌段共聚物兼具有PTHF与PIB的优良性能,在生物医用、智能修复等功能材料领域具有潜在的应用前景.     

Chitooligosaccharide Copolymers: Synthesis and Aqueous Self-assembly

Novel water-soluble amphiphilic graft copolymers (COS-g-PCL-b-MPEG) were synthesized by the coupling reaction between chitooligosaccharide (COS) and MPEG-b-PCL-COOH, which was synthesized via ring-opening polymerization of ε-caprolactone (CL) using MPEG as an initiator and subsequent carboxylation by succinic anhydride. The chemical composition of the graft copolymers was confirmed by ¹H-NMR spectra and FT-IR spectrometry. The thermal properties and crystallinity of the copolymers were observed by DSC and XRD measurements, which showed the existence of separate backbone and graft chain phases in the copolymer. The micellar behavior via self-assembly of the graft copolymers in aqueous solution was studied using pyrene fluorescence dye technique. AFM measurements showed that the micelles had a spherical morphology at the critical micelle concentration (CMC) and ranged in size from 20–45 nm. The amphiphilic ternary biodegradable graft copolymer endows the hydrophilic outer shell of micelles with structural and functional diversification, which might be desirable for drug delivery applications.     

Poly(2-oxazoline)-Containing Triblock Copolymers: Synthesis and Applications

This review focuses on poly(2-oxazoline) containing triblock copolymers and their applications. A detailed overview of the synthetic techniques is provided. Triblock copolymers solely based on poly(2-oxazoline)s can be synthesized by sequential monomer addition utilizing mono- as well as bifunctional initiators for the cationic ring-opening polymerization of 2-oxazolines. Crossover and coupling techniques enable access to triblock copolymers comprising, e.g., polyesters, poly(dimethylsiloxane)s, or polyacrylates in combination with poly(2-oxazoline) based segments. Besides systematic studies to develop structure property relationships, these polymers have been applied, e.g., in drug delivery, as (functionalized) vesicles, in segmented networks or as nanoreactors.     

Synthesis of Well-Defined Dendritic-Linear Diblock and Triblock Copolymers by Controlled Free Radical Polymerization

Recently, significant progress has been made in the field of living free radical polymerization such as nitroxide-mediated stable free radical polymerization, atom transfer radical polymerization (ATRP), reverse ATRP and reversible addition-fragmentation chain transfer1. Among them, ATRP has been successfully applied to the synthesis of well-defined comb, gradient, star and dendritic macromolecules. Recent advances have been carried toward new initiators, metals and ligands. As a new cl…     

Polyisobutylene-Based Thermoplastic Elastomers. I. Synthesis and Characterization of Polystyrene-Polyisobutylene-Polystyrene Triblock Copolymers

Abstract

Polystyrene-polyisobutylene-polystyrene triblock copolymer thermoplastic elastomers have been synthesized by living carbocationic sequential copolymerization using the tert-butyl dicumyl chloride/TiCl₄/methylcyclohexane:methyl chloride (60:40 v:v)/ ?80°C system in the presence of the proton trap 2,6-di-tert-butylpyridine. Structure-property relationships have been examined by varying the M_n of the PIB middle block (39,000 to 156,000) and that of the PSt end-segment (1,000 to 19,000). The tensile strength is controlled by the molecular weight of the PSt segment and independent of the PIB middle block length in the studied range. Phase separation starts when the M_n of the PSt segment reaches ～ 5,000, and it is complete when the M_n reaches ～ 15,000. These triblocks exhibited 23-25 MPa tensile strength, similar to that of styrenic thermoplastic elastomers obtained by anionic polymerization.