多嵌段共聚物(P4VP-b-PS-b-P4VP)_n的胶束化行为研究

研究了一系列具有不同链段长度和组成的聚4-乙烯基吡啶-聚苯乙烯-聚4-乙烯基吡啶多嵌段共聚物(P4VP-b-PS-b-P4VP)n在其选择性溶剂甲苯和pH<3的水中的胶束化过程,主要研究了多嵌段共聚物链段长度、溶液浓度和溶剂对其胶束形态的影响.透射电镜和原子力显微镜结果表明随着P4VP段链的相对增长,多嵌段共聚物在甲苯中的胶束形态由蠕虫链状向短棒状到球状胶束变化,而其在pH<3的水溶液中均形成球形胶束.由于特殊的链结构,聚合物的浓度对(P4VP-b-PS-b-P4VP)n多嵌段共聚物的胶束行为和胶束形态有着重要的影响.同时,(P4VP-b-PS-b-P4VP)n多嵌段共聚物分子量分布的多分散性对其在选择性溶剂中的胶束形态也有所影响.     

AB型聚乙二醇单甲醚-聚(L-丙氨酸)嵌段共聚物自组装过程的核磁共振研究

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.     

化学酶法合成五嵌段聚合物及其自组装行为的研究

用酶促开环聚合与ATRP方法相结合,制备了聚甲基丙烯酸六氟丁酯-聚己内酯-聚乙二醇-聚己内酯-聚甲基丙烯酸六氟丁酯(PHFMA-b-PCL-b-PEG-b-PCL-b-PHFMA)五嵌段聚合物.首先用Novozym e 435作为催化剂合成了聚己内酯-聚乙二醇-聚己内酯三嵌段聚合物,然后通过端基官能化法合成了大分子引发剂,并用其引发甲基丙烯酸六氟丁酯(HFMA)的ATRP反应,合成了五嵌段聚合物.通过核磁和GPC证明了大分子引发剂和五嵌段共聚物的结构,五嵌段共聚物的GPC分析表明这种合成方法的可行.共聚物胶束的直径和大小通过动态光散射方法和原子力显微镜测试,五嵌段共聚物在水中的的自组装行为也被研究.结果证明胶束是球形,其平均直径为77 nm.聚合物在四氢呋喃中的浓度对聚合物的聚集形貌有很大的影响.     

温度/pH敏感性嵌段共聚物P(HEMA-co-DEAEMA)-b-PDEAM-b-P(DEAEMA-co-HEMA)的合成与性质研究

利用原子转移自由基聚合方法(ATRP)合成了组成递变的嵌段共聚物P(HEMA-co-DEAEMA)-b-PDEAM-b- P(DEAEMA-co-HEMA). 用FTIR, ¹H NMR和GPC技术表征了聚合物的组成、结构、分子量及其分布. 通过透光率测定、粘度、激光粒度分析和透射电镜研究了共聚物组成、温度及溶液pH对其溶液相行为和胶束化作用的影响. 结果表明: 所合成的嵌段共聚物具有温度和pH敏感性, 共聚物水溶液的低临界溶解温度(LCST)随HEMA量的增加而降低, 临界相变pH随HEMA量的增加而降低, 温度和pH诱导均可实现嵌段共聚物的胶束化. 控制HEMA量可以调控嵌段共聚物的LCST和pK_a.     

磷酰胆碱基pH敏感性ABA型嵌段共聚物的合成与胶束化

采用氯化亚铜/2,2-联二吡啶催化体系, 2,5-二溴己二酸二乙酯为引发剂, 甲醇为溶剂运用希莱克技术, 利用原子转移自由基聚合(ATRP)方法合成了ABA型三嵌段共聚物PDEAEMA-b-PMPC-b-PDEAEMA. ¹H NMR和GPC(凝胶渗透色谱)对聚合物组成、结构及分子量进行了表征, 利用透光率、粘度测定研究了嵌段共聚物溶液的pH敏感性, 利用表面张力测定、荧光探针和透射电镜研究了嵌段共聚物胶束化作用, 确定了共聚物水溶液的临界胶束浓度(CMC). 结果表明所合成的ABA型三嵌段共聚物水溶液具有pH敏感性, 其临界相变pH 7～7.5. 调节溶液pH值可实现嵌段共聚物胶束化形成“花状”胶束, 并测定了其临界胶束浓度.     

聚苯乙烯-丙烯酸嵌段共聚物在不同pH值和Ca2+浓度下的胶束行为

近年来, 对具有纳米尺寸的聚合物自组装结构的研究日益增多. 其中, 嵌段共聚物在选择性溶剂中的胶束行为研究得最为广泛和深入[1~5]. 纳米胶束表现出诸多常规尺寸材料所不具备的特殊性能, 在材料化学、生物医学以及环境科学等领域有广阔的应用前景. Webber等[6]对聚丙烯酸和聚苯乙烯接枝共聚物的研究发现, 聚合物的接枝率和聚合物浓度以及溶液离子强度对胶束结构有影响; Eisenberg等[1,7]对不同嵌段比例的苯乙烯-丙烯酸嵌段共聚物的自组装行为进行研究发现, 不同嵌段比例所对应的胶束结构不同. 胶束形成的环境对胶束的形成与稳定性的影响是人们研究的重点. 本文报道了聚苯乙烯-丙烯酸嵌段共聚物在水中的胶束行为, 着重讨论了溶液pH值和钙离子浓度对聚丙烯酸链段相互作用的影响.     

聚苯乙烯-丙烯酸嵌段共聚物在Ca~(2 )或乙二胺存在下的自组装行为

近 1 0年来 ,人们对于具有纳米尺度聚合物自组装结构的研究日益增多 .其中 ,嵌段共聚物在选择性溶剂中的胶束行为的研究非常引人瞩目 [1～ 3] .其表现出诸多常规尺寸所不具备的特殊性能 ,使得纳米胶束不仅在理论上有研究价值 ,而且在材料化学、生物医学和环境科学等领域都具有广阔的应用前景 .Ma等[4 ] 对聚丙烯酸和聚苯乙烯接枝共聚物的研究发现聚合物接枝率和聚合物浓度以及溶液离子强度对胶束结构有影响 ;Zhang等 [1,5] 对不同嵌段比例的苯乙烯 -丙烯酸嵌段共聚物的自组装行为的研究 ,发现不同嵌段比例所对应的纳米结构不同 ;而胶束表面…     

光/温度双响应三嵌段共聚物的合成及溶液自组装行为

以双官能团聚乙二醇(Br-PEO-Br)为引发剂, 利用原子转移自由基聚合(ATRP)制得了含偶氮苯(AZO)和N-异丙基丙烯酰胺(NIPAM)的两亲性三嵌段共聚物P(AZO₉-co-NIPAM₉)-b-PEO₄₈-b-P(AZO₉-co-NIPAM₉), 并通过核磁共振(¹H NMR)和凝胶渗透色谱(GPC)对产物进行了表征. 该共聚物能够在溶液中自组装形成纳米胶束, 运用透射电子显微镜(TEM)、荧光探针技术和动态光散射(DLS)研究了胶束的形貌、粒径及其在光或温度刺激下的响应行为. 结果表明, 该三嵌段共聚物胶束显现出我们以往报道的二嵌段共聚物所不具有的光释放行为: 包覆有尼罗红的胶束在多次紫外-可见光循环照射之后, 荧光强度和初始状态相比下降了大约40%, 说明尼罗红在此过程中逐渐被释放. 胶束的尺寸随着温度的升高而逐渐缩小.     

CO2调控的温敏性聚合物的制备及其响应行为

通过原子转移自由基聚合制备了含甲氧基聚乙二醇(mPEG)、N-异丙基丙烯酰胺(PNIPAM)和2-(二乙基氨基)甲基丙烯酸乙酯(PDMAEMA)的三嵌段共聚物。该共聚物具有较为明显的温度响应特征,并且温敏性的范围可以通过CO₂进行调控。该三嵌段聚合物在水溶液中存在最低临界溶液温度(LCST),且该聚合物水溶液在CO₂调节的LCST下具有各种聚集状态。随着温度的升高,三嵌段聚合物表现出双重LCST行为,并最终导致PNIPAM嵌段和PDMAEMA嵌段分别在各自相转变温度下收缩,聚合物的疏水性增强,出现收缩-收缩-聚集的三相变过程。CO₂通过调控PDMAEMA嵌段中的叔胺基团电性,可以使聚合物的亲水性增强,使得三嵌段聚合物在较高温度下难以聚集,实现了CO₂对聚合物相转变温度的调控。      

牛血清白蛋白影响聚氧乙烯-聚氧丙烯-聚氧乙烯嵌段共聚物胶团形成的荧光光谱研究

应用芘荧光光谱研究了牛血清白蛋白(BSA)对聚氧乙烯-聚氧丙烯-聚氧乙烯嵌段共聚物(PEO-PPO-PEO)Pluronic系列聚集行为的影响, BSA可以使Pluronic嵌段共聚物水溶液的临界胶团温度(CMT)增加. 应用“紧密堆积模型”获得了胶团形成过程中的标准自由能(ΔG⁰)、标准焓(ΔH⁰)和标准熵(ΔS⁰)等热力学参数, 胶团形成的标准焓和标准熵随着BSA浓度的增加而降低, 嵌段共聚物的PPO含量越高, 焓和熵的改变越大. 疏水的PPO嵌段是Pluronic嵌段共聚物与BSA作用的主要因素. PPO和BSA之间的疏水相互作用会引起PPO嵌段之间相互作用的改变, 进而使CMT升高和Pluronic嵌段共聚物胶团形成的热力学参数改变.     

Water-dispersible, uniform nanospheres by heating-enabled micellization of amphiphilic block copolymers in polar solvents

Uniform nanospheres with tunable size down to 30 nm were prepared simply by heating amphiphilic block copolymers in polar solvents. Unlike reverse micelles prepared in nonpolar, oily solvents, these nanospheres have a hydrophilic surface, giving them good dispersibility in water. Furthermore, they are present as individual, separated, rigid particles upon casting from the solution other than continuous thin films of merged micelles cast from micellar solution in nonpolar solvents. These nanospheres were generated by a heating-enabled micellization process in which the affinity between the solvent and the polymer chains as well as the segmental mobility of both hydrophilic and hydrophobic blocks was enhanced, triggering the micellization of the glassy copolymers in polar solvents. This heating-enabled micellization produces purely well-defined nanospheres without interference of other morphologies. The micelle sizes and corona thickness are tunable mainly by changing the lengths of the hydrophobic and hydrophilic blocks, respectively. The heating-enabled micellization route for the preparation of polymeric nanospheres is extremely simple, and is particularly advantageous in producing rigid, micellar nanospheres from block copolymers with long glassy, hydrophobic blocks which are otherwise difficult to prepare with high efficiency and purity. Furthermore, encapsulation of hydrophobic molecules (e.g., dyes) into micelle cores could be integrated into the heating-enabled micellization, leading to a simple and effective process for dye-labeled nanoparticles and drug carriers.     

1H NMR spectroscopic investigations on the micellization and gelation of PEO-PPO-PEO block copolymers in aqueous solutions

The effects of temperature, polymer composition, and concentration on the micellization and gelation properties of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers in aqueous solutions were investigated by 1H NMR spectroscopy. It was found that the temperature-dependent behavior of PPO blocks, observed as changes in chemical shift, half-height width, and integral value, could be attributed as an intrinsic tool to characterize the transition states during unimer to micelle formation. The 1H NMR spectral analysis revealed that the hydrophobic part, PPO, of the Pluronic polymers plays a more significant role in the temperature-induced micellization, whereas the transitional behavior of Pluronic polymer, i.e., from micellization to liquid crystals formation, resulted in the drastic broadening of the spectral signals for the PEO, indicating that the PEO segments play a more significant role in the crystallization process. It was also observed that the temperature-dependent changes in the half-height width of the PEO -CH2- signal are sensitive to the liquid crystalline phase formation, which could be attributed to the close packing of spherical micelles at high polymer concentrations or temperatures.     

环形嵌段共聚物的胶束化行为模拟简

利用Monte Carlo模拟,对比了相同组成下环形二嵌段共聚物AB和线形三嵌段共聚物ABA在选择性溶剂中的胶束化行为. 结果发现,相同链组成的环形和线形嵌段共聚物的临界胶束浓度(cmc)的差别与A嵌段的比例(fA)及B嵌段间的吸引强度(ε)密切相关. 在fA较小、ε较大的情况下,相应环形嵌段共聚物的cmc值更小;而在fA较大、ε较小的情况下,线形嵌段共聚物的cmc值更小. 为了进一步理解胶束化行为同fA及ε的关系,计算了胶束化过程中熵和势能部分对自由能的贡献. 结果表明,在所研究的fA和ε范围内,环形嵌段共聚物形成胶束时的熵损失更小,因而从熵贡献角度来看,环形嵌段共聚物更易发生胶束化. 而从势能贡献角度来看,当fA较小、ε较大时,环形嵌段共聚物形成胶束时势能有较大程度的降低,对自由能的贡献更大,因而此时环形嵌段共聚物更易发生胶束化. 而当fA较大、ε较小时,线形嵌段共聚物形成胶束时势能有较大程度的降低,对自由能的贡献更大,因而此时线形嵌段共聚物更易发生胶束化. 由此可见,对体系的胶束化自由能进行系统分析,有助于更好地理解环形和线形嵌段共聚物的胶束化行为.     

Synthesis and self-assembly behavior of thermoresponsive triblock copolymer

Block copolymers comprising thermosensitive poly(N-isopropylacrylamide) (PNIPAM) and hydrophobic poly(n-butyl acrylate) (PBA) blocks, were synthesized using the reversible addition-fragmentation chain transfer polymerization (RAFT), their thermosensitive behavior was studied by ultraviolet spectrophotometer (UV) and dynamic light scattering (DLS). The lower critical solution temperature (LCST) was strongly correlated to the hydrophobic/hydrophilic ratio of the copolymers. Their micellization and self-assembly behavior in dilute aqueous solution were studied by surface tension (SFT), DLS and TEM. The resulting block copolymers reversibly formed or deformed micellar assemblies during their LCSTs. The critical micelle concentration (CMC) was controlled by the composition of PBA and PNIPAM, indicating the successful formation of the block copolymers.     

Studies on the self-assembly behavior of the amphiphilic block copolymer of PSt-b-PAA in apolar solvents with polar fluorescent probe

The block copolymer of polystyrene-b-poly(butyl acrylate) (PSt-b-PBA) with a well-defined structure was synthesized by atom transfer radical polymerization (ATRP); its structure was characterized, and the living polymerization was also validated by gel permeation chromatography, Fourier transform infrared, and ¹H NMR measurements. Then, the amphiphilic block copolymer of polystyrene-b-poly(acrylic acid) (PSt-b-PAA) has been prepared by hydrolysis of PSt-b-PBA, and copolymers of PSt-b-PAA with longer PSt blocks and shorter PAA blocks were obtained by controlling the conditions of ATRP polymerization. The reversed micelle solution of PSt-b-PAA in toluene was prepared by using the single-solvent dissolving method, and the reverse micellization behavior of PSt-b-PAA in toluene was mainly investigated in this paper. The fluorescent probe technique was used by using polar fluorescence compound N-(1-Naphthyl)ethylenediamine dihydrochloride (NEAH) as a polar fluorescent probe to study the reverse micellization behavior of PSt-b-PAA. It was found that the reverse micellization behaviors of PSt-b-PAA in toluene can be clearly revealed by using NEAH as a polar fluorescence probe, and the critical micelle concentrations (cmcs) can be well displayed. The experimental results showed that the self-assembling behavior of PSt-b-PAA in toluene depends apparently on the microstructure of the macromolecules and is also influenced by the temperature. For the copolymers of PSt-b-PAA with the same length of hydrophobic PSt blocks, the copolymer with a longer hydrophilic block PAA has lower cmc, and at higher temperature, the copolymer has lower cmc.     

Melt, hydration, and micellization of the PEO-PPO-PEO block copolymer studied by FTIR spectroscopy

Fourier transform infrared (FTIR) spectroscopy was used to study the conformational changes of the polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) block copolymer, Pluronic P104, in a large concentration range in a polymer-water system as a function of temperature. The melt in which the conformational transition of the PEO blocks occurs gives remarkable changes in the spectral behavior. A small amount of water in Pluronic P104 can induce the PEO block amorphism. The addition of more water only swells the PEO dominant region and gives no significant difference in the conformational structure of the block copolymer in the ordered phases of Pluronic P104-water mixtures. The PPO blocks of Pluronic P104 are hydrated only in a condition of lower temperature and higher water content. The temperature dependent micellization of Pluronic P104 in water was analyzed by a FTIR spectroscopic method. The appearance of the symmetric deformation band of the anhydrous methyl groups at temperature below the CMT indicates the existence of a hydrophobic microenvironment. The appearance of the symmetric deformation band of the hydrated methyl groups at higher temperatures indicates that the micellar core must contain some amount of water. The results of FTIR data show that the proportion of the anhydrous methyl groups increases and water content in the micellar core decreases during the micellization process.     

环形嵌段共聚物的胶束化行为模拟

利用Monte Carlo模拟, 对比了相同组成下环形二嵌段共聚物AB和线形三嵌段共聚物ABA在选择性溶剂中的胶束化行为. 结果发现, 相同链组成的环形和线形嵌段共聚物的临界胶束浓度(cmc)的差别与A嵌段的比例(f_A)及B嵌段间的吸引强度(ε)密切相关. 在f_A较小、 ε较大的情况下, 相应环形嵌段共聚物的cmc值更小; 而在f_A较大、 ε较小的情况下, 线形嵌段共聚物的cmc值更小. 为了进一步理解胶束化行为同f_A及ε的关系, 计算了胶束化过程中熵和势能部分对自由能的贡献. 结果表明, 在所研究的f_A和ε范围内, 环形嵌段共聚物形成胶束时的熵损失更小, 因而从熵贡献角度来看, 环形嵌段共聚物更易发生胶束化. 而从势能贡献角度来看, 当f_A较小、 ε较大时, 环形嵌段共聚物形成胶束时势能有较大程度的降低, 对自由能的贡献更大, 因而此时环形嵌段共聚物更易发生胶束化. 而当f_A较大、 ε较小时, 线形嵌段共聚物形成胶束时势能有较大程度的降低, 对自由能的贡献更大, 因而此时线形嵌段共聚物更易发生胶束化. 由此可见, 对体系的胶束化自由能进行系统分析, 有助于更好地理解环形和线形嵌段共聚物的胶束化行为.     

Double thermoresponsive block–random copolymers with adjustable phase transition temperatures: From block‐like to gradient‐like behavior

Stimuli‐responsive block–random copolymers are very useful “smart” materials as their switching behavior can be tuned by simply adjusting the composition of the random copolymer block. Because of that, we synthesized double thermoresponsive poly(N‐acryloylpyrrolidine)‐block‐poly(N‐acryloylpiperidine‐co‐N‐acryloylpyrrolidine) (PAPy‐b‐P(APi‐co‐APy)) copolymers via reversible addition fragmentation chain transfer (RAFT) polymerization and investigated their temperature‐induced self‐assembly in aqueous solution. By varying the APi/APy ratio in the random copolymer block, its phase transition temperature (PTT₁) can indeed be precisely adjusted while the temperature‐induced collapse upon heating leads to a fully reversible well‐defined micellization. By making the two blocks compositionally similar to more than 60%, the polymers' mechanistic thermoresponsiveness can furthermore be changed from block‐like to rather gradient‐like behavior. This means the micellization onset at PTT₁ and the corona collapse at the PTT of the more hydrophilic pure PAPy block (PTT₂) overlap resulting in one single broad transition. This work thus contributes to the detailed understanding of design, synthesis and mechanistic behavior of tailored “on‐demand” switchable materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 399–411     

Chain-length dependence of diblock copolymer micellization kinetics studied by stopped-flow pH-jump

A series of well-defined poly(ethylene oxide)- b-poly(2-(diethylamino)ethyl methacrylate) (PEO- b-PDEA) diblock copolymers containing PEO block of identical chain length and PDEA block with varying degrees of polymerization (DP, in the range of 32-154) were prepared via atom transfer radical polymerization (ATRP) employing a PEO-based macroinitiator (DP = 113). Upon a pH-jump from 3 to 12 under highly efficient stopped-flow mixing conditions, PEO- b-PDEA copolymers spontaneously form spherical micelles of increasing sizes and aggregation numbers ( N agg) with increasing PDEA chain lengths. Stopped-flow light scattering technique was used to probe the pH-induced micellization kinetics of PEO- b-PDEA copolymers, aiming to elucidate the PDEA chain-length effects on the unimer-to-micelle transition process. Upon a stopped-flow pH-jump from 3 to 12, the obtained dynamic traces can be well-fitted with double exponential functions. The calculated fast and slow characteristic relaxation times (tau 1 and tau 2) can be ascribed to the formation of quasi-equilibrium micelles (fast process) and subsequent relaxation into final equilibrium micelles (slow process), respectively. For PEO 113- b-PDEA 32 and PEO 113- b-PDEA 61, tau 2 is almost independent of polymer concentrations, suggesting that the relaxation from quasi-equilibrium micelles into final equilibrium micelles mainly proceeds via insertion/expulsion of unimer chains. Upon increasing the DP of pH-responsive PDEA block to 89, 117, and 154, the obtained slow relaxation time, tau 2, tends to decrease with increasing polymer concentrations, suggesting that the slow process is dominated by the micelle fusion/fission mechanism. The apparent activation energy ( E a) associated with tau 2 has also been determined from temperature-dependent micellization kinetics for five PEO- b-PDEA copolymers. It was found that during micellization, copolymers with longer PDEA blocks exhibit much lower E a compared to those with shorter blocks. Thus, we observed experimentally for the first time that increasing the hydrophobic block length in double hydrophilic block copolymers (DHBCs) can transform the mechanism of the slow process from unimer insertion/expulsion to micelle fusion/fission.