分子刷聚合物环境响应特性及应用的研究进展

近些年来,分子刷聚合物的研究受到了广泛关注,这种单分子尺度的聚合物的结构、体积及形状在纳米级别均可以得到精确、灵活的控制,同时,分子刷聚合物的独特结构使其在与不同溶液相互作用时,能够呈现出许多独特的分子形态,为研究溶液与聚合物的相互作用提供了一个理想的平台。本文对环境响应性分子刷聚合物的概念、分类、应用等内容进行了概述,介绍了环境刺激响应性聚合物因其物理化学性质可随外界环境的温度、pH值或离子浓度等因素的变化而变化,这一性能使得它有望在药物输送、催化、制备纳米导线等领域得到广泛的应用。     

刺激响应型聚合物刷的研究进展

本文综述了刺激响应型聚合物刷的研究进展,阐述了刺激响应型聚合物刷的分类、与基体表面的连接方式以及常规制备方法,介绍了离子强度、温度、pH值、光、溶剂等刺激响应型聚合物刷及其研究现状,并对相应的刺激响应机理进行了探讨。此外,本文还综述了多重刺激响应型聚合物刷的制备设计思路及其刺激响应特性,概述了聚合物刷在响应外界刺激后对基体的弯曲作用以及利用该作用进行可控三维自组装,并对刺激响应型聚合物刷的应用前景进行了展望。     

表面引发聚合新进展及应用

综述了近年来聚合物刷合成与应用方面的新进展.简要介绍了利用表面引发原子转移自由基聚合(SI-ATRP)制备聚合物刷的历程和重要进展.重点论述了通过电化学、光诱导以及牺牲阳极技术、仿生合成等发展了多种表面引发ATRP新方法,基于如何将聚合物从分子尺度过渡到微米尺度的思考,实现了多尺度聚合物刷结构的制备.简要综述了聚合物刷在以下3个方面的应用研究:(1)智能驱动,利用聚合物刷构象变化,实现微悬臂驱动、辅助放大的电驱动以及仿毛毛虫运动.(2)生物润滑,利用聚合物的环境响应行为实现了对摩擦系数的调控,并发展了球刷型润滑材料.(3)表面防污,表面接枝含离子液体官能团的聚合物刷,并与仿生技术相结合,利用化学组成和结构化协同效应,得到一系列高性能低毒海洋防污界面材料.     

刺激响应性聚合物载药纳米胶束研究进展

刺激响应性聚合物纳米胶束是目前药物控制释放体系的研究热点之一,其原理是将疏水性药物以物理或化学方法包覆在具有核/壳结构的纳米微球中,通过环境刺激响应控制药物的包覆与释放,可增加疏水性药物溶解度、提高药物利用率、降低药物毒副作用,具有显著的研究价值和应用前景.本文中我们主要介绍了不同类型刺激响应性聚合物纳米胶束在药物控制释放体系的研究进展.     

刺激响应聚合物在生物医药中的应用

刺激响应聚合物是一类能够根据外界环境变化,如p H、离子、温度、光等刺激而改变自身物理化学性质的功能性聚合物。近年来,刺激响应聚合物由于其独特的刺激-响应功能性,在疾病诊断、药物递送、传感器等领域具有广泛的应用。根据不同刺激类型,刺激响应聚合物有不同分类。本文根据化学刺激、物理刺激及生物刺激三方面,综述了刺激响应聚合物的合成方法及其响应机理,并对这类功能材料的应用前景进行了展望。     

超分子作用介导的瓶刷聚合物构建及组装

瓶刷聚合物(BBPs)具有独特的分子结构和富有前景的应用领域,因此受到学者们日益广泛的关注。通过共价键接枝策略来合成瓶刷聚合物费时、合成困难,难以功能化。而通过非共价键作用,则容易将侧链接枝到共聚物主链上,为构建超分子瓶刷共聚物提供有利条件。超分子作用的引入,不仅带来瓶刷聚合物制备方面的灵活性,同时使材料具备更多的响应性、可逆性等功能。本文介绍了氢键、主客体相互作用、金属配位作用、离子相互作用等多种超分子作用介导的瓶刷聚合物的构建及组装,分析讨论了其各自特点、构筑策略,阐明了超分子作用介导的瓶刷聚合物的巨大应用潜能和重要研究意义,最后对其目前仍面临的问题和未来发展进行了分析和展望。     

刺激响应梯度聚合物

近年来,刺激响应聚合物因其独特的性质而受到广泛关注,这类聚合物能够感受外界环境刺激(包括光、电、热、力、氧化还原、pH、化学、环境和生物信号等刺激)而产生响应,从而引起体系物理或化学性质的改变。而梯度聚合物则是伴随着可控自由基聚合技术的诞生、发展而出现和形成的一类新型聚合物,区别于无规和嵌段聚合物,梯度聚合物表现出单体组成沿分子链渐变的性质,其中,由亲水性单元和憎水性单元组成的两亲性梯度聚合物在选择性溶剂中可自组装形成多种聚集体,因此具有多方面的潜在应用价值,比如超分子组装体、智能涂料、网络或这些可能应用的组合。本文调研了有关梯度聚合物方面的研究工作,综述了几种梯度聚合物的合成方法,如活性阴离子聚合法、可控自由基聚合法(包括氮氧稳定自由基聚合、原子转移自由基聚合及可逆加成断裂链转移自由基聚合)和开环聚合法等,同时阐述了梯度聚合物的自组装及刺激响应行为,尤其是其独特的热和pH敏感性。此外,还对由两亲性嵌段聚合物和两亲性梯度聚合物自组装形成的聚集体的刺激响应行为进行了详细地论述和比较,并指出了梯度聚合物的应用前景和发展方向。     

响应性支化聚合物的合成、组装及其生物医药应用

环境响应性超支化聚合物作为超支化聚合物中一类智能聚合物,备受研究者关注,已被广泛用于生物医药领域.本文主要介绍了本课题组在响应性支化聚合物的合成、组装及其生物医药应用方面的部分研究工作.主要包括以下三方面的内容:第一部分介绍了酸响应性支化聚合物、温敏性支化聚合物、还原响应性支化聚合物和光响应性支化聚合物的合成;第二部分介绍了含有二硫键的温敏性超支化聚合物在温度诱导下的自组装及自交联反应制备纳米凝胶、纳米胶囊和交联复合囊泡;第三部分介绍了响应性支化聚合物在药物传递和基因传递方面的应用.     

三亚甲基碳酸酯基响应性脂肪族聚碳酸酯的研究进展

脂肪族聚碳酸酯是一类可生物降解、生物相容性的材料,在生物医药方面引起广泛关注。两亲性脂肪族聚碳酸酯聚合物中,聚碳酸酯部分凭借其疏水性能处于胶束内核部位,且该部分通过物理包覆、化学键合等方式使聚合物与药物相结合,提升了响应环境下药物运输与释放的方式与能力。因此,本工作对近年来响应性脂肪族聚碳酸酯的研究进展进行了综述,主要阐述了具有外环境刺激响应(pH、光、温度和氧化还原)脂肪族聚碳酸酯的合成、响应原理、在药物传递和释放方面的应用。     

聚合物刷与生物分子相互作用的研究进展

聚合物刷是由一端紧密接枝在一个曲面或平面的聚合物链组成的大分子结构。近年来,随着聚合物制备方法和表面修饰技术的不断发展,聚合物刷的应用范围也在不断拓宽,相关研究已成为功能高分子材料领域的热点之一。具有特殊结构和功能的聚合物刷在生物分子固定、蛋白质分离、酶催化、药物控释等方面具有广阔的应用前景。本文综述了聚合物刷与生物分子相互作用及应用的最新研究进展,并展望了今后的发展方向。     

Templation,Water Content,and Zeta Potential of Polyelectrolyte Nanoassemblies: a Comparison Between Polyelectrolyte Multilayers and Brushes

This feature article deals with the self assembly and physical chemistry of polyelectrolytes: multilayers and brushes. The article highlights the interesting behavior of polyelectrolytes in nanoscale assemblies, giving more insight into the complexity of the formation of the assemblies. The water content of multilayers and brushes is studied during the assembly and in different ionic strengths. Similarities are found in the behavior of the brushes and multilayers with ionic strength, with regard to changes in the thickness and the water content. An invariance of the zeta potential with ionic strength is also observed for both systems, which can be explained as a result of conformational changes of the polymer chains. Finally, the combination of brushes and multilayers for surface modification is presented.     

Architecture and solution properties of amphiphilic polymer brushes with peripheral charged ions

Functionalized poly(ethylene oxide) (PEO) macromonomers (alpha -tertiary amino and omega -methacryloyl groups) were prepared by ring-opening polymerization of live PEO anions end-capped with styrene oxide using 2-[2-(N ,N -dimethylamino)-ethoxy]ethanol potassium alkoxides as an initiator with methacryloyl chloride. PEO brushes were synthesized by free-radical homopolymerization of such PEO macromonomers. These brushes were converted into peripherally charged brushes by quaternization. We studied the solution properties of both types of brushes from the viewpoint of charge effect. It was found from dynamic light scattering (DLS) that the polymer brushes formed a single macromolecule in solution due to crowding of side chains. It was speculated from angular dependence measurements that the polymer brushes with large aspect ratios took a geometrical anisotropic conformation such as a cylinder. In methanol with a low dielectric constant, radius of gyration (R(G)), and cross-sectional radius of gyration (R(G,C)) of the polymer brushes with charged side chains were smaller than those of the polymer brushes without charges. In a solvent with a low dielectric constant such as methanol, ionic groups do not dissociate and condense. On the other hand, these physical values in an aqueous solution were somewhat larger than those of the polymer brushes without charges. In water with a high dielectric constant, peripherally charged brushes were strongly stabilized by electric double layers.     

Strongly stretched polymer brushes

Polymer “brushes” are formed when long-chain molecules are somehow attached by one end at an interface with a relatively small area per chain. Such adsorbed brushes in the presence of solvent may be used to modify surface properties, stabilize colloidal particles, etc. Strongly segregated block copolymer phases, or interfacial layers of such “polymeric surfactants” may also be modeled in terms of “melt brushes,” (i.e., brushes without solvent). In both cases, when chain attachments are crowded on the interface, the chains stretch out to avoid neighboring chains. The resulting physical state has properties markedly different from polymer solutions, gels, or weakly adsorbed polymer layers. When the chains are strongly stretched, their statistical mechanics become simpler, as fluctuations around the set of most probable conformations are suppressed. This makes possible many pencil-and-paper calculations of brush properties, including bending and compressional moduli, and detailed knowledge of the chain conformations. As a recent example, I will describe calculations of phase diagrams of strongly segregated block copolymers including bicontinuous double-diamond phases. © 1994 John Wiley & Sons, Inc.     

Oligo(ethylene glycol) containing polymer brushes as bioselective surfaces

The nitroxide-mediated polymerization of styrenic monomers containing oligo(ethylene glycol) (OEGn) moieties was chosen for the preparation of biocompatible polymer brushes tethered to silicon oxide surfaces due to the broad range of monomer structures available and the use of a nonmetallic initiator. These surfaces were characterized by near-edge X-ray absorption fine structure and water contact angle measurements. The biocompatibility of these grown polymer brushes was studied and compared with deposited assemblies of surface-bound OEGn-terminated silanes with selected chain lengths. Grown polymer brushes with short OEGn side chains suppressed protein adsorption significantly more than the deposited assemblies of short OEGn chains, and this was attributed to higher surface coverage by the brushes. Cell adhesion studies confirmed that OEGn-containing polymer brushes are particularly effective in preventing nonspecific adhesion. Studies of protein adsorption and cell localization carried out with specific ligands on surfaces patterned demonstrated the potential of these surface-tethered polymer brushes for the formation of micro- and nanoscale devices.     

Control of surface properties using fluorinated polymer brushes produced by surface-initiated controlled radical polymerization

Surface-grafted styrene-based homopolymer and diblock copolymer brushes bearing semifluorinated alkyl side groups were synthesized by nitroxide-mediated controlled radical polymerization on planar silicon oxide surfaces. The polymer brushes were characterized by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and time-dependent water contact angle measurements. Angle-resolved XPS studies and water contact angle measurements showed that, in the case of the diblock copolymer brushes, the second block to be added was always exposed at the polymer-air interface regardless of its surface energy. Values of z*/Rg were estimated based on the radius of gyration, Rg, of the grafted homopolymer or block copolymer chains for the grafted brushes and thickness of the brush, z*. The fact that z*/Rg > 1 suggests that all these brushes are stretched. These results support the idea that after grafting the first block onto the surface the nitroxide-end capped polymer chains were able to polymerize the second block in a "living" fashion and the stretched brush so formed was dense enough that the outermost block in all cases completely covers the surface. NEXAFS analysis showed a relationship between the surface orientation of the fluorinated side chains and brush thickness with thicker brushes having more oriented side chains. Time-dependent water contact angle measurements revealed that the orientation of the side chains of the brush improved the surface stability toward reconstruction upon prolonged exposure to water.     

Spectroscopic Investigation of Polypeptide Plane Brushes

Fourier transform infrared spectroscopy (FTIR) was used for determination of orientational and conformational characteristics of plane polypeptide brushes with different density of polypeptide chains grafted to modified silicon surface. The determination of grafting density of polypeptide chains in brushes, which depends on chemical structure of spacer groups, was carried out using ultraviolet (UV) spectroscopy. The influence of chemical structure of modifying spacer groups and outer conditions on the characteristics of plane polypeptide brushes was established. The peculiarities of α-helical structure (random coil transfer of polymer chains in brushes under the action of denaturants) were investigated.     

Correlation between conformation change of polyelectrolyte brushes and lubrication

We directly monitor the absolute separation profiles that function as film thickness between a single glass disk and the charged polyelectrolyte brushes decorated steel slider in water using a home-made slider-on-disk apparatus, which reflects the structural conformation variations and interactions of polymer brushes under externally applied pressure, in addition to probing the relative variation of friction forces under different applied loads and sliding velocities. We find that the polyelectrolyte brushes modified surfaces can sustain high pressure and have extremely low friction coefficients(around 0.006 at pressures of 0.13 MPa; 0.5-0.6 without brushes). The water-lubrication characteristics are correlated to the structural conformation changes of the polyelectrolyte brushes that are mainly governed by electrostatic interactions and the osmotic pressure of counterions inside the polymer chains, which can be used to support and distribute the normal pressure. The apparent thickness of the brush decreases with the increase of loading forces, an increase in the ionic strength causes the polymer chains collapse, and the friction forces increase. This fundamental research is of great importance to understand the mechanical and structural properties of polyelectrolyte brushes and their influences on the tribological behaviors, and helps to design friction/lubrication-controlled surface/interface by taking advantage of polyelectrolyte brushes.     

双峰聚合物分子刷的层化机理

建立了用于模拟双峰聚合物分子刷相结构的自洽场理论. 模拟结果表明, 良溶剂条件能够促使双峰聚合物分子刷裂分为内外两个亚分子层, 其中短链居于内分子层, 而长链伸展到外分子层. 体系溶解性的加强不仅使聚合物的密度分布逐渐趋近强分凝理论的解析结果, 而且加大了分子链的伸展和链段的局部取向程度. 分子链接枝密度的增加能够促使分子刷的层化, 并且在良溶剂区域, 不同接枝密度的分子链密度分布可以回归到同一条主线. 在良溶剂条件下, 长链的聚合度对短链的密度分布影响不大, 但能够导致长链向外分子层扩展.     

PS/PMMA mixed polymer brushes on the surface of clay layers: Preparation and application in polymer blends

Polystyrene (PS) and poly(methyl methacrylate) (PMMA) mixed polymer brushes on the surface of clay layers were prepared by using in situ free radical polymerization. Free radical initiator molecules with two quaternary ammonium groups at both ends were intercalated into the interlayer spacing of clay layers. The amount of polymer brushes grafted on the surface of clay layers can be controlled by controlling the polymerization time. Thermogravimetric analysis, X‐ray diffraction, and high‐resolution transmission electron microscope results indicated successful preparation of the mixed polymer brushes on the surface of clay layers. The kinetics of the grafting of the monomers was also studied. The mixed polymer brushes on the surface of clay layers were used as compatibilizers in blends of PS and PMMA. In the blends, the intercalated clay particles tend to locate at the interface of two phases reducing the interfacial tension. In the meanwhile, PMMA homopolymer chains tend to intercalate into clay layers. The driving force for the intercalation is the compatibility between homo‐PMMA chains and PMMA brushes on the surface of clay layers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5329–5338, 2007     

Optical and Morphological Characteristics of Polymer Molecular Brushes with Varied Grafting Density and Binary Bioactive Radachlorine-Containing Nanosystems Based on Them

The optical and morphological characteristics of polymer molecular brushes with the polyimide backbone and polymethacrylic acid side chains, and also of binary nanosystems based on the molecular brushes and Radachlorine®, a photosensitizer of second generation, were studied. The brushes had the same backbone and approximately equal molecular mass of side chains, but strongly differed in the side chain grafting density. The side chain grafting density influences the molecular-conformation and morphological parameters of free molecular brushes and of the corresponding binary nanosystems.