Synthesis and Characterization of Thermo-responsive Poly(N-vinyl-2-pyrrolidinone)-block-poly(N-isopropylacrylamide) Micelles

A novel thermo-responsive diblock copolymer of poly(N-vinyl-2-pyrrolidinone)-block-poly(N-isopropylacrylamide) (PNVP-b-PNIPAM) was synthesized. FT-IR, ¹H-NMR and SEC results confirmed the successful synthesis of PNVP-b-PNIPAM diblock copolymer via anionic polymerization. The polymeric micelles formed from PNVP-b-PNIPAM copolymer in aqueous solution were developed and characterized as a potential thermo-responsive and biocompatible drug delivery system. Micellization of the diblock copolymer in aqueous solution was characterized by dynamic laser scattering (DLS), turbidity measurement, tension measurement and transmission electron microscopy (TEM). The thermo-responsive polymeric micelles with the size ranges of 200 to 260 nm and thickness of 30 nm are localized, selected and targeted for drug release, having a great potential in response to external-stimulus such as temperatures from 35 to 39°C. The critical micellization concentration (cmc) of PNVP-b-PNIPAM in aqueous solution is 0.0026 wt% determined by turbidity measurement. The size of micelles determined by DLS increased from 163 to 329 nm with increasing concentration of PNVP-b-PNIPAM from 0.25 to 0.5 wt% in aqueous solution at 40°C, which is determined by DLS.     

Mechanically Strong Janus Poly(N-isopropylacrylamide)/Graphene Oxide Hydrogels as Thermo-responsive Soft Robots

Simple preparation of stimuli-responsive hydrogels with good mechanical properties and mild stimuliresponsiveness is essential for their applications as smart soft robots.Mechanically strong Janus poly(Nisopropylacrylamide)/graphene oxide (PNIPAM/GO) nanocomposite hydrogels with stimuli-responsive bending behaviors are prepared through a simple one-step method by using molds made of a Teflon plate and a glass plate.Residual oxygen in the air bubbles on the Teflon plate surface affects the polymerization and hence the cross-linking density,leading to the different swelling/deswelling rates of the two sides of the gels.Therefore,the hydrogels exhibit bending/unbending behaviors upon heating/cooling in water.The incorporation of GO nanosheets dramatically enhances the mechanical properties of Janus hydrogels.Meanwhile,the photo-responsive property of the GO nanosheets also imparts the hydrogels with remotecontrollable deformation under IR irradiation.The application of the Janus PNIPAM/GO hydrogels as thermo-responsive grippers is demonstrated.     

激光光散射表征聚N－异丙基丙烯酰胺的分子量分布

采用自由基聚合法合成了聚N-异丙基丙烯酰胺(PNIPAAM)样品,由激光光散射法(LLS),包括绝对累积散射光强的角度依赖性(静态LLS)和线宽分布的角度依赖性(动态LLS)表征了合成的PNIPAAM样品的分子量分布。通过对动态光散射测得的电场-电场时间相关函数的拉普拉斯变换,求得平动扩散系数分布G(D);结合静态和动态光散射测量的结果,即M_w和G(D),确定了PNIPAAM样品的平动扩散系数D对分子量M的标定关系式D=2.84×10^-4M^-0.55,并将G(D)转换成分子量分布F_w(M).     

PNIPA和PDEA在水-甲醇混合溶剂中性质的研究

分别研究了聚N-异丙基丙烯酰胺（PNIPA）和聚N,N-二乙基丙烯酰胺（PDEA）在水-甲醇混合溶剂中的溶液性质.结果表明,在PDEA和PNIPA体系中均存在水和甲醇分子之间的复合.由于PDEA比PNIPA的亲脂性强,在水-甲醇混合溶剂中,水与甲醇分子形成的复合物对PDEA和PNIPA的溶剂化作用不同,导致随着体系中甲醇体积分数（φ）的增大,PNIPA体系的低临界溶解温度（TLCS）发生了再进入相转变,而PDEA体系的TLCS则逐渐升高.     

Preparation of Hollow Silica Microspheres via Poly(N-isopropylacrylamide)

Core-shell structured SiO₂/poly(N-isopropylacrylamide) (SiO₂/PNIPAM) microspheres were successfully fabricated through hydrolysis and condensation reaction of tertraethyl or-thosilicate (TEOS) on the surface of PNIPAM template at 50 oC. The PNIPAM template can be easily removed by water at room temperature so that SiO₂ hollow microspheres were finally obtained. The transmission electron microscope and scanning electron microscope observations indicated that SiO₂ hollow microspheres with an average diameter of 150 nm can be formed only if there are enough concentration of PNIPAM and TEOS, and the hy-drolysis time of TEOS. FTIR analysis showed that part of PNIPAM remained on the wall of SiO₂ because of the strong interaction between PNIPAM and silica. This work provides a clean and efficient way to prepare hollow microspheres.     

聚-N-异丙基丙烯酰胺的制备及应用进展

聚(N-异丙基丙烯酰胺)(PNIPAM)是一种温敏性高分子聚合物,在最低临界溶解温度(LCST)处会发生构象转变。对PNIPAM加以改性,可拓宽温敏性聚合物材料的研究领域,使其在药物负载运输、基因传递、化学分析和表面浸润性等领域发挥更大的应用价值。本文对PNIPAM的活性自由基聚合方法及其应用进展进行了综述,并展望了其发展前景。     

乙基纤维素接枝聚N-异丙基丙烯酰胺共聚物合成及其胶束化研究

通过单电子转移“活性”/可控自由基聚合的方法制备了具有双亲性及温度响应性的乙基纤维素接枝聚N-异丙基丙烯酰胺共聚物(EC-g-PNIPAm). 通过凝胶渗透色谱、核磁氢谱和红外光谱等对合成的接枝共聚物进行了表征. 我们发现此反应在混合溶剂四氢呋喃/甲醇的混合溶剂中是活性可控的. EC-g-PNIPAm接枝共聚物能够在选择性溶剂水中发生自组装现象, 形成稳定的以乙基纤维素为核、聚N-异丙基丙烯酰胺为壳的球形胶束. 并且随着温度的升高, 支链聚N-异丙基丙烯酰胺发生塌缩使得球形胶束发生收缩.     

Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide) synthesized by ATRP

Novel Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide),PEG-b-(PNIPAM)_2,were successfully synthesized through atom transfer radical polymerization(ATRP).A difunctional macroinitiator was prepared by esterification of 2,2-dichloroacetyl chloride with poly(ethylene glycol) monomethyl ether(PEG).The copolymers were obtained via the ATRP of N-isopropylacrylamide(NIPAM) at 30℃with CuCl/Me_6TREN as a catalyst system and DMF/H_2O(v/v = 3:1) mixture as solvent.The resulting copo...     

聚(N-异丙基丙烯酰胺)类材料的应用

聚(N-异丙基丙烯酰胺)(PNIPAAm)及其共聚物,在水溶液中表现出最低临界溶液温度(LCST),在LCST附近会发生可逆相转变。利用这种特性,可将热敏性高分子材料应用于生物医学工程、免疫分析、催化、分离提纯等领域。主要综述了热敏性PNIPAAm类高分子材料,在这些领域中的应用情况。     

Synthesis of thermoresponsive polystyrene-based comb-type grafted poly(N-isopropylacrylamide)

Narrowly distributed polystyrene-g-p(N-isopropylacrylamide) (PSt-g-PNIPAM) was prepared by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide using the brominated polystyrene as macroinitiator and CuCl combined with hexamethyltriethylenetetramine as catalyst. Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy confirmed the structure of PSt-g-PNIPAM. The gel permeation chromatography (GPC) showed that the graft copoly- mer had a single distribution peak with molecular weight, Mn (g/mol) of 19815 g/mol (using polystyrene as the standard). Differential scanning calorimetry (DSC) revealed that due to both effects of hydro- phobic isopropyl groups and hydrogen bonds in the amide group, the glass transition temperature (Tg) of PSt-g-PNIPAM enhanced 16.0 ℃ compared to the Tg of the polystyrene.     

交联聚(N-异丙基丙烯酰胺)/(海藻酸钠/聚(N-异丙基丙烯酰胺))半互穿网络水凝胶的制备及其溶胀性能

将线性聚(N-异丙基丙烯酰胺)(PNIPAAm)和海藻酸钠(SA)分子同时引入到PNIPAAm凝胶中,制备了交联聚(N-异丙基丙烯酰胺)/(海藻酸钠/聚(N-异丙基丙烯酰胺))半互穿网络(Cr-PNIPAAm/(SA/PNIPAAm)semi-IPN)水凝胶。在弱碱性条件下(pH=7.4),改变SA与线性PNIPAAm的质量比对Cr-PNIPAAm/(SA/PNIPAAm)semi-IPN水凝胶的溶胀度没有太大的影响。在酸性条件下(pH=1.0),其溶胀度随着SA与线性PNIPAAm质量比的减小而增大。由于亲水性SA与线性PNIPAAm的协同作用,Cr-PNIPAAm/(SA/PNIPAAm)semi-IPN水凝胶的消溶胀速率得到很大提高。     

Concentration of Whey Proteins by Using Temperature-Sensitive Polymer Gel Poly(N-isopropylacrylamide)

Summary: In this work, the use of a temperature-sensitive polymer gel, poly(N-isopropylacrylamide), for the concentration of whey proteins was studied. The studied variables were: gel mass/solution volume ratio and concentration temperature. The concentration percentage and the selectivity were determined. The gel 20 × 5 (20% w/w total monomer/solution and 5% w/w crosslinking agent/total monomer), contacted with whey proteins solutions, at 5 °C and at 20 °C, was capable of concentrating the solution, in protein, from 10 to 33%, depending on the gel mass/solution volume ratio. The separation efficiencies, for the different studied systems, varied from around 40 to 80%. The results were discussed in the context of gels thermodynamics and through correlations between synthesis parameters and structure of the obtained gels. The obtained results for the concentration of whey proteins solutions, by using temperature-sensitive polymer gel, poly(N-isopropylacrylamide), showed that the Gel Process can indeed be used as an advantageous alternative for such separation, either from an economic or from an environmental view point.     

相转变温度范围窄的聚(N-异丙基丙烯酰胺)温敏性微凝胶

采用间歇式、半间歇式和连续式无皂乳液聚合(SFEP)法合成温敏性聚(N-异丙基丙烯酰胺)(PNIPAM)微凝胶。连续式或半间歇式SFEP法合成的PNIPAM微凝胶相转变温度范围明显地比间歇式SFEP法合成的窄,其中又以连续式SFEP法的效果最明显。相同交联剂用量的情况下,连续式SFEP法合成的PNIPAM微凝胶的粒径和溶胀比最大,而间歇式SFEP法合成的最小。通过研究微凝胶合成过程中溶胀比随反应时间的变化关系,证明了连续式或半间歇式SFEP法合成的PNIPAM微凝胶具有比较均匀的内部交联结构。     

Poly(N-isopropylacrylamide)-based thermo-responsive surfaces with controllable cell adhesion

Poly(N-isopropylacrylamide) (PNIPAAm)-based thermo-responsive surfaces can switch their wettability (from wettable to non-wettable) and adhesion (from sticky to non-sticky) according to external temperature changes. These smart surfaces with switchable interfacial properties are playing increasingly important roles in a diverse range of biomedical applications; these controlling cell-adhesion behavior has shown great potential for tissue engineering and disease diagnostics. Herein we reviewed the recent progress of research on PNIPAAm-based thermo-responsive surfaces that can dynamically control cell adhesion behavior. The underlying response mechanisms and influencing factors for PNIPAAm-based surfaces to control cell adhesion are described first. Then, PNIPAAm-modified two-dimensional flat surfaces for cell-sheet engineering and PNIPAAm-modified three-dimensional nanostructured surfaces for diagnostics are summarized. We also provide a future perspective for the development of stimuli-responsive surfaces.     

聚N-异丙基丙烯酰胺接枝聚苯乙烯高分子刷的构象

当长链高分子高密度接枝到一个表面上时,由于分子链间的相互作用使得接枝的高分子链扩张而形成伸直链的构象,这种形态被称为高分子刷.     

仿生各向异性聚(N-异丙基丙烯酰胺)水凝胶智能响应驱动器的研究进展

各向异性水凝胶在外界的响应刺激下可以具有不同的反应机制与驱动过程.本文综述了近期基于PNIPAM水凝胶智能响应驱动器的设计方法,总结了多种各向异性结构对驱动性能的影响,并对该领域所面临的挑战进行了讨论.     

温敏性纤维素/聚N-异丙基丙烯酰胺复合水凝胶的固体核磁共振表征及动力学研究

利用半互穿网络方法将具有温度响应的高分子聚N-异丙基丙烯酰胺(PNIPAM)与天然纤维素复合得到温敏性水凝胶. 通过固体核磁共振的 ¹H, ¹³C CP/MAS(交叉极化/魔角旋转)和QCP(定量交叉极化)等实验手段对复合凝胶的结构进行了定性及定量研究, 并利用固体静态变温核磁共振实验和偶极滤波-自旋扩散实验研究了复合凝胶中PNIPAM分子链段的动力学行为.     

Effect of urea on the conformational behavior of poly(N-isopropylacrylamide)

The effect of urea on the conformational behavior of poly(N-isopropylacrylamide) (PNIPAM) in dilute aqueous solution has been investigated using fluorescence spectroscopy, fluorescence quenching and fluorescence anisotropy measurements via pyrene (Py) probe and acenaphthylene (ACE) label studies. It was demonstrated that urea promotes the partitioning of the hydrophobic probe, Py, towards the bulk aqueous phase at temperatures above the lower critical solution temperature (LCST) of the polymer due to swelling of the compact coil conformation. However, the compact coil structure of the polymer at temperatures greater than its LCST is not completely destroyed, even for urea concentrations up to 3 M, at which the phase transition is hardly observed. As expected, urea has little effect on the conformational behavior of PNIPAM at temperatures below its LCST. Received: 9 February 2000/Accepted: 13 June 2000     

端炔基对水溶液中聚(N-异丙基丙烯酰胺)相转变的影响

通过原子转移自由基聚合,制备出低分子量、窄分布、端炔基的线形聚(N-异丙基丙烯酰胺)(alkynylPNIPAM),利用高灵敏示差扫描微量热技术,在升—降温循环过程中确定端炔基对alkynyl-PNIPAM相转变行为的影响.结果显示,随循环次数增加,升温热容曲线明显变宽,降温热容曲线由双峰逐渐变为单峰;升温和降温的相转变温度有逐渐降低的趋势,但焓变的变化很小.聚合物的低的分子量使端基效应不可忽视,alkynylPNIPAM的端炔基可诱导分子链聚集,形成小的端基聚集体,由于这些聚集体中链内和链间氢键作用,链构象调整变得困难,导致PNIPAM链在升温时更易塌缩、降温时更难解离.     

Total Internal Reflection Ellipsometry under SPR Conditions: In-Situ Monitoring of the Growth of Poly(N-isopropylacrylamide) (PNIPAAm) Brushes

Total internal reflection ellipsometry (TIRE) under surface plasmon resonance (SPR) conditions represents a powerful characterization technique combining the conveniences of spectroscopic ellipsometry with SPR. Besides the very high sensitivity to small changes in the optical constants (up to 10 times more sensitive than conventional ellipsometry), the possibility to investigate media of different optical densities or even opaque media makes this analytical method very convenient for different sensing applications. This article presents an example of application of TIRE under SPR conditions for the continuously in-situ monitoring of the growth of covalently tethered poly(N-isopropylacrylamide) (PNIPAAm) chains on a gold surface.