聚N-异丙基丙烯酰胺水溶液在线团-球体转变过程中的溶剂化-去溶剂化效应

聚 N-异丙基丙烯酰胺 (PNIPAM)由于每一重复结构单元上同时存在亲水和疏水基团 ,它的水溶液性质具有异常的特性 ,当溶液的温度从常温逐渐升高到 32℃左右时 ,高分子链的形态尺寸发生突变 ,即所谓线团 -球体转变 .由于 PNIPAM的这种转变过程在理论和实际上的重要性 ,它已成为近年来高分子科学研究中的一个热点[1～ 8] .前人对线团 -球体转变的理论研究都局限在高分子链的形态尺寸变化的描述上 [9～ 18] .新近的实验研究结果证明 ,从线团转变过来的球体里还含有数量不少的溶剂[19,2 0 ] .溶剂的存在与高分子链在溶液中的溶剂化作用有关 …     

高分子的折叠与聚集

总结了作者有关高分子折叠和聚集方面的工作。最初,作者研究了聚（N-异丙基丙烯酰胺）（PNIPAM）均聚物的折叠或叫做“线团-塌缩球的转变”,然后研究了含有疏水和亲水基团的PNIPAM共聚物的折叠。作者研究了疏水作用和亲水作用对折叠的影响,发现了融化球,有序线团等折叠过程中的中间态。另一方面,作者研究了两亲性高分子在水中的聚集与稳定。作者的结果表明,如果高分子链所形成的稳定聚集体为核-壳结构,则每个亲水基团所占有的面积为一个常数。如聚集体不是核-壳结构,即部分亲水基团分布在聚集体内部,则上述关系不再成立。随亲水基团含量的增加,聚集体将由球状变为超枝化结构。     

共聚N-异丙基丙烯酰胺单链微凝胶

聚 N -异丙基丙烯酰胺 (PNIPAM)的水溶液具有下临界共溶温度 LCST(约 3 2℃左右 ) ,即当体系温度高于 3 2℃时 ,高分子链的构象发生 Coil- to- Globule的变化 [1～ 3 ] ,而由 N -异丙基丙烯酰胺制备的水凝胶亦存在体积相转变 ,该转变与网络链的构象变化相关 ,文献 [1 ,4,5 ]对从大块凝胶到微米级凝胶的性质进行了研究 .本文成功地制备了聚 N -异丙基丙烯酰胺的单链微凝胶 ,与相应的线性高分子在分子量和化学组成上完全相同 ,初步研究了它们与十二烷基硫酸钠 (SDS)的混合水溶液的粘度性质 ,从而在两者之间建立了直接而明确的联系 .1…     

聚N-异丙基丙烯酰胺硅胶键合固定相的应用

采用N-异丙基丙烯酰胺制备了聚N-异丙基丙烯酰胺硅胶键合固定相。试验将聚N-异丙基丙烯酰胺硅胶键合固定相应用于碱性物质和酯类物质的分离,各组分实现了基线分离,且色谱峰形对称;并利用聚N-异丙基丙烯酰胺硅胶键合固定相,在甲醇-水(30+70)混合液为流动相,28~32℃时发生了相转变,由亲水性构象转变为疏水性构象的温敏特性,可将其用于两种极性差异较大的极性化合物分析中。     

微波法制备聚(苯乙烯-N-异丙基丙烯酰胺)热敏性微球

聚(N-异丙基丙烯酰胺)(PNIPAM),由于其大分子链上同时具有亲水性的酰氨基和疏水性的异丙基,使得PNIPAM的水溶液,在32℃附近具有最低临界溶液温度(LCST)．PNIPAM及其共聚物表现出相转变,产生热敏性质．利用PNIPAM的热敏性质,可以制备多种智能高分子材料．这些高分子材料在生物医学、免疫分析、     

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。     

DTPA-PNIPAAm的合成及热敏性研究

热敏水溶性高分子聚(N-异丙基丙烯酰胺)(PNIPAAm)在水溶液中有最低临界溶液温度(LCST).当温度在LCST附近发生变化时,PNIPAAm可发生逆相转变.基于该特性,可通过PNIPAAm将放射性治疗核素运输到病变组织通过射线杀灭病变细胞.通过4,4′-偶氮二(氰戊酸)、乙二胺、二乙三胺五乙酸酐(DTPAA)、N-异丙基丙烯酰胺合成了带DTPA端基的PNIPAAm,合成的DTPA-PNIPAAm保持了与PNIPAAm相似的LCST.本文的工作为PNIPAAm运输金属治疗核素奠定了基础.     

含pH敏感聚(4-乙烯基吡啶)的嵌段共聚物成核胶束化过程的NMR研究

利用NMR技术研究了聚乙二醇-b-聚(4-乙烯基吡啶)(PEG114-b-P4VP107)和聚(N-异丙烯基丙烯酰胺)-b-聚(4-乙烯基吡啶)(PNIPAM53-b-P4VP260)在逐步降低聚(4-乙烯基吡啶)链段质子化程度时嵌段共聚物的胶束化过程.在开始形成胶束时,吡啶环上氢原子的自旋-晶格弛豫时间(T1)急剧减小.结果表明,PEG114-b-P4VP107在质子化程度降为0.54时已有胶束生成;PNIPAM53-b-P4VP260在质子化程度降为0.58时也能观测到胶束生成的信号.将两个嵌段共聚物各自制得胶束的溶液相混合,观测到了发生在高分子链间的2DNOE信号,这表明所制得溶液中胶束与高分子链间有链交换的动态平衡.     

超声波合成温敏型聚合物——聚(N-异丙基丙烯酰胺)

以N-异丙基丙烯酰胺为单体,N,N′-亚甲基双丙烯酰胺为交联剂,THF为溶剂,采用超声辐照聚合法合成了一种温敏型聚合物——聚(N-异丙基丙烯酰胺)(1),其结构经FT-IR表征.用UV-Vis研究了1的热相转变性能.结果表明,1具有温度敏感性,其最低临界共溶温度为34℃.     

温度敏感性PNIPAM-b-PZLL-b-mPEG三嵌段共聚物的合成与自组装研究

通过大分子引发剂引发ε-苄氧羰基-L-赖氨酸-N-羧酸酐(Lys-NCA)开环聚合和大分子缩合的方法合成了聚(N-异丙基丙烯酰胺)-b-聚(ε-苄氧羰基-L-赖氨酸)-b-聚乙二醇单甲醚三嵌段共聚物(PNIPAM-b-PZLL-b-mPEG).用GPC和1H-NMR对其结构进行了表征.用芘荧光探针法证明了该三嵌段聚合物形成胶束的性质并测定了临界胶束浓度(CMC).动态光散射(DLS)研究表明,在固定PNIPAM-b-PZLL链段长度的情况下,mPEG分子量为2000时,胶束在温度高于临界溶解温度(LCST)时发生聚集,mPEG分子量为5000时,胶束在LCST以上没有发生聚集.     

Thermosensitivity of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone): Effect of transition-metal halides

The effect of the halides of a series of transition metals on the properties of aqueous solutions of poly(N-vinylpyrrolidone) is studied. It is shown that the introduction of ZnCl₂ into solutions of poly(N-vinylpyrrolidone) causes phase separation with an increase in temperature. In the presence of halides of other transition metals (CdCl₂, CuCl₂), this phenomenon is not observed. However, the addition of HCl and/or alkali-metal halides to these systems likewise gives rise to phase separation, and in the ZnCl₂-based systems, the cloud point of solution substantially decreases with the introduction of alkali-metal salts. The same situation is observed in the case of polyvinylcaprolactam. Thus, it is concluded that the observed phenomena are associated with the formation of MtCl₄²⁻ complex anions in solutions that promote the globulization of polymer chains with participation of water molecules surrounding polymer chains and cations of transition-metal salts bound to complexes with C=O groups of lactam rings of the polymers.     

Rheological properties of concentrated aqueous solutions of anionic and cationic polyelectrolyte mixtures

The rheological properties of aqueous solutions of poly(acrylic acid), poly(diallyldimethyldiammonium chloride), and their mixtures at 25°C have been studied. The concentrated solutions of the mixtures contain 18 wt % of both polymers taken at different ratios. The ratio of cationogenic and anionogenic groups φ varied from 0 to 0.4 is taken as a criterion for selection of mixture composition. An increase in φ, reflecting a more intense formation of polyelectrolyte complexes in solution, is accompanied by a significant rise in the low-frequency loss modulus and, especially, in the storage modulus, as well as by an increase in viscosity over the entire studied range of shear rates. This behavior may be explained by the presence of an additional spatial structure with junctions formed by interacting complementary charged groups. In the general case, the formation of poly(acrylic acid)-poly(diallyldimethyldiammonium chloride) polyelectrolyte complexes is said to take place in solution. The excess of rheological characteristics of mixture solutions over the corresponding characteristics of poly(acrylic acid) solutions is found to be the power function of parameter φ. The additional spatial network derived from polyelectrolyte complexes and occurring in solution is destroyed at lower shear stresses than is the network of intermolecular entanglements. At high shear stresses, orientational effects may cause phase separation of the systems owing to a change in the hydrophilic-hydrophobic balance between complexes of poly(acrylic acid) with poly(diallyldimethyldiammonium chloride) and water.     

FT-IR and 2D-IR spectroscopic studies on the effect of ions on the phase separation behavior of PVME aqueous solution.

Thermosensitive phase transition behavior of poly(vinyl methyl ether) (PVME) in an aqueous solution and the effect of inorganic ions on the coil-globule transition have been investigated by Fourier transform infrared (FT-IR) spectroscopy with attenuated total reflection (ATR) accessory. ATR-IR spectra of PVME aqueous solution indicate that in water-PVME-inorganic salts system, the phase separation temperature of PVME aqueous solution decreased with the increase of ion concentration and the increase of anion electronegativity. Meanwhile, two-dimensional infrared (2D-IR) measurements have been made to clarify the microcosmic conformational changes of PVME during the coil-globule transition. Results show that the conformation changes of main chains occur earlier than those of ether groups during heating. Furthermore, the 2D correlation spectroscopy of PVME aqueous solution during heating and the increase of concentration of potassium chloride have been studied. The features of 2D-IR spectra during heating did not change compared to the features of PVME aqueous solution during the increase of concentration of potassium chloride. This result implies that, although the addition of inorganic ions shifts the phase separation temperature, it does not alter the internal mechanism of the coil-globule transition of PVME.     

Phase separation dynamics of aqueous solutions of thermoresponsive polymers studied by a laser T-jump technique

Poly(N-isopropylacrylamide) and poly(vinyl methyl ether) are well-known thermoresponsive polymers. The aqueous solutions of these polymers exhibit a phase transition followed by phase separation with LCST approximately 305-310 K. In the present study, the dynamic behavior of the phase separation was analyzed by a laser T-jump method. Two different T-jump methodologies were employed: the first was a dye-photosensitized T-jump technique (indirect heating) using 532 nm laser pulses, while the other was a direct heating T-jump technique using 1.2 mum laser pulses. Both methods gave similar results. The time constants (tau) of the phase separation were systematically determined for 1-10 wt % aqueous solutions of the polymers, and a hydrodynamic radius (R) dependence for tau was clearly observed. The values of tau increased linearly with increasing square of R. The present behavior is interpretable in the framework of Tanaka's model for the volume phase transition of a gel, since each of the polymer chains are entangled in the present sample solutions, which can be regarded as approximating to a gel in solution.     

Associative and segregative phase separations of poly(N-tert-butylacrylamide)/poly(acrylic acid) mixtures. Effect of solvent

Poly(N-tert-butylacrylamide) (PNtBAm) and poly(acrylic acid) (PAA) form interpolymer complexes in 1- and 2-propanol, blend in ethanol, whereas a segregative phase separation is observed when using methanol as solvent as shown by Fourier transform infrared (FTIR) spectrometry and elemental analysis studies. The composition of PNtBAm/PAA complexes has been determined. Thermal studies demonstrated that all complexes show unique glass transition temperatures, higher than those of the polymer components. Complexation of PAA with PNtBAm results in an improvement of its thermal stability. Solvent effects and specific interactions in the system PNtBAm/PAA have been studied by FTIR, revealing that differences in the polymer–solvent interactions are a decisive factor governing complex formation in solution.     

Untersuchungen zur Trennung der Pt-Metalle Durch Mehrstufige Extraktion mit Tributylphosphat aus Salzsaurer Lösung

The separation of compounds of Rh, Pd, Ir and Pt by multistage batch liquid-liquid extraction with tributyl phosphate (TBP) from hydrochloric acid solution has been studied. The existence of complexes of the same platinum group metal, which are capable of being extracted to different degrees, has been concluded from the variation of the distribution coefficient of the respective platinum group metals with the stage number. In addition to monomeric chlorocomplexes, metastable inert species (presumably polymeric chloroaquo or aquo/oxo complexes) were found, which were not formed during the extraction, but had been present already in the initial solutions. Because the solvent TBP does not enter the internal coordination sphere, the separation effect attainable is determined by the extraction behaviour and the content of these complex types in the initial solutions. This fact explains the strong influence of solution preparation on the separation effect.      

Unusual phase behavior in mixtures of poly(ethylene oxide) and ethyl alcohol

Poly(ethylene oxide) (PEO), soluble in both aqueous and organic solvents, is one of the most intriguing polymers. PEO solution properties have been extensively studied for decades; however, many of the studies have focused on specific properties, such as clustering, of PEO in aqueous solutions, and the behavior of PEO in organic solvents has not been adequately explored. The results presented here demonstrate that PEO crystallizes into a lamellar structure in ethyl alcohol after the mixture is quenched to room temperature from a temperature above the crystal melting point. Above the melting temperature, PEO completely dissolves in ethyl alcohol, and the mixture exhibits regular polymer solution thermodynamic behavior with an upper critical solution temperature (UCST) phase diagram. Remarkably, the UCST phase boundary is significantly below the melting temperature, and this indicates that the system undergoes a crystallization process before the phase separation can occur upon cooling and, therefore, possesses an unusual phase transition. The phase transition from the crystalline state to the miscible solution state is reversible upon heating or cooling and can be induced by the addition of a small amount of water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 557–564, 2006     

Microphase separation of cationic poly(N-isopropylacrylamide) copolymers in water: Effect of the migration of charges

The structures of aqueous copolymer solutions have been examined through small angle neutron scattering. The copolymers contained mostly N-isopropylacrylamide (NIPAM) monomers. Poly (NIPAM) solutions have a lower critical solution temperature (LCST), above which the macromolecules separate from water. A small fraction of ionizable N,N-[(dimethylamino) propyl] methacrylamide (MADAP) monomers was introduced into the macromolecules. This had dramatic consequences on the solution behavior at temperatures above the LCST of PNIPAM, where phase separation would have been expected for the homopolymer. When all MADAP monomers were ionized, it was found that the solutions resisted the phase separation. At short spatial scales, the chains were collapsed but at large scales they formed branched aggregates that did not separate out of water. When only half of the MADAP monomers are ionized, the electrical charges were able to redistribute themselves along the chains. In this case, the rise in temperature caused a microphase separation where the electrical charges were relocated on a fraction of the chains that remained in solution.The other chains (or section of chains) formed large nodules of a polymer rich phase.     

Extraction of actinides in two-phase water-poly(ethylene glycol)—Salt systems in the presence of potassium phosphotungstate

Extraction of actinides has been examined in two-phase aqueous systems based on poly(ethylene glycol) (PEG) from sulfate solutions in the presence of potassium phosphotungstate, which forms strong complexes with ions of tri- and tetravalent transuranium elements. Extraction of these complexes by aqueous PEG solution is complete in contrast to that of penta- and hexavalent actinides. Conditions have been chosen for the separation of actinides in different oxidation states.