2,3-二氢-2-苯基咪唑[2,1-b]苯并噻唑的合成研究

以2-氯苯并噻唑为原料,在N,N-二异丙基乙基胺存在下与D或L-苯甘氨醇反应后,不经分离直接与甲磺酰氯在N,N-二异丙基乙基胺作用下关环,一锅法合成了(R)或(S)-2,3-二氢-2-苯基咪唑[2,1-b]苯并噻唑,利用IR、~1HNMR、MS谱和旋光度对其结构进行了表征.通过优化研究2,3-二氢-2-苯基咪唑[2,1-b]苯并噻唑的合成工艺条件,可得到总收率为80%的(R)或(S)-2,3-二氢-2-苯基咪唑[2,1-b]苯并噻唑.     

温敏性萃取水凝胶对生物大分子的分离

合成了均聚的聚N 异丙基丙烯酰胺(PNIPAM)水凝胶以及N 异丙基丙烯酰胺与丙烯酰胺共聚的〔P(NIPAM-AM)〕水凝胶,并研究了它们的溶胀性能及其对生物大分子的萃取分离性能。结果表明,两种温敏凝胶具有很好的溶胀性能,其低临界共溶温度(LCST)分别为30 4和31 0℃,它们对蛋白质和酶的分离效率在LCST附近发生突跃,如PNIPAM水凝胶对白蛋白的分离效率在LCST前后从96 2%降至59 8%。当交联剂N,N 次甲基双丙烯酰胺(Bis)的质量分数w(Bis)>4%时,分离效率大于90%(LCST以下)。     

PAA/PNIPAAm互穿网络水凝胶的微波合成与性能研究

以微波为辐射源,对丙烯酸(AA)水溶液进行辐照制得了PAA水凝胶。将脱水后的PAA水凝胶浸泡于含引发剂过硫酸钾(K_2S_2O_8)和交联剂N,N’-亚甲基双丙烯酰胺(BIS)的N-异丙基丙烯酰胺(NIPAAm)水溶液中,待溶胀平衡后取出,进行第二次微波辐照反应,制备了聚丙烯酸/聚N-异丙基丙烯酰胺互穿聚合物网络(PAA/PNIPAAm IPN)水凝胶,并对其溶胀性能进行了研究。研究结果表明,合成的IPN水凝胶兼具pH敏感性和温度敏感性,有望在药物控制释放领域得到应用。     

NIPA系温敏凝胶的制备及应用研究进展

N-异丙基丙烯酰胺(NIPA)同时具有亲水性的酰胺基和疏水性的异丙基,使其系列聚合物具有优良的温敏智能特性和记忆效应,已在药物缓释、物料分离、酶的固定、生物医学材料等领域得到广泛应用.综述了NIPA系温敏凝胶的制备方法及应用方面的研究进展,并提出了未来的发展方向.     

RAFT法制备窄分布温敏性PNIPAAm

以N,N-二甲基甲酰胺(DMF)为反应介质,偶氮二异丁氰(AIBN)、三硫代碳酸二(α,α′-二甲基-α-乙酸)酯(BDATC)作为链转移剂,使N-异丙基丙烯酰胺(NIPAAm)进行可逆加成—断裂链转移自由基(RAFT)聚合,考察了引发剂(I)与链转移剂(CAT)的浓度比对NIPAAm的RAFT反应结果的影响。结果表明:70℃下,当[CAT]0/[I]0介于20:1～5:1,均可得到分子量分布窄、分子量可控的PNIPAAm,说明其聚合过程符合活性聚合反应的特征。     

NIPAAM共聚物的合成与应用研究进展

N-异丙基丙烯酰胺(NIPAAM)由于具有独特的温敏性能,其共聚物作为一种智能材料被广泛应用。综述了NIPAAM的温敏机理和系列NIPAAM共聚物的合成方法,对其在药物运输、物料分离、细胞附着脱附和色谱分析等领域的应用进行了介绍,并简要评述了NIPAAM共聚物的研究开发前景。     

温度对温敏性固定化酶的相对活力影响研究

以N 异丙基丙烯酰胺 (PNIPAM)均聚凝胶和N 异丙基丙烯酰胺与丙烯酰胺 [P(NIPAM -AM) ]共聚凝胶为载体制备了四种温敏性固定化酶。其相对活力 (f)随温度的升高而降低 ,在凝胶低临界溶解温度LCST(32 0℃ )附近骤降 (均聚枯草杆菌蛋白酶的f在 32 0℃前后由 86 2 %降至 18 8% ) ,即高温下 (LCST以上 )酶从凝胶中释放出来 ,说明温敏性凝胶可用作生物固定化催化剂的功能性载体。     

紫外光辐射接枝及胺化法制备温敏性聚乙烯薄膜

实验探索在水性体系中经紫外光辐射,引发丙烯酸(AAC)在聚乙烯(PE)薄膜表面接枝,并经过胺化反应,在已改性的丙烯酸-聚乙烯(AAC-g-PE)薄膜上继续引入功能团,使改性后的PE薄膜具有温度敏感性。考察了引发剂用量、紫外光照射时间对接枝率的影响,并对不同胺化剂合成产物的温敏效应进行比较,从而达到实验目的。通过红外光谱和尺寸变化率证明丙烯酸接枝在PE表面,胺化反应后,生成聚N-异丙基丙烯酰胺聚合聚乙烯(PNIAAm-g-PE)薄膜和聚N-正丙基丙烯酰胺聚乙烯(NNPA-g-PE)薄膜具有温敏性。     

表面强化交联聚(N-异丙基丙烯酰胺) 水凝胶的温敏和浓缩分离性能

为了提高聚(N-异丙基丙烯酰胺)(PNIPA)凝胶粒子的浓缩分离效果,以过硫酸铵/N,N,N,N,-四甲基乙二胺为引发体系,N,N′-亚甲基双丙烯酰胺(BIS)和二乙烯苯(DVB)为复合交联剂,通过反相悬浮聚合合成了表面强化交联的PNIPA凝胶粒子.考察了凝胶颗粒形态、温敏特性及其浓缩分离聚乙二醇/水性能.发现得到的凝胶为紧密珠状粒子,低临界溶解温度为32℃;随着溶质聚乙二醇相对分子质量增大或浓度减小,凝胶对聚乙二醇/水的分离效率提高;增加合成PNIPA凝胶时的BIS用量,可提高凝胶对聚乙二醇/水的分离效率,但溶胀率显著下降;增加DVB用量,分离效率大幅提高,而凝胶溶胀率基本不变.     

含β-环糊精单元温敏性聚合物的制备及其温敏性能测试

文章通过N-异丙基丙烯酰胺(NIPAAm)同马来酸酐(MAH)改性的β-环糊精发生共聚反应得到一种新型温敏性共聚物,表征确认其结构,并对其温敏性能进行了研究。结果:由于环糊精单元的引入,产品较NIPAAm均聚物有更高的最低临界共溶温度(LCST),环糊精单元在产品中所占的比例越多,其LCST值越大,并且在高pH和低离子浓度环境下,产品有更高的LCST。     

Solution thermal properties of a family of thermo-responsive N-isopropyl acrylamide-co-N-hydroxymethyl acrylamide copolymers - Aspects intrinsic to the polymers

A family of (N-isopropyl acrylamide-co-N-hydroxymethyl acrylamide) copolymers, p(NIPAAm-co-HMAAm), was synthesised and characterised with respect to solution thermal behaviour. A notable increase in cloud point (CP) was observed as the concentration of the polymer solutions was lowered, though the effect of concentration on CP of pure p(NIPAAm), was relatively small. In all cases, the elevation of CP was most evident at low concentration between 0.1 wt.% and 0.01 wt.%. Both at fixed and decreasing concentrations of p(NIPAAm) solutions, a direct relationship between molecular weight and CP was observed, where CP shifted to higher temperatures as the molecular weight increased. The polymer coil size in solution below the CP in the concentration range studied was between 4 and 11 nm for all the polymers in this study, irrespective of the concentration and of the fraction of hydroxy monomer incorporated, but increased dramatically above the CP. CPs obtained by Dynamic Light Scattering (DLS) were lower than those obtained by UV absorbance as the latter is less sensitive. Copolymer compositions with more than 13% hydroxy monomer showed no thermal hysteresis, in contrast to pure p(NIPAAm). The rate of heating/cooling had almost no effect on the CP values recorded.     

Characterization and caffeine release properties of N‐isopropylacrylamide/hydroxypropyl methacrylate copolymer hydrogel synthesized by gamma radiation

Research efforts have been devoted to demonstrate that the temperature sensitivity characters of poly(N‐isopropylacrylamide)(PNIPAAm) can be applied in the field of drug carriers. A copolymer hydrogel of N‐isopropylacrylamide/hydroxypropyl methacrylate (NIPAAm/HPMA) was synthesized by gamma irradiation. The nature of bonding was characterized by FTIR spectroscopy, whereas the thermal stability was characterized by thermogravimetric analysis (TGA). The influence of NIPAAm/HPMA composition on the swelling properties in water, at different temperatures and different pH values was studied. The release characters of caffeine drug from NIPAAm/HPMA hydrogels were also investigated. The gel fraction of NIPAAm/HPMA was found to increase slightly by increasing the ratio of HPMA in the initial solution. The IR spectra indicate the formation of copolymer hydrogels, whereas the TGA study showed that the NIPAAm/HPMA copolymer hydrogels displayed higher thermal stability than NIPAAm hydrogel. PNIPAAm hydrogel showed higher swelling in water than NIPAAm/HPMA hydrogels. Based on Fick's law, it was demonstrated that the diffusion of water into NIPAAm/HPMA is controlled. It was found that the main parameters affecting the drug release behavior from the hydrogels are composition and pH. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of dual responsive graft copolymers composed of casein and poly(N-isopropylacrylamide)

A series of novel temperature- and pH- responsive water-soluble graft copolymers, casein-g-poly(N-isopropylacrylamide)(PNIPAAm), were prepared via a direct graft copolymerization of N-Isopropylacrylamide (NIPAAm) from casein. The polymerization was induced by tert-butyl hydroperoxide (TBHP) in water at general condition. Chemical structures of the graft copolymers were characterized by Fourier transform infrared spectra (FTIR), Thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect elements on graft copolymerization, such as concentration of initiator, reaction time, reaction temperature and ratio of NIPAAm to casein were investigated in terms of NIPAAm conversion, grafting percentage (GP) and grafting efficiency (GE), respectively. The graft copolymers are stimuli-sensitive with respect to both temperature and pH in aqueous solutions. It could self-assembly into core-shell particles in aqueous solution with collapsed PNIPAAm as core as well as inverse core-hair particles with expanded casein as core on changing temperature or pH, as indicated by transmission electron microscopy (TEM).     

Physical properties of poly(vinyl chloride)–grafted N‐isopropylacrylamide graft copolymers and corresponding polyblends

The physical properties of poly(vinyl chloride) (PVC) and poly(N‐isopropylacrylamide) [poly(NIPAAm)] blend systems, and their corresponding graft copolymers such as PVC‐g‐NIPAAm, were investigated in this work. The compatible range for PVC–poly(NIPAAm) blend systems is less than 15 wt % poly(NIPAAm). The water absorbencies for the grafted films increase with increase in graft percentage. The water absorbencies for the blend systems increase with increase in poly(NIPAAm) content within the compatible range for the blends, but the absorbencies decrease when the amount of poly(NIPAAm) is more than the compatible range in the blend system. The tensile strengths for the graft copolymers are larger than the corresponding blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 170–178, 2000     

Environmentally sensitive hydrogels: N‐isopropyl acrylamide/Acrylamide/ Mono‐, Di‐, Tricarboxylic acid crosslinked polymers

Environmentally sensitive hydrogels responsive to various stimuli such as temperature, pH, ionic strength of the medium and the solvent were prepared by using N‐isopropyl acrylamide (NIPAM), acrylamide (AAm) and monomers that have various number of carboxylic acid (XA) functionality using N,N′‐methylene bisacrylamide (Bis) as crosslinker. Hydrogels were prepared via free radical polymerization reaction in aqueous solution. P(NIPAAm‐co‐AAm) and p(NIPAAm‐co‐AAm)/XA hydrogels that contain monoprotic crotonic acid (CA) exhibit a lover critical solution temperature (LCST) at 28°C, whereas p(NIPAAm‐co‐AAm)/IA (IA:itaconic acid), and P(NIPAAm‐co‐AAm)/ACA (ACA:acotonic acid) hydrogels exhibit a lover critical solution temperature at 30.7°C and 34.4°C, respectively. Spectroscopic and thermal analyses were performed for the structural and thermal characterizations of the prepared hydrogel. The swelling experiments as equilibrium swelling percentages by gravimetrically were carried out in different solvents, at different solutions temperature, pH, and ionic strengths to determine their effects on swelling characteristic of hydrogels. POLYM. ENG. SCI., 55:843–851, 2015. © 2014 Society of Plastics Engineers     

A study of hydrogel thermal-dynamics using Fourier transform infrared spectrometer

A rapid and reliable method was presented for studying hydrogel dynamics/kinetics. Two temperature-sensitive hydrogels, poly-N-isopropylacrylamide (poly(NIPAAm)) and the copolymer of N,N-diethylacrylamide and sodium methacrylate (molar ratio=97:3, poly(NDEAAm-co-MAA)) were synthesized. The thermal-behaviors of the gels were studied through the absorbance intensities of both swollen water and gel frame components, and the peak positions of amide band along heating/cooling pathways under dynamic Fourier transform infrared (FTIR) probing. The results showed that the lower critical solution temperature (LCST) of poly(NIPAAm) is about 33-35 °C, which is consistent with reported value of ∼34 °C. Compared to poly(NIPAAm), poly(NDEAAm-co-MAA) has relatively continuous volume phase transition, starting at ∼35 °C and a better thermal-reversibility with similar swelling and deswelling profiles over a larger temperature range (10-80 °C for poly(NDEAAm-co-MAA) vs. 10-33 °C for poly(NIPAAm)). The H-bonding water along phase transition was also studied, showing a less reversibility of poly(NIPAAm) compared to poly(NDEAAm-co-MAA). In addition, FTIR spectrometer was also used to study the volume changes of poly(NDEAAm-co-MAA) under variations in environmental salinity.     

Synthesis,properties, and functions of thermosensitive copolymers having pyridyl and/or pyridinium groups

Thermosensitive copolymers with pyridyl and/or pyridinium groups were prepared by copolymerization of 4-vinylpyridine (4VP) and N-isopropylacrylamide (NIPAAm) followed by the reaction of 4VP–NIPAAm copolymers with benzyl chloride.The copolymer 4VP–NIPAAm was soluble in dilute HCl below 32 °C, but the quaternized 4VP–NIPAAm copolymer was soluble even in aqueous solutions of pH 6.5 below 28 °C. The thermosensitivity of both 4VP–NIPAAm and the quaternized 4VP–NIPAAm copolymer was observed. The quaternized 4VP–NIPAAm copolymer could adsorb food dyes dissolved in water and the copolymer–dye complexes became water-insoluble. The quaternized 4VP–NIPAAm copolymer also exhibited high antibacterial activity against bacteria such as Escherichia coli.     

Thermoreversible hydrogels VI: Swelling behavior of the (N-isopropylacrylamide-co-diethyl methyl methacryloyloxyethyl ammonium iodide) copolymeric hydrogels in aqueous salt solutions

A series of N-isopropylacrylamide/diethyl methyl methacryloyloxyethyl ammonium iodide (NIPAAm/DEMMAI) copolymeric gels were prepared from blending NIPAAm, cationic monomer DEMMAI, and N,N′-methylene bisacrylamide (NMBA) in various molar ratios in this article. The effects of the amount of the cationic monomer in the copolymeric gels on the swelling behaviors in water and various saline solutions at various temperatures were investigated. Results showed that the swelling ratios of copolymeric gels were significantly larger than those of pure NIPAAm gel, and that the more the DEMMAI content, the higher the gel transition temperature. In the saline solution, results showed that the swelling ratio for pure NIPAAm gel had not changed significantly with an increase of the salt concentration until the salt concentration was larger than 0.1 M. The swelling ratios for the copolymeric gels NIPAAm/DEMMAI were decreased with increasing salt concentration. In various saline solutions, results showed that the anionic effects were greater than cationic effects in the presence of common anion with different cations and common cation with different anions for these hydrogels. Finally, we also tested the reversibility of the NIPAAm/DEMMAI copolymeric gels. The deswelling and reswelling kinetics were dependent on the temperature which was below or above the gel transition temperature. The gel with a small DEMMAI content has a good reversibility.     

Immobilization of α-Amylase to Temperature-Responsive Polymers by Single or Multiple Point Attachments

Temperature-responsive N-isopropylacrylamide (NIPAAm) polymer (PNIPAAm) with a free carboxyl functional end group and a copolymer (NIPNAS) of NIPAAm and N-acryloxysuccinimide (NAS) were synthesized and used for immobilization of α-amylase. The enzyme forms covalent bonds with the former polymer by single point attachment and with the latter polymer by multiple point attachment. Such a difference influences the enzyme activity and properties of the immobilized enzymes. The polymers are temperature-sensitive with lower critical solution temperatures (LCST) of 34·7 and 36·0°C for NIPNAS and PNIPAAm, respectively. The immobilized enzyme exhibited an LCST of 35·5°C for NIPNAS-amylase and 37·1°C for PNIPAAm-amylase. They precipitated and flocculated in aqueous solution above the LCST and redissolved when cooled below that temperature. The activity of the immobilized enzyme depended on the pH of the coupling buffer, with 8·0 being the optimum value. The specific activities of the immobilized enzymes were 87% and 108% compared with that of free enzyme with soluble starch as the substrate for NIPNAS-amylase and PNIPAAm-amylase, respectively. By characterizing the properties of the immobilized enzymes and comparing with those of free enzyme, no diffusion limitation of substrate was found for the immobilized enzymes and they are more thermal stable than the free enzyme. Within the two immobilized enzymes, NIPNAS-amylase showed better thermal stability and reusability. Repeated batch hydrolysis of soluble starch can be carried out efficiently with the immobilized enzymes by intermittent thermal precipitation and recycle of the enzyme. © 1997 SCI.     

Photografting of N‐isopropylacrylamide and glycidyl methacrylate binary monomers on polyethylene film: Effect of mixed solvent consisting of water and organic solvent

Photografting (λ > 300 nm) of N‐isopropylacrylamide (NIPAAm) and glycidyl methacrylate (GMA) binary monomers (NIPAAm/GMA) on low‐density polyethylene film (thickness = 30 μm) was investigated at 60°C using mixed solvent consisting of water and an organic solvent such as acetone. Xanthone was used as a photoinitiator by coating it on the film surfaces. A maximum percentage of grafting was observed at a certain concentration of acetone in the mixed solvent, which was commonly observed for both ratios of NIPAAm/GMA, 8/2 and 7/3. Based on the photografting of NIPAAm/GMA on xanthone‐coated film, monomer reactivity ratios of NIPAAm (r₁) and GMA (r₂) were calculated using the Fineman–Ross method. The values were 0.31 ± 0.1 and 4.8 ± 0.2 for the water solvent system, while they were 0.96 ± 0.1 and 4.9 ± 0.1 for the mixed solvent system. NIPAAm/GMA‐grafted films with a homogeneous distribution of grafted chains were formed by photografting using water and mixed solvents. The NIPAAm/GMA‐grafted films exhibited temperature‐responsive characters, whereas the grafted films showed a reversible change in the degree of swelling between 0 and 50°C, respectively. Epoxy groups in the grafted poly(NIPAAm/GMA) chains could be aminated with ethylenediamine in N,N′‐dimethylformamide at 70°C for 3 h. Complexes of the aminated NIPAAm/GMA‐grafted chains with cupric ion exhibited catalytic activity for the decomposition of hydrogen peroxide at 20 to 50°C. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2469–2475, 2005