EFFECTS OF L-PHENYLALANINE ON THE RADIATION SYNTHESIS OF POLY （N,N＇-METHYLENEBIS A CR YLAMIDE-co-4-VINYLPYRID INE） （MICRO）GELS

The effects of L-phenylalanine （L-Phe） on the synthesis ofpoly（N,N＇-methylenebisacrylamide-co-4-vinylpyridine） （poly（Bis-co-4-VP）） （micro）gels by γ-ray irradiation were studied. The addition of L-Phe could not only decrease the gelation dose （Dg） of the synthesis obviously, but also transform the morphology of copolymer from microgel to gel. In addition, the swelling ability of the （micro）gels was also affected in the presence of L-Phe. The decrease of Dg was ascribed to the effect of pH, while the transformation of the morphology was ascribed to the effect of L-Phe on the stability of the poly（Bis-co-4-VP） microgel. Such an effect was confirmed further as compared with the effects of L-alanine, L-glutamic acid, L-arginine, sulfuric acid and aqueous ammonia.     

N,N′-亚甲基双丙烯酰胺与4-乙烯基吡啶共聚微凝胶的γ-射线辐照合成

通过γ 射线辐照技术 ,在稀水溶液中实现了N ,N′ 亚甲基双丙烯酰胺 (Bis)与 4 乙烯基吡啶 (4 VP)的无皂乳液共聚 ,得到平均流体力学半径 (Rh)为 5 6～ 15 2nm的一系列微凝胶 ,并通过红外光谱、热分析、透射电镜进行了表征 .通过测定Rh、吸光度、凝胶比 ,研究了与Bis共聚的单体及比例、剂量和剂量率对微凝胶合成的影响 .结果表明 ,微凝胶的大小可以通过吸收剂量、单体相对含量的改变来进行控制 .最后 ,对微凝胶的形成机理进行了初步探讨 .     

STABILITY OF POLY(N,N''''-METHYLENEBISACRYLAMIDE-co-4-VINYLPYRIDINE)MICROGEL DISPERSION AND ADJUSTMENT OF THE HYDROPHOBICITY IN THE MICROGELS

In the UV-Vis spectra of pure light-scattering systems,there is an exponential relationship between absorbance and wavelength(A=Kλ~(-n)).Here,the exponent n is named as flocculation-coagulation parameter.In the present paper,the effects of different additives on the stability of poly(N,N'-methylenebisacrylamide-co-4-vinylpyridine)(poly(Bis-co-4-VP)) microgel dispersion were studied in detail via this parameter.The results showed that the stability of the dispersion mainly comes from the ionization of pyridine groups,making the microgel positively charged on its surface.This was confirmed by the measurement of Zeta potential and the result of conductometric titration.The result of fluorescence analysis indicated that the hydrophobicity in the microgels is enhanced with the increase in total 4-VP unit content.     

STABILITY OF POLY（N,N＇-METHYLENEBISACRYLAMIDE-co-4-VINYLPYRIDINE） MICROGEL DISPERSION AND ADJUSTMENT OF THE HYDROPHOBICITY IN THE MICROGELS

In the UV-Vis spectra of pure light-scattering systems, there is an exponential relationship between absorbance and wavelength （A = Kλ^-n）. Here, the exponent n is named as flocculation-coagulation parameter. In the present paper, the effects of different additives on the stability of poly（N,N＇-methylenebisacrylamide-co-4-vinylpyridine） （poly（Bis-co-4-VP）） microgel dispersion were studied in detail via this parameter. The results showed that the stability of the dispersion mainly comes from the ionization of pyridine groups, making the microgel positively charged on its surface. This was confirmed by the measurement of Zeta potential and the result of conductometric titration. The result of fluorescence analysis indicated that the hydrophobicity in the microgels is enhanced with the increase in total 4-VP unit content.     

Isothermal titration calorimetric studies of the acid-base properties of poly(N-isopropylacrylamide-co-4-vinylpyridine) cationic polyelectrolyte colloidal microgels

Isothermal titration calorimetry (ITC) and potentiometric titration were used to study the protonation properties of the 4-vinylpyridine (4-VP) moiety in cationic poly(N-isopropylacrylamide-co-4-vinylpyridine) colloidal microgels [poly(NIPAM-co-4-VP)]. Calorimetric pH titrations were performed using microgels of different 4-VP content and the influence of ionic strength and counter ions have been examined. The calorimetric titration output consists of several thermal contributions reflecting the complex nature of the interactions in the aqueous microgel dispersions. In contrast to the potentiometric results, the calorimetric titration data could not be completely described by a theoretical model solely taking into account protonation equilibria. Deviations from the proposed model correlate with swelling or shrinking of the gel particles. The calorimetric results also reveal a pronounced counter-ion effect of perchlorate compared to chloride ions. In the presence of perchlorate ions, small secondary thermal effects accompany protonation of the 4-VP moiety due, in part, to kinetically limited conformational changes in the co-polymer microgel.     

Fabrication of Poly（4-vinylpyridine） Nanofiber and Fluorescent Poly（4-vinylpyridine）/Porphyrin Nanofiber by Electrospinning

Poly（4-vinylpyridine）（P4-VP） nanofiber and fluoresent poly（4-vinylpyridine）/porphyrin（P4-VP/TPPA） nanofiber were respectively prepared by electrospinning. The effect of the concentration of P4-VP/dimethylformamide （DMF） electrospinning solutions on the morphology of P4-VP nanofiber was investigated and it was found that the average diameter of the nanofiber of P4-VP/DMF increased with the increase of the concentration of the spinning solution. After the addition of TPPA to the P4-VP/DMF spinning solution, the diameter of P4-VP/TPPA nanofiber became even due to the increase of the conductivity of the P4-VP/DMF-TPPA solution. The photoluminescent（PL） spectral analysis indicates that the emission peak position of P4-VP/TPPA nanofiber is almost the same as that of pure TPPA at about 650 nm without peak shift, and when it was stored for 20 days, the emission peak of P4-VP/TPPA nanofiber is also at 650 nm, indicating that the fluorescent property of P4-VP/TPPA nanofiber is stable. Fourier-transform iufrared（FTIR） spectrum confirms the chemical composition of the resulting P4-VP/TPPA composite nanofiber.     

γ辐照引发无皂乳液聚合法一步合成Ag-聚4-乙烯基吡啶杂化微凝胶

无机-聚合物纳米复合材料是将聚合物与一种或多种无机纳米粒子复合而成的一种材料,它同时具有无机纳米粒子和聚合物的优良特性,在许多重要技术领域具有广泛的应用前景.近20年来,无机-聚合物纳米复合材料的制备及应用备受关注[1~6].包括杂化微凝胶在内的纳米复合微球是无机-聚合     

Stimulus-responsive particulate emulsifiers based on lightly cross-linked poly(4-vinylpyridine)-silica nanocomposite microgels

Lightly cross-linked poly(4-vinylpyridine)-silica nanocomposite microgel particles have been recently reported to act as pH-responsive particulate emulsifiers [Fujii, S.; Read, E. S.; Armes, S. P.; Binks, B. P. Adv. Mater. 2005, 17, 1014]. In this work, the synthesis and performance of such nanocomposite microgel particles are studied in more detail. Scanning electron microscopy, dynamic light scattering, nitrogen microanalyses, thermogravimetric analysis, aqueous electrophoresis, and acid-base titration were used to characterize the nanocomposites in terms of their particle size and morphology, polymer and silica contents, surface compositions, and critical swelling pH, respectively. Depending on the polarity of the oil phase and the purity of the nanocomposite particles, either oil-in-water or water-in-oil emulsions could be prepared at pH 8-9, but not at pH 2-3. These emulsions were characterized in terms of their emulsion type, mean droplet diameter, and morphology using electrical conductivity, light diffraction, and both electron and optical microscopy. In some cases, rapid demulsification could be induced by lowering the solution pH: addition of acid led to protonation of the 4-vinylpyridine residues, which imparted cationic microgel character to the nanocomposite particles. Cross-linking of the nanocomposite microgel particles is essential for their optimum performance as a pH-responsive emulsifier, but unfortunately it is not sufficient to allow recycling.     

Absorption of cetylpyridinium chloride into poly(N-isopropylacrylamide)-based microgel particles, in dispersion and as surface-deposited monolayers

The addition of cetylpyridinium chloride (CPC) to aqueous dispersions of poly(N-isopropylacrylamide) [poly(NIPAM)] and poly(N-isopropylacrylamide-co-acrylic acid) [poly(NIPAM-co-AAc)] microgel particles leads to absorption of the CPC into the particles and to corresponding changes in their hydrodynamic diameter. With the latter set of particles there is a strong pH dependence. The dependence of both hydrodynamic diameter and electrophoretic mobility of the microgel particles on the added CPC concentration show a strong correlation with CPC uptake, as obtained from direct CPC absorption measurements. Various mechanisms for CPC absorption into the microgel particles are postulated, including electrostatic, polar, and hydrophobic interactions. A comparison has also been made between the effect of added CPC on the hydrodynamic diameter of free microgel particles in dispersion, determined by dynamic light scattering, and the thickness of adsorbed monolayers of the same microgel particles deposited on cationically modified, oxidized silicon surfaces, as determined from ellipsometry measurements. The trends observed in both cases are broadly similar. This work opens the way for development of microgel layers for controlled uptake and release applications.     

聚(N-异丙基丙烯酰胺)水凝胶微球体积相变的研究

窄分散的聚（Ｎ 异丙基丙烯酰胺）水凝胶微球用乳液聚合方法制备，并用动态和静态光散射对其体积相变进行了研究．与水中聚（Ｎ 异丙基丙烯酰胺）线性单链比较，水中凝胶微球的体积相变温度较高，对温度的响应比较平缓．相变是连续的，有别于大块凝胶非连续的体积变化．在体积相变过程中，凝胶微球始终是密度均一的热力学稳定球体．从相变过程网络密度的变化可以确定，绝大部分的水在收缩过程被排了出来，但在紧缩的凝胶微球中仍含有约７０％的水．     

Synthesis and molecular-mass characteristics of some cardo poly(benzimidazoles)

The GPC procedure for analyzing molecular mass characteristics of cardo poly(benzimidazoles) has been developed. In most cases, the reaction between 4,4′-oxydibenzene-1,2-diamine and 4,4′-(3-oxo-1,3-dihydroisobenzofuran-1,1-diyl)dibenzoic acid in Eaton’s reagent is accompanied by formation of a microgel. Depending on the synthesis conditions (temperature, duration of heating, and content of phosphorus pentoxide in the reaction mixture), polymers with both unimodal and bimodal molecular mass distributions can be prepared. Formation of the microgel fraction is observed for many representatives of poly(benzimidazoles) of various chemical structures. Based on the experimental evidence, the most probable pathway is suggested for the branching side reaction of poly(benzimidazoles) during their synthesis in Eaton’s reagent.     

Antibacterial activities of polystyrene-block-poly(4-vinyl pyridine) and poly(styrene-random-4-vinyl pyridine)

Styrene was polymerized in the presence of benzoyl peroxide (BPO) and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) to yield polystyrene-TEMPO (PS-TEMPO) macroinitiator. The PS-TEMPO macroinitiator with different molecular weight was reacted with 4-vinyl pyridine (4-VP) to synthesize polystyrene-block-poly(4-vinyl pyridine) (PS-b-PVP), which was then quaternized with n-octyl iodide. Antibacterial activity of the quaternized copolymers was assessed against a gram negative bacterium (Pseudomonas aeruginosa) and a gram positive one (Staphylococcus aureus) by using the shake flask test method, and the results were compared with those of poly(styrene-random-4-vinyl pyridine) (P(ST-r--VP)). The quaternized copolymers inhibited greatly the growth of the bacteria, and PS-b-PVP was more active than P(ST-r-VP), which was ascribed to the fact that the content of quaternized 4-VP units on the surface of the particles of the former copolymer was higher than that corresponding to the latter one.     

铅离子敏感N-异丙基丙烯酰胺共聚物微凝胶的制备

采用对N-异丙基丙烯酰胺-丙烯酸共聚微凝胶进行改性的方法合成了含苯并18-冠-6功能基团的PNIPAM微凝胶.红外和核磁光谱等手段证明苯并18-冠-6基团被引入到微凝胶中.改性后的微凝胶仍具有很好的温敏性,但是相转变温度由改性前的30℃提高到42℃,并且溶胀度也大大增加.在不控制离子强度的条件下微凝胶的粒径随Na+浓度增加而减小,但是随Pb2+浓度增加微凝胶粒径先减后增.在控制离子强度不变的条件下Na+浓度对微凝胶的粒径影响很小,但是随Pb2+浓度增加微凝胶粒径明显增大,显示较强的铅离子敏感性。     

葡萄糖敏感微凝胶的溶胀动力学研究

通过沉淀聚合法合成了P(NIPAM-co-AA)微凝胶,然后在EDC催化下用3-氨基苯硼酸对微凝胶进行改性,制备了P(NIPAMI-co-AAPBA)微凝胶.红外光谱检测证明改性完全.改性后的微凝胶仍具有很好的温敏性,但由于引入疏水的苯硼酸基团,微凝胶的体积相转变温度大大降低.P(NIPAM-co-AAPBA)微凝胶具...     

Effect of chain length on the interaction between modified organic salts containing hydrocarbon chains and poly(N-isopropylacrylamide-co-acrylic acid) microgel particles

A series of four hydrophobically modified, diphenylazo-based organic salts have been prepared and characterized. To achieve this a C(x) (x = 4, 6, 8, or 10) hydrocarbon chain was inserted between the diphenylazo moiety and the quaternary ammonium headgroup of the salt. The absorption of each of the four modified organic salts into anionic microgel particles of poly(N-isopropylacrylamide-co-acrylic acid) has been studied at pH 8. In addition, the hydrodynamic diameters and electrophoretic mobilities of the microgel particles have been studied as a function of the organic salt concentration, also at pH 8. In addition to the electrostatic attraction between the quaternary ammonium head groups of the organic salts and the anionic groups within the microgel particles, hydrophobic association between the chains of the organic salts within the microgel particles plays a role, with this effect increasing strongly from x=4 to 10. Desorption of the x=4 and 6 organic salts occurs readily on changing, in situ, the pH from 8 to 2.5 (and thereby eliminating the electrostatic interaction) but is only partially achieved for the x=8 and 10 organic salts. Indeed, for the x=10 organic salt, only about 80% of the organic salt is desorbed upon dilution of the microgel particles into a large excess of water.     

Cross-linked poly (4-vinylpyridine) supported azide ion as a versatile and recyclable polymeric reagent for synthesis of 1-substituted-1H-1,2,3,4-tetrazoles

Cross-linked poly (4-vinylpyridine) supported azide ion, [P₄-VP]N₃, is easily prepared and used as an efficient polymeric reagent for synthesis of 1-substituted-1H-1,2,3,4-tetrazoles via condensation reaction of azide ion, primary aromatic amines, and triethyl orthoformate in glacial acetic acid. After optimization of the reaction conditions, a wide variety of primary aromatic amines were also subjected to preparation of the corresponding 1-aryl-1 H-1,2,3,4- tetrazoles using [P₄-VP]N₃ under heterogeneous conditions. In this method, the reaction times were very short and the isolated yields were excellent (90–98 %). 1-Aryl-1H-1,2,3,4- tetrazole products were characterized by Fourier transform infrared (FT-IR) and some of them were also characterized by proton nuclear magnetic resonance (¹H NMR) spectroscopy, and physical properties were compared with the literature values of known compounds. The spent polymeric reagent were regenerated quantitatively and reused for several cycles without significant loss of their activity.     

Study of pH-responsive microgels containing methacrylic acid: effects of particle composition and added calcium

pH-responsive microgel dispersions contain cross-linked polymer particles that swell when the pH approaches the pKa of the ionic monomer incorporated within the particles. In recent work from our group, it was demonstrated that the mechanical properties of degenerated intervertebral discs (IVDs) could be restored to normal values by injection of pH-responsive microgel dispersions (Saunders, J. M.; Tong, T.; LeMaitre, C.; Freemont, A. J.; Saunders, B. R. Soft Matter 2007, 3, 486). These dispersions change from a fluid to a gel with increasing pH. The present work investigates the pH-dependent properties of dispersions of microgel particles containing MAA (methacrylic acid) and also the effects of added Ca2+. Two microgels are discussed: microgel A is poly(EA/MAA/AM) (EA and AM are ethyl acrylate and allyl methacrylate), and microgel B is poly(EA/MAA/BDDA) (butanediol diacrylate). The pH-dependent particle properties investigated include hydrodynamic diameters and electrophoretic mobilities. The critical coagulation concentrations (CCC) of dilute dispersions and the elastic modulus (G') of concentrated, gelled microgel dispersions were also investigated. In the absence of added Ca2+, the particle swelling and G' were smallest and largest, respectively, for microgel A. The changes in hydrodynamic diameter and mobility with pH were explained in terms of a core-shell swelling mechanism. Added Ca2+ was found to significantly decrease the CCCs, extents of particle swelling, and magnitude of the electrophoretic mobility. This was attributed to the ionic cross-linking of neighboring RCOO- groups by Ca2+. It is suggested that the formation of ionic cross-links is inefficient within the microgel particles because of the presence of covalent cross-links that oppose the large-scale conformational rearrangement of neighboring RCOO- groups. The effect of Ca2+ on the properties of the gelled dispersions is important from the viewpoint of potential application in vivo. Rheological studies of the gelled microgel dispersions showed that added Ca2+ did not have a specific influence on G'. The differences observed in the presence of Ca2+ were attributed to ionic strength effects (screening). The key parameter that controls G' of the gelled microgel dispersions is pH. The results from this work suggest that the elasticity of the gels would be slightly reduced in vivo as a consequence of the high ionic strength present.     

Effect of ionization on the temperature- and pressure-induced phase transitions of poly(N-isopropylacrylamide) gels

The ionization effects on the pressure-induced phase transition of weakly charged poly(N-isopropylacrylamide-co-acrylic acid) (PNIPA-AAc) gels have been investigated by small-angle neutron scattering. At low temperature, T, and pressure, P, the structure factor of PNIPA-AAc gels was well represented by a Lorentzian (L) function, which was similar to noncharged PNIPA gels. However, at high Ps, the contribution of inhomogeneities became large and a squared-Lorentzian term had to be added in addition to the L term. At high Ts, on the other hand, a scattering maximum appeared, indicating microphase separation. This scattering maximum was suppressed by increasing P up to P approximately 100 MPa and then reincreased at higher Ps. The following facts were disclosed: (1) The peak position and height were very sensitive to P, which is mainly ascribed to strong pressure dependence of hydrophobic interaction, (2) ionization leads to microphase separation at elevated temperatures, (3) the re-entrant phase behavior is commonly observed in the P-T plane due to the parabolic variation of the polymer-solvent interaction with P, and (4) the pressure and temperature dependence of the structure factor was reproduced with the Rabin-Panyukov theory and was interpreted with a convexity of hydrophobic interaction with respect to pressure.     

Plum-pudding gels as a platform for drug delivery: understanding the effects of the different components on the diffusion behavior of solutes

The internal structure of composite gels made of responsive microgel particles inserted into a bulk hydrogel (N-isopropylacrylamide microgel particles in a cross-linked dimethylacrylamide matrix) has been investigated from the diffusion behavior of poly(ethylene glycol) (PEG) probes through the network, in the absence of specific interactions between the diffusing molecules and the system. The effect of the different components has been examined, for example, the size of the probe, the bulk structure, and the microgel nature. Particles were characterized prior to their insertion into the hydrogel in order to describe their properties as a function of size and cross-linker content, thus revealing different swelling behaviors. The biggest effects on the diffusion of the PEG probes were related to the bulk structure, and no major effects were registered by the addition of different microgels into the hydrogel network. We attempt to rationalize this behavior in terms of the composite gel structure and discuss the results in terms of their meaning for controlled drug delivery strategies.     

聚甲基丙烯酸与修饰聚丙烯酰胺间的络合作用

利用荧光各向异性,荧光探针和荧光猝灭等静态光物理技术研究了稀水溶液中聚甲基丙烯酸（ＰＭＡＡ）与阳离子修饰聚丙烯酰胺（ＱＣＰＡＭ）间的络合作用。结果表明：在ｐＨ＝２－８范围内,ＰＭＡＡ与ＱＣＰＡＭ之间发生明显络合,但以ｐＨ为４时络合作用最大,最佳络合本比为１：１（单体单元比）,络合作用的发生大大地改变了ＰＭＡＡ的构象行为,ＰＭＡＡ构象对ｐＨ和络合作用的双重依赖性有可能在新型“智能”凝胶的设计合成上获