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1.
pH响应性阳离子型微凝胶的制备及性质研究 总被引:1,自引:0,他引:1
以甲基丙烯酸-(N,N-二甲氨基)乙酯(DMAEMA)和丙烯酸乙酯(EA)为共聚单体, 二甲基丙烯酸乙二醇酯(EGDMA)为交联剂, 采用半连续乳液聚合法, 制备了具有pH响应性的阳离子型微凝胶, 并研究不同聚合条件对所合成的微凝胶性质的影响. 利用透射电子显微镜(TEM)、激光粒度分析仪和流变仪对微凝胶进行一系列表征. 研究了介质pH值对微凝胶的形态、平均粒径、zeta电位、溶液浊度(透光率)的影响, 以及NaCl盐溶液对微凝胶分散体系稳定性的影响. 结果表明, 这类阳离子型微凝胶体系具有良好的pH响应性, 在pH=7左右发生相转变. 此外, 研究表明不同浓度NaCl溶液对微凝胶的稳定性有一定影响, 临界絮凝浓度约为1.3 mol8226;L-1. 相似文献
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分散聚合法制备PVP微球的研究 总被引:1,自引:0,他引:1
以N-乙烯基吡咯烷酮(NVP)为初始单体,乙酸乙酯为分散介质,采用分散聚合法制备了分散性能良好、粒径为3~4μm的聚乙烯基吡咯烷酮(PVP)微球.考察了单体、分散剂及引发剂浓度对PVP微球的粒径、单体转化率及分子量的影响,并对PVP的结构和性能进行研究.结果表明,单体浓度增加,PVP微球粒径和分子量增大,单体转化率升高;分散剂浓度增加,PVP微球粒径变小,分子量增大,单体转化率升高;引发剂浓度增加,PVP微球粒径变大,分子量减小,单体转化率升高.与溶液聚合法相比,分散聚合法制备的PVP分子量较小且具有一定的结晶性. 相似文献
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利用预乳化乳液法制备了不同单体配比的聚(甲基丙烯酸甲酯-co-甲基丙烯酸-co-甲基丙烯酸羟乙酯)(P(MMA-co-MAA-co-HEMA))微凝胶分散液;采用透射电子显微镜、动态光散射仪研究了微凝胶的微观形态、粒径大小及其溶胀率;利用试管倒转法对微凝胶分散液的凝胶化相转变行为进行了研究,借助椎板流变仪考察了所形成胶态凝胶的储能模量与单体配比、微凝胶分散液浓度和温度的关系.结果表明,所制备的微凝胶的数均粒径为90 nm左右,当MMA与MAA的投料质量不变时,随着HEMA含量的增加,分散液凝胶化所需的临界最小浓度增大,临界最大pH值减小,胶态凝胶的储能模量增加.当保持单体MMA与HEMA的投料质量不变时,随着单体MAA投料质量的增多,微凝胶的数均粒径和溶胀率增大,胶态凝胶的储能模量先升高后降低;当MAA占单体总摩尔数的25%时,浓度为15 wt%的微凝胶分散液在扫描频率为100 rad/s时,胶态凝胶的储能模量最高可达2×104Pa.这类微凝胶分散液在组织工程支架材料方面有潜在的应用价值. 相似文献
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无皂种子分散聚合法制备单分散双重响应性微凝胶 总被引:1,自引:0,他引:1
以N-异丙基丙烯酰胺及2-乙烯基吡啶为主要单体, 采用无皂种子分散聚合法制备了单分散的、具有温度及pH双重响应性能的核-壳结构微凝胶, 并以扫描电镜及动态激光光散射等手段对微凝胶粒子的结构和性能进行了研究. 溶胀行为研究表明, 微凝胶粒子具有独立的互不干扰的温度及pH敏感性能, 其体积相变温度与纯聚N-异丙基丙烯酰胺(PNIPAM)凝胶基本一致, 说明局部分布的弱电离单体不会对PNIPAM凝胶的体积相变温度造成影响. 相似文献
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以苯乙烯(St)、马来酸酐(MA)、香豆素苯乙烯醚化物(CS)为单体, 通过自由基溶液聚合合成了双亲性交替共聚物P(St/CS-alt-MA), 用凝胶渗透色谱、核磁共振等对聚合物结构进行表征, 并对其溶液自组装及组装体的乳化性进行了研究. 结果表明双亲性P(St/CS-alt-MA)可以在选择性溶剂中进行自组装形成马来酸酐单元为亲水微区、CS与苯乙烯单元为疏水微区的胶体粒子, 用紫外分光光度计, XPS, TEM研究了聚合物胶体粒子性质, 结果显示, P(St/CS-alt-MA)在水溶液中可以形成两亲性聚合物胶体粒子, 亲水单元在胶粒表面富集, 该两亲性聚合物胶体粒子具有良好的乳化性能. 相似文献
9.
用溶液聚合法制备出轻度交联的含铅微凝胶,用光子相关光谱技术测定其在良溶剂中与H2S反应前、后的扩散行为,由外推法得到在浓度无限稀时的分子扩散系数,给出微凝胶的流体力学半径。结果表明:相同量的含铅微凝胶在不同的初始浓度下与H2S反应,生成含PbS纳米微粒的凝胶;但其体积增大不同,这说明H2S与含铅微凝胶的反应既可以在分子内也可以在分子间进行,分子间的反应使含硫化铅微凝胶扩散系数随浓度的变化曲线的线性范围变小。 相似文献
10.
侧链含不同功能性羟基的温敏性N-异丙基丙烯酰胺共聚物微凝胶的制备及性能比较 总被引:5,自引:0,他引:5
选择含有活性羟基的亲水单体多缩乙二醇单甲基丙烯酸酯(PEGMA)、甲基丙烯酸羟乙酯(HEMA),分别和N-异丙基丙烯酰胺(NIPAM)交联共聚,制备了侧链含有功能性羟基、链长不同的温敏性微凝胶.研究发现,亲水单体HEMA和PEGMA的引入对微凝胶的去溶胀性能有不同的影响,PEGMA的引入使得微凝胶的体积相转变温度升高,微凝胶的去溶胀比随着PEGMA投料比的增加而降低.而HEMA的引入使得微凝胶的体积相转变温度降低;微凝胶的去溶胀比随着HEMA投料比的增加先是增加然后降低,当HEMA的投料比为8mol%时,去溶胀比达到最大. 相似文献
11.
Cao Z Du B Chen T Nie J Xu J Fan Z 《Langmuir : the ACS journal of surfaces and colloids》2008,24(22):12771-12778
By utilizing the hydrolysis and condensation of the methoxysilyl groups, thermo-sensitive organic/inorganic hybrid poly[ N-isopropylacrylamide- co-3-(trimethoxysilyl)propylmethacrylate] [P(NIPAm- co-TMSPMA)] microgels were successfully prepared via two different methods without addition of any surfactant. First, the microgels were obtained by a two-step method; that is, the linear copolymer P(NIPAm- co-TMSPMA) was first synthesized by free radical copolymerization, and the aqueous solution of the copolymer was then heated above its low critical solution temperature (LCST) to give colloid particles, which were subsequently cross-linked via the hydrolysis and condensation of the methoxysilyl groups to form the microgels. Second, the microgels were also prepared via conventional surfactant-free emulsion polymerization (SFEP) of the monomers NIPAm and TMSPMA. TMSPMA can act as the cross-linkable monomer. No surfactant was involved in the preparation of the hybrid microgels. The obtained microgels were rather spherical and exhibited reversible thermo-sensitive behavior. The size, morphology, swellability, and phase transition behavior of the microgels were dependent on the initial copolymer or monomer concentration, preparation temperature, and the content of TMSPMA. The size of microgels obtained by SFEP was found to be more uniform than that by the two-step method. The hybrid microgels obtained by these two methods had more homogeneous microstructures than those prepared via conventional emulsion polymerization with chemical cross-linker N, N'-methylene-bisacrylamide. 相似文献
12.
Novel monodisperse cationic pH-responsive microgels were successfully prepared by dispersion polymerization in ethanol/water mixture using N,N'-dimethylamino ethyl methacrylate (DMAEMA) as the monomer, poly(vinyl pyrrolidone) (PVP) as the steric stabilizer and N,N'-methylenebisacrylamide (MBA) as the cross-linker. The effects of various polymerization parameters, such as medium polarity, concentration of cross-linker, concentration of monomer, and concentration and molecular weight of stabilizer on the final diameter and monodispersity of poly(N,N'-dimethylamino ethyl methacrylate) (PDMAEMA) microgels were systematically studied. The pH-responsive characteristics of PDMAEMA microgels were also investigated. The experimental results showed that these microgels exhibited excellent pH-responsivity and significantly swelled at low pH values. The maximum ratio of volume change of the prepared microgels in response to pH variation was more than 11 times. It was found that the prepared microgels completely aggregated at the isoelectric point (IEP) around pH 6. On the other hand, the microgels were stable in aqueous solution at both low and high pH values. The results can be used for effectively controlled separation of particles. 相似文献
13.
The chain and radial functional group distributions in carboxylic acid-functionalized poly(N-isopropylacrylamide)-based microgels have significant impacts on the types of swelling responses exhibited by the microgels upon the application of a temperature and/or pH stimulus. Potentiometric, conductometric, and calorimetric titration approaches are used in this work to characterize the chain distributions of -COOH groups in five microgels prepared using different -COOH-functionalized monomers. A direct correlation is observed between the kinetically predicted formation of functional monomer blocks within the microgel, the excess Gibbs free energy of ionization, and the apparent pK(a) versus degree of ionization profiles generated from potentiometric titration. Isothermal titration calorimetry (ITC) can be used to quantify the relative number of functional groups present in microgels prepared with the same functional monomer and/or identify differences between microgels with the same bulk -COOH content but different chain distributions. In particular, microgels prepared with diacid-functionalized monomers exhibit a characteristic two-step ITC profile. For microgels with the same bulk -COOH content, the heat of ionization measured via ITC increases systematically with the overall change in both the pK(a) and the excess Gibbs free energy for microgels prepared with monoacid-functionalized monomers. Diacid monomer-functionalized microgels have lower ionization enthalpies attributable to the break-up of hydrogen-bonded intramolecular ring complexes upon carboxylic acid ionization. The inferred chain functional group distributions can be used to understand differences in microgel swelling across the pH-induced phase transition. 相似文献
14.
J. H. de Groot A. Zurutuza C. R. Moran N. B. Graham K. A. Hodd S. Norrby 《Colloid and polymer science》2001,279(12):1219-1224
The goal of this study was to prepare and characterize water-soluble, high-molecular-weight microgels. N-Vinylpyrrolidone (NVP) and vinylacetate (VAc) in combination with cross-linkers diethylene glycol dimethacrylate (DEGDMA)
or diethylene glycol divinyl ether (DEGDVE) were copolymerized in solution to high conversion. Polymerization was performed
in different solvents or solvent mixtures, with solubility parameters ranging from 16.0 to 47.6 J0.5cm−1.5, and at different initial monomer concentrations. In solvent mixtures with solubility parameters of 20–40 J0.5cm−1.5, macrogelation did not occur below a critical gelation concentration and microgels were formed. For NVP/VAc/DEGDMA (85.0/10.0/5.0 wt%,
84.8/12.9/2.4 mol%) and NVP/VAc/DEGDVE (85.0/10.0/5.0 wt%, 84.8/12.9/3.5 mol%) the critical gelation curves were determined.
The molecular weights of the microgels depend on the solvent systems and the initial monomer concentration. Microgels of high
molecular weight but low cross-linking density gave aqueous solutions with high viscosities. Increasing the amount of cross-linker
to 20 wt% gave high-molecular-weight microgels with lower solution viscosity. Microgels with a monomer composition NVP/VAc/DEGDVE
(65.0/15.0/20.0 wt%, 66.2/19.5/14.3 mol%) were prepared in ethanol at different monomer concentrations (3–20 wt%). The molecular
weights were determined by a combination of field-flow fractionation and light scattering. By increasing the initial monomer
concentration, the molecular weight and the molecular-weight distribution as well as the intrinsic viscosity increased. The
exponent of the Mark–Houwink equation was 0.26.
Received: 19 March 2001 Accepted: 20 July 2001 相似文献
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Thermosensitive poly[N-isopropylacrylamide(NIPAM)-co-N-acryloyl-L-phenylalanine ethyl ester (NALPE)] microgels were prepared by the free radical polymerization of NIPAM and chiral monomer, NALPE. Such microgels exhibited spherical shape and favorable monodispersity. Increasing the content of NALPE units would enhance the average diameter, but decrease the thermosensitivity and volume-phase transition temperatures of the microgels. Compared with PNIPAM microgels, the microgels containing NALPE units performed chiral recognozable capacities for D-phenylalanine and D-tartaric acid, and the enantioselectivity and adsorption capacity of the microgels improved with increasing the temperature and/or the content of NALPE units. 相似文献
16.
Emulsion copolymerization of poly(methacrylic acid) and poly(2-(diethylamino)ethyl methacrylate) (PMAA/PDEA) yielded pH-responsive polyampholyte microgels of 200-300 nm in diameter. These microgels showed enhanced hydrophilic behavior in aqueous medium at low and high pH, but formed large aggregates of approximately 2500 nm at intermediate pH. To achieve colloidal stability at intermediate pH, a second batch of microgels of identical monomer composition were synthesized, where monomethoxy-capped poly(ethylene glycol)methacrylate (PEGMA) was grafted onto the surface of these particles. Dynamic light-scattering measurements showed that the hydrodynamic radius, Rh, of sterically stabilized microgels was approximately 100 nm at intermediate pH and increased to 120 and 200 nm at pH 2 and 10, respectively. Between pH 4 and 6, these microgels possessed mobility close to zero and a negative second virial coefficient, A2, due to overall charge neutralization near the isoelectric pH. From the Rh, mobility, and A2, cross-linked MAA-DEA microgels with and without PEGMA retained their polyampholytic properties in solution. By varying the composition of MAA and DEA in the microgel, it is possible to vary the isoelectric point of the colloidal particles. These new microgels are being explored for use in the delivery of DNA and proteins. 相似文献
17.
含β-CD单元VCL共聚物微凝胶的合成与性能研究 总被引:1,自引:0,他引:1
采用无皂沉淀聚合法,在水溶液中通过N-乙烯基己内酰胺(VCL)与一种单取代乙烯基β-环糊精单体(GMA-EDA-β-CD)的共聚反应,合成出了含有β-CD结构单元的温敏性VCL/GMA-EDA-β-CD共聚物微凝胶.用红外光谱仪(FTIR)、1H核磁共振仪(1H-NMR)、透射电镜(TEM)及激光粒度仪(DLS)对其结构、形态和性能进行了表征.研究结果表明,β-CD结构单元的加入使共聚物微凝胶的粒径减小,粒径分布变窄,但其温敏性降低. 相似文献
18.
Bradley M Ramos J Vincent B 《Langmuir : the ACS journal of surfaces and colloids》2005,21(4):1209-1215
The use of microgels for controlled uptake and release has been an area of active research for many years. In this work copolymer microgels of N-isopropylacrylamide (NIPAM) and acrylic acid (AAc), containing different concentrations of AAc and also cross-linking monomer, have been prepared and characterized. These microgels are responsive to pH and temperature. As well as monitoring the equilibrium response to changes in these variables, the rates of swelling/de-swelling of the microgel particles, on changing either the pH or the temperature, have also been investigated. It is shown that the rate of de-swelling of the microgel particles containing AAc is much faster than the rate of swelling, on changing the pH appropriately. This is explained in terms of the relative mobilities of the H(+) and Na(+) ions, in and out of the particles. It was observed that the microgels containing AAc, at pH 8, de-swelled relatively slowly on heating to 50 degrees C from 20 degrees C. This is attributed to the resistance to collapse associated with the large increase in counterion concentration inside the microgel particles. The swelling and de-swelling properties of these copolymer microgels have also been investigated in aqueous poly(ethylene oxide) (PEO) solutions, of different MW (2000-300 000). The corresponding absorbed amounts of PEO from solution onto the microgels have also been determined using a depletion method. The results, as a function of AAc content, cross-linker concentration, PEO MW, pH, and temperature, have been rationalized in terms of the ease and depth of penetration of the PEO chains into the various microgel particles and also the H-bonding associations between PEO and either the -COOH of the AAc moeities and/or the H of the amide groups (much weaker). Finally, the adsorption and desorption of the PEO molecules in to and out of the microgel particles have been shown to be extremely slow compared to normal diffusion time scales for polymer adsorption onto rigid surfaces. 相似文献
19.
Thermoresponsive colloidal microgels were prepared by polymerisation of N-isopropylacrylamide (NIPAM) with varying concentration of a cross-linking monomer, N,N-methylenebisacrylamide (MBA), in water with either 0.4 or 6.7 mM concentration of an anionic surfactant, sodium dodecylsulphate (SDS). Volume phase transitions of the prepared microgels were studied in D2O by 1H-NMR spectroscopy including the measurements of spin–lattice (T1) and spin–spin (T2) relaxation times for the protons of poly(N-isopropylacrylamide) (PNIPAM) at temperature range 22–50 °C. In addition, microcalorimetry, turbidometry, dynamic light scattering and electrophoretic mobility measurements were used to characterise the aqueous microgels. The results from the different characterisation methods indicated that PNIPAM microgels prepared in 6.7 mM SDS concentration are structurally different compared to their correspondences prepared in 0.4 mM concentration. Increasing MBA concentration in the microgel synthesis appears to increase the structural heterogeneity in both cases of SDS concentration. PNIPAM structures with significantly higher molecular mobilities at temperatures above 35 °C were observed in the microgels prepared in 0.4 mM SDS concentration, as indicated by the 1H NMR relaxation times of different PNIPAM protons. We conclude that the high mobilities measured with NMR at elevated temperatures and also the clearly negative values of zeta potential are in connection to a fairly mobile surface layer with polyelectrolyte nature and a consequent high local lower critical solution temperature. 相似文献
20.
A series of crosslinked microgels with quaternary ammonium ions on the surface was prepared by quaternization with N,N-dimethylbenzylamine in the presence of microgel particles prepared by emulsion copolymerization of styrene (St), chloromethylstyrene (CMS) and divinylbenzene (DVB). Microgels with diameters in the range of 15–100 nm were successfully dispersed in organic solvents such as 2-methoxyethanol and 2-ethoxyethanol without an emulsifier. A photosensitive layer was formed by coating a photosensitive solution on a grained aluminum plate. The solution was comprised of the microgels, the multifunctional monomer and standard ultraviolet (UV) photoinitiators, such as 2,4-diethyl thioxanthone (DETX)/ethyl p-di-ethylaminobenzoate (EPA). This gave a heterogeneous photosensitive layer which produced good polymer patterns after exposure to UV light followed by development in tap water. A typical polymer layer, consisting of the microgels (poly(styrene-co-N,N-dimethylbenzylvinyl-benzylammonium chloride-co-divinylbenzene)), DETX/EPA, and the multifunctional acrylate monomers, exhibited photosensitivity of 0.06 mJ/cm2 for UV light. This sensitivity is much higher than the homogeneous photopolymerization system with an analogous composition. 相似文献