Hydrophobic Monomers Recognize Microenvironments in Hydrogel Microspheres during Free‐Radical‐Seeded Emulsion Polymerization

The three‐dimensional structure of nanocomposite microgels was precisely determined by cryo‐electron micrography. Several nanocomposite microgels that differ with respect to their nanocomposite structure, which were obtained from seeded emulsion polymerization in the presence of microgels, were used as model nanocomposite materials for cryo‐electron micrography. The obtained three‐dimensional segmentation images of these nanocomposite microgels provide important insights into the interactions between the hydrophobic monomers and the microgels, that is, hydrophobic styrene monomers recognize molecular‐scale differences in polarity within the microgels during the emulsion polymerization. This result led to the formation of unprecedented multi‐layered nanocomposite microgels, which promise substantial potential in colloidal applications.     

Preparation and properties of thermo-sensitive organic/inorganic hybrid microgels

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.     

Polyurethane acrylate microgel synthesized by emulsion polymerization using unsaturated self-emulsified polymer

Polyurethane (PU) acrylate microgels were obtained by emulsion polymerization of self-emulsified PU acrylate terminated by 2-hydroxyethyl methacrylate without any extra emulsifier and crosslinker. Moreover, the PU acrylate was also used as stabilizer and crosslinker to synthesize poly(methyl methacrylate) (PMMA)–PU composite microgels via emulsion polymerization, which provided a new method to synthesize PU microgels and their composite microgels. The kinetics of microgel synthesis was studied by gel permeation chromatography. The dynamic rheological behaviors indicated that a crosslinked structure was formed. The frequency dependency of the loss tangent and complex viscosities showed strong relationships with the microgel structure. Those microgels with rigid PMMA core showed higher ability to slide than the soft PU acrylate microgel, which had influence on the changing of loss tangent with frequency. All the microgels swollen in tetrahydrofuran exhibited high viscosities and strong shear-thinning behaviors. As a sort of flexible microgel, the PU microgel was able to form a coherent film at room temperature, which was distinct from hard microgels.     

Synthesis and characterization of Poly(N-isopropylacrylamide)/Poly(acrylic acid) semi-IPN nanocomposite microgels

A novel pH- and temperature-sensitive nanocomposite microgel based on linear Poly(acrylic acid) (PAAc) and Poly(N-isopropylacrylamide) (PNIPA) crosslinked by inorganic clay was synthesized by a two-step method. First, PNIPA microgel was prepared via surfactant-free emulsion polymerization by using inorganic clay as a crosslinker, and then AAc monomer was polymerized within the PNIPA microgel. The structure and morphology of the microgel were confirmed by FTIR, WXRD and TEM. The results indicated that the exfoliated clay platelets were dispersed homogeneously in the PNIPA microgels and acted as a multifunctional crosslinker, while the linear PAAc polymer chains incorporated in the PNIPA microgel network to form a semi-interpenetrating polymer network (semi-IPN) structure. The hydrodynamic diameters of the semi-IPN microgels ranged from 360 to 400 nm, which was much smaller than that of the conventional microgel prepared by using N,N′-methylenebis(acrylamide) (MBA) as a chemical crosslinker, the later was about 740 nm. The semi-IPN microgels exhibited good pH- and temperature-sensitivity, which could respond independently to both pH and temperature changes.     

Preparing and physicochemical properties of microcrystalline polyacrylic acid gels

The facile synthesis of microcrystalline polyacrylic acid (PAA) gels via emulsion polymerization is presented and the effects of experimental factors that determine the microcrystallization of PAA microgels were investigated. Both reaction temperature and emulsifier type play important roles in the crystallization of PAA microgels. Selected-area electron diffraction and X-ray diffraction patterns show that the PAA microgels formed using sodium dodecyl sulfate as emulsifier are single-crystallized, and low reaction temperature favors the formation of the PAA microgels with high crystallinity. Controlling the reaction temperature may also improve morphology controllability by emulsion polymerization in synthesizing microcrystalline PAA gels. In addition, the microcrystalline PAA gels exhibit good Young’s modulus, which is 7.8 times higher than that of the PAA microgels.     

Synthesis of polytetrafluoroethylene/polyacrylate core-shell nanoparticles via emulsifier-free seeded emulsion polymerization

Polytetrafluoroethylene (PTFE)/polyacrylate core-shell nanoparticles were produced via the emulsifier-free seeded emulsion polymerization of acrylate monomers with PTFE latex as seed. The monomer conversions under different synthesis parameters were monitored by a gravimetric method. The polymerization conditions for preparing PTFE/polyacrylate core-shell nanoparticles were surveyed and optimized. The chemical component of the PTFE/polyacrylate particles was confirmed by comparing the Fourier-transform infrared spectra of PTFE and PTFE/polyacrylate particles. The core-shell structure of the resulting PTFE/polyacrylate nanocomposite particles was investigated by transmission electron microscopy. The water contact angles of the films prepared from PTFE/polyacrylate nanocomposite particles showed that the films were hydrophilic, which confirmed that polyacrylate covered the surface of the PTFE particles. This kind of PTFE/polyacrylate core-shell nanoparticles might advance the compatibility of PTFE with other materials due to the covering of the polyacrylate shell on the surface of PTFE, which would make them promising in various fields.     

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。     

pH响应性阳离子型微凝胶的制备及性质研究

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 mol•L－1.     

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 .     

温敏性P(St-NIPAM)/PNIPAM-Ag复合微凝胶制备及性能研究

通过无皂乳液聚合和种子乳液聚合两步法合成苯乙烯与N-异丙基丙烯酰胺共聚物/聚N-异丙基丙烯酰胺[P(St-NIPAM)/PNIPAM]核-壳结构复合微凝胶, 再以其为模板在硝酸银水溶液中充分溶胀, 并以乙醇为还原剂, 在NH₃气氛条件下还原, 制备得到高分子微凝胶负载纳米银P(St-NIPAM)/PNIPAM-Ag的复合微凝胶材料. 通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外光谱仪(FT-IR)、X射线衍射仪(XRD)、热分析(TGA)、紫外-可见分光光度计(UV-vis)、激光粒度分析等手段对复合微凝胶进行结构、组成和性质表征. 研究结果表明, 复合纳米银后的P(St-NIPAM)/PNIPAM-Ag复合微凝胶仍具有温敏性, 且其温度敏感性随壳层中复合纳米银含量的增加而减弱. P(St-NIPAM)/PNIPAM-Ag复合微凝胶对对硝基苯酚的还原反应具有良好的催化活性, 在45 min内基本将对硝基苯酚催化还原为对氨基苯酚.     

Mechanochemical Synthesis of Stimuli Responsive Microgels

Mechanochemical approaches are widely used for the efficient, solvent-free synthesis of organic molecules, however their applicability to the synthesis of functional polymers has remained underexplored. Herein, we demonstrate for the first time that mechanochemically triggered free-radical polymerization allows solvent- and initiator-free syntheses of structurally and morphologically well-defined complex functional macromolecular architectures, namely stimuliresponsive microgels. The developed mechanochemical polymerization approach is applicable to a variety of monomers and allows synthesizing microgels with tunable chemical structure, variable size, controlled number of crosslinks and reactive functional end-groups.     

Preparation and characterization of surfactant-free polystyrene/layered double hydroxide exfoliated nanocomposite via soap-free emulsion polymerization

The soap-free emulsion polymerization has been applied for preparing the surfactant-free polystyrene/layered double hydroxide exfoliated nanocomposite. The XRD and TEM determinations have been used to monitor the changes of interlayer spacing and morphology during polymerization. The results show that the obtained nanocomposite has the homogeneous structure of polymeric and inorganic components. Due to the absence of organic surfactant, the PS/LDH nanocomposite shows a remarked improvement on the onset decomposition temperature compared with virgin PS.     

无皂种子分散聚合法制备单分散双重响应性微凝胶

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.     

粘土对N-异丙基丙烯酰胺和丙烯酸叔丁酯共聚形成微凝胶的影响

以无机粘土(锂蒙脱石)作为物理交联剂,在不加任何乳化剂的条件下,通过无皂乳液聚合制备了一系列粒径在250nm左右且具有温敏性的N-异丙基丙烯酰胺(NIPAM)和丙烯酸叔丁酯(tBA)共聚微凝胶,并通过傅立叶变换红外光谱、扫描电镜、准静态光散射、X射线衍射仪和差示扫描量热法对所合成微凝胶的化学结构、表面形态和温度敏感性进行了表征.研究表明,粘土起到交联剂的作用;tBA的引入可以调节微凝胶的体积相转变温度;所制得的粘土交联微凝胶具有较好的粒径分布且粒径在140nm至350nm之间.     

Preparation of poly (styrene-methyl methacrylate)/SiO2 composite nanoparticles via emulsion polymerization. An investigation into the compatiblization

Inorganic/organic nanocomposite systems, in which inorganic particles are encapsulated into the polymer matrix, are new classes of polymeric materials. These materials combine the properties of both components. It means that polymer component with excellent optical property, flexibility and toughness could improve the brittleness of inorganic particles and besides, inorganic particles could increase the strength and modulus of polymers. There are various methods to make these inorganic/organic nanocomposites. One of them is the chemical process, in which polymerization is performed directly in the presence of the inorganic particles. Examples of miniemulsion, suspension or dispersion polymerization can be found in the literature but emulsion polymerization is by far the technique most frequently used.In this work, latex containing nanostructure hybrid of copolymer (styrene, methyl methacrylate, acrylic acid) and inorganic nanoparticles (silica) with core/shell structure was prepared via semi-batch emulsion polymerization. At first, silica nanoparticles were dispersed in water phase in an ultrasound bath to prevent the aggregation of nanoparticles, and then emulsion polymerization was performed in the presence of silica nanoparticles. Related tests and analysis confirmed the success in synthesis of nanostructure hybrids. Induced coupled plasma (ICP) analysis and thermal gravimetric analysis (TGA) showed the presence and amount of silica nanoparticles in the final latex. Dynamic light scattering (DLS) analysis confirmed the presence of 25-35 nm particles in the system and transmission electron microscopy (TEM) showed the core/shell morphology of nanoparticles. It has been shown that with an appropriate surfactant, adjusting the pH of media, using suitable monomers and under controlled conditions, it would be possible to produce stable organic/inorganic composite nanoparticles with core/shell structure. In another attempt and in order to investigate the effect of compatiblizing system, styrene-methyl methacrylate was copolymerized in the presence of modified silica particles with oleic acid as the inorganic dispersed phase at the same condition. Similar characterizations were performed in order to have a worthwhile comparison. The results for the late procedure show the effect of oleic acid in formation of aggregates as the core for polymeric nanocomposite particles.     

高浓度丙烯酸酯类微凝胶分散液的制备及性质

用微乳液聚合方法合成了浓度高达30wt%的丙烯酸酯类微凝胶,研究了乳化剂用量和微乳液浓度对微凝胶粒径及分布的影响,以及交联剂用量对微凝胶二甲苯分散液的流变行为的影响。利用制备的微凝胶对高固体份羟基丙烯酸树脂进行了改性。实验结果表明,微凝胶改性的树脂具有显著的切力变稀现象。     

Emulsion polymerization of divinyl monomers stabilized by sodium dodecyl sulfate and bis(2‐ethylhexyl)sulfosuccinate sodium salt

The emulsion polymerization of divinyl monomers is investigated. Emulsions were obtained in the presence of sodium dodecyl sulfate and bis(2‐ethylhexyl)sulfosuccinate sodium salt as surfactants. The influence of monomer type and kind of surfactant on the particle size distribution is studied. The porous structure of the broken emulsions is also determined. The results indicate that the diameter of nanospheres obtained from two divinyl monomers are significantly larger than those obtained from polystyrene. Aggregation of the particles and the pore‐forming diluent added to the emulsion are responsible for the existence of pores. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3967–3973, 2002     

UCST-like hybrid PAAm-AA/Fe3O4 microgels. Effect of Fe3O4 nanoparticles on morphology, thermosensitivity and elasticity

The incorporation of metal oxide nanoparticles into microgels forming hybrid systems gives additional functionalities to the system and widens the field of potential application in biomedicine, biotechnology, and other fields. In particular, there have been very few investigations regarding UCST-like hybrid microgels. In connection with this, we report the preparation of UCST-like hybrid microgels of magnetite nanoparticles (Fe(3)O(4)) encapsulated in poly(acrylamide-acrylic acid) microgel matrix via an inverse emulsion polymerization method. The key factor in the preparation of hybrid microgels is the need to divide in two the aqueous phase of the emulsion and feed them separately in order to avoid the aggregation of magnetic nanoparticles prior to polymerization reaction. The morphology, size, and spherical shape of hybrid microgels are determined by scanning electron microscopy. The encapsulation of magnetite nanoparticles within the polymer matrix is confirmed by transmission electron microscopy. Dynamic light scattering is employed to study both the swelling UCST-like behavior and the surface charge of the hybrid microgels. Swelling measurements confirm that the incorporation of magnetite does not affect the thermosensitivity of the system. In order to highlight the rheological behavior that can affect the final potential applications of these hybrid systems, a deep study of the viscoelastic properties is carried out by means of an oscillatory rheometer. The dependence of G' and G' of the microgel dispersions with the frequency suggests a gel-like behavior and hence the occurrence of structural organization. In order to understand this structure formation and the influence of the magnetite in the interaction between hybrid microgels, scaling theory was applied. In terms of rheology, the addition of magnetite leads to a change in the interaction between hybrid microgels giving rise to an increase in the elasticity of the system.     

Use of functional microgels with vinyl groups to accelerate photopolymerization reaction

Three types of functional microgels with vinyl groups on their surface were prepared. For the first type, the counter anion from clorin was exchanged with β-methacryloylethyl sulfonic acid, styrene sulfonic acid or allyl sulfonic acid in a microgel with ammonium anions. For the second and third types, a quaternization with N,N-dimethylaminoethyl methacrylate of 3-chloro-2-hydroxypropyl methacrylate in the presence of microgel particles was prepared by emulsion copolymerization of styrene, chloromethylstyrene or N,N-dimethylamino-methylbenzene, and divinylbenzene. The resulting samples show good dispersibility in organic solvents without an emulsifier. A functional microgel-based photopolymer combined with an acrylate monomer and ultraviolet (UV) or visible (VIS) light-absorbing photoinitiators provides oleophilic images when exposed to UV or VIS light and developed in tap water. This photopolymer has a higher sensitivity than those of photopolymers based on microgels with an analogous composition but without vinyl groups. Photopolymers pepared by using functional microgels with a methacryloyl group exhibited a higher rate of polymerization (R_p) than that of photopolymers based on microgels without a vinyl group. The R_p of photopolymers prepared by using a functional microgel with either an allyl group or vinylphenyl group was nearly equal to that of photopolymers based on microgels with ammonium ions. Their high sensitivities are attributed to the rapid photopolymerization in the methacryloyl group. To determine how the photoreaction mechanism enhances sensitivity, the photoreaction products were investigated using a model photopolymerization system. It was found that the gelation reactions enhancing sensitivity are predominantly the polymerization and crosslinking ones when a microgel with the methacryloyl group is used, and the graft copolymerization with acrylate monomers when a microgel with either the allyl group or vinylphenyl group is used.     

不饱和端基超支化聚合物/丙烯酸酯共聚乳液的研究

利用Si—H加成反应制得了以CC为端基的超支化含硅聚合物,并将其与丙烯酸酯类单体进行乳液共聚,对聚合反应机理及所得聚合物的性能进行了测试分析.结果表明,含有大量CC端基的超支化含硅聚合物能与丙烯酸酯类单体稳定聚合,制得了平均粒径小于100nm高度交联的乳胶粒子.共聚物的红外光谱证实,超支化聚合物的不饱和端基已全部反应,形成了以超支化聚合物为多臂交联点的交联型乳胶粒子.随聚合体系中超支化聚合物用量的增加,乳液聚合反应速率增大,乳胶粒粒径减小,共聚物热稳定性显著提高.