Preparation and colloidal stability of monodisperse magnetic polymer particles

A previously proposed method was examined for producing monodisperse, submicrometer-sized magnetic polymer particles. The method applies soap-free emulsion polymerization during which Fe3O4 magnetic nanoparticles are heterocoagulated onto precipitated polymer nuclei. To chemically fix the magnetic particles to the polymer nuclei, vinyl groups were introduced on the Fe3O4 particles in a preliminary surface modification reaction with methacryloxypropyltrimethoxysilane, and methacryloxypropyldimethoxysilane (MPDMS) was added to reaction systems of the soap-free emulsion polymerization. The colloidal dispersion stability of magnetic polymer particles was improved by the addition of an ionic monomer, sodium p-styrenesulfonate (NaSS), during the polymerization. The polymerizations were carried out with styrene monomer and potassium persulfate initiator in ranges of NaSS concentrations (0-2.4 x 10(-3) M), NaSS addition times (60-80 min), and monomer concentrations (0.3-0.6 M) at fixed concentrations of 1.6 x 10(-2) M initiator and 1.3 x 10(-2) M MPDMS for pH 4.5 adjusted with a buffer system of [CH3COOH]/[NaOH]. The addition of NaSS during the polymerization could maintain the dispersion stability of magnetic polymer particles during the polymerization. Selection of the reaction conditions enabled the preparation of colloidally stable, submicrometer-sized magnetic polymer particles that had coefficients of variation of distribution smaller than the standard criterion for monodispersity, 10%.     

Multiphase Polymer Dispersions and Nanocomposites by Catalytic/Free Radical Emulsion Polymerization

Summary: Free radical emulsion polymerization of styrene (S) or butyl acrylate (BA) in the presence of latices of linear polyethylene (PE) prepared by catalytic emulsion polymerization affords colloidally stable multiphase latices. Coagulation of a PE/PS latex affords nanocomposites composed of small PE phases dispersed in a PS matrix, as evidenced by the large supercoolings of PE crystallization (by DSC). TEM of PE/PBA latices indicates a PBA phase around the PE particles under the emulsion polymerization conditions investigated. Films formed from these dispersions exhibit homogeneously dispersed PE particles.

Multiphase latices are obtained by free radical emulsion polymerization of butyl acrylate in the presence of latices of linear polyethylene (PE) prepared by catalytic emulsion polymerization.     

氧化-还原引发剂引发苯乙烯超浓乳液聚合的研究

以过氧化羟基二异丙苯(CHPO)和四乙烯五胺(TEPA)为氧化-还原引发剂,以十二烷基硫酸钠(SDS)为乳化剂,十六醇(CA)为共乳化剂,通过超浓乳液聚合方法制备了聚苯乙烯乳胶粒子.探讨了乳化剂浓度及配比、分散相体积分数、引发剂种类、引发剂浓度及配比和温度等各因素对乳液稳定性、聚合速率、乳胶粒子大小、形态及分布的影响.用透射电子显微镜(TEM)观察了乳胶粒子的形态,用粘度法测定了聚苯乙烯的粘均分子量.考察了苯乙烯进行超浓乳液聚合的反应动力学,求得在30℃时聚合速率方程为Rp=K[M]^0.36[I]^0.49[E]^0.72,表观活化能为19.72kJ/mol.所得乳胶粒子的直径在0.1～0.3μm之间,粘均分子量在2×10⁶～4×10⁶之间.为低温下实现超浓乳液薄层聚合提供了参考数据.     

超声无皂乳液聚合制备BA/St/AM三元共聚物乳胶粒及其聚合机理研究

将超声技术引入到无皂乳液聚合方法中,在不加入任何引发剂和乳化剂的情况下,制备了丙烯酸丁酯(BA)/苯乙烯(St)/丙烯酰胺(AM)三元共聚纳米乳胶粒.研究了不同超声时间对单体转化率、乳胶粒粒径以及乳液粘度的影响.同时还探讨了超声无皂乳液聚合机理,认为AM在聚合过程中起到了引发和稳定的作用.TEM照片表明,乳胶粒直径大约在80nm左右,FTIR及DSC分析表明产物为三元共聚物,而不是共混物.     

含树枝状大分子PAMAM的苯乙烯乳液聚合

将树枝状大分子PAMAM (4 5代 )作为种子 ,以苯乙烯为代表性单体进行乳液聚合 .研究结果表明 ,加入树枝状大分子PAMAM时 ,所制得的聚合物乳液粒子平均粒径在 30～ 5 0nm之间 ,小于 10 0nm ,且大小分布均匀 ;所制备的聚合物在 16 70cm- 1 左右处出现酰胺的特征吸收峰 ,在 330 0cm- 1 左右处出现N—H伸缩振动特征峰 ;说明树枝状大分子PAMAM起到种子的作用 ,所制备的聚合物含树枝状大分子PAMAM .     

NONCONVENTIONAL EMULSION POLYMERIZATION OF ACRYLONITRILE CATALYZED BY in situ METAL COMPLEXw

 Nano-sized polyacrylonitrile (PAN) particles were prepared under the catalytic effect of in situ developed CoCl₂/EDTA complex with ammonium persulfate as the initiator in the absence of any added emulsifier. The emulsion polymerization was studied at varying concentrations of the initiator, monomer, complex and solvent over a temperature range of 30-70^oC. The overall activation energy (Ea, 49.79 kJ/mol), energy of dissociation of initiator (Ed, 82.68 kJ/mol), number of micelles (0.163 x 1018) and the viscosity average molecular weight of the polymer were computed. The distribution of particle sizes was determined by transmission electron microscopy (TEM). It was found that the oil-in-water polymerization was stabilized by the presence of the CoCl₂/EDTA in situ complex reducing the particle size into the nano order. The average diameters of PAN nano particles, obtained by TEM, were in the range of 50–150 nm at the maximum conversion. The experimental particle size was mainly dependent on the concentration of the complex and temperature.     

一种单分散醋-丙乳液的合成与应用研究

以醋酸乙烯酯(VAc)、丙烯酸正丁酯(BA)和甲基丙烯缩水甘油酯(GMA)为共聚单体,采用预乳化-半连续种子乳液聚合的方法,合成了一类改性醋丙乳液.用透射电子显微镜(TEM)、激光光散射(LLS)等测定了乳胶粒的粒径、粒径分布和粒子形态,发现其粒径在120 nm左右,并呈现较好的单分散特性;Zeta电位和流变测定结果显...     

Ultrathin films of variable polarity and crystallinity obtained from 1,2-polybutadiene nanoparticle dispersions

Characterization of ultrathin films of different polymer nanoparticles obtained at room temperature via spin-coating of aqueous dispersions and their morphology are described. Very small nanoparticles of semicrystalline 1,2-polybutadiene (PB), noncrystalline poly(1-butene) (PH), and poly(1-butenal) (PHF) were prepared via catalytic emulsion polymerization and subsequent hydrogenation or hydroformylation. The prefabricated nanoparticles were used as building blocks. The thin films obtained are continuous and transparent (n=1.5; κ=0). The properties of these films, formed from different constituents, are analyzed. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images show that the PB-films are very smooth (rms roughness=10 nm) and polycrystalline. Recrystallization of these PB films reveals that edge-on lamellae are the constituent units. Films with very low roughness values (rms roughness <2 nm) are obtained with PH nanoparticles, due to the soft character of the nanoparticles. The AFM profile of the PHF films reveals that the surface remains structured after drying due to the high degree of the internal cross-linking that occurs in the nanoparticles. Quantification of the films' polarity (I(3)/I(1)=0.89, 1.3, and 2.1 for PHF, PB, and PH, respectively) agrees well with the previous values obtained for the polymer dispersions. Surfactant molecules are desorbed during the film formation; however, these aggregates can be removed by rinsing with water with no undesirable effects observed on the films.     

NONCONVENTIONAL EMULSION POLYMERIZATION OF ACRYLONITRILE CATALYZED BY in situ METAL COMPLEX

Nano-sized polyacrylonitrile (PAN) particles were prepared under the catalytic effect of in situ developed CoCl2/EDTA complex with ammonium persulfate as the initiator in the absence of any added emulsifier. The emulsion polymerization was studied at varying concentrations of the initiator, monomer, complex and solvent over a temperature range of 30-70℃. The overall activation energy (Ea, 49.79 kJ/mol), energy of dissociation of initiator (Ed,82.68 kJ/mol), number of micelles (0.163×1018) and the viscosity average molecular weight of the polymer were computed. The distribution of particle sizes was determined by transmission electron microscopy (TEM). It was found that the oil-in-water polymerization was stabilized by the presence of the CoCl2/EDTA in situ complex reducing the particle size into the nano order. The average diameters of PAN nano particles, obtained by TEM, were in the range of 50-150 nm at the maximum conversion. The experimental particle size was mainly dependent on the concentration of the complex and temperature.     

Poly(Acrylic Acid-b-Styrene) Amphiphilic Multiblock Copolymers as Building Blocks for the Assembly of Discrete Nanoparticles

In order to expand the utility of current polymeric micellar systems, we have developed amphiphilic multiblock copolymers containing alternating blocks of poly(acrylic acid) and poly(styrene). Heterotelechelic poly(tert-butyl acrylate-b-styrene) diblock copolymers containing an α-alkyne and an ω-azide were synthesized by atom transfer radical polymerization (ATRP), allowing control over the molecular weight while maintaining narrow polydispersity indices. The multiblock copolymers were constructed by copper-catalyzed azide-alkyne cycloaddition of azide-alkyne end functional diblock copolymers which were then characterized by (1)H NMR, FT-IR and SEC. The tert-butyl moieties of the poly(tert-butyl acrylate-b-styrene) multiblock copolymers were easily removed to form the poly(acrylic acid-b-styrene) multiblock copolymer ((PAA-PS)(9)), which contained up to 9 diblock repeats. The amphiphilic multiblock (PAA-PS)(9) (M(n) = 73.3 kg/mol) was self-assembled by dissolution into tetrahydrofuran and extensive dialysis against deionized water for 4 days. The critical micelle concentration (CMC) for (PAA-PS)(9) was determined by fluorescence spectroscopy using pyrene as a fluorescent probe and was found to be very low at 2 × 10(-4) mg/mL. The (PAA-PS)(9) multiblock was also analyzed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The hydrodynamic diameter of the particles was found to be 11 nm. Discrete spherical particles were observed by TEM with an average particle diameter of 14 nm. The poly(acrylic acid) periphery of the spherical particles should allow for future conjugation of biomolecules.     

Development of an ab initio emulsion atom transfer radical polymerization: from microemulsion to emulsion

Atom transfer radical polymerization (ATRP) has been successfully extended to an ab initio emulsion system using a "two-step" procedure, in which the final emulsion polymerization system was formed by adding monomer to an ongoing microemulsion ATRP. The newly developed AGET (activators generated by electron transfer) initiation technique was employed in the first stage of this ab initio ATRP. It allows using oxidatively stable Cu(II) species that is reduced in situ by ascorbic acid. The surfactant concentration in the final emulsion system was efficiently decreased to approximately 2 wt % (approximately 10 wt % vs monomer) by decreasing the catalyst concentration and changing the ratio of the monomer added at the microemulsion stage to the monomer added during the second stage. This two-step procedure avoids the necessity of transporting catalysts through the aqueous media during polymerization, resulting in a controlled emulsion polymerization, as evidenced by a linear first-order kinetic plot and formation of a polymer with a relatively narrow molecular weight distribution (Mw/Mn = 1.2-1.4). The polymerization typically reached 70-90% monomer conversion in 5-6 h. The resulting polymer had high chain-end functionality and was successfully chain extended to form in situ block copolymers by adding the second monomer to an ongoing emulsion polymerization. The stable latex from the ab initio emulsion ATRP had a particle size approximately 120 +/- 10 nm.     

Synthesis and Characterization of β‐CD‐Coated Polystyrene Microspheres by γ‐Ray Radiation Emulsion Polymerization

Polystyrene (PS) microspheres coated with β‐cyclodextrin (β‐CD) were fabricated via γ‐ray‐induced emulsion polymerization in a ternary system of styrene/β‐CD/water (St/β‐CD/water). The solid inclusion complex of St and β‐CD particles formed at the St droplets–water interface can stabilize the emulsion as the surfactant. TEM and XPS results showed that β‐CD remains on the surface of PS particles. The average size of the PS particles increases from 186 to 294 nm as the weight ratio of β‐CD to St rises from 5% to 12.5%. The water contact angle (CA) of PS latex film is lower than 90°, and reduces with the β‐CD content even to 36°. Thus, this work provides a new and one‐pot strategy to surface hydrophilic modification on hydrophobic polymer particles with cyclodextrins through radiation emulsion polymerization.     

Emulsion polymerization of styrene and methyl methacrylate using a hydrophobically modified inulin and comparison with other surfactants

The use of a new class of graft polymer surfactants, based on inulin, in emulsion polymerization of poly(methyl methacrylate) (PMMA) and polystyrene (PS) particles is described. PS and PMMA were synthesized by emulsion polymerization, and stable particles with a high monomer content (50 wt %) were obtained with a very small amount of polymeric surfactant ([surfactant]/[monomer] = 0.0033). The latex dispersions were characterized by dynamic light scattering and by transmission electron microscopy to obtain the average particle size and the polydispersity index, and the stability was determined by turbidimetry measurements and expressed in terms of critical coagulation concentration. The last section gives a comparison of PMMA particles prepared by emulsion polymerization using classical surfactants from different types as emulsifiers with that obtained using the copolymer surfactant. It shows the superiority of INUTEC SP1 as it is the only one that allows stable particles at 20 wt % monomer content, with a smaller ratio [surfactant]/[monomer] = 0.002.     

光引发常规乳液聚合制备氨基聚苯乙烯纳米粒子

采用一种简单易行的方法制备了氨基功能化的聚苯乙烯纳米粒子.首先,采用4-乙烯基苄氯与1,3-丙二胺置换反应制备了含有氨基功能基团的可聚合单体N-(3-氨基丙基)对乙烯基苄基亚胺(CVPD).然后,采用乳液聚合,以苯乙烯(St)和CVPD为共聚单体,水溶性的4-(2-羟乙氧基)苯基-(2-羟基-2-丙基)酮(Irgacure 2959)为光引发剂,十六烷基三甲基溴化铵(CTAB)为乳化剂,经紫外光辐照引发,合成了P(St-co-CVPD)二元共聚物的纳米胶乳.体系的乳化剂用量仅为体系总质量的0.1 wt%～0.8 wt%,远小于常用来制备纳米粒子的微乳液体系的乳化剂用量.用透射电子显微镜(TEM)和激光粒度分析仪(DLS)表征了P(St-co-CVPD)纳米粒子的粒径和粒径分布.用红外光谱(FTIR)和核磁共振(NMR)证明了P(St-co-CVPD)纳米粒子上氨基的存在,并通过茚三酮显色反应定量检测了氨基含量.分别研究了单体配比,引发剂浓度,乳化剂用量以及紫外光强度对反应体系的影响.实验结果表明,产物粒子尺寸为30～600 nm,氨基通过共价键连接在粒子上,其含量为1.2×10-5～1.6×10-4 mol/g.该乳液体系聚合反应速率较快,单体转化率在60 min内即可达到80%.所得粒子的氨基含量可以通过单体配比进行调节.粒子尺寸可通过单体配比,引发剂浓度,乳化剂用量以及紫外光强度进行调节.     

Interaction forces in thin liquid films stabilized by hydrophobically modified inulin polymeric surfactant. 2. Emulsion films

The interaction forces in emulsion films stabilized using hydrophobically modified inulin (INUTEC SP1) were investigated by measuring the disjoining pressure of a microscopic horizontal film between two macroscopic emulsion drops of isoparaffinic oil (Isopar M). A special measuring cell was used for this purpose whereby the disjoining pressure Pi was measured as a function of the equivalent film thickness hw. The latter was determined using an interferometric method. In this way Pi-hw curves were established at a constant INUTEC SP1 concentration of 2x10(-5) mol.dm-3 and at various NaCl concentrations. At a constant disjoining pressure of 36 Pa, a constant temperature of 22 degrees C, and a film radius of 100 microm, hw decreased with an increase in the NaCl concentration, Cel, and reached a constant value of 11 nm at Cel=5x10(-2) mol.dm-3. This reduction in film thickness is due to the compression of the electrical double layer, and at the above critical NaCl concentration any electrostatic repulsion is removed and only steric interaction remains. This critical electrolyte concentration represents the transition from electrostatic to steric interaction. At a NaCl concentration of 2x10(-4) mol.dm-3 the Pi-hw isotherms showed a gradual decrease in hw with an increase in capillary pressure, after which there was a jump in hw from approximately 30 to approximately 7.2 nm when Pi reached a high value of 2-5.5 kPa. This jump is due to the formation of a Newton black film (NBF), giving a layer thickness of the polyfructose loops of approximately 3.6 nm. The film thickness did not change further when the pressure reached 45 kPa, indicating the high stability of the film. Pi-hw isotherms were obtained at various NaCl concentrations, namely, 5x10(-2), 5x10(-1), 1.0, and 2.0 mol.dm-3. The initial thicknesses are within the range 9-11 nm, after which a transition zone starts, corresponding to a pressure of about 0.5 kPa. In this zone all films transform to an NBF with a jump, after which the thickness remains constant with a further increase in the disjoining pressure up to 45 kPa, with no film rupture. This indicates the very high stability of the NBF in the presence of high electrolyte concentrations. The high emulsion film stability (due to strong steric repulsions between the strongly hydrated loops of polyfructose) is correlated with the bulk emulsion stability.     

茂金属聚乙烯的支化非均匀性与结晶形态

以美国Exxon公司生产的茂金属短支链聚乙烯 (SCBPE)为研究对象 ,用DSC热分级方法研究了不同支链含量聚乙烯的支化非均匀性 ,并用TEM表征茂金属聚乙烯在不同条件下熔体结晶的形态 .SCBPE经逐步结晶分级后 ,其DSC熔融曲线出现多峰 ,表明茂金属SCBPE仍具有很大的非均匀性 .支链含量愈高 ,熔点愈低 ,非均匀性增加 .SCBPE的晶体形态随平均支链含量的增加片晶厚度减小 ,片晶尺寸分布增加 ;含量较低时 ,SCBPE在不同温度下均生成球晶结构 .随结晶温度的降低支链含量较多的分子也能参与结晶 ,故生成的片晶厚度减小 .从相分离的熔体中结晶 ,大尺度的片晶集聚体间的分离和小尺度的片晶之间相分离同时存在 .     

Preparation of macroporous functionalized polymer beads by a multistep polymerization and their application in zirconocene catalysts for ethylene polymerization

Macroporous functionalized polymer beads of poly(4‐vinylpyridine‐co‐1,4‐divinylbenzene) [P(VPy‐co‐DVB)] were prepared by a multistep polymerization, including a polystyrene (PS) shape template by emulsifier‐free emulsion polymerization, linear PS seeds by staged template suspension polymerization, and macroporous functionalized polymer beads of P(VPy‐co‐DVB) by multistep seeded polymerization. The polymer beads, having a cellular texture, were made of many small, spherical particles. The bead size was 10–50 μm, and the pore size was 0.1–1.5 μm. The polymer beads were used as supports for zirconocene catalysts in ethylene polymerization. They were very different from traditional polymer supports. The polymer beads could be exfoliated to yield many spherical particles dispersed in the resulting polyethylene particles during ethylene polymerization. The influence of the polymer beads on the catalytic behavior of the supported catalyst and morphology of the resulting polyethylene was investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 873–880, 2003     

Formulation development of a filter-sterilizable lipid emulsion for lipophilic KW-3902, a newly synthesized adenosine A1-receptor antagonist

KW-3902 (a newly synthesized adenosine A1-receptor antagonist) has potent diuretic and renal protective activities. The objective of the present study was to develop an injectable formulation of KW-3902, that was water-insoluble and less than 1 microg/ml, and so lipid emulsion was selected as a favorable formulation. Changing the mixing ratio of oil to lecithin, the particle size of the lipid emulsion was controlled, and by adjusting the mixing ratio of oil/lecithin=1:1, the weight ratio, a lipid emulsion with a mean particle size of 130 nm was prepared. This small particle size makes this emulsion filter-sterilizable, which is a favorable feature for heat labile products. The stability of the KW-3902 lipid emulsion was assessed from the viewpoint of the electrostatic repulsion, and by including the oleic acid a stable lipid emulsion was developed, which was stable for at least 12 months at 10 and 25 degrees C and for 3 months at 40 degrees C. The feature of this small particle size emulsion was also characterized by comparing it with a conventional emulsion (oil/lecithin=1:0.12, the weight ratio, particle size is 220 nm). The release of KW-3902 from the oil particles was measured and the apparent permeability of KW-3902 was calculated from the equation according to Fick's theory. The apparent permeability, P, of KW-3902 was not affected by the particle size of the emulsion (1.78x10(-11) cm/s for the small emulsion and 1.76x10(-11)cm/s for the conventional emulsion). The distribution mode of KW-3902 in the lipid emulsion was also discussed by considering the findings of the permeability and solubility of KW-3902.     

Kinetic flow-injection determination of hydrogen peroxide by use of iron(III)-catalyzed coloration and its application to the determination of biological substances.

A kinetic flow-injection (FI) method is described for the determination of hydrogen peroxide. This method is based on an iron(III)-catalyzed oxidative coupling of 4-aminoantipyrine with N,N-dimethylaniline by hydrogen peroxide. By measuring the change in the absorbance of the dye formed at 560 nm, 1 x 10(-6) - 6 x 10(-4) M hydrogen peroxide could be determined with a sampling rate of 15 h(-1). The relative standard deviation (n = 30) was 0.8% for 5 x 10(-5) M hydrogen peroxide. There was little interference of the co-existing ions and compounds. After introducing some immobilized enzyme reactors to the FI system, the proposed method allowed the determination of glucose and uric acid ranging from 1 x 10(-6) to 6 x 10(-4) M with relative standard deviations of below 2%. The applicability of the method was demonstrated by determining these substances in serum samples.     

The polymerization of acrylonitrile in miniemulsions: “Crumpled latex particles” or polymer nanocrystals

Stable dispersions of polyacrylonitrile (PAN) nanoparticles in the size range between 100 nm < d < 180 nm were made by polymerization in miniemulsion and characterized by dynamic light scattering, transmission electron microscopy (TEM), and wide angle X‐ray scattering (WAXS). Due to the insolubility of the polymer in its monomer, such particles are not accessible by classical emulsion polymerization. The pure PAN particles are composed of ca. 10 nm large polymer nanocrystals, i. e., the formed polymer precipitates and crystallizes direct after formation. As a consequence, the final latexes do not adopt spherical shape, but show a well defined, narrowly distributed boulder‐like phenotype which is called “crumpled latexes”. Copolymerization with styrene results in a continuous transition between the crumpled and a smooth spherical morphology, which is again related to a decreased degree of crystallinity.