Multihollow structured poly(methyl methacrylate)/silver nanocomposite microspheres prepared by suspension polymerization in the presence of dual dispersion agents

Poly(methyl methacrylate) (PMMA)/silver nanocomposite microspheres with unique multihollow structures were prepared by suspension polymerization in the presence of dual dispersion agents. The addition of a lipophilic emulsifier, polyethylene glycol (30EO) dipolyhydroxystearate (Arlacel P135), not only stabilized water-in-oil (W/O) emulsion, but also converted silver nanoparticles from hydrophilic to lipophilic. When a suspension polymerization dispersion agent, poly(vinyl alcohol), was added to the above W/O emulsion system, a water-in-oil-in-water suspension was formed with silver nanoparticles dispersed in the oil phase. The suspension polymerization was carried out at low temperature with 2,2’-azobis(2,4-dimethylvaleronitrile) as the initiator. When modified silver nanoparticles were added, the rate of polymerization increased slightly. High monomer conversion (about 85%) was obtained in spite of low polymerization temperature of 30 °C. Under controlled conditions, PMMA/silver microspheres with various hollow structures were synthesized. The PMMA/silver microspheres with multihollow structure showed high antibacterial ability.     

Magnetic poly(glycidyl methacrylate)-based microspheres prepared by suspension polymerization in the presence of modified La0.75Sr0.25MnO3 nanoparticles

With the aim of preparing new magnetic poly(glycidyl methacrylate) (PGMA) microspheres suitable for magnetic separation, La_0.75Sr_0.25MnO₃ nanoparticles were selected as a core material. In order to improve their compatibility with PGMA, the surface of the nanoparticles was treated with penta(methylethylene glycol) phosphate methacrylate (PMGPMA) as a stabilizer. Subsequently, the nanoparticles were encapsulated by the suspension polymerization of glycidyl methacrylate (GMA) resulting in a relatively homogeneous distribution of La_0.75Sr_0.25MnO₃ nanoparticle aggregates inside the polymer microspheres. Microspheres in the size range of a hundred micrometers with a broad particle size distribution were obtained. PMGPMA can be considered to be an efficient compatibilizer between La_0.75Sr_0.25MnO₃ nanoparticles and PGMA. Both PMGPMA-coated La_0.75Sr_0.25MnO₃ nanoparticles and magnetic PGMA microspheres were characterized in terms of morphology, particle size, composition and magnetic properties by the appropriate methods, such as X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), light microscopy and SQUID magnetometry.     

Synthesis of high-molecular-weight poly(vinyl alcohol) with high yield by novel one-batch suspension polymerization of vinyl acetate and saponification

Generally, owing to tautomerism of vinyl alcohol monomer, poly(vinyl alcohol) (PVA) cannot be obtained by direct polymerization but it can be obtained by the saponification of poly(vinyl ester) precursors such as poly(vinyl acetate) (PVAc). In this study, to obtain high-molecular-weight (HMW) PVA with high yield through a one-batch method, we tried continuous saponification of PVAc prepared by suspension polymerization of vinyl acetate (VAc). We controlled various polymerization conditions, such as polymerization temperature, initiator concentration, suspending agent concentration, agitation speed, and VAc/water ratio, and obtained PVAc with a maximum conversion of VAc into PVAc of over 95-98%. PVA beads having various molecular parameters were prepared by continuous saponification of PVAc microspheres. Despite our employing a one-batch process, a maximum degree of saponification of 99.9% could be obtained. Continuous heterogeneous saponification of prepared PVAc yielded HMW PVA having a number-average degree of polymerization of 2,500-5,500, a syndiotactic diad content of 51-52%, and degree of saponification of 85.0-99.9%.     

Electrospinning and characterization of medium-molecular-weight poly(vinyl alcohol)/high-molecular-weight poly(vinyl alcohol)/montmorillonite nanofibers

Submicron fibers of medium-molecular-weight poly(vinyl alcohol) (MMW-PVA), high-molecular-weight poly(vinyl alcohol) (HMW-PVA), and montmorillonite clay (MMT) in aqueous solutions were prepared by electrospinning technique. The effect of HMW-PVA and MMT on the morphology and mechanical properties of the MMW-PVA/HMW-PVA/MMT nanofibers were investigated for the first time. Scanning electron microscopy, viscometer, tensile strength testing machine, thermal gravimetric analyzer (TGA), and transmission electron microscopy (TEM) were utilized to characterize the PVA/MMT nanofibers morphology and properties. The MMW-PVA/HMW-PVA ratios and MMT concentration played important roles in nanofiber's properties. TEM data demonstrated that exfoliated MMT layers were well distributed within nanofibers. It was also found that the mechanical property and thermal stability were increased with HMW-PVA and MMT contents.     

Preparation of poly(vinyl pivalate) microspheres by dispersion polymerization in an ionic liquid and saponification for the preparation of poly(vinyl alcohol) with high syndiotacticity

We report here a successful free-radical dispersion polymerization of vinyl pivalate (VPi) in an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][TFSI]) using poly(vinyl pyrrolidone) (PVP) as a stabilizer. Morphological analysis by FE-SEM revealed that poly(vinyl pivalate) (PVPi) obtained from dispersion polymerizations were in the form of spherical particles. Micron-sized, PVPi particles with a number-average molecular weight (M_n) of 166,400 g/mol could be obtained using 5% stabilizer (w/w to monomer) at 65 °C for 20 h. The effects of varying concentration of stabilizer, initiator and monomer upon polymer yield, molecular weight, and morphology of PVPi were also investigated. Analogous polymerizations in dimethyl sulfoxide (DMSO) and bulk served as references. In addition, the preparation of poly(vinyl alcohol) (PVA) by saponification of the resultant PVPi was described.     

Monodisperse and isolated microspheres of poly(N-methylaniline) prepared by dispersion polymerization

Monodisperse and isolated microspheres of poly(N-methylaniline) were successfully prepared through chemical polymerization of N-methylaniline by in adipic acid containing poly(vinylpyrrolidone) (PVP). Mean diameters of the microspheres with smooth surfaces changed from 320 to 100 nm by increasing the reaction temperature from 25 to 75 °C. The concentration of PVP did not affect much the size of microspheres, but the increased PVP concentration led to longer induction times for the onset of dispersion polymerization.     

Preparation and properties of poly(vinyl alcohol)/silica nanocomposites derived from copolymerization of vinyl silica nanoparticles and vinyl acetate

Nanocomposites of poly(vinyl alcohol)/silica nanoparticles (PVA-SNs) were prepared by in-situ radical copolymerization of vinyl silica nanoparticles functionalized by vinyltriethoxysilane (VTEOS) and vinyl acetate with benzoyl peroxide (BPO, i.e., initiator), subsequently saponified via direct hydrolysis with NaOH solution. The resulting vinyl silica nanoparticles, PVA-SNs were characterized by means of fourier transformation spectroscopy (FTIR), transmission electron microscopy (TEM) and the elemental analysis method. Effects of silica nanoparticles on viscosity and alcoholysis of PVA-SNs were studied by a ubbelohode capillary viscometer and the back titration method. The morphological structure of PVA-SN films was investigated by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile test were used to determine the thermal and mechanical properties of PVA-SN films. The results indicated that the content of vinyl groups on the surface of the vinyl silica nanoparticles was up to 3.02 mmol/g and vinyl silica nanoparticles had been successfully copolymerized with vinyl acetate. Furthermore, compared to pure PVA, silica nanoparticles bonded with polymer matrix in a low concentration affected the viscosity and alcoholysis of the PVA-SNs materials. At the same time, it resulted in the improvement of the thermal and mechanical properties of the PVA-SN materials due to a strong interaction between silica nanoparticles and the polymer matrix via a covalent bond. It could be found that the optical clarity of the membrane was changed through UV-Vis absorption spectrum due to the introduction of silica nanoparticles.     

Synthesis of high molecular weight poly(methyl methacrylate) microspheres by suspension polymerization in the presence of silver nanoparticles

To prepare high molecular weight (HMW) poly(methyl methacrylate) (PMMA)/silver microspheres, methyl methacrylate was suspension-polymerized in the presence of silver nanoparticles using a low-temperature initiator at different conditions. The rate of conversion was increased with increasing initiator concentration. In the case of adding silver nanoparticles, the rate of polymerization decreased slightly. High monomer conversion (about 95%) was obtained in spite of low polymerization temperature of 30 °C. Under controlled conditions, PMMA/silver microspheres with various viscosity-average degree of polymerization (6,000–37,000) were prepared.     

Preparation and characterization of poly(propylene carbonate)/montmorillonite nanocomposites by solution intercalation

Poly(propylene carbonate) (PPC) is a new biodegradable aliphatic polycarbonate. However, the poor thermal stability and low glass transition temperatures (T_g) have limited its applications. To improve the thermal properties of PPC, organophilic montmorillonite (OMMT) was mixed with PPC by a solution intercalation method to produce nanocomposites. An intercalated-and-flocculated structure of PPC/OMMT nanocomposites was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal and mechanical properties of PPC/OMMT nanocomposites were investigated by thermal gravimetric analysis (TGA), differential scanning calorimetric (DSC), and electronic tensile tester. Due to the nanometer-sized dispersion of layered silicate in polymer matrix, PPC/OMMT nanocomposites exhibit improved thermal and mechanical properties than pure PPC. When the OMMT content is 4 wt%, the PPC/OMMT nanocomposite shows the best thermal and mechanical properties. These results indicate that nanocomposition is an efficient and convenient method to improve the properties of PPC.     

Characterization of poly(vinyl alcohol) during the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier

During the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates from the aqueous phase contributing to the formation of polymer particles. Since particle formation and therefore the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PVA. In this work, the quantitative separation and characterization of the grafted water-insoluble PVA was carried out by a two-step selective solubilization of the PVAc latex, first with acetonitrile to separate PVAc homopolymer, followed by water to separate the water-soluble PVA from the remaining acetonitrile-insoluble material. After the separation, the water-soluble and water-insoluble PVA were characterized by Fourier Transform Infrared (FTIR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, from which the details of the PVA-graft-PVAc structure were obtained. © 1996 John Wiley & Sons, Inc.     

Poly(hydroxyether of bisphenol A)/poly(vinyl acetate) blends: In situ polymerization preparation,morphology, and properties

The blends of poly(hydroxyether of bisphenol A) (phenoxy) and poly(vinyl acetate) (PVAc) were prepared through in situ polymerization, i.e., the melt polymerization of diglycidy ether of bisphenol A (DGEBA) and bisphenol A in the presence of PVAc. The polymerization reaction started from the initial homogeneous ternary mixture of PVAc/DGEBA/bisphenol A; the phase separation induced by reaction occurred as the polymerization proceeded. The phenoxy/PVAc blends with PVAc content up to 20 wt % were obtained and were further characterized by the solubility, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electronic microscopy (SEM). The results indicate that no intercomponent reaction occurred during the in situ polymerization. All the blends display separate glass transition temperatures (Tg's); the very fine phase-separated morphology was obtained by this polymerization blending method. Mechanical tests show that the prepared blends exhibited substantial improvement of mechanical properties, especially in impact strength, which could be ascribed to the formation of the fine phase-separation morphology during in situ polymerization. The thermogravity analysis (TGA) of the blends showed that the thermal stability of the PVAc-rich phases in the blends was enhanced in comparison to the pure PVAc due to the synergistic contribution of the two phases in energy transportation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2329–2338, 1999     

Relationships between nanostructure and thermomechanical properties in poly(vinyl alcohol)/montmorillonite nanocomposite with an entrapped polyelectrolyte

Poly(vinyl alcohol)/montmorillonite (PVA/MOM) hydrogels containing coacervated microparticles of sulfonated polyester (PES) were prepared by direct mixture of the components in water. The system was characterized by using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamical mechanical analysis (DMA). The influence of PES and MOM on the microstructure of the nanocomposite hydrogels was established. The presence of PES causes a significant change on the crystallinity of PVA. Furthermore, the presence of MOM leads to a hierarchical nanostructure that also contributes to change the crystallinity of PVA. The results of structural investigation are correlated with the mechanical properties of the composites obtained by DMA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2618–2629, 2008     

Poly(vinyl alcohol)/GO-MMT nanocomposites: Preparation,structure and properties

A facile, efficient and environment friendly method is established to prepare poly(vinyl alcohol)(PVA) based graphene oxide-montmorillonite(GO-MMT) nanocomposites in aqueous media. GO-MMT nanohybrid is obtained by the combination of GO and MMT in water without any reducing or stabilizing agents. The formation of GO-MMT nanohybrid is due to the hydrogen bonding and crosslinking effects. The sodium ions within MMT sheets act as crosslinkers between GO sheets and MMT platelets. The resultant nanocomposites are characterized by means of X-ray diffraction(XRD), scanning electron microscopy(SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA) and mechanical testing. Compared to that of pure PVA, PVA nanocomposites show enhanced thermal stabilities and mechanical properties, which results from strong interfacial adhesion of the nanoadditives in PVA matrix. The further increase in the tensile strength and modulus results from strong interaction between PVA chains and layered GO-MMT as well as good mechanical properties of GO-MMT hybrid, compared to PVA/GO and PVA/MMT nanocompsoites.     

Low temperature suspension polymerization of vinyl acetate using 2,2′-azobis(2,4-dimethylvaleronitrile) for the preparation of high molecular weight poly(vinyl alcohol) with high yield

 To obtain high molecular weight (HMW) poly(vinyl acetate) (PVAc) with high conversion and high linearity for a precursor of HMW poly(vinyl alcohol) (PVA), vinyl acetate (VAc) was suspension-poly-merized using a low-temperature initiator, 2,2′-azobis (2,4-dimethyl-valeronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior and molecular structures of PVAc and PVA prepared by saponifying PVAc were investigated. On the whole, the experimental results well corres-ponded to the theoretically predicted tendencies. Suspension polymerization was slightly inferior to bulk polymerization in increasing molecular weight of PVA. In contrast, the former was absolutely superior to the latter in increasing conversion of the polymer, which indicated that the suspension polymerization rate of VAc was faster than the bulk one. These effects could be explained by a kinetic order of ADMVN concentration calculated by initial-rate method and an activation energy difference of polymerization obtained from the Arrhenius plot. Suspension polymerization at 30 °C by adopting ADMVN proved to be successful in obtaining PVA of HMW (number-average degree of polymerization (P _n)): (4200–5800) and of high yield (ultimate conversion of VAc into PVAc: 85–95%) with diminishing heat generated during polymerization. In the case of bulk polymerization of VAc at the same conditions, maximum P _n and conversion of 5200–6200 and 20–30% was obtained, respectively. The P _n, lightness, and syndiotacticity were higher with PVA prepared from PVAc polymerized at lower temperatures. Received: 10 February 1998 Accepted: 15 April 1998     

Reactive poly(glycidyl methacrylate) microspheres prepared by dispersion polymerization

Poly(glycidyl methacrylate) [poly(GMA)] microspheres of narrow size distribution were prepared in a simple one‐step procedure by dispersion radical polymerization. Depending on the solvent used, poly(GMA) particle size could be controlled in the range of 0.5–4 μm by changing the solubility parameter of the reaction mixture. In N,N′‐dimethylformamide (DMF)/methanol mixture, the particle size increased and the size distribution broadened with decreasing initial solubility parameter. While in the DMF/methanol solvent system, hydroxypropyl cellulose (HPC) or cellulose acetate butyrate (CAB) were taken as steric stabilizers of the dispersion polymerization, poly(vinylpyrrolidone) (PVP) was used in alcoholic media. Contrary to the DMF/methanol system, narrow particle size distributions were obtained with PVP‐stabilized polymerizations in ethanolic, methanolic, propan‐1‐olic or butan‐1‐olic medium. Both the particle size and polydispersity were reduced with increasing stabilizer concentration. If lower molecular‐weight PVP was used, larger microspheres were obtained. Poly(GMA) samples prepared in a neat alcoholic medium virtually quantitatively retained oxirane group content after the polymerization. Reactivity of the poly(GMA) microspheres was confirmed by their hydrolysis and aminolysis. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3855–3863, 2000     

聚有机硅丙烯酸酯/蒙脱土纳米复合乳液的流变性

本文采用原位插层聚合的方法,单体插层插入有机蒙脱土片层中,然后引发原位聚合,制备了聚有机硅丙烯酸酯与有机蒙脱土的复合乳液。并用旋转粘度计对其流变性进行了研究。发现乳液的表观粘度(ηa)、稠度系数(K)、零剪切粘度(η0)、粘流活化能(Ea)随有机硅含量增加而增加,而流动指数(η)则减小;ηa、K、η0、Ea随有机蒙脱土含量的增加先增大后减小,当蒙脱土含量为1％时达最大值,n则为最小值。     

聚丙烯酰胺/蒙脱土纳米复合物-聚乙烯醇共混膜的制备及其渗透汽化性能

用原位聚合法制备聚丙烯酰胺/蒙脱土(PAM/MMT)纳米复合材料, 通过透射电镜研究了蒙脱土在聚丙烯酰胺基体中的形貌和分布. 结果表明, 蒙脱土以片层结构分布在聚合物基体中. 用超声波分散聚乙烯醇和聚丙烯酰胺-蒙脱土共混铸膜液制得共混膜, 用红外吸收光谱和扫描电镜研究了两者的相互作用和形貌. 考察了共混膜在异丙醇-水混合溶液中的溶胀吸附性能及共混比和蒙脱土含量对膜分离性能的影响, 结果显示, 聚乙烯醇膜中添加适量的蒙脱土纳米粒子可以大大改善膜的分离选择性.     

Molecularly imprinted microspheres and nanospheres for di(2-ethylhexyl)phthalate prepared by precipitation polymerization

Molecularly imprinted microspheres (MIMs, >3 μm) and nanospheres (MINs, ≈450 nm) for the environmental endocrine disruptor di(2-ethylhexyl)phthalate (DEHP) were prepared by a precipitation polymerization (PP) procedure. The effect of the dispersive solvents acetonitrile (ACN) and cyclohexane (CH), the cross-linkers ethylene glycol dimethacrylate (EDMA) and trimethylpropane trimethacrylate (TRIM), and the template on particle size and morphology of polymers was investigated in detail by scanning electron microscopy (SEM) and BET adsorption isotherm determination. When used as HPLC stationary phase, the microspheres exhibited strong affinity for the template DEHP with an imprint factor (IF) higher than 8.0 in ACN/water (60:40, v/v) as mobile phase. Furthermore, baseline separation of DEHP from benzyl butyl phthalate (BBP) and dibutyl phthalate (DBP) could be achieved. In contrast, no or only poor separation could be observed with non-imprinted polymeric polymers (NIPs) or imprinted bulk polymers (MIB), respectively. Similarly, the obtained MINs exhibited an imprinting effect in pure ACN, i.e. the bond amount of DEHP was significantly higher compared to NIPs, as was shown in rebinding experiments. Besides their use as an HPLC stationary phase, MIMs might further be applicable for SPE sample cleanup, while MINs could be used as a recognition layer on sensor surfaces. Figure Molecularly imprinting of di(2-ethylhexyl)phthalate (DEHP)     

Narrowly dispersed molecularly imprinted microspheres prepared by a modified precipitation polymerization method

A modified precipitation polymerization (MPP) method was established to prepare narrowly dispersed molecularly imprinted polymeric microspheres. MPP was stabilizer and surfactant free and needed only small amount of porogen (about 50 wt.%). Only part of alcohols and all the alkanes tested formed particles. Using a mixture of alkane and toluene as porogen, the carbon numbers of alkanes and solubility parameter of porogenic solvents were important factors in controlling particle morphology. Nearly mono-dispersed microspheres with diameter of about 2-3 μm were synthesized by MPP using mineral oil:toluene = 2:3 as porogen. Template did not affect the formation of globe microspheres in MPP. Microspheres prepared under the lowest reaction temperature had the highest binding capability. When used as sorbents of high performance liquid chromatography (HPLC), the microspheres prepared by MPP using bisphenol A, estradiol, and tebuconazole as template had similar binding selectivity and higher binding capability compared to microspheres synthesized by classical precipitation polymerization. Photoinitiation and low reaction temperature were important factors attributed to better binding capability of microspheres prepared by MPP.     

Production of hollow polymer particles by suspension polymerization

 Polymer particles having single hollow in the inside were successfully prepared by suspension polymerization for divinylbenzene/ toluene droplets dissolving polystyrene (PS) in an aqueous solution of poly(vinyl alcohol). Such a hollow polymer particle was not obtained without PS. The hollow structure was affected by the molecular weight and the concentration of PS. Received: 3 December 1997 Accepted: 27 March 1998