Preparation of styrene/methacrylic acid copolymer microspheres and their composites with metal particles

 Poly(styrene-co-methacrylic acid) [P(St-co-MAA)] microspheres were prepared by emulsifier-free emulsion copolymerization of St with MAA. Fourier transform IR spectroscopy and elemental analysis were used to study the change in the content of MAA in the microspheres. The results of X-ray photoelectron spectroscopy measurements indicated the presence of carboxylic functionality on the surface of the microspheres. The P(St-co-MAA) metal composite particles were prepared by chemical metal deposition. Transmission electron microscopy observation and X-ray diffraction measurement were used to study the distribution and structure of the metal particles deposited. Received: 15 September 1999 Accepted: 24 December 1999     

Monodisperse thermosensitive particles prepared by emulsifier-free emulsion polymerization with microwave irradiation

The emulsifier-free emulsion polymerization of styrene (St) and N-isopropylacrylamide (NIPAAm) was successfully carried out with microwave irradiation, and the monodisperse thermoresponsive poly(styrene-co-N-isopropylacrylamide) (poly(St-co-NIPAAm)) particles with diameters in the range 100–130 nm were prepared. The morphology, size and size distribution of the poly(St-co-NIPAAm) particles were characterized by transmission electron microscopy, scanning electron microscopy (SEM) and photon correlation spectroscopy (PCS), respectively. The results showed that poly(St-co-NIPAAm) particles had spherical morphology, and the poly(St-co-NIPAAm) particles prepared by emulsifier-free emulsion polymerization with microwave irradiation were smaller, more uniform than those obtained with conventional heating. The hydrodynamic diameters of poly(St-co-NIPAAm) particles were decreased as the temperature increased from 25 °C to 40 °C, and poly(St-co-NIPAAm) particles collapsed remarkably at 32 °C, which is the lower critical solution temperature of the poly(N-isopropylacrylamide). The morphology of the assembled poly(St-co–NIPAAm) particles was observed by SEM, it was found that monodisperse poly(St-co-NIPAAm) particles could assemble to form the two-dimensional order structures.     

Fabrication of novel temperature and pH sensitive poly (N-isopropylmaleamic acid-co-acrylonitrile) hydrogels

To combine temperature and pH sensitive capabilities, N-isopropylmaleamic acid (NIPMMA), having isopropylamide group and weakly acidic group (–COOH), was synthesized and used as a precursor for fabrication of temperature and pH sensitive hydrogels. In this paper, a new class of intelligent hydrogel with pH and temperature sensitivity originated from only one precursor (NIPMMA) was designed and demonstrated. Resultant poly(NIPMMA-co-acrylonitrile) [P(NIPMMA-co-AN)] hydrogels were characterized by Fourier transform infrared spectroscopy for structural determination and scanning electron microscope for morphology observation. Their temperature and pH sensitive behaviors were also examined in detail. The data obtained exhibited that the magnitude of sensitive properties of P(NIPMMA-co-AN) hydrogels depended on the composition ratio of two precursors. By increasing the content of NIPMMA, the temperature and pH sensitive capabilities of P(NIPMMA-co-AN) hydrogels were improved correspondingly since AN has no sensitivity upon temperature or pH changes.     

Preparation of thermoresponsive core–shell polymeric microspheres and hollow PNIPAM microgels

A reliable and efficient route for preparing thermoresponsive hollow microgels based on cross-linked poly(N-isopropyl acrylamide) (PNIPAM) was developed. Firstly, monodisperse thermoresponsive core–shell microspheres composed of a P(styrene (St)-co-NIPAM) core and a cross-linked PNIPAM shell were prepared by seeded emulsion polymerization using P(St-co-NIPAM) particles as seeds. The size of the P(St-co-NIPAM) core can be conveniently tuned by different dosages of sodium dodecyl sulfate. The thickness of the cross-linked PNIPAM shell can be controlled by varying the dosage of NIPAM in the preparation of PNIAPM shell. Then, hollow PNIPAM microgels were obtained by simply dissolving the P(St-co-NIPAM) core with tetrahydrofuran. The core–shell microspheres and the hollow microgels were characterized by transmission electron microscopy, dynamic light scattering, atomic force microscopy, and Fourier-transform infrared spectroscopy.     

Preparation of styrene/acrylic acid copolymer microspheres: polymerization mechanism and carboxyl group distribution

 Poly(styrene-co-acrylic acid) (St/AA) copolymer microspheres were prepared by batch emulsifier-free emulsion copolymerization of St with AA. The monomer conversion, the morphology and the composition of the particles along the polymerization process were monitored by a gravimetric method, transmission electron microscopy observation and Fourier transform IR analysis, respectively. A shift of the polymerization locus from inside the particles to “outside” the particles in the postnucleation stage was proposed. The results of the study of the distribution of carboxyl groups by a combination of elemental and X-ray photoelectron spectroscopy analyses implied a core/shell structure for the St/AA copolymer microspheres. By chemical metal deposition, nickel particles were formed and deposited on the surface of St/AA microspheres, forming polymer/metal composite particles. Received: 16 February 2001 Accepted: 8 August 2001     

Electrospun microfibrous poly(styrene-alt-maleic anhydride)/poly(styrene-co-maleic anhydride) mats tailored for enzymatic remediation of waters polluted by endocrine disruptors

Novel bicomponent microfibrous mats containing targeted amount of reactive maleic anhydride groups were prepared by electrospinning of mixed solutions of poly(styrene-alt-maleic anhydride) and poly(styrene-co-maleic anhydride). Then, amino-functionalized P(St-alt-MA)/P(St-co-MA) mats were obtained by reaction with p-phenylenediamine. ATR-FTIR and XPS spectroscopy were used to characterize pristine and modified P(St-alt-MA)/P(St-co-MA) mats. On the next step, laccase from Trametes versicolor was covalently attached onto the modified mats; the average amount of immobilized enzyme was 40 ± 0.7 mg/g mat. The catalytic activity of the immobilized enzyme was studied in respect to bisphenol A (BPA) endocrine disruptor. The optimum activity of the immobilized enzyme was reached at maximum flow rate of 1.3 mL/s. After 90 min the BPA concentration was reduced by 60% and the catalytic activity of microfibrous mats remained stable for about 30 successive reuses. In addition, the relative activity of laccase immobilized on the microfibrous mats was displayed in a broader pH range as compared to that of the free one.     

Synthesis and adsorption properties of gold nanoparticles within pores of surface‐functional porous polymer microspheres

Mesoporous polymer microspheres with gold (Au) nanoparticles inside their pores were prepared considering their surface functionality and porosity. The Au/polymer composite microspheres prepared were characterized by transmission electron microscope (TEM), X‐ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) techniques. The results showed that the adsorption of Au nanoparticles could be increased by imparting the pore structure and surface‐functional groups into the supporting polymer microspheres (in this study, poly (ethylene glycol dimethacrylate‐co‐acrylonitrile) and poly (EGDMA‐co‐AN) system). Above all, from this study, it was established that the porosity of the polymer microspheres is the most important factor that determines the distribution and adsorption amount of face‐centered cubic (fcc) Au nanoparticles in the final products. Our study showed that the continuous adsorption of Au nanoparticles with the aid of the large surface area and surface interaction sites formed more favorably the Au/polymer composite microspheres. The BET measurements of Au/poly(EGDMA‐co‐AN) composite microspheres reveals that the adsorption of Au nanoparticles into the pores kept the pore structure intact and made it more porous. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5627–5635, 2004     

Preparation of hollow composite spheres with raspberry‐like structure based on hydrogen‐bonding interaction

The hollow composite spheres with a raspberry‐like structure were prepared by a self‐assemble heterocoagulation based on the inter‐particle hydrogen‐bonding interaction between the amide groups of hollow poly (N,N′‐methylenebisacrylamide‐co‐N‐isopropyl acrylamide) (P(MBA‐co‐NIPAAm)) microspheres and the carboxylic acid groups of poly(ethyleneglycol dimethacrylate‐co‐methacrylic acid) (P(EGDMA‐co‐MAA)) nanoparticles, in which P(EGDMA‐co‐MAA) nanoparticle acted as the corona and the hollow P(MBA‐co‐NIPAAm) microsphere behaved as the core. The control coverage of the corona particles on the surface of hollow core microspheres of P(MBA‐co‐NIPAAm)/P(EGDMA‐co‐MAA) hollow composite sphere was studied in detail through adjustment of the mass ratio between the core and corona particles. The effect of the pH on the stability of the raspberry‐like hollow spheres was investigated. The polymer particles and the resultant heterocoagulated raspberry‐like hollow spheres were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Copyright © 2008 John Wiley & Sons, Ltd.     

X-ray photoelectron spectroscopy as a tool for studies of the surface layer of microspheres. The case of polystyrene and poly(styrene–acrolein) microspheres with attached human serum albumin

The application of X-ray photoelectron spectroscopy (XPS) for studies of surface layers of objects with spherical shape was investigated using as examples polystyrene and poly(styrene–acrolein) microspheres with attached human serum albumin (HSA). The amounts of immobilized protein were determined by the standard biochemical Lowry method and by XPS, using the intensity of the N1s signals of HSA as a basis for evaluation. The XPS data were treated by taking into account the spherical shape of the particles analyzed (variable take-off angle of ejected electrons). The best agreement between the results of the biochemical and XPS determinations was found assuming that for the average particle the takeoff angle varies from 0° to 72.7°. This reflects the fact that in the multilayer arrangement of particles, placed onto the support of the XPS apparatus, the particles from the upper layer partially screen the edges of the particles in the layer below. Received: 23 November 1999 Accepted: 16 March 2000     

Controlled synthesis of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles by interfacial post-cross-linking reactions

 The chemical synthesis and the physicochemical properties of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles are presented. Copolymers of poly(vinyl formamide) (PVFA) and poly(vinyl amine) (PVAm) and their protonated forms were adsorbed onto silica from aqueous solutions. The influences of the pH strength and the ion concentration of the aqueous solution as well as the copolymer composition (degree of hydrolyzation of PVFA), and the molecular mass on the adsorption process were investigated by electrokinetic measurements, potentiometric titration, and quantitative elemental analyses. Silica surface-charge neutralization is achieved at a pH strength above 10 for highly hydrolyzed (95%) PVFA polymers. Decreasing the amino content in the PVAm chain shifts successively both the point of zero charge and the isoelectric point to lower pH values. PVFA-co-PVAm layers onto silica are adsorbed weakly. To fix these layers irreversibly, cross-linking reactions with (4,4′-diisocyanate)diphenyl methane were carried out on the surface of solid PVFA-co-PVAm/silica hybrid particles suspended in acetone. The cross-linking reaction, which is connected with the conversion of amino groups, is also a tool to control the surface charge of the PVFA-co-PVAm/silica hybrids. X-ray photoelectron spectroscopy and solid-state ¹³C cross-polarization magic-angle spinning NMR spectroscopy were used to obtain information on the number of and the structure of the functionalized polyelectrolyte layers on silica. The success of cross-linking was also shown by the results of these spectroscopic methods. Received: 28 June 1999 /Accepted: 27 August 1999     

Synthesis, characterization, and temperature-dependent colloidal stability of poly(N-isopropylacrylamide)-grafted polystyrene/poly(styrene-co-4-vinylbenzyl N, N-diethyldithiocarbamate) hairy particles

Poly(N-isopropylacrylamide)-grafted polystyrene/poly(styrene-co-4-vinylbenzyl N, N-diethyldithiocarbamate) [PNIPAM-grafted PS/P(St-co-VBDC)] hairy particles were synthesized by photo-polymerizing N-isopropylacrylamide monomer in the presence of PS/P(St-co-VBDC) core particles. Here, the VBDC unit, which was incorporated into the surface of core particles by seeded soap-free emulsion copolymerization, acted as a photo-iniferter. By varying the polymerization conditions, a series of hairy particles having different grafting heights and grafting densities was successfully obtained. The hairy particles exhibited well-defined core/shell morphology. PS/P(St-co-VBDC) formed the core which was surrounded by PNIPAM shell. The determination of critical coagulation concentration (CCC) indicated that the hairy particles were stabilized via both electrostatic and steric mechanisms (i.e., electrosteric mechanism) at a temperature lower than LCST of PNIPAM. However, these particles gave much lower CCCs when heated to the temperature higher than LCST, exhibiting temperature-dependent colloidal stability.     

Characterization of Fe3O4/poly(styrene-co-N-isopropylacrylamide) magnetic particles with temperature sensitivity

 The average diameter, diameter distribution and surface morphology of Fe₃O₄/poly(styrene-co-N-isopropylacrylamide)[P(St-NIPAM)] particles were characterized by scanning electron microscopy. The copolymer structure was confirmed by IR spectroscopy, differential scanning calorimetry and elemental analysis. The content of Fe₃O₄ entrapped in the particles was determined by atomic absorption spectrometry. A coarse structure was observed on the surface of the Fe₃O₄/P(St-NIPAM) particles. The hydrodynamic diameter of the Fe₃O₄/P(St-NIPAM) particles was found to exhibit about a 15% decrease in diameter on changing the temperature from 25 to 40 °C. The results also showed that Fe₃O₄/P(St-NIPAM) an advantage of exploited magnetic separation. Received: 6 August 1999 Accepted in revised form: 16 November 1999     

Preparation and characterization of multiresponsive polymer composite microspheres with core–shell structure

Fe₃O₄/SiO₂/poly (N-isopropylacrylamide-co-N,N-dimethylaminoethyl methacrylate) [P(NIPAM-co-DMA)] multiresponsive composite microspheres with core–shell structure were synthesized by template precipitation polymerization. First, the magnetite nanoparticles were coated with silica and then modified with 3-(trimethoxysilyl)-propyl methacrylate (MPS). Subsequently, the Fe₃O₄/SiO₂ particles grafted with MPS were used to seed the precipitation copolymerization of NIPAM and DMA. The composite microspheres with core–shell structure were superparamagnetic, pH-sensitive, and thermoresponsive. The swelling ratio (D_{25 °C, pH = 3}/D_{50 °C, pH = 9})³ coupling of pH and temperature increased up to 21.2, which was much higher than that without comonomer DMA.     

Synthesis of polymeric microspheres from a Merrifield resin by surface‐initiated nitroxide‐mediated radical polymerization

Polymeric microspheres were prepared from a Merrifield resin via nitroxide‐mediated radical polymerization. Polystyrene, poly(acetoxystyrene), and poly[styrene‐b‐(methyl methacrylate‐co‐styrene)], poly(acetoxystyrene‐b‐styrene), and poly(styrene‐co‐2‐hydroxyethyl methacrylate) copolymers were demonstrated to graft onto 2,2,6,6‐tetramethyl‐1‐piperidinyloxy nitroxide bound Merrifield resins. The polymerization control was enhanced both on the surface and in solution by the addition of sacrificial nitroxide. The significant increase in the particle diameter (more than a fivefold volume increase for polystyrene brushes) showed that polymer growth was not only on the surface but also within the particles, and this diameter increase could be adjusted through changes in the molecular weight of the polymers. The microspheres were characterized by elemental analysis, IR spectroscopy, particle size analysis, and optical microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2145–2154, 2005     

Preparation of biodegradable microspheres by anionic dispersion polymerization with PLA copolymeric dispersion stabilizer

We prepared poly(d,l-lactide) (PLA) microspheres by anionic dispersion polymerization of d,l-lactide. The polymerization was carried out in xylene/heptane (1:2 in v/v) mixture solution at 368 K for 9 h, with poly(dodecyl methacrylate)-co-poly[α-methacryloxyethoxy-poly(l-lactide)] (PDMA-co-P(MA-PLLA)) synthesized in this study, as a dispersion stabilizer. The number-averaged diameter and diameter distribution (coefficient of variation) of obtained PLA microspheres ranged from 180 to 800 nm and 14–40%, respectively, depending on the preparation condition. Furthermore, the time courses of monomer conversion, particle diameter, and particle number were investigated to clarify the formation mechanism of microspheres with PDMA-co-P(MA-PLLA) as a dispersion stabilizer. From this experiment, we found that the aggregation of primary particles occurred in anionic dispersion polymerization, and the particle diameter of obtained PLA microspheres decreased with increasing PDMA-co-P(MA-PLLA) concentration. In conclusion, we clarified that PDMA-co-P(MA-PLLA) effectively contributed to the stability of primary particles.     

Ag-polymer composite microspheres with patterned surface structures

Novel silver-poly(acrylamide-co-methacrylic acid) [Ag-P(AM-co-MAA)] composite microspheres, in tens of micrometer size range, with patterned surface and core/shell structures were prepared by chemical reduction of Ag₂CrO₄-P(AM-co-MAA) composite microspheres in ethanol. Characterization with various techniques revealed that the chemical composition of the “shell” is dominated by Ag, but the “core” is dominated by the template, P(AM-co-MAA). It was also demonstrated that the surface morphology of the Ag-polymer composite microspheres is similar to that of their precursors and can be controlled to a certain extent by varying the composition of template copolymer, approaches, and amount of Ag₂CrO₄ deposited. This morphology transfer technique is also applicable for other silver salts-polymer composite microspheres. The same silver-polymer composite microspheres with very different morphology have also been prepared by utilizing this technique, but the different precursor microspheres, Ag₃PO₄-P(AM-co-MAA), were used. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

ABA triblock copolymers with pendant hydroxyl groups prepared by controlled cationic polymerization and their use as delivery carrier for paclitaxel

To improve the hydrophilicity of poly(styrene-b-isobutylene-b-styrene) (SIBS), this study focuses on the synthesis of novel functional ABA triblock copolymer thermoplastic elastomers (TPEs) with polyisobutylene (PIB) as rubbery segments. The precursor poly{(styrene-co-4-[2-(tert-butyldimethylsiloxy) ethyl]styrene)-b-isobutylene-b-(styrene-co-4-[2-(tert-butyldimethylsiloxy)ethyl]styrene)}(P(St-co-TBDMES)-PIB-P(St-co-TBDMES)) triblock copolymer was first synthesized by living sequential cationic copolymerization of isobutylene (IB) with styrene (St) and 4-[2-(tert-butyldimethylsiloxy) ethyl]styrene (TBDMES) using 1,4-di(2-chloro-2-propyl)benzene (DiCumCl)/titanium tetrachloride (TiCl₄)/2,6-di-tert-butylpyridine (DtBP) as the initiating system. Then, P(St-co-TBDMES)-PIB-P(St-co-TBDMES) was hydrolyzed in the presence of tetra-butylammonium fluoride to yield poly{[styrene-co-4-(2-hydroxyethyl)styrene]-bisobutylene-b-[styrene-co-4-(2-hydroxyethyl)styrene]} (P(St-co-HOES)-PIB-P(St-co-HOES)) with pendant hydroxyl groups. P(St-co-HOES)-PIB-P(St-co-HOES) used as the paclitaxel carrier was also investigated in this study. Comparing with SIBS, P(St-co-HOES)-PIB-P(St-co-HOES) has exhibited better compatibility with paclitaxel and higher release rate.     

Adsorption of poly(vinyl formamide-co-vinyl amine) onto silica particle surfaces and stability of the formed hybrid materials

In order to produce silica/polyelectrolyte hybrid materials the adsorption of the polyelectrolyte poly(vinyl formamide-co-vinyl amine), P(VFA-co-VAm) was investigated. The adsorption of the P(VFA-co-VAm) from an aqueous solution onto silica surface is strongly influenced by the pH value and ionic strength of the aqueous solution, as well as the concentration of polyelectrolyte. The adsorption of the positively charged P(VFA-co-VAm) molecules on the negatively charged silica particles offers a way to control the surface charge properties of the formed hybrid material. Changes in surface charges during the polyelectrolyte adsorption were studied by potentiometric titration and electrokinetic measurements. X-ray photoelectron spectroscopy (XPS) was employed to obtain information about the amount of the adsorbed polyelectrolyte and its chemical structure. The stability of the adsorbed P(VFA-co-VAm) was investigated by extraction experiments and streaming potential measurements. It was shown, that polyelectrolyte layer is instable in an acidic environment. At a low pH value a high number of amino groups are protonated that increases the solubility of the polyelectrolyte chains. The solvatation process is able to overcompensate the attractive electrostatic forces fixing the polyelectrolyte molecules on the substrate material surface. Hence, the polyelectrolyte layer partially undergoes dissolving process.     

Design of polyglycidol-containing microspheres for biomedical applications

The paper presents a short review on the synthesis, characterisation and selected medical applications of poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) (P(S/PGL)) microspheres. The soap-free emulsion-polymerisation of styrene and α-tert-butoxy-ω-vinylbenzyl-polyglycidol macromonomer (PGL) in water yielded core-shell microspheres with a low particle-diameter dispersity (ratio of the weight average particle diameter and the number average particle diameter). The interfacial fraction of PGL units, estimated by XPS, was in the range of 0–42 mole % depending on the concentration of the macromonomer in the polymerisation feed. The studies of adsorption of model proteins showed that the surface fraction of adsorbed protein was significantly reduced when the PGL interfacial fraction was higher than 40 mole %. The P(S/PGL) particles with covalently immobilised proteins were used for the preparation of photonic crystal assemblies suitable for applications in optical biosensors and the medical diagnostic test for the detection of Helicobacter pylori antibodies in the blood serum.     

Preparation of P(MBA‐co‐MAA)/Zr(OH)4/P(EGDMA‐co‐MAA)/TiO2 Tetra‐layer Hybrid Microspheres and the Corresponding ZrO2/TiO2 Double‐shelled Hollow Microspheres

Double‐shelled zirconia/titania (ZrO₂/TiO₂) hollow microspheres were prepared by the selective removal of the polymer components via the calcination of the corresponding tetra‐layer poly(N,N′‐methylenebisacryl amide‐co‐methacrylic acid) (P(MBA‐co‐MAA))/Zr(OH)₄/poly(ethyleneglycol dimethacrylate‐co‐methacrylic acid) (P(EGDMA‐co‐MAA))/TiO₂ hybrid microspheres. These tetra‐layer microspheres were synthesized by the combination of the distillation copolymerization of N,N(‐methylenebisacryl amide‐co‐methacrylic acid (MBA) or ethyleneglycol dimethacrylate (EGDMA) crosslinker and methacrylic acid (MAA) for the preparation of polymer core and third‐layer as well as the controlled sol‐gel hydrolysis of inorganic precursors for the construction of zirconium hydroxide (Zr(OH)₄) and titania (TiO₂) layers. The thicknesses of zirconia and titania shell‐layers were conveniently controlled via varying the feed of zirconium n‐butoxide (Zr(OBu)₄) and titanium tetrabutoxide (TBOT) during the sol‐gel hydrolysis, while the sizes of polymer layers were tuned through a multi‐stage distillation precipitation copolymerization. The structure and morphology of the resultant microspheres were characterized by transmission electron microscopy (TEM), X‐ray diffractometer (XRD), X‐ray photoelectronic spectroscopy (XPS), and thermogrametric analysis (TGA).