Controllable preparation,rheology, and plugging property of micron‐grade polyacrylamide microspheres as a novel profile control and flooding agent

A series of micron‐grade polyacrylamide microspheres were prepared by inverse suspension polymerization of acrylamide (AM) and N,N′‐methylene bisacrylamide (MBA) in oil phase, with Span80 and Tween80 as dispersion stabilizers, and ammonium persulfate (APS) as an initiator. The conversion rate and coagulum rate were introduced to optimize the inverse suspension polymerization conditions of micron‐grade polyacrylamide microspheres. The swelling property of polyacrylamide microspheres in aqueous solution and the rheology of polyacrylamide microspheres suspension were characterized. The matching factor was introduced to characterize the matching relationship between the particle size of polyacrylamide microspheres and pore‐throat size of reservoirs. The optimized synthesis results show that the conversion rate is high, and the coagulum rate is low when the mass ratio of Span80 to Tween80 is 3 : 1. The particle size of the polyacrylamide microspheres is controlled by varying the concentration of dispersion stabilizer. The polyacrylamide microspheres show an obvious swelling property, which depends on the concentration of NaCl and temperature. The polyacrylamide microspheres suspension shows different rheological properties at different temperature and shear rate. When the temperature is low, it behaves as pseudoplastic fluid, dilatant fluid and quasi‐newtonian fluid in turn with the increase of shear rate. When the temperature is high, it behaves as dilatant fluid and quasi‐newtonian fluid in turn with the increase of shear rate. The micron‐grade polyacrylamide microspheres prefer to plug sand pack with optimal matching factor. When the matching factor is 1.35–1.55, the polyacrylamide microspheres can be transported into the deep area of sand pack, and the ultimate plugging rate is more than 85%, which indicates that the matching factor is an effective parameter to evaluate the matching relationship between polyacrylamide microspheres and reservoirs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1124‐1130, 2013     

One‐pot synthesis of monodispersed phosphazene‐containing microspheres with active amino groups

An amine‐terminated nucleophile Hexakis (4‐aminophenoxy) cyclotriphosphazene (HACP) was synthesized. Its chemical structure was identified by ¹H NMR and ³¹P NMR. Novel monodispersed phosphazene‐containing microspheres with active amino groups on the surface have been successfully prepared through a one‐pot precipitation polymerization of hexachlorocyclotriphosphazene with HACP. Just by single step, the microspheres were synthesized without stirring, surfactant and ultrasonic irradiation. The diameter of the obtained microspheres ranged from 0.1 to 0.5 μm with the rough surface. And, the onset of the thermal‐degradation temperature was 460°C, which is attributed to the highly cross‐linked structure and the introduced of the cyclotriphosphazene rings. Moreover, the products at variable stages of polymerization were measured by TEM. The formation mechanism was proposed which is corresponding with an oligomeric species absorbing mechanism. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43336.     

Preparation,characterization, and drug‐release properties of poly(N‐isopropylacrylamide) microspheres having poly(itaconic acid) graft chains

An inverse suspension polymerization method for the preparation of thermoresponsive hydrogel microspheres based on N‐isopropylacrylamide was described in this article. The polymerization reaction was carried out at 200 rpm stirring rate and the microspheres obtained were in the size range of 71–500 μm in the swollen states. The particles were sieved by using ASTM sieves. The selected fraction (180–250 μm) of poly(N‐isopropylacrylamide) (PNIPAAm) microspheres was used for radiation‐induced modification with itaconic acid (IA) to obtain PNIPAAm/poly(itaconic acid) graft copolymer. Viagra and lidocaine were used as model drugs for the investigation of controlled‐release behavior of the microspheres. Incorporation of IA graft chains onto microspheres enhanced significantly the uptake of both drugs and further controlled release at specific pH values. The release studies showed that some of the basic parameters affecting the drug‐loading and ‐release behavior of the microspheres were pH, temperature, particle size, and chemical nature of drug. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1115–1124, 2005     

Preparation and solution performance for the amphiphilic polymers with different hydrophobic groups

An amphiphilic polymer with twin‐tailed hydrophobic groups was prepared by micellar polymerization of acrylamide as hydrophilic monomers, 2‐acryloylamino‐2‐methyl‐1‐propanesulfonic acid as functional monomers and N,N‐dodecyl acrylamide as hydrophobic monomers. Using the same method, containing single‐tailed hydrophobic group of the amphiphilic polymer and not containing the hydrophobic group of ordinary polymer were prepared. The molecular structure of the product was characterized by infrared spectrum and ¹H nuclear magnetism resonance spectrum. By inclusion complexation of β‐cyclodextrin (β‐CD), the hydrophobic association on the apparent viscosity contribution rate was studied. Relationship between hydrophobic group structure and its performance was investigated by the rotational viscometer, scanning electron microscopy (SEM), fluorescence spectroscopy, and rheometer. The results showed that amphiphilic polymers containing twin‐tailed hydrophobic groups had a lower critical aggregation concentration (CAC). When the amphiphilic polymer concentration was higher than CAC, hydrophobic association was stronger, which led to a higher apparent viscosity contribution rate. At the same polymer solution concentration, amphiphilic polymer containing twin‐tailed hydrophobic group had better performance on temperature resistance, salt tolerance, and mechanical shear resistance compared with the other two polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44744.     

Preparation of poly(vinyl acetate) microspheres with narrow particle size distributions by low temperature suspension polymerization of vinyl acetate

To estimate influences of suspension polymerization conditions including conversion, polymerization temperature, stirring rate, initiator concentration, monomer concentration, and suspending agent concentration on the volume average diameter (D_avg) and particle size distribution (PSD) of poly(vinyl acetate) (PVAc) microspheres, vinyl acetate (VAc) was suspension‐polymerized at low temperature using 2,2′‐azobis(2,4‐dimethylvaleronitrile) as an initiator. The effects of each condition, on D_avg of PVAc microspheres, were expressed as follows, D_avg = [conversion]^a[temperature]^b[rpm]^c[ADMVN]^d[VAc]^f [suspending agent]^g. Logarithms of D_avg were linearly proportional to those of polymerization conditions, and their exponents, a, b, c, d, f, and g were calculated as 0.27, ?13.7, ?1.37, ?0.21, 0.58, and 0.29, respectively. Variations of PSDs, according to polymerization conditions, were examined by considering polymerization rate, droplet or suspension viscosity, and droplet break‐up/coagulation equilibrium. From these results, PVAc microspheres with various sizes and narrow PSDs were obtained effectively under carefully controlled polymerization conditions, which can be used as promising precursors of novel PVA microspheres through heterogeneous surface saponification. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4064–4070, 2006     

Copolymer hydrogel microspheres consisting of modified sulfate chondroitin‐co‐poly(N‐isopropylacrylamide)

Modified chondroitin sulfate (π‐CdS) microspheres were synthesized by way of crosslinking‐copolymerization reaction with N‐isopropylacrylamide (NIPAAm), yielding CdS‐co‐PNIPAAm copolymer network. The incorporation of vinyl groups onto the CdS was processed with the use of glycidyl methacrylate (GMA) in an aqueous solution of pH 3.5 under stirring speed of 800 rpm at 50°C. ¹³C NMR and ¹H NMR spectra of CdS treated with the GMA indicated the formation of 3‐methacryloyl‐1‐glyceryl ester of π‐CdS and 3‐methacryloyl‐2‐glyceryl ester of π‐CdS that are the reaction products resultant of an epoxide ring‐opening mechanism via. The synthesis of microspheres was performed via radical reaction of the vinyl groups at the π‐CdS with vinyl groups at the NIPAAm in a water−benzyl alcohol microemulsion. The formation of spherical structures is the result of the polymerization‐crosslinking reaction of the π‐CdS with the NIPAAm monomers at the droplets of water, in view that both reactants have hydrophilic characteristics at the temperature at which the reaction was processed. The pure CdS hydrogel microspheres showed a slightly cracked structure with a lower diameter range while the CdS‐co‐PNIPAAm hydrogel microspheres showed a flat and tight structure with a more regular mass distribution. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Water‐dispersible porous polyisoprene‐block‐poly(acrylic acid) microspheres

Two polyisoprene‐block‐poly(tert‐butyl acrylate) (PI‐b‐PtBA) samples and a poly(tert‐butyl acrylate) (PtBA) homopolymer (hPtBA) were prepared by anionic polymerization and characterized by light scattering, size exclusion chromatography, and NMR. The tert‐butyl groups were removed from one of the diblocks to yield amphiphilic polyisoprene‐block‐poly(acrylic acid) (PI‐b‐PAA). PI‐b‐PAA was then used as the surfactant to disperse dichloromethane containing PI‐b‐PtBA and hPtBA at different weight ratios as oil droplets in water. Solid microspheres containing segregated polyisoprene (PI) and PtBA/hPtBA domains were obtained after dichloromethane evaporation. Permanent microspheres were obtained after PI domain crosslinking with sulfur monochloride. Porous microspheres were produced after the hydrolysis of PtBA and the extraction of the homopoly(acrylic acid) chains. The shape and connectivity of the poly(acrylic acid)‐lined pores were tuned by changes in the PtBA/hPtBA content in the precursor microspheres. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2785–2793, 2003     

Synthesis,characterization, and drug‐release behavior of amphiphilic quaternary ammonium chitosan derivatives

A new type of amphiphilic quaternary ammonium chitosan derivative, 2‐N‐carboxymethyl‐6‐O‐diethylaminoethyl chitosan (DEAE–CMC), was synthesized through a two‐step Schiff base reaction process and applied to drug delivery. In the first step, benzaldehyde was used as a protective agent for the incorporation of diethylaminoethyl groups to form the intermediate (6‐O‐diethylaminoethyl chitosan). On the other hand, NaBH₄ was used as a reducing agent to reduce the Schiff base, which was generated by glyoxylic acid, for the further incorporation of carboxymethyl groups to produce DEAE–CMC. The structure, thermal properties, surface morphology, and diameter distribution of the resulting chitosan graft copolymers were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR, thermogravimetric analysis, differential scanning calorimetry, X‐ray powder diffraction, scanning electron microscopy, and laser particle size analysis. Benefiting from the amphiphilic structure, DEAE–CMC was able to be formed into microspheres in aqueous solution with an average diameter of 4.52 ± 1.21 μm. An in vitro evaluation of these microspheres demonstrated their efficient controlled release behavior of a drug. The accumulated release ratio of vitamin B₁₂ loaded DEAE–CMC microspheres were up to 93%, and the duration was up to 15 h. The grafted polymers of DEAE–CMC were found to be blood‐compatible, and no cytotoxic effect was shown in human SiHa cells in an MTT [3‐(4, 5‐dimethyl‐thiazol‐2‐yl)‐2, 5‐diphenyltetrazolium bromide] cytotoxicity assay. These results indicate that the DEAE–CMC microspheres could be used as safe, promising drug‐delivery systems. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39890.     

Preparation of novel amphiphilic copolymer microspheres and their drug‐release and glucose‐sensitive properties

A novel amphiphilic copolymer was prepared by the copolymerization of N‐acryloyl‐3‐aminophenylboronic acid with β‐cyclodextrin containing maleic anhydride. The copolymer was fully characterized with ¹³C‐NMR, ¹H‐NMR, IR, and scanning electron microscopy. The self‐assembling mechanism of the copolymer in H₂O–CH₃OH cosolvents was studied. Gliclazide as a model drug was loaded inside the copolymer microspheres, and the drug‐release behavior of the microspheres was studied. The results of in vitro oscillating release tests indicated that the microspheres responded to glucose rapidly in 30 min, and the microspheres exhibited self‐regulated on–off release behavior four to six times in 6 h between the solution with 3 g/L glucose and the medium without glucose; this met the clinical requirements of multidrug delivery. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Grafting of poly[styrene‐co‐N‐(4‐vinylbenzyl)‐N,N‐diethylamine] polymer film onto the surface of silica microspheres and their application as an effective sorbent for lead ions

Amino containing polymer of poly[styrene‐co‐N‐(4‐vinylbenzyl)‐N,N‐diethylamine] (PS‐co‐PVEA) was successfully grafted onto the surface of silica microspheres via the seed dispersion polymerization of styrene and N‐(4‐vinylbenzyl)‐N,N‐diethylamine in the presence of divinylbenzene employing the 3‐(methacryloxy)propyltrimethoxysilane activated silica microspheres as the seed. The polymerization led to thin chelating polymer films (30 nm) coated silica microspheres (silica@polymer) as determined by transmission electron microscopy. The synthesized silica@polymer composites were used as sorbents for lead ions (Pb²⁺). The adsorption properties, such as the pH effect, the adsorption kinetic, adsorption isotherm as well as the reuse of the silica@polymer sorbent were evaluated. The results demonstrated that the optimized adsorption condition was under neutral and the silica@polymer sorbent was efficient since it showed higher adsorption amounts (8.0 mg/g) and shorter adsorption equilibrium time (8 h) than that of the PS‐co‐PVEA microspheres and the pristine silica microspheres. Moreover, the silica@polymer sorbent was reusable even after four cycles of adsorption. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39973.     

Preparation of phenolic hollow microspheres via in situ polymerization

BACKGROUND: Phenolic hollow microspheres with a closed structure have a set of outstanding thermal characteristics. In the work reported here, a facile method is introduced to fabricate phenolic closed hollow microspheres by in situ polymerization in oil‐in‐water emulsion. Although in situ polymerization has been widely used to prepare hollow microspheres, it has not been utilized for the preparation of phenolic hollow microspheres. RESULTS: The average particle size of the produced microspheres was about 500 µm. Fourier transform infrared spectroscopy indicated that the phenolic microspheres were partially cured during preparation and a significant number of hydroxymethyl groups remained in the microspheres. Thermogravimetric analysis showed that the thermal decomposition temperature of the phenolic hollow microspheres was 420 °C, and residual weight at 800 °C was 62%. Differential thermal analysis showed that the glass transition temperature of the phenolic hollow microspheres was 200 °C. CONCLUSION: Using in situ polymerization, high thermal performance phenolic hollow microspheres are produced. The resultant product possesses a satisfactory closed hollow structure with controlled morphology. Copyright © 2009 Society of Chemical Industry     

Synthesis of poly (γ‐benzyl‐L‐glutamate) with well‐defined terminal structures and its block polypeptides with alanine,leucine and phenylalanine

The ring‐opening polymerization of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (BLG‐NCA) was initiated by n‐hexylamine in N,N‐dimethyformamide under normal pressure at 0 °C. The products were characterizated by gel permeation chromatography, matrix‐assisted laser desorption/ionization time of flight mass spectroscopy (MALDI‐TOF MS), nuclear magnetic resonance etc. MALDI‐TOF MS gave direct evidence that the side reactions during the polymerization of BLG‐NCA could be greatly reduced by decreasing the reaction temperature, e.g. from room temperature to 0 °C. As a result, over 90% of the products were amino‐terminated poly(γ‐benzyl‐L ‐glutamate) (PBLG) with low polydispersity index when the polymerization was carried out at 0 °C, which could be used to re‐initiate the polymerization of other NCAs. Then several well‐defined PBLG‐containing block copolypeptides were successfully synthesized in a convenient way. Copyright © 2012 Society of Chemical Industry     

Synthesis,characterization, and in vitro release of ibuprofen from poly(MMA‐HEMA) copolymeric core–shell hydrogel microspheres for biomedical applications

This article describes the development of a new crosslinked poly(methyl methacrylate‐2‐hydroxyethyl methacrylate) copolymeric core–shell hydrogel microsphere incorporated with ibuprofen for potential applications in bone implants. Initially poly(methyl methacrylate) (PMMA) core microspheres were prepared by free‐radical initiation technique. On these core microspheres, 2‐hydroxyethyl methacrylate (HEMA) was polymerized by swelling PMMA microspheres with the HEMA monomer by using ascorbic acid and ammonium persulfate. Crosslinking monomers such as ethylene glycol dimethacrylate (EGDMA) has also been included along with HEMA for polymerization. By this technique, it was possible to obtain core–shell‐type microspheres. The core is a hard PMMA microsphere having a hydrophilic poly(HEMA) shell coat on it. These microspheres are highly hydrophilic as compared to PMMA microspheres. The size of the hydrogel microspheres almost doubled when swollen in benzyl alcohol. These microspheres were characterized by various techniques such as optical microscopy, scanning electron microscopy, Fourier‐transformed infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The particle size of both microspheres was analyzed by using Malvern Master Sizer/E particle size analyzer. The in vitro release of ibuprofen from both microspheres showed near zero‐order patterns. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3045–3054, 2002; DOI 10.1002/app.10310     

Preparation of poly(acrylamide‐co‐acrylic acid)/silica nanocomposite microspheres and their performance as a plugging material for deep profile control

In this work, poly(acrylamide‐co‐acrylic acid)/silica [poly(AM‐co‐AA)/SiO₂] microspheres were prepared by inverse phase suspension polymerization in the presence of γ‐3‐(trimethoxysilyl) propyl methacrylate (or 3‐methacryloxypropyltrimethoxysilane) modified SiO₂. The effects of SiO₂ nanoparticles on tuning morphology and properties of the nanocomposite microspheres were studied. Plugging ability and oil displacement performance were also systematically investigated by single‐ and double‐tube sand pack models. The results showed that SiO₂ nanoparticles can effectively adjust surface smoothness, swelling behavior, and thermal stability of the nanocomposite microspheres. Compared with pure copolymer microspheres, these nanocomposite microspheres also displayed better salt tolerance and shear resistance. Such multifunctional nanocomposite microspheres can provide effective plugging in the high‐permeability channels and can also achieve deep profile control. The highest plugging rate can be 86.11% and the oil recovery for low‐permeability tube was enhanced by 19.69%. This research will provide a candidate material for the further enhanced oil recovery (EOR) research and supply the theoretical support for profile control system in field application. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45502.     

Synthesis of monodisperse crosslinked poly(styrene‐co‐divinylbenzene) microspheres by precipitation polymerization in acetic acid

Poly(styrene‐co‐divinylbenzene) microspheres with size ranging from 1.6 to 1.8 μm were prepared in acetic acid by precipitation polymerization. The particle size and particle size distribution were determined by laser diffraction particle size analyzer, and the morphology of the particles was observed with scanning electron microscope. Besides, effects of various polymerization parameters such as initiator and total monomer concentration, divinylbenzene (DVB) content, polymerization time and polymerization temperature on the morphology and particle size were investigated in this article. In addition, the yield of microspheres increased with the increasing total monomer concentration, initiator loading, DVB concentration and polymerization time. In addition, the optimum polymerization conditions for synthesis of monodisperse crosslinked poly(styrene‐co‐divinylbenzene) microspheres by precipitation polymerization in acetic acid were obtained. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Molecularly imprinted polymer microspheres derived from pickering emulsions polymerization in determination of di(2‐ethylhexyl) phthalate in bottled water samples

The mono‐dispersed macroporous Molecularly Imprinted microspheres (MIPMs) selective for Diethylhexyl Phthalate (DEHP) were synthesized by Pickering emulsion polymerization. Silica nanoparticles were stabilizers in forming a stable oil‐in‐water emulsion, while the polymeric system was prepared by radical polymerization using methacrylic acid as functional monomer and ethylene glycol dimethacrylate as cross‐linker. The results of scanning electron microscopy and nitrogen adsorption desorption measurement indicated that the obtained polymer microspheres had regularly porous structure and narrowly diameter distribution (100 nm), besides the specific surface area (S_BET) was 452 m² g^?1, pore volume was 9.685 cm³ g^?1, and pore diameter was 5.089 nm. The equilibrium adsorption capacity of MIPs was 1.75 mg g^?1 at 298 K. Good selectivity for DEHP in another two kinds of analogies (DBP and DAP) was demonstrated with high selectivity coefficients, respectively 17.753 and 19.450. In the end, DEHP‐MIP was used as packing of solid‐phase extraction to form an sensitive analytical method in extraction and enrichment DEHP in bottled water samples with the limits of detection of 1.7–2.5 μg L^?1.The recoveries at three spiking level (0.05, 0.1, and 1 mg L^?1) were varied between at 97.5 and 103.1% with RSD values below 3.5. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43484.     

Biobased polyisocyanates from plant oil triglycerides: Synthesis,polymerization, and characterization

In this study, an easy and efficient synthesis of unsaturated plant oil triglycerides having isocyanate groups is reported. In the first step of the synthesis, the triglyceride was brominated at the allylic positions by a reaction with N‐bromosuccinimide, and in the second step, these brominated species were reacted with AgNCO to convert them to isocyanate‐containing triglycerides. At the end of the reaction, approximately 60–70% of the bromine was replaced by NCO groups, and the double bonds of the triglyceride were not consumed. When the amount of AgNCO was increased, the yield also increased. The final products were characterized with IR and ¹H‐NMR, and polyurethanes and polyureas were obtained from these fatty isocyanates with alcohols and amines, respectively. The polymers were characterized by differential scanning calorimetry and thermogravimetric analysis. Differential scanning calorimetry curves showed that glycerin polyurethane showed a glass‐transition temperature at 19°C, castor oil polyurethane showed two glass‐transition temperatures at ?43 and 36°C, and triethylene tetraamine polyurea showed a glass‐transition temperature at 31°C. Some properties of the polymers, such as the tensile strength and swelling ratios, were also determined. The swelling rate of glycerin polyurethane was higher than that of castor oil polyurethane in dichloromethane. The equilibrium swelling ratio was highest for the castor oil polyurethane. The polyurethanes synthesized in this study had a Young's modulus around 50 kPa and a tensile strength around 0.01 N/mm² (100 kPa). The tensile strength of glycerin polyurethane was higher than that of castor oil polyurethane. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Precipitation polymerization of molecularly imprinted polymers for recognition of melamine molecule

Molecular imprinted polymer microspheres (MIPs) were prepared by precipitation polymerization using melamine as template molecule, methacrylic acid (MAA) as functional monomer, trimethylol‐propane trimethacrylate (TRIM) as crosslinking agent, acetonitrile as solvent and dispersion medium. Release of the template was performed by continuous extraction with methanol containing 10% acetic acid. The microspheres were observed by scanning electron microscopy (SEM). The perfect microspheres were produced when the addition of crosslinker was 7.48 mmol. The binding capacity of MIPs was examined, Q_max = 68.36 μmol g^?1, and the dissociation constant at binding site of MIPs, K_d = 0.761, was estimated. Compared with the performance of conventional imprinted polymer, the imprinted microspheres showed high selectivity in special binding to template molecule. The imprinted microspheres could be used as the stationary phase in HPLC or SPE for selective extraction of melamine in daily products. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation,structure, and properties of poly(vinyl acetate‐co‐methyl methacrylate) nanocomposite microspheres with exfoliated montmorillonite through using two‐stage in situ suspension polymerization

Effective encapsulation of montmorillonite intermediate particles (I‐MMT) within poly (vinyl acetate‐co‐methyl methacrylate) (PVAMMA) copolymer by in situ suspension polymerization was performed. The I‐MMT encapsulation, layer exfoliation behavior, chemical composition, particle size distribution and thermostability of PVAMMA/I‐MMT nanocomposite microspheres were characterized by electron microscopies, X‐ray diffraction (XRD), laser particle analyzer, and thermogravimetric analysis (TGA). Swelling behaviors of the nanocomposite microspheres in various cationic salt solutions (NaCl and CaCl₂) and anionic salt solution (NaCl and Na₂SO₄) were also investigated. Results showed that the properties of layer dispersion surface and expansion of these nanocomposite microspheres were well achieved. The synthetic yields of the nanocomposites decreased as the I‐MMT loading increased. These nanocomposite microspheres had an average size from 96.8 μm to 138.4 μm with narrow particle size distribution, loose, and porous surface morphology. XRD patterns clearly proved the exfoliation of MMT layers in the copolymer matrix, which was consistent with TEM analysis. These nanocomposite microspheres showed higher negative zeta potential and higher thermal stability than those of the copolymer microspheres, which was due to the layer exfoliations in encapsulated microspheres. These selected microspheres with 10 to 70 μm diameters provided effectively plugging in the micrometer‐sized core channels through deformation and migration process in plugging experiments, which made them be the candidate materials for modifying the porous reservoir to enhance oil recovery in petroleum engineering. POLYM. COMPOS., 35:1104–1116, 2014. © 2013 Society of Plastics Engineers     

α‐Amylase immobilized by Fe3O4/poly(styrene‐co‐maleic anhydride) magnetic composite microspheres: Preparation and characterization

Fe₃O₄/poly(styrene‐co‐maleic anhydride) core–shell composite microspheres, suitable for binding enzymes, were prepared using magnetite particles as seeds by copolymerization of styrene and maleic anhydride. The magnetite particles were encapsulated by polyethylene glycol, which improved the affinity between the magnetite particles and the monomers, thus showing that the size of the microspheres, the amount of the surface anhydrides, and the magnetite content in the composite are highly dependent on magnetite particles, comonomer ratio, and dispersion medium used in the polymerization. The composite microspheres, having 0.08–0.8 μm diameter and containing 100–800 μg magnetite/g microspheres and 0–18 mmol surface‐anhydride groups/g microsphere, were obtained. Free α‐amylase was immobilized on the microspheres containing reactive surface‐anhydride groups by covalent binding. The effects of immobilization on the properties of the immobilized α‐amylase [magnetic immobilized enzyme (MIE)] were studied. The activity of MIE and protein binding capacity reached 113,800 U and 544.3 mg/g dry microspheres, respectively. The activity recovery was 47.2%. The MIE had higher optimum temperature and pH compared with those of free α‐amylase and showed excellent thermal, storage, pH, and operational stability. Furthermore, it can be easily separated in a magnetic field and reused repeatedly. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 328–335, 2005