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Poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) microspheres with a high copolymerized AA content were fabricated using rapid membrane emulsification technique. The uniform size, good hydrophilicity, and thermo sensitivity of the microspheres were favorable for trypsin immobilization. Trypsin molecules were immobilized onto the microspheres surfaces by covalent attachment. The effects of various parameters such as immobilization pH value, enzyme concentration, concentration of buffer solution, and immobilization time on protein loading amount and enzyme activity were systematically investigated. Under the optimum conditions, the protein loading was 493 +/- 20 mgg(-1) and the activity yield of immobilized trypsin was 155%+/- 3%. The maximum activity (V-max) and Michaelis constant (K-m) of immobilized enzyme were found to be 0.74 Ms-1 and 0.54 mM, respectively. The immobilized trypsin showed better thermal and storage stability than the free trypsin. The enzyme-immobilized microspheres with high protein loading amount still can show a thermo reversible phase transition behavior. The research could provide a strategy to immobilize enzyme for application in proteomics. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43343.

Polyethylene glycol) (PEG) propionaldehyde is an important polymer derivative used in protein modification; it is usually synthesized by the Williamson reaction of 3-chloropropionaldehyde diethyl acetal (CPADA) with PEG alkoxide followed by hydrolysis to deprotect the aldehyde group. However, the side reaction of the Williamson reaction has been a severe drawback leading to a low-aldehyde-content product. In this study, we established a kinetic model to depict the competition of the Williamson reaction and its side reaction. Based on a kinetic analysis, experiments were performed to systemically investigate the influence of the process parameters on the yield of PEG aldehyde, including the reaction solvents, reaction temperature, and molar equivalents of CPADA. The best reaction solvent was determined to be dioxane because the conversion of methoxy pol(ethylene glycol) in dioxane was higher than that in other solvents and because dioxane has low toxicity and is easily handled. The reaction temperature was set as the refluxing point of dioxane to effectively convert PEG into its alkoxide. The equivalents of CPADA were optimized to be 15 to obtain a quantitative yield of mPEG propionaldehyde and avoid wasting the reagent. The quantitative yield of mPEG propionaldehyde was achieved under these optimum conditions. 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1638-1643, 2009

Heterotelechelic poly(ethylene glycol)s are widely used in the modification, conjugation, and crosslinking of biomacromolecules. A series of heterotelechelic PEGs with amino acid at one end and hydroxyl group at another end, including alpha-glycine-omega-hydroxyl-PEG, alpha-proline-omega-hydroxyl-PEG, and alpha-phenylalanine-omega-hydroxyl-PEG, were first synthesized in this study. The reaction proceeded at ambient temperature under alkaline conditions via an aqueous solution polymerization of ethylene oxide. Amino group of glycine, proline, and phenylalanine was the initiating center in the polymerizations, and carboxyl group of these amino acids was reserved as one of the active end groups of the obtained heterotelechelic PEG. Purification of the desired products was accomplished by silica gel column chromatography. The obtained heterotelechelic PEGs were characterized by means of FT-IR, H-1 NMR, C-13 NMR, MS, and RP-HPLC. They were in different forms depending on the type of initiating amino acid, e.g. alpha-glycine-omega-hydroxyl-PEG and alpha-phenylalanine-omega-hydroxyl-PEG are in branched form, and alpha-proline-omega-hydroxyl-PEG is linear. Amino acids were conjugated to PEG chains through the stable carbon-nitrogen bond. Compared with the traditional critical polymerization conditions, the advantage of this method is that various amino acid ended heterotelechelic PEGs can be designed and obtained by using different amino acid as the initiator through a much more convenient route, which proceeded in aqueous solution at ambient temperature. (C) 2008 Wiley Periodicals, Inc.

Porous poly(2-hydroxyethyl methacrylate-coethylene chmethacrylate) [p(HENIA-co-EDNIA)] microspheres have important applications in chromatography. In this study, p(HENIA-co-EDNIA) microspheres with controllable size were successfully prepared by modified membrane emulsification technique. The CV value of the obtained n-Licrospheres was as low as 14.4%. An oil phase mainly composed of toluene was permeated through a membrane with uniform pores into an aqueous phase to form fairly uniform seed emulsion. The secondary emulsion composed of HEMA and EDMA was prepared by a homogenizer. Then, the two emulsions were mixed together. HEMA and EDMA diffused into the aqueous phase, and then were absorbed by the seed droplets. The swollen droplets were further polymerized to prepare monodisperse porous microspheres. It was found that HEMA/EDMA ratio and toluene/monomer ratio showed a significant influence on swelling degree, diameter, and morphology of the obtained microspheres. The swelling degree of the microspheres increased with the increase of toluene/monomer ratio, whereas the average diameter increased with decrease of the ratio. Microspheres with controllable size (28-73 mu m) and porosity were obtained, by varying HEMA/EDMA ratios and toluene/monomer ratios. It can be expected that the p(HEMA-co-EDMA) microspheres with controllable size and porosity will provide many advantages in their applications. (c) 2007 Wiley Periodicals, Inc.

Since monomethoxy poly(ethylene glycol) (mPEG) inevitably contains diol PEG and is difficult to get high molecular weight through traditional synthesis at high temperature under high pressure, a novel synthetic tech- nique via anionic solution polymerization was reported in this study. With a new initiating system, potassium naph- thalene and methanol, was introduced, the polymerization proceeded at ambient temperature and side reactions were well restrained. Furthermore, a slight excess of potassium naphthalene can effectively remove the trace of water and oxygen in the reaction system. Under this condition, mPEG was nearly quantitatively obtained without containing diol PEG. Its Mn ranged from 1 to 30 kDa and the polydispersity was kept lower than 1.07. Characterization of the mPEG obtained was carried out using GPC to determine the con- tent of diol PEG and 1 H-NMR and MALDI-ToF MS spectro- scopic analysis to confirm the exact structure. � 2007 Wiley

Uniform poly(glycidyl methacrylate-divinylbenzene) (P(GMA-DVB)) and poly(glycidyl methacrylate-ethylene dimethacrylate) (P(GMA-EGDMA)) porous microspheres with several 10 mu m were successfully prepared by membrane emulsification-polymerization technology. Conventional suspension polymerization method was first investigated by examining the effects of recipe components on the morphologies of P(GMA-DVB), including stabilizer, diluent, and crosslinker to select a optimum recipe. The membrane emulsification-polymerization process was developed to prepare uniform PGMA porous microspheres as the following: the oil phase composed of monomer, diluent and initiator was pressed through membrane pores into the aqueous phase to form uniform droplets, and subsequent suspension polymerization was carried out. GMA and 4-methyl-2-pentanol in the selected recipe were relatively hydrophilic, and therefore oil phase could wet the hydrophilic glass membrane and bring about polydispersed droplets. However, when isooctane was added as a component of diluents, the uniform droplets could be prepared by membrane emulsification method. In the membrane emulsification-polymerization, the coagulation between microspheres obviously decreased while yield of microspheres slightly increased. To extend the application of PGMA, as a trail, uniform P(GMA-EGDMA) porous microspheres were also successfully prepared by membrane emulsification-polymerization with a isooctane contained diluent, even though EGDMA was more hydrophilic than DVB. Therefore, recipe was found the important factor to prepare uniform PGMA porous microspheres using membrane emulsification-polymerization method. (c) 2006 Wiley Periodicals, Inc.

Seeded preswelling emulsion polymerization was carried out by using monodispersed poly(4-vinylpyridine-co-butyl acrylate) [P(4VP-BA)] particles as the seed, and styrene and butyl acrylate as the second-stage monomers under different polymerization conditions, to obtain hemispherical polystyrene (PST)-rich-P4VP-rich microspheres. Prior to polymerization, toluene was added into the preswelling system together with the second-stage monomers. It was found that, with the increase of the amount of toluene, the particle morphology showed a tendency toward desirable hemispherical structure, and the colloidal stability of composite latex was improved. When the weight ratio of toluene/seed latex was increased up to 7.5/40 (g/g), the stable hemispherical latex could be obtained. However, when toluene was not added, the coagulum formed on the wall of the reactor during polymerization, and the composite particles with multiple surface domains (such as sandwich-like, popcorn-like) were formed. In addition, the final morphology of composite particles was influenced by the polarity of the seed crosslinker and the hydrophilicity of the second-stage initiator, which could affect the mobility of poly(styrene-co-butyl acrylate) [P(ST-BA)] chains. The morphology development during the polymerization was investigated in detail, and a schematic model was derived to depict the formation mechanism of hemispherical P(4VPBA)/P(ST-BA) composite microspheres. The results revealed that the mobility of the P(ST-BA) chains influenced the diffusion of the P(ST-BA) domains on the surface of the P(4VP-BA) matrix. When the mobility of the P(ST-BA) chains allowed small-size P(ST-BA) domains to coalesce into one larger domain, complete phase-separated morphology (hemisphere) could be achieved. (C) 2003 Wiley Periodicals, Inc.

Uniform polyurethaneurea-vinyl polymer (PUU-VP) hybrid microspheres of about 20 mum were prepared by a Shirasu porous glass (SPG) membrane emulsification technique and a subsequent radical suspension polymerization process, that is, a mixture of a 40 wt% urethane prepolymer (UP) solution of xylene and a vinyl monomer (VP) containing an initiator was permeated through the uniform pores of the SPG membrane into a continuous phase containing a stabilizer to form uniform droplets. Then, the droplets were allowed to stand for chain extension at room temperature with di- or triamines for 2 h in the absence or presence of ethyl acetate (EA), followed by suspension polymerization at 70degreesC for 24 h. The effect of the type and the amount of the monomer composition, crosslinker, and chain extender on the monomer conversion, particle morphology, and stability of the dispersion was investigated. A strong relationship was found between the compatibility of PUU with VP and the stability of the dispersion. The monomer conversion increased and the stability of the dispersion was improved as the amount of the crosslinker was increased. Solid and spherical PUU-VA hybrid particles with a smooth surface and a higher destructive strength were obtained when a trifunctional crosslinker and a chain extender were used together. (C) 2003 Wiley Periodicals, Inc.

Hollow polymer particles with large voids were prepared with styrene (St) as the main component and in the presence of a small amount of N,N-dimethylamino- ethyl methacrylate (DMAEMA) via a glass-membrane emul- sification technique and a subsequent suspension polymer- ization. A mixture of the monomer, hexadecane (HD), and N,N-azobis(2,4-dimethylvaleronitrile) as an initiator was used as a dispersed phase (oil phase). By the careful pushing of the dispersed phase through the pores of the glass mem- brane into the aqueous phase, an emulsion of fairly mono- disperse monomer droplets was formed. Then, the polymer- ization was performed by temperature being elevated to 70°C. The aqueous phase (continuous phase) contained poly(N-vinyl pyrrolidone) as a stabilizer, sodium lauryl sul- fate as a surfactant, Na2SO4 as an electrolyte, and sodium nitrite (NaNO2) as a water-soluble inhibitor. Results related to the effects of the HD content, DMAEMA, and the com- position of the comonomer, including the crosslinker and flexible segment, on the features of the hollow particles were investigated. When the content of DMAEMA was higher than 1.0 wt % based on the total monomer, small, secondary particles were generated in the aqueous phase, but the gen- eration was effectively prevented when DMAEMA was lim- ited to 0.5 wt %. Hollow particles, with an average diameter of around 7 m, were obtained with an St-DMAEMA sys- tem. The void size of the hollow particles was controlled by the HD content. When the HD content was lower (25 wt % based on the oil phase), unbroken hollow particles were easily obtained. However, they tended to break into halves after drying when the HD content was increased to 50 wt %. A soft segment, lauryl acrylate, and a crosslinker, ethylene glycol dimethacrylate, were added to overcome this prob- lem. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 244 -251, 2003

Hydrophilic poly(dimethyl aminoethyl methacrylate) (PDMAEMA) copolymer was obtained by suspension polymerization using 2,2′-azobisisobutyronitrile as an initiator, and by emulsion polymerization using 2,2′-azobis(2-amidinopropane)·2HCl (V-50). The influences of reaction parameters on the particle size and size distribution were investigated. For suspension polymerization, these included the concentrations of ethylene glycol dimethacrylate (EGDMA) crosslinking agent, ethyl acetate (EA), and Na2SO4 electrolyte, the types of comonomer [methyl methacrylate (MMA) or styrene (ST)], solvent (EA or acetone), and stabilizer [poly(oxyethylene nonylphenylether) with 23 units of ethylene oxide (PEO23) or polyvinylpyrrolidone K30 (PVP)], polymerization temperature, and ST content in the comonomer feed. For the emulsion polymerization, the reaction parameters included the concentration of cetyltrimethyl ammonium chloride and V-50, and types of initiator [V-50 or potassium persulfate] and crosslinking agent [EGDMA or divinylbenzene]. The solubility of hydrophilic comonomers in the aqueous phase was a key factor for the stability and morphology of the PDMAEMA particles. It was found that the stable uncrosslinked PDMAEMA latex could be prepared by charging 20 wt % (based on the monomer) of ST. Moreover, the crosslinking agent significantly affected the coagulum in both the suspension and the emulsion polymerizations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1057–1070, 2002

Recent interest in synthetic emulsion products has shifted from mass-produced solid materials to specialty products such as paints, adhesives, and binders. High solid content latices are typically prepared in industrial practice, and used for coatings and adhesives. These latices offer definite advantages for most of the commercial applications, for example, low shipping costs and less energy to remove water. One of the major difficulties encountered in the preparation of these latices is the increase in viscosity once a certain value of the particle volume fraction is achieved. It is well known that this increase in the viscosity is due to the effect of particle–particle interactions and the formation of complex flow elements, which become crucially important when the volume fraction of the dispersed phase approaches the maximum packing density. The preparation of polymer emulsions with broad particle size distribution is an area of considerable industrial interest. High solid content, good filmformation characteristics, and improved mechanical and rheological properties can be obtained from polymer emulsions with broad particle size distribution. The polymer emulsions with broad size distribution have higher maximum packing concentration of polymer particles than that with monodisperse rigid spheres. Usually, semibatch and multiple-shot processes are the most common techniques for preparation of this type of latex to ease the extensive heat of polymerization by controlling the reaction rate. Inevitably, carefully controlled addition of monomers is required as well as use of sophisticated controlling devices. Molecular weight is lower than that of the batch process. High solid content emulsion copolymerization of styrene, butyl acrylate, and methacrylic acid has been carried out, and polymer latices with a multimodal particle size distribution (PSD) prepared by introducing additional surfactants during the semicontinuous emulsion polymerization. Bimodal and trimodal PSD polymer latices can be obtained by this method, and the secondary generation of particles is greatly affected by the nature and the amount of additional surfactants, as well as the moment at which they are introduced. High solid content ( 65%), low viscosity, and coagulum-free latices have been obtained through the secondary nucleation of polymer particles, and a minimum in viscosity was observed when the weight fraction of the large particles was around 80%. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2478– 2483, 2002Correspondence to: S. Omi (omi@cc.tuat.ac.jp).

In a previous study, it was found that monodisperse polystyrene (PSt) hollow particles can be prepared under special conditions by combining a Shirasu Porous Glass (SPG) emulsification technique and subsequent suspension polymerization process. That is, a mixture of styrene (St), N,N-dimethylamino ethyl methacrylate (DMAEMA), hexadecane (HD), and initiator N,N'-azobis(2,4-dimethylvaleronitrile) (ADVN) was used as the dispersed phase in an aqueous phase containing poly(vinyl pyrrolidone) (PVP), sodium lauryl sulfate (SLS), and water-soluble inhibitor. The dispersed phase was created by pushing the oil phase through the uniform pores of an SPG membrane into the continuous phase to form uniform droplets. Then, the droplets were polymerized at 70degreesC. It has been puzzling that hollow microspheres were obtained only when sodium nitrite (NaNO2) was used as a water-soluble inhibitor, while one-hole particles were formed when hydroquinone (HQ) or diaminophenylene (DAP) was used. In this study, the mechanism of formation of the hollow microspheres was verified by measuring the variation of diameter, molecular weight distribution, and monomer conversion, and by observing morphological changes during the polymerization, as well as by changing the type and amount of hydrophilic monomer, and initiator. It was found that the diameter of the oil droplets decreased, and a large amount of secondary new particles formed immediately after polymerization started in the case of NaNO2, However, there was no such apparent behavior to be observed when HQ or DAP was used. It was determined that the hollow particles formed due to the rapid phase separation between PSt and HD, and as a consequence, a large amount of monomer diffused into the aqueous phase to form the secondary particles. Rapid phase separation confined the HD inside the droplets, a nonequilibrium morphology. On the other hand, one-hole particles, representing an equilibrium morphology, formed when the phase separation occurred slowly because a lot of monomer existed inside of the droplets to allow mobility of the PSt. The addition of DMAEMA allowed the hollow particles to be formed more easily by decreasing the interfacial tension between the copolymer and aqueous phase. (C) 2002 Wiley Periodicals, Inc.

The thermally initiated emulsion copolymerization of styrene (ST) and methyl methacrylate (MMA) was carried out in the absence of conventional initiators. The hydroperoxide (HPO) concentration in the monomers, sodium dodecyl sulfate (SDS), deionized water, and the formulation of those for emulsion copolymerization were measured. The HPO concentration in ST and MMA increased with the storage time, and were considered to be the major sources of HPO. The thermal decomposition of hydroperoxide in monomers, the thermal initiation of ST by Mayo mechanism, and the complex formation between SDS and the monomers were proposed to be three main sources of the radical generation. It was confirmed that new polymer particles were generated throughout the polymerization process, and consequently resulted in a broader distribution of polymer particle size, compared with that for conventional emulsion polymerization. Approximately 80 wt % of monomer conversion was obtained in the presence of SDS at 373 K in 24 h. The initiation rate of the 30 wt % monomer charge was faster than those of 10 wt % and 20 wt % monomer charge. The latex instability at higher solid content was improved by adding electrolyte to promote the electrostatic repulsion force between the polymer particles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 455–467, 2002; DOI 10.1002/app.2343

Monodispersed crosslinked cationic poly(4-vinylpyridine-co-butyl acrylate) [P(4VP-BA)] seed latexes were prepared by soapless emulsion polymerization, using 2,2′-azobismethyl(propionamidine)dihydrochloride (V50) as an initiator and divinylbenzene (DVB) or ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The optimum condition to obtain monodispersed stable latex was investigated. It was found that the colloidal stability of the P4VP latex can be improved by adding an adequate amount of BA (BA/4VP = 1/4, w/w), and adopting a semicontinuous monomer feed mode. Subsequently, poly(4-vinylpyridine-co-butyl acrylate)/Poly(styrene-co-butyl acrylate) [P(4VP-BA)/P(ST-BA)] composite microspheres were synthesized by seeded polymerization, using the above latex as a seed and a mixture of ST and BA as the second-stage monomers. The effects of the type of crosslinker, the degree of crosslinking, and the initiators (AIBN and V50) on the morphology of final composite particles are discussed in detail. It was found that P(4VP-BA)/P(ST-BA) composite microspheres were always surrounded by a PST-rich shell when V50 was used as initiator, while sandwich-like or popcorn-like composite particles were produced when AIBN was employed. This is because the polarity of the polymer chains with AIBN fragments is lower than for the polymer with V50 fragments, hence leading to higher interfacial tension between the second-stage PST-rich polymer and the aqueous phase, and between PST-rich polymer and P4VP-rich seed polymer. As a result, the seed cannot be engulfed by the PST-rich polymer. Furthermore, the decrease of Tg of the second-stage polymer promoted phase separation between the seeds and the PST-rich polymer: sandwich-like particles formed more preferably than popcorn-like particles. It is important knowledge that various morphologies different from PST-rich core/P4VP-rich shell morphology, can be obtained only by changing the initiator, considering P4VP is much more hydrophilic than PST. The zeta potential of composite particles initiated by AIBN in seeded polymerization shifted from a positive to a negative charge. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1190–1203, 2002

The dumbbell-like/egglike microspheres of poly(4-vinylpyridine/n-butyl acrylate)/polystyrene [P(4VP/nBA)/PS] were prepared by soap-free seed emulsion polymerization. The effects of various polymerization parameters, such as the amount of ethyl acetate (EA) in the continuous phase, swelling time, degree of crosslinking of seed polymer, polymerization temperature, and compatibility of seed polymer and the secondary polymer, and so forth, on the formation of dumbbell-like/egglike morphology were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that secondary particles could be eliminated either by drastically increasing the number of seed particles or by stripping EA from the seed latex by dialysis and evaporation under a vacuum. Swelling the seed particle with the secondary monomer was essential for the preparation of egglike microspheres. For the localization of PS domains on one side of the egglike particle, the most effective factors were to elevate the polymerization temperature up to 90°C and simultaneously to lower the compatibility of the polymer on the seed particle surface with the phase of PS, while using the uncrosslinked seed latex. Crosslinking the seed latex was not suitable for localizing the PS domains in the seed particle, especially when the degree of crosslinking exceeded 0.5 wt % of EGDMA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2002–2017, 2001

Monodispersed poly(styrene-co-N-dimethylaminoethyl methacrylate) [P(St-DMAEMA)] composite microspheres were prepared by employing a Shirasu Porous Glass (SPG) emulsification technique. A mixture of monomer, hexadecane (HD), and initiator N,N′-azobis(2,4-dimethylvaleronitrile) (ADVN) was used as a dispersed phase and an aqueous phase containing stabilizer [poly(vinyl pyrrolidone) (PVP) or poly(vinyl alcohol) (PVA)], sodium lauryl sulfate (SLS), and water-soluble inhibitor [hydroquinone (HQ), diaminophenylene (DAP), or sodium nitrite (NaNO2)], was used as a continuous phase. The dispersed phase was permeated through the uniform pores of SPG membrane into the continuous phase by a gas pressure to form the uniform droplets. Then, the droplets were polymerized at 70°C. The effects of inhibitor, stabilizer, ADVN, and DMAEMA on the secondary nucleation, DMAEMA fraction in the polymer, conversion, and morphologies of the particles were investigated. It was found that the secondary nucleation was prevented effectively in the presence of HQ or DAP when PVP was used as the stabilizer. The secondary particle was observed when ADVN amount was raised to 0.3 g (/18 g monomer); however, no secondary nucleation occurred even by increasing DMAEMA fraction to 10 wt %. This result implied that the diffusion of ADVN into the aqueous phase was a main factor responsible to the secondary nucleation more than that of DMAEMA. The hollow particles were obtained when NaNO2 was used, while one-hole particles formed in the other cases. By adding crosslinking agent, the hole disappeared and the monomer conversion was improved. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2408–2424, 2001

The properties and morphologies of poly(4-vinylpyridine-co-styrene) [P(4VP/St)] lattices, prepared by soap-free emulsion polymerization using the water-soluble initiator 2,2′-azobis(2-amidinopropane) · 2HCl (V50), were greatly affected by the addition of ethyl acetate (EA). The properties and morphologies of the resultant lattices were characterized by measuring the zeta potential, viscosity average molecular weight, particle size and distribution, glass-transition temperature (Tg), and photographs taken by SEM and TEM. The effects of two kinds of monomer feeding modes, that is, the batch and semicontinuous emulsion copolymerization, were also investigated. For batch emulsion copolymerization, by charging EA, the core–shell morphology resulting from the disparate reactivity ratios of the 4VP(1)/St(2) copolymerization system (r1= 1.04, r2= −0.73) disappeared. Instead, first a bimodal particle size distribution, with an apparently asymmetric composition structure, and then spherical microspheres were obtained as the amount of EA charged increased from 2 to 10 wt %. The particle size increased twofold by the addition of EA. The zeta potential of particles increased from +64.4 to more than +100 mV, and viscosity average molecular weight decreased from 9.70 to 0.97 × 105 g/mol, as EA increased from 0 to 8 wt %. With the semicontinuous copolymerization, raspberry-like particles were obtained by charging 10 wt % EA, whereas a sandwich-like morphology was obtained without EA. The DSC curves showed one Tg for all the lattices prepared with charging EA, but two Tg's for the latex prepared without using EA, regardless of the monomer feeding modes. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1988–2001, 2001

A series of experiments were carried out on the soap-free emulsion polymerization mechanism of 4-vinyl pyridine (4VP)/styrene (St) and the solvent, ethyl acetate (EA), by using the cationic initiator, 2,2'-azobis(2-amidinopropane) 2HCl (V50). To investigate the mechanism of polymerization in detail, a particular quasi-static polymerization system-the reaction mixture in a sealed bottle allowed to stand without agitation during the whole polymerization period-was employed. The partition of monomers at ambient and solid content of the latex during the quasi-static polymerization in the presence of 8 wt % EA was measured by 1 H-NMR, and the variation of particle size was observed by scanning electron microscopy (SEM ). The solubility of 4VP and St in water decreased as the amount of EA increased. Meanwhile, most of the EA was partitioned in the oil phase, even in the cases where the charged amount of EA was much lower than the solubility of EA (∼ 8 wt %) in water at ambient. The solubility of EA in water was also affected by the composition of 4VP and St (i.e., increased as the fraction of 4VP increased, but decreased as the fraction of St increased). This observation, as well as the quantitative analysis of the quasi-static emulsion polymerization, indicated that the initial reaction in the soap-free emulsion polymerization was closely related to the disturbance of the interface of monomer/water phase, which triggered the generation of monomer droplets. Therefore, a new mechanism was proposed for the nucleation of soap-free emulsion polymerization, namely, the nucleation was performed in the droplets. The droplets absorbed the oligomeric radicals generated in the aqueous phase to continue the polymerization, as well as to promote the colloidal stability of the droplets.

The stable latex of poly(4-vinylpyridine-co-n-butyl acrylate) (P4VP/nBA) with a solid content as high as 10 wt % was prepared by a modified soap-free emulsion polymerization. A mixture of water and organic solvents was employed as the continuous phase for increasing the solid content of the latex. Several organic solvents were investigated and, among them, ethyl acetate (EA) and diethyl ether (DE) were effective. The stable latex with 10 wt % solid content was prepared by charging 10 wt % EA or a EA/DE mixture (5 wt % each); however, more than 10 wt % solid content of the stable latex could not be obtained even by charging more than 10 wt % EA or a EA/DE mixture. The stable latex with 10 wt % solid content, which was crosslinked with less than 0.5 wt % (based on monomer) of ethylene glycol dimethacrylate, was prepared by charging 10 wt % of EA. In this case, however, the pH of the continuous phase had to be adjusted to lower than 4. The effects of EA on the characteristics of the resulting uncrosslinked latex were investigated by employing ζ-potential measurements and scanning electron microscopy. It was found that the mass of coagulum decreased as the EA increased. At 8 wt % of EA, a stable latex of 10 wt % solid content without any coagulum was obtained. The ζ potential of particles increased from −100 up to 45.7 mV as the EA increased from 0 to 10 wt %. The effects of batch and semicontinuous copolymerization on the morphology of the microspheres were investigated by using DSC and ultrathin cross-sectional transmission electron miscroscopy photos. A core–shell structure was not found, despite the batch copolymerization of 4VP(1)/nBA(2) (r1 = 4.3, r2 = 0.23), even with disparate reactivity ratios. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1731–1740, 2000

The mechanism of the unique suspension polymerization of uniform monomer droplets, without coalescence and breakup during the polymerization, was investigated using styrene (S) as a monomer mixed with water-insoluble hexadecane (HD). The glass membrane (Shirasu Porous Glass, SPG) emulsification technique was employed for the preparation of uniform droplets. Depending on the pore sizes of the SPG membranes (1.0, 1.4, and 2.9 μm), polymer particles of an average diameter ranging from 5.6 to 20.9 μm were obtained with the coefficient of variation (CV) being close to 10%. The role of HD was to prevent the degradation of the droplets by the molecular diffusion process. Sodium nitrite was added in the aqueous phase to kill the radicals desorbed from the droplets (polymer particles), thereby suppressing the secondary nucleation of smaller particles. Each droplet behaved as an isolated locus of polymerization. With the presence of HD, the initial polymerization rate was proportional to 0.24th power of the benzoil peroxide (BPO) concentration. This peculiar behavior as compared with the ordinary suspension polymerization was explained by introducing the assumption that each droplet was composed of isolated compartments (cells) in which active polymeric radicals were dissolved in an S-rich phase and surrounded by a rather incompatible S/HD (continuous) phase. The average number of radicals in the droplet increased initially due to the separate existence of polymeric radicals in compartments. As the polymerization progressed, the HD-rich phase gradually separated, eventually forming macrodomains, which were visible by an optical microscope. The phase separation allowed polystyrene chains to dissolve in a more favorable S phase, and the homogeneous bulk polymerization kinetics took over, resulting in a gradual decrease of the average number of radicals in the droplet until the increase of viscosity induced the gel effect. When no HD was present in the droplets, the polymerization proceeded in accordance with the bulk mechanism except for the initial retardation by the entry of inhibiting radicals generated from sodium nitrite in the aqueous phase. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1025–1043, 2000

Uniform polyurethaneurea (PUU) spheres were prepared from 20–40 wt % urethane prepolymer (UP) solution of xylene. Uniform droplets were formed with the Shirasu porous glass (SPG) membranes of 1.42, 5.25, and 9.5 μm pore size, dispersed in an aqueous phase with dissolved stabilizers, and allowed to stand for the chain extension at the room temperature with diamines that were added after the emulsification. The reaction progressed rapidly by an addition of ethyl acetate to the aqueous phase, promoting the diffusion of diamines into the droplets. The reaction of —NCO groups with water did not hamper the emulsification process, which normally occurred in 1 to 2 h, yielding stable droplets with the coefficient of variation around 10%. No instability or coagulation occurred, while standing for the chain extension, and solid, spherical PUU particles of 5–20 μm were obtained after removal of the solvent. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2237–2245, 2000

Relatively uniform microspheres containing a hydrophilic monomer, 2-hy- droxyethyl methacrylate (HEMA), were prepared by employing a swelling method of uniform seed droplets. A uniform seed emulsion composed mainly of styrene (St) was prepared by the Shirasu porous glass (SPG) membrane emulsification technique; this was mixed with a secondary emulsion composed mainly of HEMA/St or HEMA/MMA (methyl methacrylate) prepared by a homogenizer for swelling. The swollen droplets obtained were polymerized at 757C under a nitrogen atmosphere. The uniform mi- crosphere with a higher content of HEMA was obtained successfully by the swelling method while it failed by a direct emulsification method. The effects of the composition of the oil phase and the inhibitor in the continuous phase on the incorporated fraction of HEMA, the morphology of particles, and monomer conversion were investigated. It was found that the incorporated fraction of HEMA increased with increasing its feed fraction, and more HEMA was incorporated into the microsphere when HEMA/MMA was used as the oil phase of the secondary emulsion rather than HEMA/St. Although the final conversion was very low when the feed fraction of HEMA was higher, it can be increased to more than 80% by using an adequate amount of ethylene glycol dimethacrylate (EGDMA) as a crosslinker and NaNO2 as an inhibitor in the aqueous phase. Various microspheres with different morphologies such as spherical, snow- manlike, and popcornlike were observed, depending on composition of the oil phase. Furthermore, the porous microsphere with a high content of HEMA was obtained by employing hexanol (HA) as a porogen. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1325-1341, 1997

Fairly uniform spheres of crosslinked polystyrene (PS) and polymethyl methacrylate (PMMA), prepared by a particular emulsification process using SPG (Shirasu Porous Glass) membranes and subsequent suspension polymerization, were applied for immobilizing carriers of Glucoamylase (GluA). A mixture of monomers, solvents, and oil-soluble initiator was allowed to permeate through the micropores of SPG, suspended in an aqueous solution of poly(vinyl alcohol), and polymerized while retaining the narrow size distribution during polymerization. A small amount of acrylic acid or glycidyl methacrylate (GMA) was incorporated for the immobilization of GluA via covalent bonding. Although GluA has been regarded as being difficult to retain its activity after the immobilization process, a porous structure of the carriers definitely favored the immobilization, and a maximum 55% relative activity (RA) was obtained by the physical adsorption to PMMA spheres. The reaction of epoxide in GMA with 6-aminocaproic acid provided a spacer arm for the carboxyl group. An improvement of activity was expected by the incorporation of the spacer arms; however, barely noticeable activity was observed for PMMA carriers either by the physical adsorption or by the covalent bonding. A slight improvement was observed for PS carriers with spacers compared to the carriers without them. The diffusion process of oligosaccharides in the porous carriers seemed to retard the rate of hydrolysis in the case of largest carriers, 60 μm PS-DVB-AA spheres. The activity of immobilized GluA was retained during a long storage period of more than 150 days, some of them even increasing gradually, while the activity of native GluA dropped to zero after 100 days. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2655–2664, 1997

Hair and wool fibers treated with an 11 M LiBr solution containing N-ethylmaleimide showed typical rubberlike elasticity in a solution composed of equal volumes of 8 M LiBr and diethylene glycol monobutyl ether. Stress–strain relations of the swollen fibers were treated with a two-phase structural model: a mechanically stable phase of higher crosslinked domains and a rubbery phase with lower crosslink density. Stress–strain curves were analyzed by applying non-Gaussian chain statistics to the swollen keratin network, including microdomains, which act as reinforcing filler particles in rubber. Swollen hair showed about 2.3 times higher modulus than wool. It has been suggested that: (1) the difference in the modulus between the two keratins is attributable to the difference in the volume fraction of domains, and (2) the crosslink density of rubbery phase in hair is virtually identical to that in wool.