Morphology control in polystyrene/poly(methyl methacrylate) composite latex particles

The effect of the presence of different amounts of block copolymers [polystyrene-block-poly(methyl methacrylate)] on the morphology of polystyrene/poly (methyl methacrylate) composite latex particles was investigated. The block copolymers were produced in situ by controlled radical polymerization (CRP) through the addition of the second monomer to a seed prepared by miniemulsion polymerization with a certain amount of a CRP agent. With an increase in the amounts of the block copolymers, the particle morphology changed from a hemisphere morphology (for a latex without block copolymers, i.e., without the use of a CRP agent during the polymerization) to clear core–shell morphologies as a result of decreasing polymer–polymer interfacial tension © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2484–2493, 2007     

Synthesis of functional graft copolymers by solution copolymerization and their evaluation as dispersants in nonaqueous phase dispersion polymerization

The poly(HEMA‐co‐MMA‐g‐PMMA) graft copolymer was prepared with a poly(methyl methacrylate) (PMMA) macromonomer, 2‐hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA), and its application as a dispersant for the nonaqueous phase dispersion polymerization of polystyrene (PST) was investigated. Monodisperse PST particles were obtained with two‐dimensionally tailored graft copolymers, with the number of grafted chains controlled and the polar component (HEMA) in the backbone chains balanced. As for the reactor, a stirred vessel with moderate agitation yielded uniform polymer particles, whereas sealed glass ampules with an overturning motion yielded broader size distributions. Increasing the polarity of the solvent in the continuous phase yielded smaller polymer particles with a gradual deterioration of monodispersity. Uniform polymer particles with a coefficient of variation of less than 6% were obtained up to 30 wt % solid contents. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1788–1798, 2003     

Multicomponent latex IPN materials. I. Morphology control

A series of novel structured latex particles with interpenetrating polymer network (IPN) cores and glassy SAN shells were developed in an attempt to investigate the feasibility of these polymers as both toughening and damping agents in thermoplastics. The IPN cores were composed of one impact part (polybutadiene based) and one damping part (acrylic based, with T_g around +10°C). The particle morphologies of these polymers were determined by TEM. The glass transitions and mechanical behavior of the polymers were characterized from DMS. The effect of different components on the final core/shell particle morphologies and mechanical properties was studied. The mechanical behavior of core/shell particles with IPN cores was also compared with that of separate core/shell and multilayered core/shell particles. In addition, normal core/shell synthesis (rubbery part first then the glassy part) and inverted core/shell synthesis (glassy part first then the rubbery part) were performed to provide another access for morphology control. It was found that the core/shell latex particles with poly(butyl acrylate) based copolymers are more miscible than poly(ethylhexyl methacrylate)-based copolymers. The high grafting efficiency of poly(butyl acrylate) plays an important role in governing phase miscibility. The latex particles synthesized by the inverted core/shell mode showed higher miscibility than the normal synthesized ones. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2193–2206, 1997     

Synthesis of new amphiphilic and lypophilic polymer networks containing 2‐methyl‐ and 2‐nonyl‐2‐oxazoline by the macroinitiator method

New amphiphilic and lypophilic polymer networks were obtained by the copolymerization of 2‐methyl‐2‐oxazoline (MeOXA), and/or 2‐nonyl‐2‐oxazoline (NoOXA) and 2,2′‐tetramethylenebis(2‐oxazoline) (BisOXA), respectively, initiating the copolymerization by random copolymers of chloromethylstyrene and methyl methacrylate or of chloromethylstyrene and styrene (macroinitiator method). Potassium iodide was used as an activator agent and the reaction was carried out in benzonitrile at 110 °C. In general, the polymer gels were obtained with a yield of 62 to 88%. The networks were characterized by high‐resolution magic angle spinning (HRMAS) NMR spectroscopy and by its absorption of polar and nonpolar solvents. In the case of amphiphilic polymer networks, the absorption of solvents depends on the molar ratio of 2‐methyl‐ to 2‐nonyl‐2‐oxazoline inside the polymer network favoring the absorption of polar solvents with a higher content of 2‐methyl‐2‐oxazoline. These gels showed a maximal swelling degree of 13 mL of water, 20 mL of methanol, and 13 mL of chloroform, respectively, per g of polymer. The lypophilic polymer networks containing only 2‐nonyl‐2‐oxazoline showed a maximal swelling degree of 8 mL of toluene, 14 mL of chloroform, and 2 mL of methanol, respectively, per g of the lypophilic network. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 122–128, 2005     

Hydrobromination of residual vinyl groups on divinylbenzene polymer particles followed by atom transfer radical surface graft polymerization

Rigid and monodisperse spherical polymer particles with 2.36 ± 0.18 μm diameter containing residual surface vinyl groups were prepared by photoinitiated precipitation polymerization of divinylbenzene. Anti‐Markovnikov addition of HBr to the surface vinyl groups yielded a 2‐bromoethyl functionality that was used as macroinitiator for atom transfer radical polymerization (ATRP), providing the possibility for further functionalization by controlled “grafting from” processes. This was demonstrated by grafting of glycidyl methacrylate brushes from the particle surface, using an ATRP system based on CuBr and pentamethyl diethylenetriamine. Existence of a methacrylic overlayer was verified by FTIR and XPS measurements, and the grafted particles were easily dispersed in water, confirming conversion of the particle surface from hydrophobic to hydrophilic. Hydrobromination of residual vinyl groups yields a macroinitiator that can be used for grafting of glycidyl methacrylate by ATRP. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1259–1265, 2009     

Particle monolayer formation at the air–water interface by silica particle with well‐defined grafted polymer

Particle monolayer formation at the air–water interface by polymer‐grafted colloidal silica was investigated. Methyl methacrylate (MMA) was polymerized from initiative bromide groups at colloidal silica surface by atom transfer radical polymerization. We obtained polymer‐grafted silica particle (SiO₂‐PMMA) with relative narrow polydispersity of PMMA. For the polymer‐grafted particle with high graft density, particle monolayer formation was confirmed by π‐A isotherm measurement and SEM observation. Interparticle distance was controllable by surface pressure. Furthermore, grafted polymer chains were suggested to be fairly extended at the air–water interface. However, for the polymer‐grafted particle with low graft density, monolayer structure on substrate showed aggregation and voids. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2789–2797, 2006     

Control of various morphological changes of poly(meth)acrylate microspheres and their swelling degrees by SPG emulsification

Crosslinked poly(meth)acrylate polymers with a variety of morphologies were synthesized with two steps. In the first step, a microporous glass membrane (Shirasu Porous Glass, SPG) was employed to prepare uniform emulsion droplets by applying an adequate pressure to the monomer phase, which was composed of the ADVN initiator, solvent of toluene or heptane or their mixture, and a mixture of (meth)acrylate monomers. The droplets were formed continuously through the membrane and suspended in the aqueous solution, which contained a PVA‐127 suspending agent, SLS emulsifier, and NaNO₂ inhibitor to suppress the nucleation of secondary particles. SPG pore sizes of 0.90, 5.25, and 9.25 μm were used. Then the emulsion droplets were polymerized at 343 K with a rotation rate 160 rpm for 24 h. The (meth)acrylate monomers 2‐ethylhexyl acrylate (2‐EHA), 2‐ethylhexyl methacrylate (2‐EHMA), cyclohexyl acrylate (CHA), methyl methacrylate (MMA), lauryl acrylate (LA), and lauryl methacrylate (LMA) were used in this research. The influences of the ratios of the monomer and crosslinking agent EGDMA, the amount of diluents, the monomer type on the polymer particle morphology, the swelling degree, and the polymer particle size were investigated. It was found that an increase in the concentrations of EGDMA and heptane resulted in higher coarse porous spheres and smaller polymer particle sizes. A coefficient with a variation close to 10%, or a standard deviation of about 4, was obtained. The capacity of these spheres as solvent absorption materials was examined. The highest swelling degrees of heptane and toluene were obtained when LA was employed as the monomer with 30% (by weight) of EGDMA and 70% (by weight) of heptane as an inert solvent. The highest capacity of the solvent absorption was obtained when using a polymer particle size of 4.81 μm, as prepared by SPG pore size 0.9 μm. The polymer particles were able to absorb aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, and a mix of aliphatic hydrocarbon solvents and aromatic hydrocarbon solvents, such as toluene and heptane. The capacity of solvent absorption for the aromatic hydrocarbon solvents was higher than for the aliphatic hydrocarbon solvents. In addition, the particles did not rupture or collapse after absorption in solvents. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4038–4056, 2000     

Rapid spectroscopic confirmation of the presence of polystyrene in polymer particles of mixed composition

A technique for rapid determination of the presence of polystyrene in individual micron-diameter polymer particles of mixed composition is presented. This technique is based upon observation of visible emission from conjugated regions of the polymer backbone, generated photochemically, while the particle is held in an optical trap. Particle emission characteristics are dependent upon particle size and suspending solvent. Emission spectra are provided for single component polystyrene particles and mixed polymer particles containing poly(methyl methacrylate), poly(N-vinyl pyrrolidone), and polystyrene. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 999–1004, 1998     

Synthesis of TiO2–SiO2/polymer core–shell microspheres with a microphase‐inversion method

A novel microphase‐inversion method was proposed for the preparation of TiO₂–SiO₂/poly(methyl methacrylate) core–shell nanocomposite particles. The inorganic–polymer nanocomposites were first synthesized via a free‐radical copolymerization in a tetrahydrofuran solution, and the poor solvent was added slowly to induce the microphase separation of the nanocomposite and result in the formation of nanoparticles. The average particle sizes of the microspheres ranged from 70 to 1000 nm, depending on the reaction conditions. Transmission electron microscopy and scanning electron microscopy indicated a core–shell morphology for the obtained microspheres. Thermogravimetric analysis and X‐ray photoelectron spectroscopy measurements confirmed that the surface of the nanocomposite microspheres was polymer‐rich, and this was consistent with the core–shell morphology. The influence of the synthetic conditions, such as the inorganic composition and the content of the crosslinking monomer, on the particle properties was studied in detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3911–3920, 2006     

Synthesis and characterization of micron‐sized monodisperse superparamagnetic polymer particles with amino groups

Micron‐sized monodisperse superparamagnetic polyglycidyl methacrylate (PGMA) particles with functional amino groups were prepared by a process involving: (1) preparation of parent monodisperse PGMA particles by the dispersion polymerization method, (2) chemical modification of the PGMA particles with ethylenediamine (EDA) to yield amino groups, and (3) impregnation of iron ions (Fe²⁺ and Fe³⁺) inside the particles and subsequently precipitating them with ammonium hydroxide to form magnetite (Fe₃O₄) nanoparticles within the polymer particles. The resultant magnetic PGMA particles with amino groups were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X‐ray diffractometry (XRD), and vibrating sample magnetometry (VSM). SEM showed that the magnetic particles had an average size of 2.6 μm and were highly monodisperse. TEM demonstrated that the magnetite nanoparticles distributed evenly within the polymer particles. The existence of amino groups in the magnetic polymer particles was confirmed by FTIR. XRD indicated that the magnetic nanoparticles within the polymer were pure Fe₃O₄ with a spinel structure. VSM results showed that the magnetic polymer particles were superparamagnetic, and saturation magnetization was found to be 16.3 emu/g. The Fe₃O₄ content of the magnetic particles was 24.3% based on total weight. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3433–3439, 2005     

Preparation and clinical application of immunomagnetic latex

Magnetic poly(methyl methacrylate) (PMMA)/poly(methyl methacrylate‐co‐methacrylic acid) [P(MMA–MAA)] composite polymer latices were synthesized by two‐stage soapless emulsion polymerization in the presence of magnetite (Fe₃O₄) ferrofluids. Different types and concentrations of fatty acids were reacted with the Fe₃O₄ particles, which were prepared by the coprecipitation of Fe(II) and Fe(III) salts to obtain stable Fe₃O₄ ferrofluids. The Fe₃O₄/polymer particles were monodisperse, and the composite polymer particle size was approximately 100 nm. The morphology of the magnetic composite polymer latex particles was a core–shell structure. The core was PMMA encapsulating Fe₃O₄ particles, and the shell was the P(MMA–MAA) copolymer. The carboxylic acid functional groups (COOH) of methacrylic acid (MAA) were mostly distributed on the surface of the composite polymer latex particles. Antibodies (anti‐human immunoglobulin G) were then chemically bound with COOH groups onto the surface of the magnetic core–shell composite latices through the medium of carbodiimide to form the antibody‐coated magnetic latices (magnetic immunolatices). The MAA shell composition of the composite latex could be adjusted to control the number of COOH groups and thus the number of antibody molecules on the magnetic composite latex particles. With a magnetic sorting device, the magnetic immunolatices derived from the magnetic PMMA/P(MMA–MAA) core–shell composite polymer latex performed well in cell‐separation experiments based on the antigen–antibody reaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1342–1356, 2005     

Acrylic polymer/silica organic–inorganic hybrid emulsions for coating materials: Role of the silane coupling agent

Acrylic polymer/silica organic–inorganic hybrid emulsions were synthesized by a simple method, that is, a conventional emulsion polymerization and subsequent sol–gel process, to provide water‐based coating materials. The acrylic polymer emulsions contained a silane coupling agent monomer, such as methacryloxypropyltriethoxysilane, to form highly solvent‐resistant hybrid films. On the other hand, the hybrid films from the surface‐modified polymer emulsions, in which the silane coupling agent was located only on the surface of the polymer particles and the particle core was not crosslinked, did not exhibit high solvent resistance. A honeycomblike array structure, which was derived from the polymer particles (diameter ≈ 50 nm) and the silica domain, on the hybrid film surfaces was observed by atomic force microscopy. The crosslinked core part and silane coupling agent containing the shell part of the polymer particles played important roles in attaining high solvent resistance. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4736–4742, 2006     

Dispersion polymerization of MMA in supercritical CO2 stabilized by random copolymers of 1H,1H–perfluorooctyl methacrylate and 2‐(dimethylaminoethyl methacrylate)

A series of random copolymers, composed of 1H,1H‐perfluorooctyl methacrylate (FOMA) and 2‐dimethylaminoethyl methacrylate (DMAEMA) were prepared as stabilizers for the dispersion polymerization of methyl methacrylate in supercritical CO₂ (scCO₂). Free‐flowing, spherical poly(methyl methacrylate) (PMMA) particles were produced in high yield by the effective stabilization of poly(FOMA‐co‐DMAEMA) containing 34–67 w/w % (15–41 m/m %) FOMA structural units. Less stabilized but micron‐sized discrete particles could be obtained even with 25 w/w % (10 m/m %) FOMA stabilizer. The result showed that the composition of copolymeric stabilizers had a dramatic effect on the size and morphology of PMMA. The particle size was controllable with the surfactant concentration. The effect of the monomer concentration and the initial pressure on the polymerization was also investigated. The dry polymer powder obtained from dispersion polymerization could be redispersed to form stable aqueous latexes in an acidic buffered solution (pH = 2.1) by an electrostatic stabilization mechanism due to the ionization of DMAEMA units in the stabilizer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1365–1375, 2008     

Potential switching of optical properties in polymer electrolytes

The electric field dependence of the optical properties of a series of anion-conducting polymer electrolytes at an ITO–electrolyte interface was investigated. A change in reflectance and refractive index of polymer electrolytes [poly(ethyl methacrylate)]₁₈(Bu₃SnX)₃Bu₄NX where X = Cl, Br, and SCN was observed. This was ascribed to anion accumulation/depletion in the interfacial region. Shorter response times were observed for electrolytes with higher conductivities, illustrating the interrelationship between these two phenomena. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2057–2062, 1997     

Dispersion copolymerization of poly(oxyethylene) macromonomers and styrene

The kinetics of dispersion copolymerization of methacryloyl-terminated poly(oxyethylene) (PEO-MA) and p-vinylbenzyl-terminated (PEO-St) polyoxyethylene macromonomers and styrene (St), initiated by a water- and/or oil-soluble initiator, was investigated using conventional gravimetric and NMR methods at 60°C. The batch copolymerizations in the water/ethanol continuous phase were conducted to high conversion. The rate of polymerization was described by the curve with a maximum at very low conversion. The initial rate of polymerization and the number-average molecular weight were found to decrease with increasing [PEO-MA], and the decrease was more pronounced in the range of a high macromonomer concentration. The rate per particle (at ca. 20% conversion) was found to be proportional to the −1.55th, the particle size to the −0.92nd, and the number of particles (at final conversion) to the 3.2nd power of [PEO-MA], respectively. At the beginning of polymerization the continuous phase is the main reaction locus. As the polymerization advances, the reaction locus is shifted from the continuous phase to the polymer particles. The transform of the reaction loci from the continuous phase to the polymer particles increases the rate of polymerization and the polymer molecular weights. The increase of the weight ratio PEO-MA/St favors the formation of monodisperse polymer particles, the colloidal stability of dispersion, and the formation of a larger number of polymer particles. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3131–3139, 1997     

Dispersion polymerization of methyl methacrylate in supercritical carbon dioxide: Influence of helium concentration on particle size and particle size distribution

Dispersion polymerizations of methyl methacrylate utilizing poly(1,1,-dihydroperfluorooctyl acrylate) as a steric stabilizer in supercritical carbon dioxide (CO₂) were carried out in the presence of helium. Particle size and particle size distribution were found to be dependent on the amount of inert helium present. Particle sizes ranging from 1.64 to 2.66 μm were obtained with various amounts of helium. Solvatochromic investigations using 9-(α-perfluoroheptyl-β,β-dicyanovinyl)julolidine indicated that the solvent strength of CO₂ decreases with increasing helium concentration. This effect was confirmed by calculations of Hildebrand solubility parameters. Dispersion polymerization results indicate that PMMA particle size can be attenuated by the amount of helium present in supercritical CO₂. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2009–2013, 1997     

Structure and properties of poly(methyl methacrylate) particles prepared by a modified microemulsion polymerization

Nanoscale poly(methyl methacrylate) (PMMA) particles were prepared by modified microemulsion polymerization. Different from particles made by traditional microemulsion polymerization, the particles prepared by modified microemulsion polymerization were multichain systems. PMMA samples, whether prepared by the traditional procedure or the modified procedure, had glass-transition temperatures (T_g's) greater than 120 °C and were rich in syndiotactic content (55–61% rr). After the samples were dissolved in CHCl₃, there were decreases in the T_g values for the polymers prepared by the traditional procedure and those prepared by the modified process. However, a more evident T_g decrease was observed in the former than in the latter; still, for both, T_g was greater than 120 °C. Polarizing optical microscopy and wide-angle X-ray diffraction indicated that some ordered regions formed in the particles prepared by modified microemulsion polymerization. The addition of a chain-transfer agent resulted in a decrease in both the syndiotacticity and T_g through decreasing polymer molecular weight. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 733–741, 2004     

Continuous reaction system to investigate the dispersion polymerization of vinyl monomers in supercritical carbon dioxide

A laboratory‐scale continuous reaction system using a stirred tank reactor was assembled in our laboratory to study the dispersion polymerization of vinyl monomers in supercritical carbon dioxide (scCO₂). The apparatus was equipped with a suitable downstream separation section to collect solid particles entrained in the effluent stream from the reactor, whose monomer concentration could be measured online with a gas chromatograph. The dispersion polymerization of methyl methacrylate in scCO₂ was selected as a model process to be investigated in the apparatus. The experiments were performed at 65 °C and 25 MPa with 2,2′‐azobisisobutyronitrile as the initiator and a reactive polysiloxane macromonomer as a surfactant to investigate the effect of the mean residence time of the reaction mixture on the monomer conversion, polymerization rate, polymer molecular weight, and particle size distribution. The results were compared with those obtained in batch polymerizations carried out under similar operative conditions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4122–4135, 2006     

Morphology and grafting of oxazoline-functional polymer particles with various carboxylic acids

Oxazoline-functionalized, crosslinked PMMA-particles, prepared by free radical nonaqueous dispersion polymerization, were grafted with n-decanoic acid and carboxylic acid-terminated polystyrene. Oxazoline groups, separated by an alkylspacer from the PMMA backbone, showed enhanced mobility with respect to the backbone, as evaluated by solid-state NMR spectroscopy using a dipolar filter. As a function of molecular mass of the carboxylic acid, the oxazoline conversion varied from 70 mol % for n-decanoic acid to 1% for monocarboxylate-terminated polystyrene CT-PS with M_n: 15,900 g/mol. Morphological studies, performed by TEM, showed that reaction with acid terminated polystyrene results exclusively in interfacial grafting at the particle surface. At low grafting levels a raspberry-like morphology was obtained, whereas grafting levels exceeding 14 wt % CT-PS resulted in core-shell morphology. Core-shell morphology was also verified by static light scattering using toluene solvent, which is isorefractive to the PMMA core. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1821–1827, 1998     

Thermoresponsive hyperbranched polymers via In Situ RAFT copolymerization of peg‐based monomethacrylate and dimethacrylate monomers

Here we report the preparation of PEG‐based thermoresponsive hyperbranched polymers via a facile in situ reversible addition‐fragmentation chain transfer (RAFT) copolymerization using bis(thiobenzoyl) disulphide to form 2‐cyanoprop‐2‐yl dithiobenzoate in situ. This novel one‐pot in situ RAFT approach was studied firstly using methyl methacrylate (MMA) monomer, then was used to prepare thermoresponsive hyperbranched polymers by copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMEMA, M_n = 475), poly(propylene glycol) methacrylate (PPGMA, M_n = 375) and up to 30 % of ethylene glycol dimethacrylate (EGDMA) as the branching agent. The resultant PEGMEMA‐PPGMA‐EGDMA copolymers from in situ RAFT were characterized by Gel Permeation Chromatography (GPC) and ¹H‐NMR analysis. The results confirmed the copolymers with multiple methacrylate groups and hyperbranched structure as well as RAFT functional residues. These water‐soluble copolymers with tailored compositions demonstrated tuneable lower critical solution temperature (LCST) from 22 °C to 32 °C. The phase transition temperature can be further altered by post functionalization via aminolysis of RAFT agent residues in polymer chains. Moreover, it was demonstrated by rheological studies and particle size measurements that these copolymers can form either micro‐ or macro photocrosslinked gels at suitable concentrations due to the presence of multiple methacrylate groups. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3751–3761