Total Monomer Concentration Research Articles

Novel silane based cross-linkers for preparation of methyl methacrylate gels

Abstract(2,2'-(Dimethylsilanediyl)bis(oxy)bis(ethane-1,2-diyl)bis(2-methylacrylate) (Type A cross-linker), (2,2'-(methyl) (phenyl) silanediyl)bis(oxy) bis (ethane-1,2- diyl)bis(2-methylacrylate)) (Type B cross-linker), and (2,2'-(diphenylsilanediyl)bis (oxy)bis(ethane-1,2-diyl)bis(2-methylacrylate)) (Type C cross-linker) three novel cross-linkers, (divinyl monomers), containing silanes and two methacrylates group (Si-DVM) were prepared by the condensation of 2-hydroxyethyl methacrylate (HEMA) with dichlorodimethyl, (DCDM) dichloromethyl phenyl (DCMP) and dichlorodiphenyl silane (DCDPS) in the presence of triethylamine (TEA). With these cross-linkers, methyl methacrylate, (MMA) can copolymerize by free-radical cross-linking copolymerization in toluene at a total monomer concentration of 3 molL-1 and at 70 °C. The experimental results show that increasing of Si-DVM concentration resulted in a decrease in gel point and swelling degree and an increase in conversion percent and weight fraction of the gels. The obtained crosslinkers were characterized by 1H-NMR and 13C-NMR spectroscopy and structural characteristics of the gels were examined by using equilibrium swelling in toluene solvent, gel fraction and Fourier-transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by Scanning electron microscopy (SEM).

Imprinting of protein over silica nanoparticles via surface graft copolymerization using low monomer concentration

Surface imprinting and adopting a nano-sized physical form are two effective approaches to overcome the template transfer difficulty within molecularly imprinted polymers and in particular advantageous to the imprinting of macromolecular structures like proteins. The surface protein-imprinted nanoparticles based on these two strategies are attractive for biosensor development. We here demonstrate a facile way for imprinting protein over nanoparticle supports. It was achieved simply via radical induced graft copolymerization of low concentration monomers on the surface of vinyl modified silica nanoparticles dispersed in aqueous media with lysozyme as a model protein. With a total monomer concentration of 0.4 wt%, less than tenth that employed conventionally, the possible gelation of the dispersion after polymerization was avoided and hence the unagglomerated imprinted particles could be readily collected. It was proved that thin polymer shells with imprinted sites had been formed over the support particles. In batch rebinding tests, the imprinted particles reached saturated adsorption within 5 min and exhibited significant specific recognition toward the template protein. The presented approach may be a versatile way for the fabrication of surface protein-imprinted nanoparticles via rational design of the surface chemistry of the support particles and choice of functional monomers according to the properties of the print protein.

Water-soluble copolymers from functionalized monomers (sodium o- and p-methacryloylaminophenylarsonate): Synthesis and characterization

Copolymers of sodium o-methacryloylaminophenylarsonate (o-MAPHA-Na) 1 and p-methacrylolylaminophenylarsonate (p-MAPHA-Na) 2 with sodium acrylate (AA-Na) 3, sodium methacrylate (AM-Na) 4 and acrylamide (AAD) 5 were prepared by free radical polymerization in aqueous media at 70°C using potassium persulfate (K2S2O8) as the initiator. The total monomer concentration was carried out at 0.5M and the feed ratio (M1 : M2) was varied from 10 : 90 to 90 : 10 mol%. The kinetic study was carried out by dilatometric method. The copolymer compositions were calculated by arsenic content in the copolymers. The As content (ppm) was determined by atomic absorption spectrometry (AAS). The reactivity ratios (r1, r2) were estimated by the Kelen-Tudos linearization method as well as error-in-variables method using the computer program RREVM®. In all cases, r1 1, indicating a tendency to form random copolymers. The values suggest that the copolymers contain a larger proportion of comonomer (i.e., AA-Na, AM-Na, or AAD). Weight-average molar masses (Mw) of copolymers were determined by multi-angle light scattering. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effects of TEMED and EDTA on the structural and mechanical properties of NIPAAm/Na+ MMT composite hydrogels

N-isopropyl acrylamide (NIPAAm) hydrogels are known as thermosensitive crosslinked polymer networks. In this work, the network parameters of their composites, i.e., NIPAAm/sodium montmorillonite (NIPAAm/Na+MMT) hydrogels synthesized by free radical solution polymerization in the presence of two different types of accelerator (tetramethyl ethylenediamine (TEMED) and ethylenediamine tetraacetic acid (EDTA)) and initiator (potassium persulphate (K2S2O8) and cerium ammonium nitrate ((NH4)2Ce(NO3)6), Ce(IV)) using five different clay content (in the range of 1.0–5.0 wt % of total monomer concentration) at 25 °C were presented and discussed. FTIR spectra, XRD patterns, SEM photographs, and network parameters of the samples indicated that the presence of COOH groups on EDTA molecules was resulted in the formation of exfoliated structures and the activity of EDTA/KPS redox pair was higher than those of TEMED/KPS and EDTA/Ce (IV) pairs. The compression moduli (G) of the hydrogels initiated with EDTA/Ce(IV) redox pair showed smooth and continual changings with increase in Na+MMT content (for swelling equilibrium at 25 °C) on the contrary of EDTA/KPS and TEMED/KPS pairs. It might be related to low initiator efficiency of cerium ammonium nitrate than KPS molecules, having higher effective crosslinking density with increasing clay content. On the other hand, the G moduli of NIPAAm/Na+MMT hydrogels (above their phase transition temperature) initiated with TEMED/KPS redox pair were higher than the others because of the more hydrophobic nature of TEMED molecules. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1256–1264, 2010

Precipitation polymerization in acetonitrile and 1-propanol mixture: synthesis of monodisperse poly(styrene-co -divinylbenzene) microspheres with clean and smooth surface

Precipitation polymerization of styrene (St)–divinylbenzene (DVB) has been carried out using acetonitrile/1-propanol mixture as the reaction media and 2,2′-azobisisobutyronitrile (AIBN) as initiator. Monodisperse micron-sized poly(St-co-DVB) microspheres with clean and smooth surface were synthesized in the absence of any stabilizing agent such as surfactants or steric stabilizers. The effects of various polymerization parameters such as 1-propanol fraction in the reaction media, initiator and total monomer concentration, DVB content, polymerization time and polymerization temperature on the morphology, particle size and size distribution were investigated. It was found that smoothly shaped stable particles were obtained when less than 70 vol% of 1-propanol was used in the media. The particle size increased with the AIBN concentration, whereas the change of uniformity was less obvious. Monodisperse microspheres were obtained when the total monomers loading ranged from 0.5 to 3 vol%. The particle diameter ranged from 2.73 to 1.87 µm with an increasing DVB content and the uniformity was enhanced. In addition, the yield of microspheres increased with the increasing total monomer, initiator, and DVB concentration and polymerization time. Copyright © 2010 John Wiley & Sons, Ltd.

Formation and structure of poly(methyl methacrylate) gels containing triphenyl vinyl silane

AbstractA series of Poly(methyl methacrylate) gels (PMMA) were prepared for making optical lenses by solution free radical crosslinking copolymerization of 2,2,2,‐trifluoroethyl methacrylate (TFEMA), methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), and triphenyl vinyl silane (TPVS) comonomer systems. They were then studied in toluene at a total monomer concentration of 5 molL−1 and 70°C. The conversion of monomer, volume swelling ratio, weight fraction, and gel point were measured as a function of the TPVS concentration, temperature, and chain transfer agents up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in toluene, gel fraction, and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by Scanning electron microscopy (SEM). The dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percentage of conversion and gel fraction. Finally, TPVS is a compatible vinyl type silicone comonomer for this system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Quasi-static particle formation of poly(acrylamide/methacrylic acid) in ethanol by using V-65 as initiator

Quasi-static precipitation polymerization of acrylamide (AAm) and methacrylic acid (MAc) in ethanol by using 2,2′-azobis(2,4-diemthylvaleronitrile) (V-65) as initiator was carried out. The effects of initial concentration of initiator and monomers on the kinetics of polymerization were investigated by gravimetry, SEM and HPLC. It was observed that the number of particles was severely dependent on the total initial concentration of monomers, and less affected by the concentration of initiator. The total surface area of the particles was independent of the concentration of initiator, but slightly affected by the initial concentration of monomers. In the range investigated in this paper, the lowest initial concentration of monomers, gave the maximum number of particles, whilst the highest concentration gave the minimum number of particles, but there was no significant difference observed among the total surface area of particles prepared by using various monomer concentrations. The normalized diameter against the initial concentration of monomers was linearly simulated in the range of concentration of monomers, W0, investigated in present system, R′ = 75.4W0 + 149.5. After the induction period, several pairs of curves of conversion vs. polymerization time overlapped. It indicated that the variation of conversion against time mathematically related to , where Ci,0 was the initial concentration of initiator. HPLC revealed MAc was consumed faster than AAm during the polymerization and a lot of AAm remained in dry particles.

Crosslinked methyl methacrylate/ethylene glycol dimethacrylate polymer compounds with a macroazoinitiator

AbstractA silane‐containing diamine, bis(p‐aminophenoxy) diphenylsilane (BADPS), was prepared by the condensation of p‐aminophenol with dichlorodiphenyl silane in the presence of triethylamine. Then, BADPS was condensed with 4,4‐azobis(4‐cyanopentanoyl chloride) to prepare macroazoinitiators containing silane units (Si–MAIs). A series of poly(methyl methacrylate) gels containing silane were derived by the solution free‐radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate monomers initiated by these macroazoinitiators at a total monomer concentration of 6 mol/L and 80°C. Si–MAIs were characterized with 1H‐NMR and 13C‐NMR spectroscopy, and the structural characteristics of the gels were also examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation and evaluation of a macroporous molecularly imprinted hybrid silica monolithic column for recognition of proteins by high performance liquid chromatography

A novel type of macroporous molecularly imprinted hybrid silica monolithic column was first developed for recognition of proteins. The macroporous silica-based monolithic skeleton was synthesized in a 4.6 mm i.d. stainless steel column by a mild sol–gel process with methyltrimethoxysilane (MTMS) as a sole precursor, and then vinyl groups were introduced onto the surface of the silica skeleton by chemical modification of γ-methacryloxypropyltrimethoxysilane (γ-MAPS). Subsequently, the molecularly imprinted polymer (MIP) coating was copolymerized and anchored onto the surface of the silica monolith. Bovine serum albumin (BSA) and lysozyme (Lyz), which differ greatly in molecular size, isoelectric point, and charge, were representatively selected for imprinted templates to evaluate recognition property of the hybrid silica-based MIP monolith. Some important factors, such as template–monomer molar ratio, total monomer concentration and crosslinking density, were systematically investigated. Under the optimum conditions, the obtained hybrid silica-based MIP monolith showed higher binding affinity for template than its corresponding non-imprinted (NIP) monolith. The imprinted factor (IF) for BSA and Lyz reached 9.07 and 6.52, respectively. Moreover, the hybrid silica-based MIP monolith displayed favorable binding characteristics for template over competitive protein. Compared with the imprinted silica beads for stationary phase and in situ organic polymer-based hydrogel MIP monolith, the hybrid silica MIP monolith exhibited higher recognition, stability and lifetime.

Effect of polymerization conditions on morphology and chromatographic characteristics of polyacrylamide‐based beds (monoliths) for capillary electrochromatography and capillary liquid chromatography

Pioneering research work on continuous or monolithic beds for LC was published in 1989. However, till date there is a lack of complex investigation of various factors affecting the morphology of the beds polymerized from water-soluble co-monomers. In this article the effect of buffer, used as polymerization medium, concentration and pH, and total monomer concentration on the morphology of the resultant continuous beds are discussed. Evaluation of the continuous beds was performed by means of capillary LC, CEC, and inverse size-exclusion chromatography.

Modification of Track Etchedfluorinatea Films by Radiation Induced Graft Copolymerization

With the aim of improving the basic characteristics of Track Etched Membranes (TEMs), functionalization by graft copolymerization has been attempted in the present work. Thin films (25 μm) of poly(vinyl fluoride) (PVF) (Tedlar) were irradiated by swift heavy ions (110 MeV Si 8+ ). The irradiated films were chemically etched to form latent tracks. Atomic Force Microscopy (AFM) was used to ascertain the formation of latent tracks. Irradiation effects were studied using UV-visible spectroscopic techniques. The tracks were functionalized by gamma radiation induced grafting with 4-vinyl pyridine (4-VP). In order to anticipate the best grafting conditions, percentage of grafting was studied as a function of various reaction conditions such as (i) total dose, (ii) monomer concentration and (iii) amount of water. Maximum percentage of grafting (13.66 %) was obtained at a total dose of 57.024 kGy using 2 ml of 4-VP in 10 ml of water. The grafted films were characterized by FTIR technique

Combinatorial Macrocyclizations under Thermodynamic Control: The Two-Monomer Case

Dynamic libraries of cyclophane formaldehyde acetals were generated from mixtures of two different monomeric units and quantitatively analyzed for the equilibrium concentrations of the lower cyclic oligomers. Plots of equilibrium concentration versus total monomer concentration exhibited saturation behaviors analogous to those observed in the equilibration of a single monomer. However, unlike the one-monomer case, limiting concentrations in the two-monomer case no longer provide a direct measure of the effective molarity (EM) of the various cyclic oligomers. A theoretical treatment of macrocyclization equilibria occurring in mixtures of two different monomeric units, aM and bM, is presented herein. Such a theory is based on the definition of probabilities pa and pb of the two monomers at the equilibrium and allows for realistic situations in which a monomer unit of a given type shows structural bias to be incorporated into one or more specific cyclooligomers, thus causing deviations from a purely statistical distribution. The theory allows to translate equilibrium concentrations into EM data.

Synthesis, swelling and drug release behavior of poly( N,N-diethylacrylamide-co- N-hydroxymethyl acrylamide) hydrogel

In this study, poly( N,N-diethylacrylamide-co- N-hydroxymethyl acrylamide) (poly(DEA-co-NHMAA)) hydrogels were synthesized by changing the initial DEA/NHMAA mole ratio, N,N'-methylenebisacrylamide and total monomer concentration. The thermosensitive and mechanical performances were optimized by altering the above parameters. The hydrogels were characterized by using Fourier transform infrared (FTIR) spectroscope and scanning electron microscope (SEM). In comparison with the PDEA hydrogel, the equilibrium swelling ratio (ESR) and lower critical solution temperature (LCST) of the hydrogels increased with the increase of NHMAA content in the feed. The swelling kinetics was also studied. The release behaviors of the model drug, aminophylline, are found dependent on hydrogel composition and environmental temperature, which suggests that these materials have potential application as intelligent drug carriers.

Effects of glycerol co-solvent on the rate and form of polymer gel dose response

A factor currently limiting the clinical utility of x-ray CT polymer gel dosimetry is the overall low dose sensitivity (and hence low dose resolution) of the system. Hence, active research remains in the investigation of polymer gel formulations with increased CT dose response. An ideal polymer gel dosimeter will exhibit a sensitive CT response which is linear over a suitable dose range, making clinical implementation reasonably straightforward. This study reports on the variations in rate and form of the CT dose response of irradiated polymer gels manufactured with glycerol, which is a co-solvent that permits dissolution of additional bisacrylamide above its water solubility limit (3% by weight). This study focuses on situations where the concentration of bisacrylamide is kept at or below its water solubility limit so that the influence of the co-solvent on the dose response can be explored separately from the effects of increased cross-linker concentration. CT imaging and Raman spectroscopy are used to construct dose–response curves for irradiated gels varying in (i) initial total monomer (%T) and (ii) initial co-solvent concentration. Results indicate that: (i) for a fixed glycerol concentration, gel response increases linearly with %T. Furthermore, the functional form of the dose response remains constant, in agreement with a previous model of polymer formation. (ii) Polymer gels with constant %T and increasing co-solvent concentrations also show enhanced CT response. In addition, the functional form of the response is altered in these gels as co-solvent concentration is increased. Raman data indicate that the fraction of bis-acrylamide incorporated into polymerization, as opposed to cyclization, increases as co-solvent concentration increases. The changes in functional form indicate varying polymer yields (per unit dose), akin to relative fractional monomer/cross-linker (i.e. %C) changes in earlier studies. These results are put into context of the model of polymer formation. The implications of these results on the clinical utility of polymer gels with co-solvent are highlighted.

Production of highly crosslinked microspheres by the precipitation polymerization of 2‐(diethylamino)ethyl methacrylate with two or three functional crosslinkers

AbstractPrecipitation polymerizations of 2‐(diethylamino)ethyl methacrylate were carried out with ethylene glycol dimethacrylate and then trimethylolpropane trimethacrylate in acetonitrile to produce monodisperse, highly crosslinked microspheres. Poly(diethylaminoethyl methacrylate‐co‐trimethylolpropane trimethacrylate) [poly(DEAEMA‐co‐TRIM)] microspheres, in the range of 1.2–2.7 μm, were obtained with a total monomer concentration of 1 vol % with respect to the solvent, and they kept their identity with several polymerization parameters. When the total monomer concentration was increased further, individual particles lost their identity and aggregated. Poly(DEAEMA‐co‐TRIM) particles with a total monomer concentration of 1 vol % had more discrete spherical forms with smoother surfaces, whereas in the poly(diethylaminoethyl methacrylate‐co‐ethylene glycol dimethacrylate) system, sticky microspheres were obtained with a total monomer concentration of 2.1 vol %. Moreover, several polymerization parameters were investigated to control the physical properties of microspheres of poly(DEAEMA‐co‐TRIM) and to understand the nature of the precipitation polymerization. Thus, the average particle size increased from 2.3 to 2.7 μm with an increased azobisisobutyronitrile concentration and then decreased to about 1.2 μm as the polymerization temperature was increased. All the microspheres produced under different polymerization conditions were found to be monodisperse (polydispersity index <0.1) with a narrow size distribution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Synthesis and characterisation of new cationic polyelectrolytes by inverse emulsion polymerisation and their application in activated sludge dewatering

Water soluble hydrophobically associated polyelectrolytes were copolymerised with dimethyl- [2-(2-methyl-acryloyloxy)-ethyl]-alkyl ammonium bromide (alkyl: propyl, hexyl, dodecyl) (DEACn) and acrylamide (AM) in inverse emulsion. Cationic hydrophobically modified polyacrylamides having different molecule weight and cationic degree were obtained by varying the total monomer concentration and DEACn/AM mole ratio. Polyelectrolytes were characterised by 1H-NMR and 13C-NMR. The dewatering indexes, such as CST, settling rate and water content in sludge cake were investigated and used to evaluate the dewaterability and settleability of activated sludge conditioned by these polyelectrolytes. Afterwards, some characteristics of sludge floc, such as: floc size, sludge viscosity and floc strength were measured. The function of hydrophobic association in sludge conditioning was elucidated by comparing dewatering performances with these polyelectrolytes

Structural parameters of polyacrylamide hydrogels obtained by the Equilibrium Swelling Theory

In this paper, the synthesis and structural characterization of a series of polyacrylamide hydrogels with different degrees of reticulation are reported. Although the Equilibrium Swelling Theory was recognized as a simple and reliable tool for the determination of structural hydrogels network parameters like equilibrium degree of swelling, cross-link ratio and mesh size, this is the first application of this methodology for polyacrylamide hydrogels. By changing the total monomer content in the synthesis solution (% T) from 5 to 30%, at a fixed value of cross-linker content in the total monomer amount (% C) of 5%, the final parameter obtained, the mesh size, can be tuned from 2 to 0.3 nm. It was also possible to change the mesh size (0.19–0.35) by varying % C from 5 to 12% (at % T = 20%). Scanning Electron Microscopy images for the most different formulations are shown and corroborate data obtained from the theory.

Encapsulation of silica nanoparticles by poly(methyl methacrylate-co-styrene) via emulsion polymerization using dimethylaminoethyl methacrylate

AbstractEncapsulation of silica nanoparticles was performed by emulsion copolymerization of methyl methacrylate (MMA) and styrene (St) using dimethylaminoethyl methacrylate (DM) as an auxiliary monomer. The emulsion polymerization was performed in the presence of silica nanoparticles as the seed to obtain encapsulated silica nanoparticles with polymer content and average particle sizes ranged from 35 wt. % to 85 wt. % and 114 to 272 nm respectively. Electrostatic attraction between anionic surface of silica beads and cationic amino groups of DM is the main driving force for the encapsulation of the silica nanoparticles. The influence of MMA, St and DM concentration on the coating of the silica nanoparticles was studied. It was demonstrated that DM has an important role in stabilizing the system. Transmission electron microscopy showed that coreshell structures with silica particles as core were coated with the polymer, of which the amount and morphology were influenced by the total monomer concentration and molar ratio of MMA to St. Zeta potential measurement confirmed the presence of DM on the surface of composite particles. Thermogravimetric analysis showed that the incorporation of silica in polymer matrix results in an enhancement of thermal stability in the encapsulated products. Differential scanning calorimetry studies indicated that the glass transition temperature of encapsulated particles can be either higher or lower than those of the pure terpolymer counterpart, depending on the DM content of the polymer shell. The products were also characterized by FT-IR spectroscopy.

Structure and Evolution of a Novel Dimeric Enzyme from a Clinically Important Bacterial Pathogen

Dihydrodipicolinate synthase (DHDPS) catalyzes the first committed step of the lysine biosynthetic pathway. The tetrameric structure of DHDPS is thought to be essential for enzymatic activity, as isolated dimeric mutants of Escherichia coli DHDPS possess less than 2.5% that of the activity of the wild-type tetramer. It has recently been proposed that the dimeric form lacks activity due to increased dynamics. Tetramerization, by buttressing two dimers together, reduces dynamics in the dimeric unit and explains why all active bacterial DHDPS enzymes to date have been shown to be homo-tetrameric. However, in this study we demonstrate for the first time that DHDPS from methicillin-resistant Staphylococcus aureus (MRSA) exists in a monomer-dimer equilibrium in solution. Fluorescence-detected analytical ultracentrifugation was employed to show that the dimerization dissociation constant of MRSA-DHDPS is 33 nm in the absence of substrates and 29 nm in the presence of (S)-aspartate semialdehyde (ASA), but is 20-fold tighter in the presence of the substrate pyruvate (1.6 nm). The MRSA-DHDPS dimer exhibits a ping-pong kinetic mechanism (k(cat)=70+/-2 s(-1), K(m)(Pyruvate)=0.11+/-0.01 mm, and K(m)(ASA)=0.22+/-0.02 mm) and shows ASA substrate inhibition with a K(si)(ASA) of 2.7+/-0.9 mm. We also demonstrate that unlike the E. coli tetramer, the MRSA-DHDPS dimer is insensitive to lysine inhibition. The near atomic resolution (1.45 A) crystal structure confirms the dimeric quaternary structure and reveals that the dimerization interface of the MRSA enzyme is more extensive in buried surface area and noncovalent contacts than the equivalent interface in tetrameric DHDPS enzymes from other bacterial species. These data provide a detailed mechanistic insight into DHDPS catalysis and the evolution of quaternary structure of this important bacterial enzyme.

Synthesis of submicron-sized composite particles with unique morphology by emulsifier-free seeded emulsion copolymerization

Polystyrene (PSt) microspheres with diameter of 375 nm to be used as the seeds for seeded emulsion polymerization were prepared via emulsion polymerization using potassium persulfate (KPS) as initiator in ethanol–water mixed solvents. Emulsifier-free seeded emulsion copolymerization of styrene (St) with acrylonitrile (AN) was carried out in the presence of poly(ethylene glycol) monomethoxymonomethacrylate (PEGm) macromonomer as reactive stabilizer and 2,2′-azobisisobutyronitrile (AIBN) as initiator to obtain submicron-sized PEGm graft poly(styrene-co-acrylonitrile) (PEGm-g-PSAN) composite particles with unique morphology. Scanning electron microscopy (SEM) indicated that St and AN together contributed to forming the unusual morphology. The concentration of St and AN, total monomer concentration, initiator type and the monomer adding method remarkably affected the morphology of the composite polymer particles.