Radical Copolymerization Of 2-hydroxyethyl Methacrylate Research Articles

Providing Antibacterial Activity to Poly(2-Hydroxy Ethyl Methacrylate) by Copolymerization with a Methacrylic Thiazolium Derivative.

Antimicrobial polymers and coatings are potent types of materials for fighting microbial infections, and as such, they have attracted increased attention in many fields. Here, a series of antimicrobial copolymers were prepared by radical copolymerization of 2-hydroxyethyl methacrylate (HEMA), which is widely employed in the manufacturing of biomedical devices, and the monomer 2-(4-methylthiazol-5-yl)ethyl methacrylate (MTA), which bears thiazole side groups susceptible to quaternization, to provide a positive charge. The copolymers were further quantitatively quaternized with either methyl or butyl iodide, as demonstrated by nuclear magnetic resonance (NMR) and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). Then, the polycations were characterized by zeta potential measurements to evaluate their effective charge and by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to evaluate their thermal properties. The ζ-potential study revealed that the quaternized copolymers with intermediate compositions present higher charges than the corresponding homopolymers. The cationic copolymers showed greater glass transition temperatures than poly(2-hydroxyethyl methacrylate) (PHEMA), with values higher than 100 °C, in particular those quaternized with methyl iodide. The TGA studies showed that the thermal stability of polycations varies with the composition, improving as the content of HEMA in the copolymer increases. Microbial assays targeting Gram-positive and Gram-negative bacteria confirmed that the incorporation of a low number of cationic units into PHEMA provides antimicrobial character with a minimum inhibitory concentration (MIC) of 128 µg mL−1. Remarkably, copolymers with MTA molar fractions higher than 0.50 exhibited MIC values as low as 8 µg mL−1.

Toward Tertiary Amine-Modulated Acid-Triggered Hydrolysis of Copolymers Containing Pendent Ortho Ester Groups

We describe an efficient approach to modulate the hydrolysis of the ortho ester-containing polymers by incorporating different amount of tertiary amino (TA) groups. The block copolymers (NE0–NE3) contain a hydrophilic poly(ethylene glycol) (PEG) segment and hydrophobic chains constituted by random methacrylate copolymers with pendent acid-labile cyclic ortho ester and TA groups and were synthesized by a two-step approach. First, atom transfer radical copolymerization of 2-hydroxyethyl methacrylate and 2-(diethylamino)ethyl methacrylate using mPEG45-Br as a macroinitiator afforded the block copolymer precursors. Then, reaction of the precursors with 2-ethylidene-4-methyl-1,3-dioxolane transformed the pendent hydroxyl groups into cyclic ortho ester groups. The hydrophobic chains are similar in degree of polymerization, but the percent molar content of TA increases from 0% for NE0 to ∼15% for NE3. In phosphate buffer at pH 8.4, all the four amphiphilic block copolymers can self-assemble into stable nanoparticles with a monomodal distribution, which have a similar hydrophilic/hydrophobic balance as revealed by using pyrene and Nile red (NR) as fluorescent probes. Kinetic measurements of the ortho ester hydrolysis in the copolymer nanoparticles were studied at different pH values by 1H NMR spectroscopy, NR fluorescence probe, and light scattering. The results indicated that all the copolymer nanoparticles exhibit the pH-dependent hydrolysis behaviors with the half-life times ranging from hundreds of minutes at pH 5.4 to several days at neutral pH. More importantly, we found that the TA units have an amphoteric effect on the hydrolysis kinetics of the surrounding pendent ortho esters in acidic media. When compared with copolymer nanoparticles of NE0 with no TA unit, the NE1 nanoparticles with a small amount of TA unit hydrolyzed much slower, whereas a faster hydrolysis was observed for the NE3 nanoparticles containing a higher amount of TA unit.

Highly superporous cholesterol‐modified poly(2‐hydroxyethyl methacrylate) scaffolds for spinal cord injury repair

Modifications of poly(2-hydroxyethyl methacrylate) (PHEMA) with cholesterol and the introduction of large pores have been developed to create highly superporous hydrogels that promote cell-surface interactions and that can serve as a permissive scaffold for spinal cord injury (SCI) treatment. Highly superporous cholesterol-modified PHEMA scaffolds have been prepared by the bulk radical copolymerization of 2-hydroxyethyl methacrylate (HEMA), cholesterol methacrylate (CHLMA), and ethylene dimethacrylate (EDMA) cross-linking agent in the presence of ammonium oxalate crystals to establish interconnected pores in the scaffold. Moreover, 2-[(methoxycarbonyl)methoxy]ethyl methacrylate (MCMEMA) was incorporated in the polymerization recipe and hydrolyzed, thus introducing carboxyl groups in the hydrogel to control its swelling and softness. The hydrogels supported the in vitro adhesion and proliferation of rat mesenchymal stem cells. In an in vivo study of acute rat SCI, hydrogels were implanted to bridge a hemisection cavity. Histological evaluation was done 4 weeks after implantation and revealed the good incorporation of the implanted hydrogels into the surrounding tissue, the progressive infiltration of connective tissue and the ingrowth of neurofilaments, Schwann cells, and blood vessels into the hydrogel pores. The results show that highly superporous cholesterol-modified PHEMA hydrogels have bioadhesive properties and are able to bridge a spinal cord lesion.

Synthesis and Application of Co‐Poly(2‐hydroxyethyl methacrylate‐ethylene dimethacrylate) Coupled with Alizarin Yellow for Preconcentration and Determination of Lead in Water Samples by Flame Atomic Absorption Spectrometry

AbstractPoly(2‐hydroxyethyl methacrylate‐ethylene dimethacrylate) (PHEMA‐EDMA) beads were produced by free radical co‐polymerization of 2‐hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate (EDMA). Then, metal complexing ligand alizarin yellow was covalently attached onto PHEMA‐EDMA beads. The resulting resin has been characterized by FT‐IR and studied for the preconcentration and determination of trace Pb(II) ion from solution samples. The optimum pH value for sorption of the metal ion was 5. The sorption capacity of functionalized resin is 100 mg.g‐1. The chelating resin can be reused for 20 cycles of sorption‐desorption without any significant change in sorption capacity. A recovery of 96% was obtained for the metal ion with 0.1 M nitric acid as eluting agent. The equilibrium adsorption data of Pb(II) on modified resin were analyzed by Langmuir and Freundlich models. Based on equilibrium adsorption data the Langmuir and Freundlich constants were determined 2.571 and 418.7 at pH 5 and 25 °C. The method was applied for lead ions determination from well water sample.

Red/Near-Infrared Light-Emitting Organic–Inorganic Hybrids Doped with Covalently Bound Boron Dipyrromethene (BODIPY) Dyes via Microwave-Assisted One-Pot Process

Abstract Red/near-infrared (NIR) light-emitting boron dipyrromethene (BODIPY) dyes bearing methacryloyl groups were synthesized, and these dyes were covalently bonded to poly(2-hydroxyethyl methacrylate) (PHEMA)–silica hybrids. The preparation of their hybrids was performed by simultaneous sol–gel reaction of trimethoxy(methyl)silane and radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) with the dyes under microwave irradiation or conventional heating. Strong red/NIR light-emitting hybrids without discoloration of the dyes were successfully obtained under microwave irradiation, whereas the dyes lost luminescent properties in the hybrids prepared under conventional heating. Photostability test of the hybrids showed that covalent attachment of the dyes led to significant improvement in the photostability in comparison with the solution state. Further, elution amount of the dyes from the hybrids in organic solvents decreased relative to that from physical dye-admixing hybrids due to the covalent bond between PHEMA and the dyes.

The use of superporous Ac-CGGASIKVAVS-OH-modified PHEMA scaffolds to promote cell adhesion and the differentiation of human fetal neural precursors

Modifications of poly(2-hydroxyethyl methacrylate) (PHEMA) with laminin-derived Ac-CGGASIKVAVS-OH peptide sequences have been developed to construct scaffolds that promote cell adhesion and neural differentiation. Radical copolymerization of 2-hydroxyethyl methacrylate with 2-aminoethyl methacrylate (AEMA) and ethylene dimethacrylate in the presence of ammonium oxalate crystals resulted in the formation of superporous P(HEMA-AEMA) hydrogels. They were reacted with γ-thiobutyrolactone to yield 2-(4-sulfanylbutanamido)ethyl methacrylate (P(HEMA-AEMA)-SH) unit. The Ac-CGGASIKVAVS-OH peptide was immobilized to the sulfhydryl groups of P(HEMA-AEMA)-SH by 2,2′-dithiodipyridine linking reagent via 2-[4-(2-pyridyldisulfanyl)butanamido]ethyl methacrylate (P(HEMA-AEMA)-TPy). The adhesion and morphology of rat mesenchymal stem cells were investigated on the Ac-CGGASIKVAVS-OH-modified P(HEMA-AEMA) as well as on PHEMA, P(HEMA-AEMA)-SH and P(HEMA-AEMA)-TPy hydrogels. Superporous Ac-CGGASIKVAVS-OH-modified PHEMA scaffolds significantly increased the number of attached cells and their growth area on the hydrogel surface in the absence and in the presence of serum in the culture medium. Additionally, the Ac-CGGASIKVAVS-OH peptide supported the attachment, proliferation, differentiation and process spreading of human fetal neural stem cells during the first two weeks of expansion and contributed to the formation of a high percentage of more mature neural cells after four weeks of expansion. The Ac-CGGASIKVAVS-OH modification of superporous P(HEMA-AEMA) hydrogels improves cell adhesive properties and promotes neural stem cell differentiation.

Antimicrobial activity of hybrid hydrogels based on poly(vinylpyrrolidone) containing silver

In this work new hybrid hydrogels were prepared by radical copolymerization of 2-hydroxyethyl methacrylate, itaconic acid, poly(vinylpyrrolidone) and silver particles. FTIR spectroscopy has confirmed binding of silver particels in hydrogels. Swelling studies performed in in vitro conditions showed dependence on PVP content and temperature. It can be seen that the antimicrobial activity of the Ag/P(HEMA/IA)PVP hybrid hydrogels depends on the PVP moiety and with the increase of PVP content the microbial contamination is more efficiently reduced. The best sensitivity was obtained for the polymers tested for antimicrobial activity against the yeast C. albicans, one of the most commonly encountered human pathogens, causing a wide variety of infections ranging from mucosal infections in generally healthy persons to life-threatening systemic infections in individuals with impaired immunity. A slightly less susceptible to antimicrobial effect of hydrogels was obtained for the Gram-positive bacteria S. aureus, where the reduction of cells was about 70 % after two hours of exposure, for the sample with the highest PVP content. The least susceptible to the antimicrobial activity of hydrogels examined was the Gram-negative bacteria E. coli, where the percent of cell reduction was below 20 %. Bearing in mind the influence of the time of exposure of microbes to the Ag/P(HEMA/IA)/PVP hybrid hydrogels, it was observed that the reduction of the number of cells depends on time, microbial culture and type of hybrid hydrogel sample. Due to their swelling and antimicrobial properties, silver/poly(2-hydroxyethyl methacrylate/itaconic acid)/poly(vinylpyrrolidone) hybrid hydrogles show potential to use in the field of biomedicine, especially for treatment of skin and burns in dermocosmetics.

Microwave-assisted preparation of intense luminescent BODIPY-containing hybrids with high photostability and low leachability

Organic-inorganic hybrids with high luminescence were facilely obtained by a one-pot process through the combination of sol–gel condensation and radical copolymerization. The sol–gel reaction of methyltrimethoxysilane (MeTMOS) was carried out together with radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) with methacrylate-tethering boron dipyrromethene (BODIPY) dye 1, which was prepared by the reaction of a meso-butyl-substituted BODIPY dye and potassium methacrylate, under microwave irradiation or conventional heating conditions. The obtained hybrids were characterized by UV-vis and photoluminescence spectroscopies, and differential scanning calorimetry (DSC) thermogram, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) measurements. Microwave irradiation led to a more rapid and homogeneous reaction as compared to conventional heating conditions. Therefore, the obtained hybrids by means of microwave irradiation showed higher transparency owing to inhibition of aggregation derived from π–π stacking of BODIPY units. Quantum yields (ΦF = ∼94%) of the obtained hybrids were higher than those of 1 in methanol solution. Photostability of the hybrids was improved in comparison with that of poly(HEMA-co-1) film due to shielding by silica matrices; i.e., the access of oxygen in the excited state of BODIPY units is avoided. Moreover, the elution of BODIPY dye 1 from the hybrids was significantly reduced as compared to BODIPY dye without the methacrylate group due to the covalent bond between HEMA polymer and 1.

Cholesterol-modified superporous poly(2-hydroxyethyl methacrylate) scaffolds for tissue engineering

Modifications of poly(2-hydroxyethyl methacrylate) (PHEMA) with cholesterol and laminin have been developed to design scaffolds that promote cell–surface interaction. Cholesterol-modified superporous PHEMA scaffolds have been prepared by the bulk radical copolymerization of 2-hydroxyethyl methacrylate (HEMA), cholesterol methacrylate (CHLMA) and the cross-linking agent ethylene dimethacrylate (EDMA) in the presence of ammonium oxalate crystals to introduce interconnected superpores in the matrix. With the aim of immobilizing laminin (LN), carboxyl groups were also introduced to the scaffold by the copolymerization of the above monomers with 2-[(methoxycarbonyl)methoxy]ethyl methacrylate (MCMEMA). Subsequently, the MCMEMA moiety in the resulting hydrogel was hydrolyzed to [2-(methacryloyloxy)ethoxy]acetic acid (MOEAA), and laminin was immobilized via carbodiimide and N-hydroxysulfosuccinimide chemistry. The attachment, viability and morphology of mesenchymal stem cells (MSCs) were evaluated on both nonporous and superporous laminin-modified as well as laminin-unmodified PHEMA and poly(2-hydroxyethyl methacrylate-co-cholesterol methacrylate) P(HEMA–CHLMA) hydrogels. Neat PHEMA and laminin-modified PHEMA (LN–PHEMA) scaffolds facilitated MSC attachment, but did not support cell spreading and proliferation; the viability of the attached cells decreased with time of cultivation. In contrast, MSCs spread and proliferated on P(HEMA–CHLMA) and LN-P(HEMA–CHLMA) hydrogels.

Thermosensitive nanospheres of low-density core – An approach to hollow nanoparticles

A novel strategy for the preparation of hollow core–shell nano- and microparticle is reported. Nanoparticle cores were created from poly(N-isopropylacrylamide) (PNIPAM) by controlled heating above the LCST of this polymer in the presence of a small amount of sodium dodecyl sulfate. Shells were formed by radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) dimethacrylate (PEG-DMA) as cross-linking agent. The PNIPAM particles were acting as nucleating agents so that core–shell colloidal particles of PNIPAM covered with cross-linked PHEMA resulted. Subsequent release of a part of the PNIPAM chains from the interior of the particles was obtained by dialysis. The sizes and the temperature behavior of obtained particles were measured by DLS, TEM and SEM. The semi-hollow particles showed reversible volume response to cyclic temperature changes.

Biocompatible and bioadhesive hydrogels based on 2-hydroxyethyl methacrylate, monofunctional poly(alkylene glycol)s and itaconic acid

New types of hydrogels were prepared by the radical copolymerization of 2-hydroxyethyl methacrylate, itaconic acid and four different poly(alkylene glycol) (meth)acrylate components (Bisomers) in a water/ethanol mixture as solvent. The polymers swell in water at 25?C to yield homogeneous transparent hydrogels. All the hydrogels displayed pH sensitive behavior in buffers of the pH range from 2.20 to 7.40, under conditions similar to those of biological fluids. The presence of these two comonomers, which were added to HEMA, increased the swelling degree of the hydrogels and gave gels with better elasticity. The hydrogels were thermally stable in the vicinity of the physiological temperature (37?C). The copolymer containing pure poly(ethylene glycol) acrylate units generally had the best properties. The tests performed on the hydrogels confirmed that they were neither hemolytic nor cytotoxic. The copolymer samples showed better cell viability and less hemolytic activity than the PHEMA sample, confirming the assumption that poly(alkylene glycols) improve the biocompatibility of hydrogels. Due to their swelling and mechanical characteristics, as well as the very good biocompatibility and bioadhesive properties, poly(Bisomer/HEMA/IA) hydrogels are promising for utilization in the field of biomedicals, especially for the controlled release of drugs.

Stereogradient Polymers by Ruthenium-Catalyzed Stereospecific Living Radical Copolymerization of Two Monomers with Different Stereospecificities and Reactivities

Stereogradient polymers, a fundamentally new type of polymers, were prepared by the stereospecific living radical copolymerization of two monomers that have different stereospecificities and reactivities. The ruthenium-catalyzed living radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) and the silyl-capped HEMA [(tert-butyldimethylsilyl)-HEMA] (SiHEMA) in (CF3)2C(Ph)OH afforded stereogradient poly(HEMA), in which the rr content gradually increased from 62 to 77% at 0 degrees C, due to the lower reactivity and the higher syndiospecificity of SiHEMA.

Functional polymer hydrogels for embryonic stem cell support

Embryonic stem (ES) cells are pluripotent cells with the ability to differentiate among all embryonic and adult cell lineages. Derivation of human ES cells opened up the way for treatment of many serious disorders by stem cell-based transplantation therapy. One of the most exciting challenges in development of transplantation therapies is to repair the damaged part of the organ or tissue by transplantation of undifferentiated ES cells or their differentiated derivatives within three-dimensional polymer scaffold. This method allows both renewal of structure and restoration of function of the organ. To address this issue, new polymer hydrogels were synthesized and tested. Cationic hydrogel slabs were synthesized by bulk radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) with ethylene dimethacrylate (EDMA) or 1-vinyl-2-pyrrolidone (VP) with N,N'-divinylethyleneurea (DVEU) or EDMA in the presence of saccharose or NaCl as a porogen. Swelling studies of the synthesized copolymers showed a high water content in the swollen state. Biocompatibility was studied with the use of feeder-independent mouse ES cell line D3. Cells grown either on the surface or inside synthesized polymer slabs suggest that the tested slabs are not toxic. The ability of ES cells to proliferate was only partially limited in PHEMA slabs crosslinked with EDMA compared with standard culture conditions. When cultured for a limited period of time, ES cells retained their undifferentiated state independently of properties of the hydrogel slabs, presence or absence of surface charges, type of crosslinking agent and matrix (PHEMA or PVP). Notably, prolonged culture in superporous hydrogel slabs initiated ES cell differentiation. Compared with unmodified PHEMA, the number of proliferating ES cells was still lower in the presence of cationic polymers.

Interpenetrating Amphiphilic Polymer Networks of Poly(2-hydroxyethyl methacrylate) and Poly(ethylene oxide)

Interpenetrating polymer networks of poly(2-hydroxyethyl methacrylate) and poly(ethylene oxide) were synthesized by the free radical copolymerization of 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate in aqueous solutions of poly(ethylene oxide) diglycidyl ether (PEODGE), followed by amine−epoxy coupling reactions within the resultant gel network. The effects of ethylenediamine and PEODGE concentrations and coupling methods were examined and are discussed in this paper. Swelling studies and cryogenic-SEM analysis showed that these novel networks have high water intakes (equilibrium water content >3) and pore sizes on the order of up to 1 μm.

Characterization of pore structure of PHEMA-based slabs

The texture of highly porous poly(2-hydroxyethyl methacrylate) (PHEMA) slabs prepared by bulk radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate (EDMA) in the presence of porogens (cyclohexanol, dodecan-1-ol or saccharose) was studied by mercury porosimetry and solvent (water, cyclohexane) regain. Mercury porosimetry gave information on both the macroporosity (50 nm–1 μm) and superporosity (>1 μm) in dry state. The main part of pores in the prepared slabs was in the macroporous range. Low values of the apparent density of investigated polymers indicated the presence of closed pore structures. The effect of both the type of porogen and cross-linking degree on porous properties was discussed.

Grafting of Polystyrene onto Poly(butyl acrylate) and Polystyrene Backbones Using Functionalized Methacrylates

Summary: Grafting of terminal epoxide-functionalized polystyrene onto poly[styrene-co-(2-hydroxyethyl methacrylate)] or poly[(butyl acrylate)-co-(2-hydroxyethyl methacrylate)] backbones was carried out by coupling reactions catalyzed by boron trifluoride. The functionalized backbones were prepared by free radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) with styrene or butyl acrylate. For the synthesis of terminal functionalized polymer chains a side reaction of the TEMPO-mediated free radical polymerization of methacrylates could be used successfully to convert TEMPO-terminated polymers into terminal epoxide-functionalized polymers by the use of glycidyl methacrylate. The number of epoxide units attached to the backbone was directly related to the TEMPO concentration during the disproportionation reaction. Taking P(S-co-HEMA) as well as P(BuA-co-HEMA) backbones in coupling reactions with different epoxy-functionalized polystyrenes in the presence of boron trifluoride, graft polymers with up to 7 and 37 side chains per backbone were produced. Molecular weight distribution curves of a linking experiment between P(BuA-co-HEMA) backbones and epoxide-functionalized polystyrene side chains.

The copolymerization of N-vinyl-2-pyrrolidone with 2-hydroxyethyl methacrylate

The bulk free radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) with N-vinyl-2-pyrrolidone (VP) was carried out to low conversions at 50 °C, using benzoyl peroxide (BPO) as initiator. The compositions of the copolymers were determined using 13C NMR spectroscopy. The conversion of monomers to polymers was studied using FT-NIR spectroscopy in order to predict the extent of conversion of monomer to polymer. From model fits to the composition data, a statistical F-test revealed that the penultimate model describes the copolymerization better than the terminal model. Reactivity ratios were calculated by using a non-linear least squares analysis (NLLS) and r H = 8.18 and r V = 0.097 were found to be the best fit values of the reactivity ratios for the terminal model and r HH = 12.0, r VH = 2.20, r VV = 0.12 and r HV = 0.03 for the penultimate model. Predictions were made for changes in compositions as a function of conversion based upon the terminal and penultimate models.

Free radical copolymerization of 2-hydroxyethyl methacrylate with butyl methacrylate: determination of monomer reactivity ratios and glass transition temperatures

Free radical copolymerization of 2-hydroxyethyl methacrylate with butyl methacrylate using 3.0 mol l −1 N, N′-dimethyl formamide, DMF, solution and 9.0×10 −3 mol l −1 of 2,2′ azobisisobutyronitrile, AIBN, as initiator, was carried out at 50°C. Experiments performed in bulk have evidenced the possible solvent effect in the values of monomer reactivity ratios. Besides, the homopolymers glass transition temperature, T g, the intra and intermolecular structure along with Johnston's equation have enabled describing the experimental variations of HEMA–BMA copolymers' T g.

Low- and high-conversion studies of the free radical copolymerization of 2-hydroxyethyl methacrylate with styrene inN,N?-dimethylformamide solution

2-Hydroxyethyl methacrylate (HEMA) and styrene (S) have been copolymerized in a 3 mol . L -1 N,N'-dimethylformamide (DMF) solution using 2,2'azobis (isobutyronitrile) (AIBN) as an initiator over a wide composition and conversion range. From low-conversion experiments and 1 H-NMR analysis, the monomer reactivity ratios were determined according to the Mayo-Lewis terminal model. The comparison of the obtained results with those previously reported for copolymerization in bulk and in toluene reveals a relatively small but noticeable solvent effect that can be qualitatively explained by the bootstrap model. Cumulative copolymer composition as a function of conversion is satisfactorily described by the integrated Mayo-Lewis equation; overall copolymerization rate increases with increasing the HEMA/S ratio, and individual monomer conversion is closely related to the monomer molar fraction in the feed.

New radiopaque polyHEMA-based hydrogel particles

New iodine-containing polymeric hydrogel particles were prepared by suspension radical copolymerization of 2-hydroxyethyl methacrylate (HEMA), 3-(methacryloylamidoacetamido)-2,4,6-triiodobenzoic acid (MABA) and ethylene dimethacrylate (EDMA) in an aqueous medium using azobisisobutyronitrile as an initiator and magnesium hydroxide as a suspension stabilizer. To impart porosity to the product, cyclohexanol and 1-dodecanol were added as inert diluents to the polymerization mixture. Particles containing 27 wt % iodine produced radiopacity sufficient to observe a clearly visible X-ray image. The equilibrium swelling behavior of the particles in water was characterized. Swelling of the particles dramatically increased by converting the acid groups of MABA into their Na+ form. The more MABA the copolymer particle contain, the higher is their swelling in the Na+ form.