On the role of hydrophilicity and hydrophobicity in aqueous heterophase polymerization

This paper reports on experimental results of aqueous heterophase polymerizations with monomers of quite different solubility in water ranging from the water-soluble 2-hydroxyethyl methacrylate to lauryl methacrylate with solubility in water of only about 10⁻⁴ mM. A calorimetric study revealed the strong influence of both the hydrophilicity of the monomer and the stirrer speed on the rate of polymerization in the absence of surfactants. In order to obtain maximum latex yield and high efficiency (which is a measure considering colloidal properties, polymerization recipe, and polymerization parameters) the initiator-surfactant combination must be properly chosen in dependence on the hydrophilicity of the monomer. Results are presented for sodium alkyl sulfates or disodium-N-stearoyl-l-glutamate as surfactant and potassium peroxodisulfate, or poly(ethylene glycol)-azo- compounds, or 2,2′-azobis(N-2′-methylpropanoyl-2-amino-alkyl-1)-sulfonates as initiators.     

无皂乳液聚合制备PUA乳液的稳定性研究

采用无皂乳液聚合法制备丙烯酸酯一聚氨酯复合乳液（PUA）。HEMA作为交联剂引入到聚氨酯主链上,利用核壳交联制得复合乳液。研究了不同的合成工艺、丙烯酸酯单体、DMPA及HEMA含量,引发剂种类等对乳液稳定性的影响。研究发现,将丙烯酸酯单体溶胀于水性聚氨酯乳液中再进行聚合可大大提高乳液的稳定性;采用1．0％～12％的AIBN为引发剂、DMPA质量分数为4．5％、HEMA质量分数为4．0％～4．5％、丙烯酸酯单体质量分数为30％时,可制得外观及稳定性良好的PUA复合乳液。     

The Effect of Initiators on the Emulsion Polymerization of 2-hydroxyethyl Methacrylate

The emulsion polymerization of 2-hydroxyethyl methacrylate (HEMA) was conducted at 80^○C, using a series of initiators and using either sodium dodecyl sulfate (SDS) or a mixture of SDS and poly(vinyl pyrrolidone) (PVP) as the emulsifier. For the series of initiators (including 2,2'-azobisisbutyronitrile (AIBN), 2,2'-azobis-(2-amidinopropane) dihydrochloride (AAP), 4,4'-azobis(4-cyanopentanoic acid) (ACPA) and 1,1'-azobis(cyclohexane carbonitrile) (ACHC)), the aqueous (aq.) solubility sequence correlates well to the polymerization rate sequence, while the sequence of initiation coefficient correlates poorly to the polymerization rate sequence. There is significant aq. phase polymerization, and frequent particle nucleation and coagulation during the polymerization. Increasing the monomer/water ratio, the polymerization rate does not increase proportionally to the particle number. It is suggested that the dominant locus for the formation of radicals is in the oil phase, and single radicals are formed by desorption of counterpart radicals from the particles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Poly (2-hydroxyethyl methacrylate)-based hydrogels for slow release of pralidoxime chloride

Pralidoxime chloride (PAM-Cl)-loaded poly (2-hydroxyethyl methacrylate) (PHEMA)-based hydrogels were prepared by bulk copolymerization of 2-hydroxyethyl methacrylate (HEMA) with different mol fractions (0.02–0.10) of trimethylsilyl methacrylate. Characterization of the gels was done by dynamic swelling measurements. It was found that copolymerization does not alter the swelling mechanism of PHEMA and it essentially remains Fickian in nature. In vitro drug-release studies show the increase in release time from 6 to 12 h on incorporation of a 0.1 mol fraction of trimethylsilyl methacrylate on the PHEMA backbone. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 267–270, 1997     

Free-radical synthesis of narrow polydispersed 2-hydroxyethyl methacrylate-based tetrapolymers for dilute aqueous base developable negative photoresists

Novel (meth)acrylate tetrapolymers based on 2-hydroxyethyl methacrylate (HEMA) were synthesized via free-radical polymerization in refluxing xylene under monomer-starved conditions for use in negative photoresist formulations. 2,2′-Azobis(2-methylbutyronitrile) was used as initiator and 2-mercaptoethanol as chain transfer agent. Optimized resist formulations were obtained with a relatively narrow polydispersed (D=1.86) low molecular weight copolymer (M_n=1677) of 2-hydroxyethyl methacrylate (HEMA), isobornyl methacrylate (IBMA), cyclohexyl methacrylate (CHMA) and acrylic acid (AA), in a 40/30/23/7 weight ratio. A novel high-resolution single layer negative tone photoresist suitable for 193 nm and e-beam lithography that meets basic performance requirements (aqueous-base development, enhanced etch resistance, sub-0.2 μm resolution) was developed from the aforementioned (meth)acrylate tetrapolymer, the poly(2-hydroxyethyl methacrylate-co-cyclohexyl methacrylate-co-isobornyl methacrylate-co-acrylic acid) (PHECIMA) and a sulfonium salt photo acid generator. The key-components for the negative image formation (photoacid induced crosslinking) are the hydroxyl groups of the HEMA moieties. The swelling-free negative resist material was developed in diluted aqueous base [tetramethyl ammonium hydroxide, (TMAH) 0.26×10⁻²N] and presented enhanced etch resistance without the use of etch resistance promoters. 0.20-0.14 μm lines were obtained upon 193 nm and/or e-beam lithography.     

Adsorption of trypsin onto poly(2-hydroxyethyl methacrylate)/polystyrene composite microspheres and its enzymatic activity

Poly(2-hydroxyethyl methacrylate)/polystyrene (PHEMA/PS) composite microspheres were produced by emulsifier-free seeded emulsion polymerization for styrene in the presence of PHEMA seed particles. Effects of the surface characteristics of the PHEMA/PS composite microspheres on the adsorption immobilization of trypsin and on its enzymatic activity were discussed. Above 5 mol% of HEMA content, trypsin molecules adsorbed had high activity, 65–100% of the activity of free trypsin. The excellence of the composite microspheres as a carrier for trypsin seems to be closely related with the surface heterogeneity consisting of both hydrophilic and hydrophobic parts.     

Synthesis and rheological properties of soluble poly(hydroxyethyl methacrylate) and some copolymers

Methods to synthesise soluble poly(2-hydroxyethyl methacrylate) (PHEMA) with varying molar mass were developed. Conversions over 90% were achieved without losing solubility. Steady state tests (range 0.01–590 Pa) and oscillatory tests (range 0.001–40 Hz) were carried out on 40% solutions in dimethyl formamide using a Carri-Med rheometer. Only PHEMA having molar mass over 500000 showed significant shear thinning and viscoelastic properties. The copolymers of 2-hydroxyethyl methacrylate (HEMA) with n-butyl acrylate (BA) and 2-hydroxypropyl acrylate (HPA) showed higher viscosities and viscoelastic properties compared with PHEMA homopolymer prepared under identical conditions. Also, viscosity and viscoelasticity increased with increase in acrylate content in the initial mixture. This was attributed to the higher molar mass of copolymers, which resulted from faster polymerisation rates owing to the inclusion of relatively highly reactive acrylates. However, in the case of HEMA : BA copolymers, first, the viscosity and viscoelasticity increased with increasing BA content and then dropped again, giving a maximum around HEMA : BA 75 : 25. This anomaly was explained by taking the effects of changes in inter-and intra-molecular hydrogen bonding as well as conformational differences caused by inclusion of BA in the PHEMA chain into account.     

含氟丙烯酸酯共聚乳液的制备及表征

以甲基丙烯酸甲酯（MMA）、丙烯酸丁酯（BA）等为主要单体,丙烯酸全氟烷基酯（Zonyl TM）为含氟单体,甲基丙烯酸羟乙酯（HEMA）为交联单体,采用种子乳液聚合法制备了含氟丙烯酸酯共聚物乳液。研究了Zonyl TM、HEMA、引发齐（APS）用量、复合乳化剂（SDS/OP—10）、聚合温度、聚合时间和搅拌速度等因素对聚合反应最终转化率、耐水性和乳液稳定性的影响。制备的乳液单体总转化率高,乳液凝聚率低,聚合反应稳定,涂膜的综合性能优良。此外,含氟乳胶膜对水的接触角及TG分析结果表明,Zonyl TM有效参与了共聚反应,提高了涂膜的耐水性及耐热性。     

Superporous poly(2-hydroxyethyl methacrylate) based scaffolds: Preparation and characterization

Superporous poly(2-hydroxyethyl methacrylate) (PHEMA) scaffolds with pore size from 10¹ to 10² μm range were prepared by radical polymerization of 2-hydroxyethyl methacrylate (HEMA) with 2 wt.% ethylene dimethacrylate (EDMA) with the aim to obtain a support for cell cultivation. Superpores were formed by salt-leaching technique using NaCl or (NH₄)₂SO₄ as a porogen. Addition of liquid porogen (cyclohexanol/dodecan-1-ol (CyOH/DOH) = 9/1 w/w) to the polymerization mixture did not substantially affect the formation of meso- and macropores. The prepared slabs were characterized by several methods including water and cyclohexane regain by centrifugation, water regain by suction, scanning electron microscopy (SEM), mercury porosimetry and dynamic desorption of nitrogen. High-vacuum scanning electron microscopy (HVSEM) confirmed permeability of hydrogel slabs to 8-μm microspheres, whereas low-vacuum scanning electron microscopy (LVSEM) at cryo-conditions showed the undeformed structure of the frozen slabs. Interconnection of pores in the PHEMA slabs was proved. Water regain estimated by centrifugation method did not include volume of large superpores (imprints of porogen crystals), in contrast to water regain by suction method. The porosities of the slabs ranging from 81 to 91% were proportional to the volume of porogen in the feed.     

Synthesis and characterization of polypropylene-based polymer hybrids linking poly(methyl methacrylate) and poly(2-hydroxyethyl methacrylate)

Isotactic polypropylene-based polymer hybrids linking poly(methyl methacrylate) (PMMA) and poly(2-hydroxyethyl methacrylate) (PHEMA) were successfully synthesized by a graft copolymerization from maleic anhydride-modified polypropylene (PP-MAH). PP-MAH reacted with ethanolamine to produce a hydroxyl group containing polypropylene (PP-OH) and the thus obtained PP-OH was treated with 2-bromoisobutyryl bromide and converted to a 2-bromoisobutyryl group containing polypropylene (PP-Br). The metal-catalyzed radical polymerization of MMA with PP-Br was performed using a copper catalyst system in o-xylene solution at 100 °C to give the PP-based polymer hybrids linking PMMA segments (PP-PMMA hybrids). Thus obtained PP-PMMA hybrids demonstrated higher melting temperature than PP-Br and microphase-separation morphology at the nanometer level owing to the chemical linkage between both segments. On the other hand, the polymer hybrids linking PHEMA segment (PP-PHEMA hybrids) were also obtained by the radical polymerization of HEMA with PP-Br in o-xylene slurry at 25 °C. TEM observation suggested that the polymerization mainly initiated on the surface of the PP-Br powder, led to the peculiar core-shell-like morphology. These PP-PHEMA hybrid powders showed a good affinity with water due to the hydrophilicity of the PHEMA segments.     

Synthesis and polymerization of some iodine-containing monomers for biomedical applications

Triiodophenol and iothalamic acid (5-acetamido-2,4,6-triio-N-methyl isophthalamic acid) were converted to their acrylic derivatives by esterfication with methacryloyl chloride and 2-hydroxyethyl methacrylate (HEMA), respectively. The monomers due to presence of heavy iodine atoms were expected to be radiopaque in nature. The monomers were characterized using TLC, IR, and ¹H-NMR spectroscopy. Both monomers were highly resistant to homopolymerization and copolymerization with other acrylic monomers such as methyl methacrylate (MMA) or HEMA by initiators such as 2,2′-azobis isobutyronitriie (AIBN) or benzoyl peroxide (BPO) yielding only polymers of low molecular weight. The polymers obtained were charactrized by gel permeation chromatography (GPC) and differential thermal analysis (DTA). The resistance to polymerization is presumably due to the presence of bulky iodine atoms in the monomers sterically hindering the propagation step. The decomposition temperatures of the homopolymers and copolymers were close to 300°. Copolymers of HEMA with both radiopaque monomers incorporated to the extent of 25 wt % in the feed, however, produced polymers with good radiopacity. Copolymers with HEMA were also prepared in the form of microspheres by a solvent evaporation method with the aim of using them as particles in therapeutic embolization. While the polymer based on triiodophenol was found to cause extensive blood haemolysis in in vitro tests, polymer based on iothalamic acid was found to be nonhemolytic in character suggesting that copolymers based on iothalamic acid would be suitable for implantation in the living tissue.     

Synthesis of pH‐responsive polyethylene terephthalate track‐etched membranes by grafting hydroxyethyl‐methacrylate using atom‐transfer radical polymerization method

pH‐responsive polyethylene terephthalate (PET) track‐etched membranes were synthesized by grafting 2‐hydroxyethyl‐methacrylate (HEMA) on the surface of the membrane via atom transfer radical polymerization. The controllability of grafting polymerization of HEMA on membrane surface is systematically investigated. The pH‐responsive characteristics of PET‐g‐poly(2‐hydroxyethyl‐methacrylate) (PHEMA) gating membranes with different grafted PHEMA chain lengths are measured by tracking the permeation of water solution with different pH values. The results show that the grafting polymerization is controllable, and the permeation of grafted membranes is affected by the grafted PHEMA chain lengths on the surface of membrane. The results also demonstrate that the grafted PET membranes exhibit reversible pH‐response permeation to environmental pH values. Desired pH‐responsive membranes are obtained by controlling the grafted PHEMA chain lengths via atom transfer radical polymerization method. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40912.     

Structural,morphological and thermal characterization of poly (2-hydroxyethyl methacrylate-co-acrylonitrile) (P (HEMA-co-AN)) Cryogels: evaluation of water sorption potential and cytotoxicity

Cryogels are macroporous hydrogels which are synthesized through cryogelation method. In the present study cryogels of poly (2-hydroxyethyl methacrylate-co-acrylonitrile) (P (HEMA-co-AN)) were synthesized by copolymerization of 2-hydroxyethyl methacrylate (HEMA) and acrylonitrile (AN) monomers by redox polymerization using cryogelation technique. The synthesized cryogels were characterized by FTIR, SEM, XRD, DSC and TGA techniques. Different compositions of the cryogels were prepared by varying concentrations of the monomers and redox initiators in the feed mixture. These cryogels were then subjected to swelling studies and porosity determination. The swelling behavior was studied as function of concentration of the monomers, redox initiators, temperature, pH, and simulated biological fluids. The prepared cryogels were also characterized for their network parameters using water sorption data. The biocompatibility of P (HEMA-co-AN) cryogel was evaluated by in vitro cytotoxicity test. The results indicated that the P (HEMA-co-AN) cryogel had macroporous morphology and exhibited good water absorption capacity. Moreover, the cryogel was thermally stable and biocompatible in nature.     

Free-radical propagation rate coefficients for hydroxyalkyl methacrylates and cyclohexyl methacrylate

Free-radical propagation rate coefficients (k _p ) at 30°C for the homopolymerization of cyclohexyl methacrylate (CHMA), 4-hydroxybutyl methacrylate (HBMA), 2-hydroxypropyl methacrylate (HPMA), and 2-hydroxyethyl methacrylate (HEMA) were determined to be 1070, 917, 640, and 71.9 (L mol⁻¹s⁻¹), using the rotating-sector method. The k _p value increases rapidly, and the value of life time of free radicals (τ_s) increases smoothly with increasing the alkyl chain length in the hydroxyalkyl pendant group of the monomer. Values for the steady-illumination polymerization rate for CHMA, HBMA and HPMA are much larger than that for HEMA. Comparisons of k _p values from different sources were also made.     

Morphological studies in thermally initiated emulsion (co)polymerization without conventional initiators

Poly(methyl methacrylate‐co‐styrene) composite latices were prepared by thermally initiated seed emulsion (co)polymerization of styrene (ST), methyl methacrylate (MMA), or ST and MMA employing a PST or PMMA seed in the absence of conventional initiators. The changes of particle morphology, observed by transmission electron microscopy (TEM), were investigated by varying seed particle component, the weight ratio of monomer to seed polymer, monomer composition, and employing preswelling of the seed particles. The size distribution of polymer particles obtained from thermally initiated emulsion (co)polymerization was improved by employing the seed process. Hemisphere‐like, sandwich‐like, core‐shell, and inverted core‐shell particle morphologies were observed depending upon the polymerization conditions. The preswelling of seed particles did not affect the morphology of final particles. The particle morphologies, obtained from the thermal process, were compared with those obtained from conventional seed emulsion polymerization. The incorporation of an initiator fragment SO to polymer chain ends seemed to allow the PST chains to gain some hydrophilicity. From the observation of particle morphology, the hydrophilicity of involved polymers were in the following order: PMMA with ionic (? SO) chain ends > PMMA with no ionic ends > PST with ionic ends > 60% MMA P(MMA‐co‐ST) with no polar ends > 40% MMA P(MMA‐co‐ST) with no polar ends > PST with no polar ends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1737–1748, 2002; DOI 10.1002/app.10581     

Dispersion polymerization of 2-hydroxyethyl methacrylate stabilized by a hydrophilic/CO2-philic poly(ethylene oxide)-b-poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) (PEO-b-PFDA) diblock copolymer in supercritical carbon dioxide

Dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) has been successfully performed in supercritical carbon dioxide at P=370 bar and T=65 °C with azobis(isobutyronitrile) as initiator and a hydrophilic/CO₂-philic poly(ethylene oxide)-b-poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) (PEO-b-PFDA) block copolymer as steric stabilizer. The PEO-b-PFDA (2K/21K) block copolymer was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Spherical particles of poly(HEMA) were obtained in the range of 200-400 nm diameter size with a narrow particle size distribution (D_w/D_n<1.1). The effect of the stabilizer concentration on the dispersion polymerization was investigated from 20 w/w% down to 3.5 w/w% versus HEMA. Precipitation polymerization in the absence of stabilizer lead to the formation of large aggregates of partially coalesced particles whereas discrete spherical particles of poly(HEMA) were obtained by dispersion polymerization even at low concentration of PEO-b-PFDA (3.5 w/w% versus HEMA).     

Monodisperse magnetic composite poly(glycidyl methacrylate)/La0.75Sr0.25MnO3 microspheres by the dispersion polymerization

Monodisperse magnetic poly(glycidyl methacrylate) microspheres were prepared by dispersion polymerization of glycidyl methacrylate in cyclohexane in the presence of La_0.75Sr_0.25MnO₃ nanoparticles, surface of which was modified with penta(propylene glycol) methacrylate phosphate (PPGMAP). However, only agglomerates were formed by the dispersion polymerization in toluene. Sterical stabilizer was poly(styrene-block-hydrogenated butadiene-block-styrene) and initiators investigated were 2,2′-azobisisobutyronitrile (AIBN) and 4,4′-azobis(4-cyanovaleric acid) (ACVA). Effects of initiators and other reaction conditions on properties of the composite microspheres were evaluated. The phase composition of the magnetic polymer composite microspheres and the size of magnetic cores were determined by X-ray powder diffraction. The characterization was completed by magnetization measurements, atomic absorption spectroscopy, TEM, SEM and ATR FTIR spectroscopy.     

Inverse emulsion polymerization-assisted designing of superparamagnetic poly (2-hydroxyethyl methacrylate) nanoparticles and magnetically triggered release of cisplatin

Superparamagnetic nanocarriers of poly (2-hydroxyethyl methacrylate) (PHEMA) were prepared by carrying out benzoyl peroxide (BPO) initiated inverse emulsion-free radical polymerization of HEMA in the presence of poly (vinyl alcohol) (PVA) and subsequent in situ precipitation of magnetite within the PHEMA matrix. The as-prepared nanoparticles were characterized by FTIR and UV–visible spectroscopy, vibrating sample magnetometry (VSM), particle size and zeta potential analysis, and transmission electron microscopy, respectively. The PHEMA nanocarriers were investigated for their blood compatibility, and cytotoxicity response to L929 cells. The superparamagnetic nanoparticles were loaded with an anticancer drug cisplatin and the release profiles of the drug were examined as a function of various experimental parameters like composition of the PHEMA nanocarriers, percentage of drug loading, and strength of the externally imposed magnetic field. The kinetics of the drug release process was also investigated, and the obtained release data were applied to different mathematical kinetic models to explore the nature of the release mechanism.     

Synthesis of uniform microspheres with higher content of 2-hydroxyethyl methacrylate by employing SPG (Shirasu porous glass) emulsification technique followed by swelling process of droplets

Relatively uniform microspheres containing a hydrophilic monomer, 2-hydroxyethyl 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 75°C under a nitrogen atmosphere. The uniform microsphere 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, snowmanlike, 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. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1325–1341, 1997     

Monosize polystyrene latices carrying functional groups on their surfaces

In this study, monosized polystyrene (PS) latices were prepared by dispersion polymerization of styrene in isopropanol-water media using poly(acrylic acid) (PAA) as a steric stabilizer and 2,2′-azobisizobutyronitrile (AIBN) as an initiator. The effects of initiator and stabilizer concentrations, alcohol/water and monomer/dispersion medium ratio on the polymerization kinetics, and the size and monodispersity of PS latices were experimented with in a stirred reactor system. Monosize PS beads in the size range of 1.0–3.0 μm were obtained. The PS latex obtained in the first step having a diameter of 2.3 μm were used as the seed latex, and styrene/acrylate monomers, acrylic acid (AA), 2-hydroxyethyl methacrylate (HEMA), and dimethylaminoethyl methacrylate (DMAEMA) were copolymerized onto the PS latex particles. The incorporation of functional groups to the surface and bulk structure of PS was confirmed by IR, FTIR, XPS, and zeta potential measurements. © 1994 John Wiley & Sons, Inc.