Copolymerization and Properties of Multicomponent Crosslinked Hydrogels

A series of multicomponent hydrogels were prepared by the copolymerization of hydrophobic silicon-containing monomer 3-bis(trimethylsilyloxy) methylsilylpropyl glycerol methacrylate(Si MA) with the solvent-responsive monomers 2-hydroxyethyl methacrylate(HEMA) and N-vinyl pyrrolidone(NVP) and thermosensitive monomer N,N-dimethyl acrylamide(DMA). 2-Hydroxy-2-methyl phenyl acetone(D-1173) was chosen as UV initiator and five different dienes/triene monomers were selected as crosslinking agent in order to select the best crosslinker. The ethanol extraction experiments as well as the FTIR, DSC and TG results showed that the copolymerization was effective. The optical, permeability, and mechanical analysis results demonstrated that the obtained hydrogels were highly transparent with good oxygen permeability and mechanical properties. And the impact of crosslinker on the mechanical properties of the hydrogels was also discussed in detail. The basic results demonstrated that the obtained hydrogels had good stimuli-responsive effects to both p H value and solvent.     

聚甲基丙烯酸羟乙酯树脂对胆红素的吸附研究

本文通过水相悬浮聚合制备了大孔交联聚甲基丙烯酸羟乙酯（PHEMA）树脂，研究了PHEMA树脂以及用乙醇胺功能基化后的PHEMA树脂对胆红素的吸附性能。结果表明，PHEMA树脂对胆红素的吸附性能受树脂孔结构，吸附温度，离子强度以及溶液中白蛋白的影响。该类吸附剂对胆红素有良好的吸附性能，其中用乙醇胺功能基化的树脂表现出更好的吸附能力。     

共聚水凝胶溶胀特性的研究

本文用差示扫描量热法研究了聚[N-乙烯基吡咯烷酮-甲基丙烯酸甲酯] 和聚[N-乙烯基吡咯烷酮-甲基丙烯酸β羟乙酯]两种共聚水凝胶中水存在的状态,考察了聚合物结构对平衡溶胀度的影响。结果表明,共聚单体的种类、共聚物组成、序列分布、化学交联度等结构因素对水存在的状态及各种状态水的含量都有很大影响,平衡吸水率可看作各种状态溶胀的水量的加和,以此为基础,提出了估算共聚水凝胶平衡吸水率的半经验公式。     

PHEMA hydrogels obtained by a novel low-heat curing procedure with a potential for in situ preparation

In this work, we report on poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels obtained by a low heat curing reaction. These materials are suitable for in situ preparation and therefore endowed with a potential for several biomedical applications. The novel procedure adopted involves as the first step the synthesis of a soluble oligomeric PHEMA precursor containing polymerizable functions as side substituents. As the second step, the precursor is dissolved in equal amounts of 2-hydroxyethyl methacrylate (HEMA) and water, to form a viscous but still injectable syrup. A low temperature water soluble initiator is then added. The curing reaction starts promptly and is completed within few minutes. During the entire process the internal temperature never rises above 40 degrees C. Preliminary mechanical characterizations performed on the hydrogels in their water-swollen state and diffusion tests in absorption/desorption experiments clearly indicated that on all respects the novel hydrogels are comparable with conventional PHEMA hydrogels obtained according to literature from HEMA in the presence of divinyl crosslinkers. However, the much shorter curing time combined with the far lower curing temperature endow the new hydrogels with a higher potential in view of specific surgical requirements, and particularly for in situ preparation.     

Understanding mechanical characteristics of cellulose nanocrystals reinforced PHEMA nanocomposite hydrogel: in aqueous cyclic test

Cellulose nanocrystals (CNC) can be embedded within hydrogels to form tough and strong nanocomposite materials, which possess biomimetic properties from hydrogels including good biocompatibility, permeability and flexible mechanical characteristics. There are many potential applications for these strong nanocomposite hydrogels in medical devices, such as wound dressing or super absorbents. Whereas, the research on the mechanical properties of CNC reinforced nanocomposite remains at superficial level, and their nonlinear mechanical responses are rarely investigated in previous reports. Mechanical characteristics of CNC reinforced poly(2-hydroxyethyl methacrylate) (PHEMA) nanocomposite hydrogels, in terms of stress–strain correlations, fracture mechanism, and cyclic stretching responses, have been investigated in this work. Experimental results show that the modulus of the nanocomposite hydrogel tends to increase with increasing CNC content. Theoretical foundation for analysing the mechanical properties of hydrogels based on Mooney–Rivlin hyperelastic model, Voigt model and Reuss model has been developed and validated, which provides the prediction of the mechanical responses of CNC reinforced nanocomposite hydrogel to tension, especially the nonlinear responding behaviour.     

Poly(Urethane)-Crosslinked Poly(HEMA) Hydrogels

Abstract

Hydrogels have been prepared from 2-hydroxyethyl methacrylate polymerized in the presence of isocyanate-terminated poly(ethylene glycol) (PEG) crosslinking agents. PEGS of molecular weights 200, 400, and 1000 were investigated. The crosslinked nature of the hydrogels was demonstrated by their insolubility in solvents which normally dissolve poly(HEMA). Hexamethylene diisocyanate (HDI) was mainly used as the isocyanate. The molecular weight of the PEG and the crosslinker content significantly influenced the equilibrium water sorption and mechanical properties of the saturated networks. It was observed that as the molecular weight of the PEG increased, the water sorption increased and the nominal modulus decreased. However, for higher levels of cross-linker, water sorption decreased and modulus increased at low molecular weight PEG; for PEG 1000, water absorption increased as crosslinker content increased. These results are explained by the competing effects of flexibility, crosslink density, and hydrophobicity contributed by the various constituents of the hydrogels.     

不同交联剂对甲基丙烯酸-β-羟乙酯/E-51双甲基丙烯酸酯聚合物水凝胶性能的影响

以水溶性单体甲基丙烯酸-β-羟乙酯(HEMA)与大分子交联剂E-51双甲基丙烯酸酯(E-51-DMA)(质量比HEMA/E-51-DMA=90/10)为主要原料,分别引入了5种小分子交联剂:N,N′-亚甲基双丙烯酰胺(MBA)、二乙烯基苯(DVB)、双甲基丙烯酸乙二醇酯(EDMA)、1,1,1-三(丙烯酰氧甲基)丙烷(TAP)和2,2,2-三(丙烯酰氧甲基)乙醇(TAE),采用本体聚合方法合成了5个系列的聚合物水凝胶.研究了小分子交联剂的类型及用量对水凝胶溶胀性能、杨氏模量以及有效交联密度ve和聚合物-水相互作用参数χ的影响,并比较了不同交联剂的交联效率.结果表明,随着小分子交联剂用量的增大,水凝胶平衡含水量EWC逐渐降低,聚合物体积分数2逐渐增大,反映聚合物网络结构的有效交联密度ve以及热力学参数聚合物-水相互作用参数χ值也随之增大.通过理论交联密度和有效交联密度的线性拟合,得到所选用的5种小分子交联剂在E-51-DMA10/HEMA90水凝胶体系中的交联效率,其顺序为DVB>EDMA>TAE>MBA≈TAP.     

Sorption of water in hydrophilic polymers—I Sorption isotherms in copolymers of hydroxyethyl methacrylate and hydroxyethoxyethyl methacrylate

Sorption isotherms of water vapour were determined for crosslinked poly-2-hydroxyethyl methacrylate (PHEMA), poly-2-(2′-hydroxyethoxy)ethyl methacrylate (PHEOEMA) and statistical copolymers at 35°. In the case of PHEMA the amount sorbed does not depend on the porosity of structure: sorption is influenced by the crosslinking parameters only at higher activities. The isotherm of PHEMA is S-shaped, while that of PHEOEMA, is convex; at lower activities, the sorption in mol/mol is higher in PHEMA than in PHEOEMA, although the former has a lower content of polar groups per monomer unit. It seems that the differences between isotherms could be explained by the fact (in principle identical with Kargin's hypothesis) that PHEMA is in the glassy state at the temperature of measurement, while the state of PHEOEMA is viscoelastic. The sorption data were used to calculate the parameters of the B.E.T. equation modified by Anderson; the concentrations of the sorption sites thus determined do not oppose the view that strongly bound water molecules are sorbed between two hydroxyl groups. The dependence of the Flory-Huggins interaction parameter χ on the volume fraction of the polymer exhibits a marked change of slope at a concentration roughly corresponding to the water content needed to transform the polymer from the glassy into the viscoelastic state at 35°. The Zimm clustering function indicates, at a higher water content, a considerable tende`ncy towards clustering; however, for samples in the glassy state and at low amounts sorbed, this function assumes negative values, suggesting mutual isolation of the molecules of the sorbate.     

非冻结水对微球复合水凝胶机械性能的影响

本文旨在用DSC的方法研究水凝胶结合水的能力与韧性的关系。 分别以甲基丙烯酸丁酯(BMA)或甲基丙烯酸六氟丁酯(HFBMA)和烯丙基胺为单体,制备了2种核壳纳米微球(BMA微球和HFBMA微球)。 再以其作为大分子引发剂和交联剂,制备了微球交联复合水凝胶(BMA-H凝胶和HFBMA-H凝胶)。 通过差示扫描量热仪(DSC)、傅里叶变换红外光谱仪(FTIR)和透射电子显微镜(TEM)等技术手段研究凝胶的结构和性能。 结果表明,HFBMA-H凝胶具有更好的机械性能,其拉伸强度和断裂伸长率分别可达280 kPa和3960%,远高于BMA-H凝胶(101 kPa,2700%)。 通过对2种复合凝胶体系内不同状态的水进行分析,发现HFBMA-H凝胶的非冻结水的质量分数明显高于BMA-H凝胶,这种非冻结水的增塑作用对于凝胶机械强度的提升具有重要影响。     

Studies on preparation and properties of NIPAAm/hydrophobic monomer copolymeric hydrogels

A series of thermoreversible copolymeric hydrogels with various molar ratios of N-isopropylacrylamide (NIPAAm) and hydrophobic monomers such as 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate (OFPMA) and n-butyl methacrylate (BMA) were prepared by emulsion polymerization. The effect of hydrophobic monomer on the swelling behavior and mechanical properties of the present copolymeric hydrogels was investigated. Results showed that the equilibrium swelling ratio and critical gel transition temperature (CGTT) decreased with an increase of the content of hydrophobic monomer, but the gel strength of the gel increased with an increase of the content of hydrophobic monomer. Due to stronger hydrophobicity of OFPMA, the NIPAAm/OFPMA copolymeric hydrogels had lower swelling ratios and higher gel strengths than NIPAAm/BMA copolymeric gels.     

聚甲基丙烯酸甲酯/聚甲基丙烯酸-2-羟乙酯复合微球的合成及药物吸放性能

采用在甲基丙烯酸甲酯（MMA）悬浮聚合过程中滴加甲基丙烯酸-2-羟乙酯（HEMA）乳液聚合组分的悬浮-乳液耦合聚合方法,制备了大粒径聚甲基丙烯酸甲酯／聚甲基丙烯酸-2-羟乙酯（PMMA／PHEMA）复合微球。PMMA／PHEMA复合微球表面以HEMA乳液聚合物为主,且具有微孔结构。PMMA／PHEMA复合微球在水和苄醇中的平衡溶胀率大于PMMA微球。PMMA／PHEMA复合微球48h异丁苯丙酸负载百分比为35．6％,PMMA为27．6％。在磷酸盐缓冲液中释放时间达到360h,释放量占负载总量的82％;而PMMA微球的释放时间为216h,释放量仅占负载总量的60％。     

Preparation and characterization of a novel stimuli-responsive nanocomposite hydrogel with improved mechanical properties

A novel stimuli-responsive organic/inorganic nanocomposite hydrogel (NC hydrogel) with excellent mechanical properties was synthesized by in situ polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO(2)MA), oligo (ethylene glycol) methacrylate (OEGMA) and acrylic acid (AAc), as the polymeric matrix (PMOA), and fibrillar attpulgite (AT), as the reinforcer and cross-linker. The effect of the AT content on the mechanical properties for the swollen and dried NC hydrogels was determined by tensile testing and dynamic mechanical analysis (DMA), respectively. The tensile testing results showed that the incorporation of AT nanoparticles significantly enhanced the mechanical properties of NC hydrogels. As the content of AT increased, the tensile strength, tensile modulus and effective cross-linked chain density increased. The DMA results showed that the storage modulus of AT/PMOA NC hydrogels was increased and the glass transition temperatures shifted to higher temperature compared to the pure PMOA hydrogel, which further indicated that the enhancement of mechanical property depended upon the presence and content of AT. In addition, the faster swelling rates of the NC hydrogels were observed in comparison with the corresponding physically cross-linked PMOA hydrogel, except for 1% AT/PMOA sample. However, the deswelling kinetics of NC hydrogels was obviously retarded.     

STUDY ON THE SWELLING BEHAVIOUR OF COPOLYMER HYDROGEL

The states of water in poly (N-vinylpyrrolidone-methylmethacrylate) and poly (N-vinylpyrroli-done-2-hydroxyethyl methacrylate) hydrogels have been studied by means of DSC. The effect ofpolmer structure on equilibrium swelling extent of water has been examined. It was found that thestate of water and the water content in different hydrogels were dependent on the kind of monomer used,the component of copolymer, the sequence distribution of the monomer unit and the degree of cross-linking (including chemical and physical) to a great extent. The equilibrium water content of thehydrogel may be regarded as the sum of the different state of swollen water contents of the hydrogel.Based on these, a semiempirical formula used to estimate the equilibrium water content of the copolymerhydrogels was presented.     

Mechanical properties of composite heterogeneous gels

Composites with a matrix of poly(2-hydroxyethyl methacrylate) (PHEMA) and 10% by volume of various crosslinked PHEMA polymer fillers (prepared by copolymerization with 0.1, 0.4, 1.0, and 20.0% by weight of ethylenedimethacrylate) of particle size about 1 μm were prepared. Some polymer matrixes were prepared from soluble branched PHEMA (Hydron S), and others by copolymerization, in the presence of the filler with 0.4 and 1.0% of ethylenedimethacrylate as a crosslinking agent. In the case of the uncrosslinked matrix, a linear polymer–crosslinked polymer system, resulted; in the case of the crosslinked matrix, a composite heterogeneous network was formed (in the latter case, the particles of the filler were swollen with monomer during the crosslinking polymerization). Stress–strain, equilibrium, and ultimate characteristics were measured at 3, 10, 25, 40, 60, and 80°C on samples swollen to equilibrium in water (T_g ≈ ?50°C) and at 80, 110, and 140°C on dry samples (T_g ≈ 100°C). Depending on experimental conditions, above all on the distance from the main transition region and on whether the polymer is dry or swollen, it was found that the measured hydrophilic composite systems behaves as a filled system (with the polymer filler acting mostly as solid particles, irrespective of the crosslink density) or as a system with crosslink density fluctuations (where both networks, the matrix and the filler, contribute roughly additively to the properties of the system), or finally as defect heterogeneous systems (where the properties depend primarily on the character of the polymer–filler interface).     

Tensile Mechanical Properties of Hydrophobic Association Hydrogels: Effect of Crosslinking Method,Synthesis Temperature,Mineral Salt and Swelling

Hydrophobic association hydrogels (HA-gels) were prepared through micellar copolymerization of acrylamide (AM) and a small amount of octylphenol polyoxyethylene acrylate (OP-10-AC) in an aqueous solution containing sodium dodecyl sulfate (SDS). For the P(AM/OP-10-AC) HA-gels, the effect of crosslinking method, synthesis temperature, mineral salt (NaCl) and swelling on their tensile mechanical properties was investigated in detail. The experimental results show that crosslinking method, synthesis temperature, NaCl and swelling powerfully influenced tensile mechanical properties of the P(AM/OP-10-AC) HA-gels. In addition, according to the tensile experimental results of the P(AM/OP-10-AC) HA-gels swollen, an effective crosslinking density change model is proposed. The effect of swelling on tensile mechanical properties of the P(AM/OP-10-AC) HA-gels was discussed on the basis of the model.     

Photocrosslinked hydrogels based on copolymers of poly(ethylene glycol) and lysine

A group of new, water-soluble poly(ether-urethane)s, derived from poly(ethylene glycol) and the amino acid L -lysine, provide pendent carboxylic acid groups along the polymer backbone at regular intervals. The carboxylic acid groups were utilized for the attachment of acrylate and methacrylate pendent chains (hydroxyethyl acrylate, hydroxyethyl methacrylate, aminoethyl methacrylate, and aminoethyl methacrylamide), leading to functionalized polymers. The pendent chains were attached via ester and/or amide bonds having different degrees of hydrolytic stability. The attachment reactions proceeded with high yields (up to 95%). The functionalized polymers were subsequently photopolymerized (UV irradiation) to obtain crosslinked hydrogels. Crosslinked membranes with the highest degree of mechanical strength were obtained when the crosslinking reaction was performed in dioxane with benzoin methyl ether (0.1 wt %) as the initiator. the crystallinity, thermomechanical properties, and hydrolytic stability of the crosslinked membranes were studied. All membranes were transparent and highly swellable (equilibrium water content: 64–88%). The tensile strength in the swollen state ranged from 0.15 to 1.09 MPa. Under physiological conditions (phosphate buffered water, 0.1M, pH 7.4, 37°C) the hydrolytic stability of the hydrogels varied depending on the bonds used in the attachment of the acrylate pendent chains: Hydrogels with hydroxyethyl acrylate pendent chains dissolved within 30 days, while hydrogels containing aminoethyl methacrylamide pendent chains remained unchanged throughout a 30 day period. Using high molecular weight FITC-dextrans as model compounds, complete release from the swollen hydrogels required between 60 and 150 h. Overall, the evaluation of poly(ethylene glycol)-lysine derived, photocrosslinked hydrogels indicated that these materials provide a range of potentially useful properties. © 1994 John Wiley & Sons, Inc.     

Synthesis and surface properties of self-crosslinking core–shell acrylic copolymer emulsions containing fluorine/silicone in the shell

Stable emulsions of a core–shell acrylic copolymer (non-crosslinkable V0, and crosslinkable V2, V4, V6, and V8, where the numbers indicate the wt% of crosslinking agent based on the total acrylate monomer content) containing butyl acrylate (BA, 45 wt%), glycidyl methacrylate (GMA, 45 wt%), heptadecafluorodecyl methacrylate (PFA, 10 wt%), and various contents of crosslinking agent (vinyltriethoxysilane, VTES) were synthesized using a three-stage seeded emulsion polymerization process with a small amount of surfactant. The average particle size and viscosity of emulsions increased significantly with increasing VTES content. This study examined the effects of the VTES content on the surface/mechanical properties of self-crosslinked copolymer film samples containing a fixed acrylate monomer content to find the optimum VTES content. XPS showed that the film–air surface of the copolymer samples had a higher fluorine/silicone content than the film–dish interface. The tensile strength/modulus, thermal stability, and two Tgs (α and β Tgs) of the film samples increased significantly with increasing VTES content. The contact angle of the film samples increased with increasing VTES content up to approximately 6 wt%, and then decreased slightly. The optimum VTES content was approximately 6 wt% based on the total acrylate monomer content to obtain a high water/oil repellent coating material (V6) with the highest water/methylene iodide-contact angles (118.2°/81.8°) and lowest surface energy (18.4 mN/m).     

Hydrophobic interaction in poly(2-hydroxyethyl methacrylate) homogeneous hydrogel

Homogeneous poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel exhibits a narrow range of swelling at equilibrium in water (% H₂O, 41.09 ± 0.15 standard error of the mean of 24 samples), regardless of the dilution of the monomer solution and relatively low level of crosslinking. It is postulated that PHEMA hydrogel has, in addition to its covalently linked network structure, a secondary structure stabilized by hydrophobic bonding. The addition of microsolutes to the hydrogel seems to confirm this hypothesis. The hydrogel swells beyond its swelling equilibrium in water in presence of urea and its methyl derivatives. Swelling is also induced by organic solvents like alcohol and acetone, and by anions like iodide, acetate, trichloroacetate, and thiocyanate. Chlorides and sulfates produce a less swollen hydrogel than pure water, while bromides and cetylpyridinium chloride, in the concentrations tested, induce only a slight deswelling of the gel. When PHEMA gel prepared in organic solvent–water solutions is placed in water, the gel passes through an opaque state before becoming transparent again. This phenomenon is interpreted as being caused by the inability of water to solvate the hydrophilic ends of the unorganized polymer segments. Homogeneity returns to the gel after a rearrangement of the chains, directed by the interaction of the hydrophobic portions of the polymer segments, exposing to the solvent–water most of the hydrophilic sites in the network.     

甲基丙烯酸羟乙酯改性水性聚氨酯乳液的制备及性能

采用种子溶胀乳液聚合法,以水性聚氨酯为种子,甲基丙烯酸羟乙酯、甲基丙烯酸甲酯和丙烯酸丁酯为单体制备水性聚氨酯丙烯酸酯复合乳液,考察了甲基丙烯酸羟乙酯含量对复合乳液的T型剥离、胶膜的硬度、耐水性和力学性能的影响。结果表明,随着甲基丙烯酸羟乙酯含量的增加,复合乳液的T型剥离强度、胶膜的硬度和拉伸强度增大,胶膜的耐水性先增大后减小,断裂伸长率有所降低,适宜的甲基丙烯酸羟乙酯用量为3%。     

Effect of magnetic nanoparticles on the thermal properties of some hydrogels

Magnetic hydrogels (ferrogels) based on poly(vinyl alcohol) (PVA) and poly(hydroxyethyl methacrylate) (PHEMA) with magnetite (Fe₃O₄) nanoparticles were prepared. PVA ferrogels were synthesised by submitting the aqueous solution of polymer and Fe₃O₄ to freezing-thawing (F-T) cycles yielding a physical gel. Different samples were prepared by varying (i) the concentration of PVA, (ii) the concentration of magnetite and (iii) the number of F-T cycles applied. PHEMA ferrogels were prepared by a crosslinking polymerization reaction in the presence of magnetite yielding chemical gels. Different samples were prepared by varying (i) the concentration of HEMA, (ii) the concentration of EGDMA and (iii) the concentration of magnetite nanoparticles. All ferrogel samples were first dried before been analysed in a thermogravimetric analyzer. The resulting thermograms showed that the concentration of magnetite nanoparticles does affect the thermal stability of either ferrogels system, a general improvement in comparison with PVA and PHEMA hydrogels, respectively, being observed. The apparent activation energy (E_a) of the thermal degradation for PVA ferrogels was evaluated and calculated applying the Flynn-Wall and the Kissinger methods. Values of apparent E_a increased with the content of Fe₃O₄ in the ferrogel sample.