Characterisation of macroporous poly(methyl methacrylate) coated with plasma-polymerised poly(2-hydroxyethyl acrylate)

Macroporous poly(methyl methacrylate) networks with varying cross-linking density and porosity were coated with plasma-polymerised poly(2-hydroxyethyl acrylate) grafted on the pores surface. The result is a mechanically reinforced hydrogel (PMMA-gr-plPHEA) whose properties are characterised in this work using several experimental techniques. Bulk PMMA and bulk PHEA were also characterised as reference materials. The diffusion and water sorption properties of these hydrogels were studied through equilibrium water sorption isotherms and desorption starting with the sample equilibrated in immersion in liquid water or in a vapour atmosphere. Glass transition, dynamic-mechanical relaxation and thermal degradation were characterised in order to study the interphase interaction in these biphasic systems. All these experimental techniques suggested that plasma-polymerised PHEA is more homogeneously interpenetrated with highly cross-linked macroporous PMMA than if the porous substrate is a loosely cross-linked polymer network.     

Nanodomains in a hydrophilic-hydrophobic IPN based on poly(2-hydroxyethyl acrylate) and poly(ethyl acrylate)

The morphology of a series of hydrogels based on the interpenetration of poly(2-hydroxyethyl acrylate) and poly(ethyl acrylate) has been studied through transmission electron microscopy, TEM, atomic force microscopy, AFM, and dynamic-mechanical spectroscopy, DMA. For the TEM analysis phosphotungstic acid, PTA, was used as alternative selective staining agent to those commonly used. The good agreement between TEM and AFM images allowed us to confirm that the PTA technique is a very powerful tool for TEM analysis of these hydrogel systems. All the results show that the IPNs presented phase-separation with two kinds of microdomains: those preferentially with a hydrophilic nature and those with preferentially a hydrophobic one, of sizes that range from 30 nm to 100 nm. Each one of these domains is composed by smaller nanodomains of alternating hydrophobic and hydrophilic component ranging between 6 and 10 nm sizes, those preferentially with a hydrophilic nature having a larger proportion of hydrophilic nanodomains. The AFM images of the IPN with the highest PHEA mass fraction, x_PHEA = 0.75, suggest that the hydrophilic phase is co-continuous in the material. A disperse hydrophilic phase is found when the PHEA mass fraction is reduced up to x_PHEA = 0.38. This phase-separation is explained in terms of some characteristic parameters of the networks such as the mesh size and the number of units between cross-links. The morphology found makes the systems very attractive for cell adhesion substrates and for matrices of scaffolds in soft tissue engineering.     

Poly(2-hydroxyethyl acrylate) hydrogel confined in a hydrophobous porous matrix

A series of interpenetrated polymer networks (IPNs) in which the first component is a porous poly(ethyl methacrylate) (PEMA) hydrophobic network and the second one is a poly(2-hydroxyethyl acrylate) (PHEA) hydrophilic network were synthesized. Equilibrium sorption isotherms can be reduced to a single master curve for all the IPNs when the water absorbed is expressed per gram of PHEA in them. The equilibrium water sorption in immersion is always much smaller than that of pure PHEA. This feature is due to the confining effect of the stiff PEMA matrix. The plasticizing effect of the absorbed water on the PHEA phase was characterized using thermally stimulated depolarization currents, dynamic-mechanical analysis and dielectric relaxation spectroscopy. The results show that the shift of the main relaxation peak towards lower temperatures is unaffected by the presence of the PEMA matrix, and only depends on the water content per gram of PHEA in the IPN.     

Interpenetrating Polymer Networks of Uralkyd Resin Based on Hydrogenated Castor Oil and Poly(Butyl Acrylate)

Abstract

Semi‐ and full‐interpenetrating polymer networks (IPNs) of uralkyd (UA) resin based on hydrogenated castor oil and poly(butyl acrylate) (PBA) were prepared by the sequential mode of synthesis. These IPNs were characterized for their resistance to thermal behavior, swelling (%), and mechanical properties. The morphology of the IPNs was studied by scanning electron microscopy (SEM). The effect of the variations of the blend ratios on the above‐mentioned properties was examined. The mechanical properties significantly enhanced by increasing UA component in the blend. Full‐IPNs exhibited higher apparent densities, mechanical properties, and thermal stability than the corresponding semi‐IPNs.     

DSC study of the miscibility of poly(methyl acrylate)-polystyrene sequential interpenetrating polymer networks

The phenomenon of forced compatibilization has been studied in poly(methyl acrylate)-polystyrene PMA-i-PS sequential interpenetrating polymer networks, IPNs, using differential scanning calorimetry. Both networks in the IPN were prepared using the same amount of ethylene glycol dimethacrylate, EGDMA, as crosslinking agent. The samples were subjected to thermal treatments which included annealing at different ageing temperatures T _a, for 300 min. From the DSC curves, recorded on heating the enthalpy loss during the isothermal annealing, Δh _a was calculated. The dependence of Dh _a with the annealing temperature was used to define the temperature interval in which the conformational mobility is significant. The comparison of the Δh _a(T _a) curves obtained in an IPN and the results obtained with the pure component homo-networks with the same crosslinking density reveal some details of the miscibility of the IPN. In the case of the IPN crosslinked with 10% EGDMA, two peaks are apparent in the Δh _a(T _a) curve, but the high-temperature peak is shifted towards lower temperatures compared to that of the polystyrene network while the low-temperature one is nearly at the same temperature than the one of the poly(methyl acrylate) homonetwork. This means that compatibilization is not complete and phase separation still exists even at this high crosslinking density. The different behaviour of the high and low temperature transitions can be explained by the dynamic heterogeneity of the sample, i.e. by the different length of cooperativity of the conformational rearrangements of PMA and PS domains at any temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dual temperature‐ and pH‐sensitive hydrogels from interpenetrating networks and copolymerization of N‐isopropylacrylamide and sodium acrylate

Hydrogels responsive to both temperature and pH have been synthesized in the forms of sequential interpenetrating networks (IPNs) of N‐isopropylacrylamide (NIPAAm) and sodium acrylate (SA) and compared with the crosslinked random copolymers of N‐isopropylacrylamide and SA. Whereas the stimuli‐sensitive behaviors of copolymer hydrogels were strongly dependent on the ionic SA contents, the IPN hydrogels exhibited independent swelling and thermal behaviors of each network component. The sequences and media in the synthesis of IPNs influenced the swelling capacities of the IPNs, but not the temperature or pH ranges at which the swelling changes occurred. In IPNs, a more expanded primary gel network during the synthesis of the secondary network contributed to the better swelling of the final IPNs. Both the swelling and thermal behaviors of the IPNs suggest that poly(N‐isopropylacrylamide) and poly(sodium acrylate) are phase separated regardless of their synthesis conditions. The presence of the poly(sodium acrylate) network did not influence the temperature or the extent of phase transition of the poly(N‐isopropylacrylamide) network in the IPNs, but did improve the thermal stability of the IPNs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3293–3301, 2004     

Water and polymer dynamics in poly(hydroxyl ethyl acrylate-co-ethyl acrylate) copolymer hydrogels

Water and polymer dynamics in hydrogels based on random copolymers of hydrophilic poly(hydroxyl ethyl acrylate) (PHEA) and hydrophobic poly(ethyl acrylate) (PEA), in wide ranges of composition, were investigated by means of two dielectric techniques, thermally stimulated depolarization currents (TSDC) and, mainly, broadband dielectric relaxation spectroscopy (DRS) at several levels of relative humidity/water content. Water sorption of the hydrogels was studied by equilibrium sorption isotherms (ESI). Two secondary relaxations (γ and β_sw) and the primary (segmental) α relaxation associated with the glass transition of the copolymer matrix were followed and analyzed against copolymer composition and water content. The results show that the copolymers are homogeneous at nm scale, except at very high PEA content. Correlations were observed between results on the organization of water in the hydrogels and on water effects on polymer dynamics. Distinct changes in the dielectric response, in particular in the time scale and the dielectric strength of the β_sw relaxation, at the water content of the completion of the first hydration layer indicate that water molecules themselves contribute to the dielectric response at higher water contents. Proton conductivity of the hydrogels at various levels of water content was also studied and correlation to segmental dynamics (decoupling) was analyzed.     

Biodegradable polymers by reactive blending trans-esterification of thermoplastic starch with poly(vinyl acetate) and poly(vinyl acetate-co-butyl acrylate)

Wheat starch was reacted with poly(vinyl acetate) and with poly(vinyl acetate-co-butyl acrylate) in an internal mixer at 150 °C in the absence of catalyst, and in the presence of sodium carbonate, zinc-acetate and titanium(IV) butoxide. The resulted blends were pressed into film and characterized by ¹H NMR-¹³C NMR spectroscopy, differential scanning calorimetry (DSC), mechanical testing, dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), and water absorption. Partial trans-esterification took place between wheat starch and the polymers. The blends appeared as homogenous, translucent films with one glass transition temperature range, between that of starch and of the polymer. The presence of wheat starch in the blends improved the mechanical strength of the polymers, although elongation at break severely decreased, which is disadvantageous for processability. Zinc-acetate improved the tensile strength of the blends of starch with PVAC, while all catalysts resulted in an increase in strength of the blends of starch with poly(vinyl acetate-co-butyl acrylate) compared to the strength of the blends without catalyst. Water absorption of wheat starch/copolymer blends was between 150% and 250%, higher than that of the blends with the homopolymer, which was between 100% and 150% after soaking in water. The onset temperature of thermal decomposition was between 290 and 300 °C for all the blends, although the presence of sodium carbonate resulted in a decrease in the onset temperature of thermal decomposition by about 60 °C.     

A novel quartz crystal microbalance gas sensor based on porous film coatings. A high sensitivity porous poly(methylmethacrylate) water vapor sensor

We describe a novel and generally applicable approach for creating voids in films deposited on the surface of solid substrates. Such films are advantageous when a quartz crystal microbalance (QCM) is the basis of a sensor. We show that films with large void volumes produce more sensitive sensors than with the original film. Poly(methylmethacrylate) (PMMA) was used as the polymer layer deposited on a quartz crystal microbalance (QCM) to demonstrate our technique for the model system of water vapor analysis in flowing nitrogen gas. A film of pure PMMA on a QCM is a sensor for water vapor in a gas phase. A more sensitive sensor was created by dip coating QCM crystals into solutions containing mixtures of PMMA and poly(d,l-lactide) (PDLL) and then evaporating the solution films on the QCM crystals to form mixed polymer films of varying PDLL content. The PDLL was then removed from the mixed polymer films by exposure to a NaOH solution to form pure PMMA films having various void volumes. A leached PMMA film that originally contained 50% by weight PDLL had a 3.7 times larger QCM sensitivity for water vapor than a pure PMMA film.     

Interpolymer complexes of poly(acrylic acid) with poly(2-hydroxyethyl acrylate) in aqueous solutions

Complexes formed from poly(acrylic acid) and poly(2-hydroxyethyl acrylate) were studied in aqueous solutions by viscometric, turbidimetric, FTIR spectroscopic, and thermogravimetric analysis methods. The formation of interpolymer complexes stabilized by hydrogen bonds was observed. It was found that the compositions of these interpolymer complexes are strongly dependent on the concentration of polymers, the order of mixing the solutions, and the pH. It was demonstrated that the complexation ability of poly(2-hydroxyethyl acrylate) is relatively low compared to other known nonionic water-soluble polymers. However, it can be significantly increased via hydrophobic modification of the poly(acrylic acid) using cetyl pyridinium bromide.     

聚己内酯/聚酯丙烯酸酯共混物的辐射交联及其形状记忆行为

研究了聚酯丙烯酸酯 (PEA)类多官能团物质与聚己内酯 (PCL)共混物的辐射交联效应 .分别考察了多官能团PEA的用量、官能团数目、辐射交联剂量等因素对聚己内酯的辐射交联规律、动态力学性能、形状记忆行为等性能的影响 .结果表明 ,PCL PEA共混物的辐射交联规律不再遵从Charlesby Pinner关系式 ,而是符合陈欣方 刘克静 唐敖庆关系式 .多官能团PEA的加入可以显著提高PCL辐射交联的效率 ;相同剂量时 ,官能团数目越多、用量越大的样品 ,生成的凝胶含量越多 ,强化辐射交联效应越大 .DMA分析表明 ,PCL强化辐照交联后的弹性模量和耐热性能显著提高 .强化交联PCL在其熔点以上都呈现出高弹态平台 ,可以实现形状记忆 .且交联度较高 ,形状记忆恢复速率较快 .     

Poly(ethylene oxide)/poly(methyl methacrylate) (semi-)interpenetrating polymer networks: Synthesis and phase diagrams

Interpenetrating polymer networks (IPNs) of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) were prepared by simultaneous network formation. The PEO network was produced by acid-catlayzed self-condensation of α,ω-bis(triethoxysilane)-terminated PEO in the presence of small amounts of water. The PMMA network was formed by free radical polymerization of MAA in the presence of divinylbenzene as crosslinker. The reaction conditions were adjusted to obtain similar crosslinking kinetics for both reactions. An attempt was made to construct a phase diagram of the IPNs by measuring the composition of the IPNs at the moment of the appearance of the phase separation, as indicated by the onset of turbidity. This composition could be determined because the siloxane crosslinks of the PEO network could be hydrolyzed in aqueous NaOH with the formation of linear, soluble PEO chains. The phase diagram was compared with phase diagrams of blends of linear polymers and of semi-IPNs (crosslinked PMMA and linear PEO), obtained under similar conditions, i.e. polymerization of MMA in the presence of varying amounts of PEO. It was observed that the form of the phase diagrams of the linear polymers is similar to that of the IPNs, but is quite different from that of the semi-IPNs. Thus, homogeneous transparent materials containing up to 60% of PEO could be prepared in the blends and the IPNs, but in the semi-IPNs, phase separation occurred with PEO contents as low as 10%.     

Facile synthesis of poly(hydroxyethyl acrylate) by frontal free‐radical polymerization

We report the first synthesis of poly(hydroxyethyl acrylate) (PHEA) without solvent by free‐radical frontal polymerization (FP) at ambient pressure. In a typical run, the appropriate amounts of reactant (hydroxyethyl acrylate) and initiator (1,1‐di(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane) (Luperox 231) were mixed together at ambient pressure. FP was initiated by heating the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self‐propagate throughout the reaction vessel. Once initiated, no further energy was required for polymerization to occur. To study the macrokinetics, we also produced PHEA frontally with ammonium persulfate as initiator and dimethyl sulfoxide as the solvent. The dependences of the front velocity and front temperature on the initiator concentration and reactant dilution were investigated. The front temperatures were between 124 and 157 °C, depending on the ammonium persulfate concentration. Thermogravimetric analysis indicates that PHEA prepared by FP with ammonium persulfate as initiator had higher thermal stability than solvent‐free frontally prepared PHEA with Luperox 231 as initiator. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 873–881, 2007     

Synthesis, characterization and thermoreversible behaviours of poly(dimethyl siloxane)/poly(N-isopropyl acrylamide) semi-interpenetrating networks

Simultaneous and sequential poly(N-isopropyl acrylamide) (PNIPAAm)/poly(dimethyl siloxane) (PDMS) semi-interpenetrating polymer networks (IPNs) with different linear PDMS contents were prepared by free radical polymerization method. Their phase morphologies have been characterized by FTIR, DSC and SEM. The simultaneous semi-IPNs exhibited phase transition temperatures (T_pt) shifted higher temperature from glass transition temperatures (T_g) of their respective homopolymers, suggesting a heterophase morphology and only physical entanglement between the PNIPAAm network and linear PDMS with high molecular weight (Mn≈9000 g/mol). For sequential semi-IPNs, the shift of T_pts towards lower temperature suggested that the chemical interaction between the constituents of the IPNs increased with increasing PDMS content in the network. In addition, these semi-IPNs were characterized for their thermo-sensitive behaviour by equilibrium swelling studies. The results showed that incorporation of hydrophobic PDMS polymer into the thermo- and pH-sensitive PNIPAAm and P(NIPAAm-co-IA) (itaconic acid) hydrogels by semi-IPN formation decreased swelling degrees of IPNs without affecting their LCSTs whereas addition of acrylated PDMS (Tegomer V-Si 2250) as crosslinker instead of N,N^′-methylenebisacrylamide (BIS) into the structures of these hydrogels changed their LCSTs along with their swelling degrees.     

Water sorption and polymer dynamics in hybrid poly(2-hydroxyethyl-co-ethyl acrylate)/silica hydrogels

This work probes the hydration properties and molecular dynamics of hybrid poly(hydroxyethyl-co-ethyl acrylate)/silica hydrogels. Two series of hybrid copolymers were prepared by simultaneous polymerization and silica preparation by sol-gel method, the first with hydroxyethyl acrylate/ethyl acrylate (HEA/EA) composition at 100/0, 90/10, 70/30, 50/50, 30/70, 10/90 and fixed silica content at 20 wt.%, and the second with fixed HEA/EA organic composition at 70/30 and 0, 5, 10 and 20 wt.% of silica. The hydration properties of these systems were studied at 25 °C by exposure to several controlled water vapor atmospheres (water activities 0-0.98) in sealed jars and by immersion in distilled water. Finally, the molecular dynamics of the hydrated hybrids at several levels of hydration was probed with Thermally Stimulated Depolarization Currents (TSDC) in the temperature interval between −150 and 20 °C. The results indicate that a critical region of silica content between 10 and 20 wt.% exists, above which silica is able to form an inorganic network. This silica network prevents the expansion of water clusters inside the hydrogels and subsequently the total stretching of the polymer network without obstructing the water sorption at the first stages of hydration from the dry state. As concerns the copolymer composition, the presence of EA reduces water sorption and formation of water clusters affecting directly to the hydrophilic regions. The TSDC thermograms reveal the presence of a single primary main broad peak denoted as α_cop relaxation process, which is closely related to the copolymer glass transition, and of a secondary relaxation process denoted as β_sw relaxation, which originates from the rotational motions of the lateral hydroxyl groups with attached water molecules. The single α_cop implies structural homogeneity at the nanoscale in HEA-rich samples (x_HEA > 0.5), while for high EA content (x_EA ? 0.5) phase separation is detected. Both relaxation processes show strong dependence on water content and organic phase composition.     

Water sorption properties of poly(ethyl acrylate-co-hydroxyethyl methacrylate) macroporous hydrogels

Synthetic porous hydrogels are becoming more and more important in the field of biomaterials. Different studies demonstrate that the porous structure promotes the colonisation of living cells and improves the biocompatibility of the implants. The macroporous structure allows not only the control of cellular ingrowth morphology but also the mechanical integration and the regulation of nutrient and hydraulic flow in the hydrogel. In this work poly(ethyl acrylate-co-hydroxyethyl methacrylate) (PEA/PHEMA) copolymers were polymerized using 2% of ethylene glycol dimethacrylate as cross-linking agent and azoiso-botyronitrile as initiator. Five samples were prepared with the EA/HEMA weight ratios of 75/25, 50/50, 25/75 and pure PEA and PHEMA polymers, obtaining different degrees of hydrophilicity. The macroporous structure was obtained by adding poly(acrylonitrile) fibres to the monomers. After polymerization the fibres were eliminated by dissolution in dimethyl formamide. The holes are cylinders of approximately 40μm diameter and are all, more or less, in the same direction, although they are not uniformly distributed. Water sorption isotherms and diffusion properties of the macroporous samples are compared with the samples without holes.     

Phase transition in swollen gels 31. Swelling and mechanical behaviour of interpenetrating networks composed of poly(1-vinyl-2-pyrrolidone) and polyacrylamide in water/acetone mixtures

Swelling and mechanical behaviour of interpenetrating positively charged polymer networks (IPNs), composed of poly(1-vinyl-2-pyrrolidone) (PVP) networks and polyacrylamide (PAAm) networks, was investigated in water/acetone mixtures. The first PVP networks were prepared by radiation polymerization at room temperature; after that the PVP networks were swollen in PAAm aqueous solutions and the networks were prepared by thermal copolymerization at 65 °C. The IPNs were prepared with various amounts of the two charged comonomers (quaternary ammonium salts) in the presence of crosslinkers. Two transition regions, detected in the dependence of swelling ratio X on acetone concentration a, suggest that a two-phase structure was formed. The first transition, located between 44 and 60 vol% of acetone, corresponds to PAAm networks, while the second transition, located at 75 vol% of acetone, corresponds to PVP networks. Depending on the amount of positive charges bound to chains, both transitions exhibit continuous or discontinuous character; this fact indicates that intermolecular interactions between the two components occur with the formation of IPNs (e.g., more polar, charged PVP component increases the extent of hydrogen bonding and makes acetone less effective solvent for IPNs at the PAAm transition). The dependences of log G on log X are roughly the same regardless of charge concentrations; this means that the mechanical behaviour is predominantly determined by the degree of swelling for all gels.     

Polyurethane/polyethyl acrylate interpenetrating polymer networks

The thermal decomposition kinetics of polyurethane/polyethyl acrylate interpenetrating polymer networks (PU/PEA IPN) were studied by means of thermogravimetry and derivative thermogravimetry (TG-DTG), and compared with those of polyurethane (PU) and polyethyl acrylate (PEA). The decomposition temperature (T _i) of PU/PEA IPN was found to be higher thanT _i of PEA, but lower thanT _i of PU. Thermal decomposition kinetic parameters,n andE, estimated using Coats-Redfern method, are found for PU/PEA IPN, PU and PEA to be 1.6, 1.9 and 1.1, and 196.6, 258.6 and 139.2 kJ mol^–1, respectively. The results show that PU/PEA IPN is neither a simple mixture of PU and PEA nor a copolymer of them. The mechanism of thermal decomposition of PU/PEA IPN is different from those of PU and PEA. The special network in PU/PEA IPN effectually protects weak bonds in the molecular chain of PU and PEA.We express our thanks to Dr. Yaxiong Xie and Zhiyuong Ren for their help in this work,     

高分子固体电解质LiNO_3-LiOOCCH_3/聚丙烯酸锂的合成与性能研究

以丙烯酸和氢氧化锂为原料用反相乳液聚合法合成聚丙烯酸锂 (PAALi) ,将其熔于低共熔盐 (一定比例的LiNO3 LiOOCCH3混合物 )中得到新型高分子固体电解质 (SPE) ,用XRD、IR、DTA、TG DTG等技术进行了表征 ,讨论了影响合成PAALi工艺及新型固体电解质电阻率的主要因素 ,在LiNO3 LiOOCCH3摩尔比为 1∶1时 ,将其按质量百分比 80∶2 0与聚丙烯酸锂混合均匀并熔融 ,得到的电解质其室温离子电导率可达 2× 10 - 5S·cm- 1 ,大量低共熔盐的加入可明显提高SPE的离子导电率 .XRD、DTA及TG DTG结果表明低共熔盐与聚丙烯酸锂形成了新的配合物     

Depolarization thermocurrent studies in poly(hydroxyethyl acrylate)/water hydrogels

Detailed investigations on the dielectric relaxation mechanisms in poly(hydroxyethyl acrylate) (PHEA), by means of the thermally stimulated depolarization currents (TSDC) method in the temperature range 77-300 K are reported. There is particular interest in the dependence of the dielectric relaxation mechanisms on the water content h, h = 0 ? 0.5 w/w, in an attempt to contribute to a better understanding of the physical structure of water in the PHEA hydrogels. We employ thermal sampling (TS) and partial heating (PH) techniques to experimentally analyze the observed complex relaxation processes, due to the secondary (β_sw) and the main (α) relaxation, into approximately single responses and to determine the spectra of activation energies E(T) at different h values. Measurements with different electrode configurations reveal different aspects of the dynamics of the relaxation mechanisms and allow the distinction between dipolar and conductivity relaxation contributions. It is shown that by means of these techniques we can determine certain temperature characteristics for the α relaxation and investigate their dependence on water content. We discuss the relation of these characteristic temperatures to the calorimetric glass transition temperature T_g. © 1994 John Wiley & Sons, Inc.