利用聚乙烯醇结晶辅助制备多重交联的高强度聚丙烯酰胺水凝胶

在表面带有C=C双键的乙烯基杂化二氧化硅纳米颗粒(vinyl hybrid silica nanoparticle,VSNP)上接枝丙烯酰胺(AM),所得到的纳米刷状凝胶因子通过聚丙烯酰胺(PAM)间的氢键形成物理交联点,则多官能化的VSNP可作为拟共价交联点构筑双重交联的单一网络纳米复合物理水凝胶(nanocomposite physical hydrogel,NCP gel),表现出较高的强度和超拉伸性.为了进一步提高凝胶的强度和韧性,将少量PVA和PAM/VSNP纳米刷混合制成凝胶,通过冷冻-融化处理,使与PAM分子链相互缠绕并形成氢键作用的PVA结晶,形成新的交联点进一步交联PAM NCP gel,得到多交联的PAM NCP gel体系.通过拉曼光谱和示差扫描量热分析,证明凝胶中的PVA通过氢键既可以与PAM相互作用,又形成微晶为新交联点,大大增强了NCP gel的力学性能,与PAM NCP gel相比,凝胶的拉伸强度和断裂能分别从313 k Pa和1.41×104 J/m~2提高到了557k Pa和4.65×104 J/m~2.     

Liquid-liquid equilibria of polyrotaxane and poly(vinyl alcohol)

Liquid–liquid equillibria (LLE) of the tertiary system of hydroxypropylated polyrotaxane (HPPR)–poly(vinyl alcohol) (PVA)–solvent have been investigated by focusing on the internal structures of HPPR–PVA blend gels. The phase diagrams of the HPPR–PVA aqueous systems displayed two liquid phases at a high concentration and molecular weight of PVA. This result was consistent with the prediction of the Flory–Huggins lattice model. On the contrary, the HPPR–PVA–DMSO system exhibited only a single phase. The HPPR–PVA blend gels crosslinked in dimethylsulfoxide (DMSO) were highly transparent over a wide concentration range, while the gels prepared in water were opaque at high polymer concentrations. Spherical domains were observed in the opaque gels by laser scanning confocal microscopy, and the sizes of the domains were significantly dependent on the amount of cross-linking reagent utilized. These results indicated that the transparency of the HPPR–PVA blend gels was strongly affected by the competition between the liquid–liquid two-phase separation and the crosslinking HPPR and PVA polymers during the preparation of the blend gels.     

Preparation and Characterization of Interpenetrating Polymer Hydrogels Based on Poly(acrylic acid) and Poly(vinyl alcohol)

Interpenetrating polymer hydrogels (IPHs) of Poly (vinyl alcohol) (PVA) and Poly (acrylic acid) (PAAc) have been prepared by a sequential method: crosslinked PAAc chains were formed in aqueous solution by crosslinking copolymerization of acrylic acid and N, N′-methylenebisacrylamide in the presence of PVA. The application of freezing-thawing cycles (F-T cycles) leads to the formation of a PVA hydrogel within the synthesized PAAc hydrogel. The swelling and the viscoelastic properties of the prepared IPHs were evaluated on the basis of the structural features obtained from solid state ¹³C-NMR spectroscopy.     

Structural and dynamical studies of poly(vinyl alcohol) gels by high-resolution solid-state C NMR spectroscopy

The ¹³C CP/MAS NMR spectra of isotactic, syndiotactic and atactic poly(vinyl alcohol) (PVA) gels were measured in order to clarify the structure of the immobile component of PVA gel. In the ¹³C CP/MAS NMR spectra, the three CH carbon peaks I, II and III (at about 77, 71 and 65 ppm) were clearly observed, which originate from the formation of strong intermolecular or intramolecular hydrogen bonds between hydroxyl groups like solid PVA. It has been assigned that these peaks originate from the crosslinked region in the gel state. On the basis of the experimental results, intermolecular hydrogen bonds play an important role in the formation of the crosslinked-region in the gel state. Further, the effect of PVA's tacticity on the amount of the crosslinked regions by intermolecular interactions was discussed. In addition, molecular motion in the immobile and mobile region of PVA gel was discussed through the observation of ¹³C spin-lattice relaxation time T₁.     

Solute retention and the states of water in polyethylene glycol and poly(vinyl alcohol) gels

The states of water sorbed in a cross-linked polyethylene glycol (PEG) gel, TSKgel Ether-250, and cross-linked poly(vinyl alcohol) (PVA) gels of different pore sizes, TSKgel Toyopearl HW-40S, 50S, 55S and 75S, were investigated by means of differential scanning calorimetry (DSC). It was found that there were three types of water in these hydrogels, non-freezing water, freezable bound water and free water. The amount of water that functions as the stationary phase in the column packed with the each gel was also estimated by a liquid chromatographic method. The estimated amount of the stationary phase water is in good agreement with the sum of the amount of non-freezing water and that of freezable bound water for HW-40S, 50S and 55S, while it agrees with the amount of only non-freezing water for HW-75S and Ether-250. This means that the stationary phase water consists of non-freezing water and freezable bound water for HW-40S, 50S and 55S, while only non-freezing water functions as the stationary phase in HW-75S and Ether-250 gels. This result can be attributed to the difference in the structure of the gels; the PVA gels containing PVA at relatively high concentrations, HW-40S, 50S and 55S, have a homogeneous gel phase, whereas HW-75S and Ether-250 have a heterogeneous gel phase consisting hydrated polymer domains and macropores with relatively hydrophobic surface. The freezable bound water in Toyopearl HW-40S, 50S and 55S can be regarded as a component of a homogeneous PVA solution phase, while that in HW-75S and Ether-250 may be water isolated in small pores of the hydrophobic domains. The results obtained by the investigation on the retention selectivity of these hydrogels in aqueous solutions supported our postulated view on the structures of the hydrogels.     

Solid‐state 13C and 129Xe NMR study of poly(vinyl alcohol) and poly(vinyl alcohol)/lactosilated chitosan gels

Dry and hydrated poly(vinyl alcohol) (PVA) gels with 55% (a‐PVA) and 61% (s‐PVA) syndiotacticity and related PVA/lactyl chitosan (LC) blends have been investigated with ¹²⁹Xe and cross‐polarization/magic‐angle‐spinning ¹³C NMR techniques. Although the dry gels exhibit two broad ¹²⁹Xe resonances in the slow‐to‐intermediate exchange limit, both hydrated gels show three resonances. The corresponding dry blends exhibit two signals, the chemical shifts and line widths of which change with respect to those of pure PVA, whereas one (a‐PVA/LC) or two (s‐PVA/LC) signals appear in the spectra of the hydrated blends. A comparative analysis of the data demonstrates that LC rearranges the domains of the polymeric matrix in both the dry and hydrated blends according to the syndiotacticity of the PVA chains. Information on the molecular motions of the amorphous and swollen polymeric domains in the kilohertz range has been obtained from an analysis of the spin‐lattice relaxation times. These data indicate that the dynamics and arrangement of the PVA chains in the gels are strongly affected by their tacticity and the addition of the copolymer LC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3123–3131, 2003     

About the compatibility of polymer components in polymer complexes based on poly(acrylamide) and poly(vinyl alcohol)

The issue of applying the usual concepts of polymer compatibility to nonstoichiometric PVA/PAA mixtures of chemically complementary poly(vinyl alcohol) and poly(acrylamide), which form in water solution InterPC (intermolecular polymer complex) stabilyzed by H‐bonds, and PAA to PVA graft copolymers (PVA‐PAA_N) with different grafted chains number N, that are IntraPC (intramolecular polymer complexes) is discussed. PVA and PAA are compatible on molecular level. At the same time PVA/PAA mixture (50/50 W/W) is characterized by heterogeneous structure consists of InterPC with ϕ_char=9g_PVA/g_PAA and the excess of unconnected PAA. In the case of IntraPC, yet, only PVA‐PAA_N, where N=25, is characterized by a single glass transition temperature (Tg). At larger values of N separate PAA domains form giving rise to the corresponding Tg. These results are discussed in view of IntraPC structure peculiarities as a function of N investigated by IR spectroscopy.     

Association between benzalkonium chloride and a poly( acrylic acid) gel. Study by microfiltration and membrane dialysis

Interactions between benzalkonium chloride (BAK) and the respective polymers, and the related availability of BAK in the corresponding solution, were studied for aqueous preparations of hydroxyethylcellulose (HEC), polyvinyl alcohol (PVA) and crosslinked poly(acrylic acid) (PAA). The study was performed by means of a crossflow filtration process with an alumina membrane. In the presence of the PAA gel, the rejection rate of BAK is much higher than with HEC or PVA. These results can be explained by the association of the benzalkonium cation BAK⁺ with the negative carboxylate groups or the PAA. This effect, which was confirmed by dialysis experiments, leads to the trapping of BAK⁺ inside the polymer network and could be of interest in the reduction of the harmful effects of BAK observed in the treatment of eye diseases.     

Immobilization of oligonucleotides on crosslinked poly(vinyl alcohol) for application in DNA chips

In biotechnological applications there is an enormeous growth in the development of new miniaturized devices to reduce timescales, cost and amounts of reagents and starting materials. DNA chips represent miniaturized analytical tools that allow the simultaneous detection of different targets for high throughput screening. They consist of a small size support on which DNA probes are in-situ synthezised or immobilized. We present protocols for the effective immobilization of pre-synthezised 16S rRNA oligonucleotides on crosslinked poly(vinyl alcohol) (PVA). The polymeric gel consists of poly(vinyl alcohol) (PVA) crosslinked with poly(allylamin chloride) (PALAM) and monochlortriazinyl-beta-cyclodextrin (beta-CD) at pH 4,6.8,8 and 9. Mechanical characterization of the gels show that the immobilization capacity increases with increasing pH and increasing crosslinking within the gel. We will demonstrate that the hybridization efficiency on PVA chips is superior over commercially available chips based on nylon, nitrocellulose and aminoalkylsilane.     

Antimicrobial loading into and release from poly(ethylene glycol)/poly(acrylic acid) semi‐interpenetrating hydrogels

Electrostatic interactions within a semi‐interpenetrating network (semi‐IPN) gel can control the postsynthesis loading, long‐term retention, and subsequent release of small‐molecule cationic antibiotics. Here, electrostatic charge is introduced into an otherwise neutral gel [poly(ethylene glycol) (PEG)] by physically entrapping high‐molecular‐weight poly(acrylic acid) (PAA). The network structure is characterized by small‐angle neutron scattering. PEG/PAA semi‐IPN gels absorb over 40 times more antibiotic than PAA‐free PEG gels. Subsequent soaking in physiological buffer (pH 7.4; 0.15 M NaCl) releases the loaded antibiotics for periods as long as 30 days. The loaded gels elute antibiotics with diffusivities of 4.46 × 10^?8 cm²/s (amikacin) and 2.08 × 10^?8 cm²/s (colistin), which are two orders of magnitude less than those in pure PEG gels where diffusion is controlled purely by gel tortuosity. The release and hindered diffusion can be understood based on the partial shielding of the charged groups within the loaded gel, and they have a significant effect on the antimicrobial properties of these gels. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 64–72     

High-performance membranes for pervaporation II. Crosslinked poly(vinyl alcohol)–poly(acrylic acid) blends

Dense membranes made by crosslinking of poly(vinyl alcohol) (PVA) with poly(acrylic acid) (PAA) were prepared and tested in pervaporation and differential permeation of water–alcohol mixtures. Instead of a decrease of permeation flux as generally observed with most crosslinking agents, an increase in the permeability was observed with PAA crosslinked membranes at low PAA contents. The permeation flux increases with PAA contents in the polymer with no selectivity reduction for membranes containing less than 15 wt. % PAA. The membranes show good performances to water–2-propanol and water–ethanol mixtures, i.e. high fluxes and high selectivities to pure water. The membranes were stable and highly permeable to water. The enhancement of the permeability of PVA can be explained by a reduced crystallinity and an improved diffusivity due to the presence of PAA.     

Effects of microcrystallites on swelling behavior in chemically crosslinked poly(vinyl alcohol) gels

We report the swelling ratio and network structure of a poly(vinyl alcohol) (PVA) gel chemically crosslinked by glutaraldehyde with different degrees of crosslinks. Microcrystallites were formed in a chemical PVA gel during a drying process and were confirmed by X‐Ray diffraction (XRD) measurements and Fourier transform infrared (FTIR) spectroscopy. The formation of microcrystallites in the dried gels was suppressed by increasing the degrees of chemical crosslinks. When the dried samples were immersed in pure water at 25 °C, the swelling ratio depended on the degree of chemical crosslinks resulting from the destruction of physical crosslinks by microcrystallites. On the other hand, when the dried samples were immersed in a poor solvent of a mixture of dimethyl sulfoxide and water at 8 °C, the gels did not swell and stayed in the collapsed state. Starting from the collapsed state, the equilibrium swelling ratios were measured while the temperature was increased to 90 °C and then decreased to 8 °C. As a result, irreversible swelling behaviors were observed for all gels with different degrees of crosslinks, which were attributed to the destruction of microcrystallites. The swelling behavior is discussed in terms of the formation and destruction of additional physical crosslinks in the chemical PVA gels. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

PVA/PAA水凝胶纤维的电刺激响应性能

以过硫酸胺为引发剂,在PVA水溶液中原位聚合丙烯酸单体,得到的PVA／PAA混合水溶液在凝固浴硫酸胺饱和水溶液中纺丝制备了物理缠结和氢固定网络形式的PVA／PAA水凝胶纤维。该纤维于NaCl溶液中在直流电场作用下具有电流－刺激敏感性,表现为溶胀、收缩、弯曲行为。纤维的弯曲速度和最大弯曲度随电场强度和凝胶网络中PAA含量的增加而增大,随电解质溶液离子强度的变化出现临界最大值。纤维向负极弯曲的过程中,在电场下自由离子和反庆子迁移引起的渗透压主导作用,弯曲过程主要是溶胀弯曲;向正极弯曲过程中,由于电化学反应和电场作用下产生的PH梯度导致凝胶网络构像变化主导作用,弯曲主要是收缩弯曲;弯曲由负极向正极转化过程中,两种机理对弯曲的影响相对平衡。     

Simple and easy recycling of poly(amic acid) gels through microwave irradiation

Poly(amic acid)s (PAAs), which are precursors of polyimides, often undergo gel formation during their synthesis or storage, and these insoluble gels have been discarded. In this work, we discovered that the gels could be converted to homogeneous PAA solutions by fast and simple microwave (MW) irradiation. The PAA gels were placed inside a domestic MW oven, and MW irradiation was carried out with 240 W for 2 min. The recycled PAA solutions afforded polyimide films, coatings, and powders. The polyimides prepared from the recycled PAA solutions exhibited higher glass transition temperatures (T_gs), decomposition temperatures, and char yields than comparison polyimides obtained from ordinary PAA solutions. Flexible free‐standing polyimide films were obtained by drop‐casting of the MW‐treated solutions and subsequent thermal imidization. Mechanical properties and dielectric constants were measured for the polyimide films and coatings, respectively. This new method has significant advantages for the environment, economy, and industry. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 981–987     

Hydrogels of polyvinylpyrrolidone (PVP) and poly(acrylic acid) (PAA) synthesized by radiation-induced crosslinking of homopolymers

pH-sensitive PVP–PAA hydrogels have been prepared by electron-beam-induced irradiation at pH close to pKa of carboxylic groups. Protonation of these groups promoted the formation of hydrogen bonds between the PAA and PVP segments within the crosslinked structure and caused interpolymer complex formation. To demonstrate possible future application of such gels, we tested them as simple chemical detectors. When loaded with glucose oxidase, the PAA–PVP gel's turbidity and shrinkage was triggered by the presence of glucose due to a drop in pH caused by the enzymatic reaction.     

Factors influencing the swelling and elution properties of poly(vinyl alcohol) cast gels

Swelling and elution properties of physically crosslinked poly(vinyl alcohol) (PVA) cast gels depend on the network structure of the PVA and crosslink, which is characterized by the size, number, and distribution of microcrystallites. Therefore, the swelling and elution ratios can be manipulated by adept control of the conditions adopted for the preparation of gels. Among the various factors that influence the formation of microcrystallites, the temperature and relative humidity at gelation play an important role. In addition, the size of gel is also a key factor that determines the network structure of gels. To this end, this study quantitatively evaluates the macroscopic properties of swelling and elution, and the microscopic properties of the network structures in disk‐shaped PVA cast gels of the same diameter prepared by casting different weights of PVA solution in the same dish. Although the drying speed can be controlled by adjusting the three processing parameters, namely, drying temperature, humidity, and cast weight, the changes in swelling and elution ratios, microcrystallite size, and crystallinity independently depended on each parameter. Regardless of the three factors, the swelling ratio was found to correlate strongly with the elution ratio. Optimum factors to minimize the elution ratio are discussed on the basis of the change in the network structures obtained by varying the preparatory conditions. Based on the results of the systematic analyses, this study proposes a method to control the elution ratio while retaining high water‐absorbance ability. Copyright © 2015 John Wiley & Sons, Ltd.     

Microrheology of chemically crosslinked polymer gels by diffusing-wave spectroscopy

The Brownian motion of probe particles in aqueous solutions of poly(vinyl alcohol)(PVA) and in chemically crosslinked PVA gels has been studied by diffusing-wave spectroscopy (DWS). At long time scales the measurements allow us to determine the effect of the crosslinking ratio on the macroscopic viscosity of sols and the shear modulus of gels. The local shear modulus of gels as obtained from the characteristic length of the Brownian cage was found to agree with that measured by classical rheometry and dynamic light scattering (DLS). These microrheological techniques were applied to two polymer gel systems. Substrate induced gradient structure of hydrogels was studied from a microrheological point of view using DLS. It is clearly seen that hydrophobic substrate induces weakly crosslinked network formation at the interface region up to a few millimeters as expected from other experimental facts. Magnetic particle motion in gels under external magnetic field was investigated by DWS. The translational motion of the magnetic particles in gels due to the alternating magnetic force can be detected and found to be superimposed on the relaxation due to the thermal motion.     

Rheological and DSC changes in poly(vinyl alcohol) gels induced by immersion in water

Poly(vinyl alcohol) (PVA) gels were prepared by freezing and thawing aqueous solutions at temperatures from ?20 to 15°C. The temperature was varied periodically by use of a computer. The endothermic DSC peak was observed for the PVA gels at about 60°C for five specimens of different degrees of saponification (DS). Another endothermic peak was also observed in the range 67–80°C, and this peak shifted to higher temperature with increasing DS. These endothermic peaks shifted to lower temperature on immersion of the PVA gels in water. The dynamic Young's modulus E′ at room temperature was also decreased by immersion of PVA gels in water; E′ decreased monotonically with increasing temperature for PVA gels without immersion in water, while it increased up to a certain temperature and then decreased with increasing temperature for PVA gels in water. The X-ray diffraction showed a characteristic crystalline pattern for PVA gels of higher DS, and this peak was intensified by stretching the gel.     

Osmotic deswelling of weakly charged poly(acrylic acid) solutions and gels

The osmotic pressure of weakly charged aqueous poly(acrylic acid) (PAA) solutions and the swelling pressure PAA gels were studied by osmotic deswelling at different degrees of ionization (α). In solution, the osmotic pressure was found to scale linearly with concentration, whereas the scaling power of the swelling pressure of gels was higher (1.66). The effect of the ionization degree on the osmotic coefficient in PAA solutions was in agreement with the theory of Borue and Erukhimovich [Macromolecules, 21 , 3240 (1988)]. Ionization increases the swelling capacity of the PAA gels until a plateau is reached at about 35% neutralization. The concentration at equilibrium swelling scales as C_e ～ α^?0.6. The contribution of the network to the gel swelling pressure is evaluated by subtracting the osmotic pressure of the polymer solution at the same concentration and degree of ionization. In swollen gels the extended network opposes swelling. As the gel is osmotically deswelled, a state of zero network pressure exists at a certain concentration, below which the network elasticity favors swelling. The crossover concentration shifts to lower values as the degrees of ionization increases. © 1995 John Wiley & Sons, Inc.     

Compacting of poly(acrylamide)‐poly(vinyl alcohol) grafted copolymers in aqueous solution of phenol and its effect in the copolymers films structure

The interaction of phenol with graft copolymers of poly(acrylamide) to poly(vinyl alcohol) (PVA‐PAA_N) forming intramolecular polycomplexes (Intra PC), and also with PAA, is investigated by the methods of gel chromatography, viscometry, UV and IR spectroscopy. It is shown, that phenol connection with polymers is weak and carried out on the equilibrium mechanism. Under phenol influence the effect of compacting of polymer macromolecules is observed. It is revealed, in particular, by change of the ratio between different H‐bonds structures in polymer films obtained at phenol presence. PVA‐PAA_N connect phenol more effectively, than PAA; the quantity of bound phenol grows with N.