Physical Hydrogels of Poly(vinyl alcohol) with Different Syndiotacticity Prepared in the Presence of Lactosilated Chitosan Derivatives

Poly(vinyl alcohol) (PVA) physical hydrogels were prepared by repeated freeze–thawing cycles using aqueous solutions of two PVA samples having different degrees of syndiotacticity, a‐PVA and s‐PVA with 55% and 61% of syndiotactic diads, respectively. The hydrogels were prepared in the presence of different amounts of lactosilated chitosan derivatives (LC) of different molecular weight. The PVA stereoregularity was found to have a dramatic effect on the amount of PVA incorporated into the hydrogels, leading to remarkable differences in the swelling degree and porosity of a‐PVA and s‐PVA hydrogels. A significant amount of LC was retained in the hydrogels after equilibrium swelling. The swelling of the a‐PVA hydrogels was found to increase significantly by increasing the amount of LC while it was only slightly increased in the case of s‐PVA hydrogels. The amount of LC released after equilibrium swelling was lower when chitosan derivatives with higher molecular weights were used. Increased initial concentrations of LC resulted in much higher porosity of the hydrogels. TGA and DSC studies showed that LC is stabilized by the incorporation in the PVA hydrogels. The melting temperature of the crystalline regions of PVA was not significantly influenced by LC. Conversely, the extension of the crystalline domains increased in the presence of LC. The retention of a chitosan derivative bearing β‐D ‐galactose side chain residues makes these hydrogels potentially useful as scaffolds for hepatocytes culture.

Scanning electron micrographs of PVA‐LC hydrogels: (a) a‐PVA; (b) a‐PVA/LC₁₅₀ 80:20; (c) a‐PVA/LC₁₅₀ 50:50.     

MMTCA recognition by molecular imprinting in interpenetrating polymer network hydrogels based on poly(acrylic acid) and poly(vinyl alcohol)

A novel IPN hydrogel designed to recognize MMTCA is prepared by applying the molecular-imprinting method. The IPN is characterized by FT-IR, DSC, and SEM. Langmuir analysis shows that an equal class of adsorption is formed in the hydrogel. The adsorption equilibrium constant and the maximum adsorption capacity are evaluated, and the effect of the pH on MMTCA adsorption is discussed. The selectivity of the imprinted polymer for MMTCA is studied in aqueous solutions of MMTCA/aspirin/riboflavin. The results suggest that the MMTCA-imprinted polymer shows superior selectivity for MMTCA as compared to riboflavin and aspirin. The reproducibility of the imprinted polymer to MMTCA is also studied.     

P(VA-co-DBM)/PVA乳胶IPN阻尼材料的合成及动态力学性能

用种子乳液聚合法合成了聚（醋酸乙烯酯－co-马来酸二丁酯）／聚醋酸乙烯酯乳胶互穿聚合物网络阻尼材料,动态力学谱结果表明,该阻尼材料在较宽的温域具有很高的阻尼因子。     

Structure and Properties of Poly(vinyl alcohol) Hydrogels Obtained by Freeze/Thaw Techniques

The relationships between the structure and the viscoelastic properties of freeze/thaw PVA hydrogels obtained by repeatedly freezing and thawing dilute solutions of PVA in D₂O(11% w/w PVA) in as-prepared and rehydrated states are investigated. Our results indicate that the PVA chains and solvent molecules are organized at different hierarchical length scales, which include the presence of micro- and macro-pores, into a network scaffolding. The porous network is ensured by the presence of crystallites, which act as knots interconnected by portions of PVA chains swollen by the solvent. X-ray diffraction and SANS techniques are used to obtain structural information at short (angstroms) and medium (nanometers) ranges of length scales, concerning the crystallinity, the size of small crystalline aggregates and the average distance between crystallites in PVA hydrogels. Indirect information concerning the structural organization on the large length scales (microns) are provided by viscoelastic measurements. The dynamic shear elastic moduli at low frequency and low strain amplitude, G′, are determined and related to the degree of crystallinity. These data indicate that a minimum crystallinity of 1% is required for these PVA samples to exhibit gel behaviour and have allowed obtaining the order of magnitude of the average mesh size in these gels. Finally, it is shown that the negative effect of aging, inducing worse physical and mechanical properties in these systems, may be prevented using a drying/re-hydration protocol able to keep the physical properties of the as-prepared PVA hydrogels.     

Synthesis and Characterization of a Hydrophilic/Hydrophobic IPN Composed of Poly（vinyl alcohol） and Polystyrene

A hydrophilic/hydrophobic interpenetrating polymer network （IPN） of poly （vinyl alcohol） / polystyrene was prepared by conversion of the IPN of poly （vinyl acetate）/polystyrene. The hydrophilic/hydrophobic IPN was characterized by FT-IR and DSC, and the swelling ratios of the IPN in different solvents were measured.     

Synthesis and Properties of IPN Hydrogels Based on Konjac Glucomannan and Poly（acrylic acid）

As a random copolymer of β-(1,4) linked D-mannose and D-glucose, konjac gluco- mannan (KGM) is a naturally occurring water-soluble polysaccharide, and has been paid attention in the field of drug controlled release carriers potentially used in colon1,2. …     

Hydrophilic Films Based on Blends of Poly(acrylic acid) and Poly(2‐hydroxyethyl vinyl ether): Thermal,Mechanical, and Morphological Characterization

Hydrophilic films based on blends of poly(acrylic acid) and poly(2‐hydroxyethyl vinyl ether) were prepared by casting. The characterization of the films was performed by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy (SEM). It was shown that an increase of poly(2‐hydroxyethyl vinyl ether) content in the blends considerably decreases the glass transition temperature of the samples. The films containing 10 and 20 mol‐% of poly(2‐hydroxyethyl vinyl ether) show behavior of polymers in the glassy state, but a further increase of nonionic polymer content in the blend (30–50 mol‐%) provides the mechanical properties typical of a rubbery state. The content of water traces in the films has a significant effect on the mechanical properties of the materials.

Normalized DSC thermograms of PAA:PHEVE films. [PAA]:[PHEVE] = 90:10 (1), 80:20 (2), 70:30 (3), 60:40 (4), 50:50 mol‐% (5).     

瓜胶/聚丙烯酸互穿聚合物网络水凝胶对模型药物的负载与控制释放

考察了以牛乳清蛋白(BSA)为模型药物,通过相平衡分配法制备载药瓜胶(GG)/聚丙烯酸(PAA)互穿聚合物网络(IPN)水凝胶的工艺条件.借助紫外可见光谱仪研究了载药水凝胶在结肠酶存在下的控制释放行为.结果表明:载药容量(CM)随瓜胶、丙烯酸用量的增加而下降,半IPN水凝胶的Cm较全IPN的略大;结肠酶能明显提高半IPN与全IPN中的BSA释放速率,且提高幅度随GG含量的增加而加快,GG/PAA IPN水凝胶具有结肠定位降解的特性,有望成为靶向结肠给药的理想载体材料.     

互穿网络高吸水树脂IPN的合成

采用溶液聚合制备了聚乙烯醇(PVA)和部分中和的丙烯酸-丙烯酰胺共聚物复合的互穿网络高吸水树脂(IPN)。通过正交实验研究了单体浓度,交联剂用量对IPN吸水率的影响。PVA的加入能有效提高IPN的吸水能力。在较适宜的反应条件下,IPN吸蒸馏水量达1481倍,吸0.9%NaCl溶液为130倍。     

Study of the Drying Behavior of Poly(vinyl alcohol) Aqueous Solution

This paper deals with the drying behavior of poly(vinyl alcohol) aqueous solution containing an active substance and placed into a Petri box. The objective is to reduce the drying time while respecting some constraints. To succeed, it is important to understand complex mechanisms governing heat and mass transfers. During the drying, the product thickness shrinks and its properties evolve. Drying kinetics in convective and infrared radiation are presented.     

Modification and characterization of semi-crystalline poly(vinyl alcohol) with interpenetrating poly(acrylic acid) by UV radiation method for alkaline solid polymer electrolytes membrane

Semi-crystalline poly(vinyl alcohol) was modified by UV radiation with acrylic acid monomer to get interpenetrating poly(acrylic acid) modified poly(vinyl alcohol), PVAAA, membrane. The stability of various PVAAA membranes in water, 2 M CH₃OH, 2 M H₂SO₄, and 40 wt% KOH aqueous media were evaluated. It was found that the stability of PVAAA membrane is stable in 40 wt% KOH solution. The PVAAA membranes were characterized by differential scanning calorimetry, X-ray diffraction, and thermogravimetry analysis. These results show that (1) the crystallinity in PVAAA decreased with increasing the content of poly(acrylic acid) in the PVAAA membranes. (2) The melting point of the PVAAA membrane is reduced with increasing the content of poly(acrylic acid) in the membrane. (3) Three stages of thermal degradation were found for pure PVA. Compared to pure PVA, the temperature of thermal degradation increased for the PVAAA membrane. The various PVAAA membranes were immersed in KOH solution to form polymer electrolyte membranes, PVAAA-KOH, and their performances for alkaline solid polymer electrolyte were conducted. At room temperature, the ionic conductivity increased from 0.044 to 0.312 S/cm. The result was due to the formation of interpenetrating polymer chain of poly(acrylic acid) in the PVAAA membrane and resulting in the increase of charge carriers in the PVA polymer matrix. Compared to the data reported for different membranes by other studies, our PVAAA membrane are highly ionic conducting alkaline solid polymer electrolytes membranes.     

Biomaterials of Poly(vinyl alcohol) and Natural Polymers

Polysaccharides and proteins are abundantly found in nature and are highly recommended for developing eco-friendly materials due to their special properties (biodegradability, biocompatibility, non-toxicity, low cost, etc.). However, they sometimes fail to meet specific requirements due to poor mechanical and physical properties. Poly(vinyl alcohol) (PVA) is one of the promising synthetic polymers with superior properties that can be blended with natural polymers for obtaining novel biomaterials with improved performances. This review addresses recent advance in PVA/polysaccharides and PVA/proteins biocomposites design and fabrication, mainly for the past two decades.     

Poly(vinyl alcohol)/cellulose nanocrystal barrier membranes

In this study, barrier membranes were prepared from poly(vinyl alcohol) (PVOH) with different amounts of cellulose nanocrystals (CNXLs) as filler. Poly(acrylic acid) (PAA) was used as a crosslinking agent to provide water resistance to PVOH. The membranes were heat treated at various temperatures to optimize the crosslinking density. Heat treatment at 170 °C for 45 min resulted in membranes with improved water resistance without polymer degradation. Infrared spectroscopy indicated ester bond formation with heat treatment. Mechanical tests showed that membranes with 10% CNXLs/10% PAA/80% PVOH were synergistic and had the highest tensile strength, tensile modulus and toughness of all the membranes studied. Polarized optical microscopy showed agglomeration of CNXLs at filler loadings greater than 10%. Differential thermogravimetric analysis (DTGA) showed a highly synergistic effect with 10% CNXL/10% PAA/80% PVOH and supported the tensile test results.Transport properties were studied, including water vapor transport rate and the transport of trichloroethylene, a representative industrial toxic material. Water vapor transmission indicated that all the membranes allowed moisture to pass. However, moisture transport was reduced by the presence of both CNXLs and PAA crosslinking agent. A standard time lag diffusion test utilizing permeation cups was used to study the chemical barrier properties. The membranes containing ≥10% CNXLs or PAA showed significantly reduced flux compared to the control. The CNXLs were then modified by surface carboxylation in order to better understand the mechanism of transport reduction. While barrier performance improvements were minimal, the chemical modification improved the dispersion of the modified CNXLs which led to improved performance. Of special note was an increase in the initial degradation temperatures of both modified and unmodified systems, with the modified system showing an initial degradation temperature >100 °C higher than the cellulose alone. This may reflect more extensive crosslinking in the modified composite.     

Pervaporation of alcohol-toluene mixtures through polymer blend membranes of poly(acrylic acid) and poly(vinyl alcohol)

Homogeneous membranes were prepared by blending poly(acrylic acid) with poly(vinyl alcohol). These blend membranes were evaluated for the selective separation of alcohols from toluene by pervaporation. The flux and selectivity of the membranes were determined both as a function of the blend composition and of the feed mixture composition. The results showed that a polymer blending method could be very useful to develop new membranes with improved permselectivity. The pervaporation properties could be optimized by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing poly(vinyl alcohol) content for both methanol—toluene and ethanol—toluene liquid mixtures. The alcohols permeated preferentially through all tested blend membranes, and the selectivity values increased with increasing poly(vinyl alcohol) content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The fluxes increased exponentially with increasing alcohol concentration in the feed mixtures, whereas the selectivities decreased for both liquid mixtures.     

Poly(vinyl alcohol) physical hydrogels: new vista on a long serving biomaterial

Poly(vinyl alcohol), PVA, and physical hydrogels derived thereof have an excellent safety profile and a successful history of biomedical applications. However, these materials are hardly in the focus of biomedical research, largely due to poor opportunities in nano- and micro-scale design associated with PVA hydrogels in their current form. In this review we aim to demonstrate that with PVA, a (sub)molecular control over polymer chemistry translates into fine-tuned supramolecular association of chains and this, in turn, defines macroscopic properties of the material. This nano- to micro- to macro- translation of control is unique for PVA and can now be accomplished using modern tools of macromolecular design. We believe that this strategy affords functionalized PVA physical hydrogels which meet the demands of modern nanobiotechnology and have a potential to become an indispensable tool in the design of biomaterials.     

Characterisation of Redox Initiators for Producing Poly(Vinyl Alcohol) Hydrogels

Summary: This work focuses on the characterisation of ascorbic acid/persulphate initiating system. Three different persulphates were used (ammonium, potassium and sodium), and a range of initiator concentrations were tested. Gel time, gel quality, initiator toxicity, and cell survival upon encapsulation were measured. No significant differences were observed between the three types of persulphates. Higher concentrations of the initiators resulted in faster gel times (5min for 0.05wt% initiator) and higher quality gels (less than 20% sol fraction), although the lower initiator concentrations were better in terms of cell growth inhibition and survival upon encapsulation. Overall, this system shows great promise for use in biomedical applications, however there is a need to minimise the initiator concentration to increase cell compatibility while maintaining a high enough concentration for adequate gel formation.     

Viscoelastic behaviors and molecular motions of highly syndiotactic poly(vinyl alcohol) fibers

The viscoelastic behavior and molecular motion of highly syndiotactic poly(vinyl alcohol) (S‐PVA) fibers with a dyad syndiotacticity (r) of 69% were studied by dynamic mechanical thermal analysis and wide‐angle X‐ray diffraction and compared with those of atactic poly(vinyl alcohol) (A‐PVA) fibers with r = 54%. The β_c dispersion, based on the molecular motion of the chain molecules in the crystalline regions, was observed for A‐PVA around 120–140 °C, and the only primary (α_c) dispersion was observed for S‐PVA around 180 °C. The thermal expansion coefficients for the a and c axes of the A‐PVA crystal changed discontinuously around 120 °C, which corresponded to the β_c dispersion. For S‐PVA, the coefficient for the (002) plane changed discontinuously around 100 °C, similarly to A‐PVA, but that for the (100) plane remained unchanged between 20 and 220 °C. These results showed that the intermolecular hydrogen bonding of S‐PVA was stronger in the direction of the a axis than in the other directions, suppressing the β_c dispersion. The storage modulus and thermal expansion coefficient of the (020) plane (molecular axis) of S‐PVA decreased markedly around 180 °C, and this indicated that the α_c dispersion was due to the torsional motion of the molecular chains in the crystalline regions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 800–808, 2004     

Preparation of Poly(vinyl alcohol) Microspheres Based on Droplet Microfluidic Technology

A new method for preparing poly (vinyl alcohol) (PVA) microspheres was developed by using droplet microfluidic technology. In the microfluidic chip, a large number of uniform, monodispersed PVA droplets were prepared quickly and continuously by using droplet formation technology, and the droplet preparation speed reached 7 per second. The size of the PVA droplets could be controlled by changing the injection flow rate of the two-phase fluid and the width of microfluidic channel. Then the PVA microspheres were formed by physical crosslinking. This method has high preparation efficiency and good monodispersity of the obtained microspheres. Moreover, the process does not require the incorporation of chemical crosslinking agents, avoiding interference with the inclusion material, and is well suited for applications such as drug carrier.     

Novel Interpenetrating Networks (IPNs) Hydrogels Prepared In Situ by Liquid-Phase Photopolymerization

Novel interpenetrating networks (IPNs) hydrogels responsive to temperature were prepared in situ by liquid-phase photopolymerization. The first network of the IPNs (poly isopropyl acrylamide) were formed with a special kind of hectorite (Laponite XLS) modified by tetrasodium pyrophosphate as cross-linker and 2-oxogultaric acid as photoinitiator. The samples were subsequently immersed in an acrylamide (AAm) aqueous solution for at least one day for preparing IPNs hydrogels, in which acrylamide aqueous solution containing N,N′-Dimetyl acrylamide (MBAA) as cross-linker and 2-oxogultaric acid as photoinitiator. Then the second networks were in situ formed by introducing ultraviolet light irradiated PNIPAAm gels. The swelling/deswelling behaviors of IPNs hydrogels were measured. Compared with the corresponding nanocomposite PNIPAAm hydroges(NC hydrogels), chemically cross-linked PNIPAAm and PAAm IPNs hydrogels, the results indicate that the new IPN hydrogel has a faster deswelling rate above its LCST (≈32 °C). The effect was explained as being an additional contribution of the PAAm chains in IPN hydrogels, which may act as a water-releasing channel when the hydrophobic aggregation of PNIPA takes place.