Interpolymer association between poly(acrylic acid) and vinyl alcohol-vinyl acetate copolymers in dilute aqueous solutions

Interpolymer association and complexation between poly(acrylic acid) and vinyl alcohol-vinyl acetate copolymers (PVAL-AC) in dilute aqueous solutions were investigated by means of reduced viscosity and pH measurements. The influence of the degree of saponification of PVAL-AC and of the molecular weight of both polymers on complexation were examined. The viscosity measurements show the formation of gel-like or compact complexes and that association is strongly increased by the presence of acetate units in the PVAL-AC copolymer. The degree of complexation was calculated from the results of pH measurements. Some special aspects of the two different experimental approaches are discussed.     

Biodegradable and thermoreversible hydrogels of poly(ethylene glycol)-poly(epsilon-caprolactone-co-glycolide)-poly(ethylene glycol) aqueous solutions

The aqueous solutions of triblock copolymers of poly(ethylene glycol)-poly(epsilon-caprolactone-co-glycolide)-poly(ethylene glycol) [PEG-P(CL-GA)-PEG] undergoing sol-gel transition as the temperature increases from 20 to 60 degrees C were successfully prepared. The thermogelling block copolymers were synthesized by subtle control of the hydrophilic/hydrophobic balance and the chain microstructures. The amphiphilic block copolymer formed micelles in aqueous solution, and the micelle aggregated as the temperature increased. The sol-gel transition of the copolymer aqueous solutions was studied focusing on the structure-property relationship. GA was incorporated into the polymer chain to prevent crystallization of PCL component and increase the polymer degradation. It is expected to be a promising long-term delivery system for pH-sensitive drugs, proteins, and genes.     

Polymeric complexes of lidocaine hydrochloride with poly(acrylic acid) and poly(2-hydroxyethyl vinyl ether)

The specific interactions of local anesthetic lidocaine hydrochloride with poly(acrylic acid) and poly(2-hydroxyethyl vinyl ether), as well as in a triple system composed of the drug and both polymers, have been studied in aqueous solutions by viscometric, turbidimetric, potentiometric, and FTIR spectroscopic methods. The mechanism of the drug binding to the polymers and the structures of the polycomplexes formed are clarified.     

Polymeric complexes of lidocaine hydrochloride with poly(acrylic acid) and poly(2-hydroxyethyl vinyl ether)

The specific interactions of local anesthetic lidocaine hydrochloride with poly(acrylic acid) and poly(2-hydroxyethyl vinyl ether), as well as in a triple system composed of the drug and both polymers, have been studied in aqueous solutions by viscometric, turbidimetric, potentiometric, and FTIR spectroscopic methods. The mechanism of the drug binding to the polymers and the structures of the polycomplexes formed are clarified.     

Behaviour of permeation and separation for aqueous organic acid solutions through poly(vinyl chloride) and poly[(vinyl chloride)-co-(vinyl acetate)] membranes

The permeation and separation characteristics of poly(vinyl chloride) (PVC) and poly[(vinyl chloride)-co-(vinyl acetate)] (poly(VC-co-VAc)) membranes were investigated for aqueous organic acid solutions by pervaporation and evapomeation. The PVC membrane preferentially incorporates organic acids and predominantly permeates water from aqueous organic acid solutions. Water permselectivities of these aqueous solutions through the PVC membrane are significantly dependent on high diffusivity of water across the membrane. It was found that the permeation rate increases and the separation factor for the water permselectivity decreases with increasing vinyl acetate (VAc) content in the poly(VC-co-VAc) membrane. Preferential solubility of acetic acid into the poly(VC-co-VAc) membrane increases with the VAc content. This result was explained by a strong affinity between acetic acid and the VAc unit in the poly(VC-co-VAc) membrane.     

Molecular calculations of poly(ethylene glycol) transport across a swollen poly (acrylic acid)/mucin interface

The transport of poly(ethylene glycol) chains than can promote mucoadhesion across the interface between lightly cross-linked poly(acrylic acid) and mucin may be analyzed as a function of molecular characteristics using theories of chain penetration in a dilute network. The fracture energy for the ensuing adhesive bond is proportional to the number of polymer chains crossing the interface, which, in turn, is related to the polymer volume fraction, the chain diffusion coefficient, and the degree of polymerization. Relevant calculations were performed for a number of cross-linked poly(acrylic acid) gels and three different types of poly(ethylene glycol) chains.     

Formation‐destruction conditions of an interpolymer complex between a poly(acrylic acid) gel and linear poly(ethylene glycol) in methanol

The contraction of a poly(acrylic acid) gel (GPAAc) ( 1 ) induced by complexation with linear poly‐(ethylene glycol) (PEG) ( 2 ) in methanol media proceeds in a similar manner to that in aqueous solution. It was found that both the concentration and molecular mass of the PEG have a strong effect on the complexation with GPAAc. The existence of a stable interpolymer complex between components under consideration takes place in the range of lower and upper critical values of molecular mass (CMM) of the linear polymer. Outside of these CMM values of PEG no perfect complexation occurred due to thermodynamic and kinetic reasons. The structure of the interpolymer complex formed due to the hydrogen bonding is destabilized as a result of ionization and the changing of the thermodynamic characteristics of the solvent under addition of dimethylsulfoxide to methanol.     

Functionalization of poly(ethylene glycol) and monomethoxy-poly(ethylene glycol)

Simple methods are described for the substitution of poly(ethylene glycol) and monomethoxy-poly(ethylene glycol) substitution. Affinity ligands, coenzymes, or enzymes can be covalently attached to the substitution product or they can be used as liquid ionexchangers.     

Turbidimetric studies of aqueous poly(vinyl alcohol) solutions

A freezing-thawing process of aqueous poly(vinyl alcohol), (PVA) solutions was undertaken to study the supermolecular PVA structures produced. Aqueous solutions of 2,5 to 15 wt.-% PVA were frozen at ?20°C for 45 to 120min and were subsequently thawed for long periods of time (up to 12h) at 23 ± 1°C. The transmittance of visible light was recorded as a function of thawing time. Determination of the parameters of the supermolecular particles in the PVA solutions was done by application of Klenin's theory. The average radii of the particles were in the order of 1,6–2,3 μm.     

Interpolymer complex between poly(ethylene oxide) and poly(acrylic acid): Viscometric studies in THF-water mixtures

Systematic studies were performed on interpolymer complex formation between Poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) in THF-water mixtures of different compositions. Viscosity behaviour during complex formation in mixed solvents was found to be entirely different from that observed by other workers in aqueous and in pure organic solvents. The result are interpreted in terms of, (a) preferential solvation of the polymer, (b) Probable change in conformation of the polyelectrolyte moleculer. (c) association of complex molecules in a medium of low dielectric constant, and (d) expected disordering of bound water molecules around PEO by THF. Irrespective of solvent composition, interpolymer complex of PAA and PEO was always found to have 1:1 unit mole ratio.     

Properties of supercritical CO2 saturated poly(ethylene glycol) nonylphenyl ether

Density and viscosity of poly(ethylene glycol) nonylphenyl ether (PEG-NPE) saturated with supercritical carbon dioxide (SC CO₂), as well as the interfacial tension in the PEG-NPE-SC CO₂ system, were evaluated for the temperature range of 323 K to 343 K and pressures of 10.0 to 25.5 MPa. Remarkable polymer swelling as a result of solvent penetration was observed, and the coefficient of swelling for the above mentioned experimental conditions was evaluated. Data obtained show that the viscosity of polymer-rich phase is a decreasing function of both temperature and pressure. Moreover interfacial tension is a decreasing linear function of carbon dioxide density.     

Thermoresponsive UCST‐Type Behavior of Interpolymer Complexes of Poly(ethylene glycol) and Poly(poly(ethylene glycol) methacrylate) Brushes with Poly(acrylic acid) in Isopropanol

Upper critical solution temperature (UCST)‐type thermoresponsive behavior of poly(ethylene glycol)–poly(acrylic acid) (PEG–PAA) and poly(poly(ethylene glycol) methacrylate)–poly(acrylic acid) (PPEGMA–PAA) interpolymer complexes has been observed in isopropanol. For these investigations, PPEGMA and PAA with various average molecular weights have been synthesized by atom transfer radical polymerization. It has been found that both the PEG and PPEGMA have lower cloud point temperatures (T _cp) than its mixed polymer solutions with PAA, whereas PAA does not show such behavior in the investigated temperature range. These findings indicate the reversible formation of interpolymer complexes with variable structure and composition in the solutions of the polymer mixtures in isopropanol. Increasing the ethylene glycol/acrylic acid molar ratio or the molecular weight of either the PAA or the H‐acceptor PEG component of the interpolymer complexes increases the UCST‐type cloud point temperatures of these interpolymer systems. The polymer–polymer interactions by hydrogen bonds between PAA and PEG or PPEGMA and the correlations between T _cp and structural parameters of the components revealed in the course of these investigations may be utilized for exploring well‐defined UCST‐type material systems for various applications.

     

Gelation kinetics in aqueous solutions of syndiotactic-rich poly(vinyl alcohol)

Aqueous solutions of Syndiotactic-rich poly(vinyl alcohol) (PVA) form thermally reversible gels. The volume of the solution decreases with gelling time on standing at isothermal condition. Assuming that the gelation is due to the crystallization of PVA, the kinetics of isothermal crystallization from 5 wt.-% aqueous solutions of PVAs having 64,3 mol-% syndiotactic diads was investigated as a function of temperature (45–90°C), using dilatometry. The maximum in the overall rate of crystallization appeared at 60°C, regardless of the degree of polymerization of PVA. Since the values of n in the Avrami equation vary from about 1 to 2, it was apparent that the crystallization from aqueous solution of the polymer proceeded in the fashion of one-dimensional growth and heterogeneous, diffusion controlled nucleation. The phase diagram revealed that the syneresis of the gel was caused by the crystalline phase separation which supports the gelation accompanying crystallization.     

对映异构聚乳酸/聚乙二醇空间异构复合水凝胶的药物释放及形貌和细胞毒性

背景：目前生物降解水凝胶已被广泛应用于抗癌药物及生物活性大分子的装载,但为了保护生物活性大分子的活性,需要得到凝胶化条件更温和,凝胶化时间更短的凝胶体系。 目的：制备对映异构聚乳酸∕聚乙二醇的空间异构复合水凝胶,使其具有更短的凝胶化时间,实现对模拟药物溶菌酶的装载和控释。 方法：以聚乙二醇为引发剂,辛酸亚锡为催化剂,丙交酯与聚乙二醇发生开环聚合反应,得到聚乳酸/聚乙二醇的三嵌段共聚物(PLLA-PEG-PLLA 和 PDLA-PEG-PDLA)。用1H NMR,FT-IR 和 XRD表征三嵌段共聚物。10% PLLA20-PEG227-PLLA20的水溶液和10%PDLA21-PEG227-PDLA21的水溶液在室温下混合,12 h后形成凝胶。通过XRD考察凝胶化机制,以溶菌酶为模拟药物,考察凝胶的释药特性,通过扫描电镜考察凝胶的形貌,采用MTT法考察凝胶的细胞毒性。 结果与结论：成功得到聚乳酸/聚乙二醇的三嵌段共聚物,在嵌段共聚物中,聚乳酸嵌段和聚乙二醇嵌段都能结晶,但以聚乙二醇嵌段的结晶为主。通过XRD证明凝胶中存在空间异构复合作用,溶菌酶在凝胶中通过凝胶的溶蚀和降解行为,在7 d之内释放完全。通过扫描电镜观察到冻干的水凝胶呈三维贯穿的多孔结构,空隙尺寸在50~100 μm 之间。鼠成纤维细胞与浓度为100%的凝胶浸提液共培养72 h之后,细胞的存活率为99.3%。     

Self-association and micelle formation of biodegradable poly(ethylene glycol)-poly(L-lactic acid) amphiphilic di-block co-polymers

Di-block co-polymers of poly(ethylene glycol)-poly(L-lactic acid) (PEG-PLLA) were prepared by ring-opening polymerization, and their self-association and micelle formation were investigated. The block co-polymers have the same block length of the hydrophilic PEG segment (Mn = 2000), but different chain lengths of the hydrophobic PLLA segment (Mn = 700, 1000 and 1300, respectively). The di-block co-polymers synthesized were characterized by GPC, 1H-NMR, TGA and DSC. The critical micelle concentration (CMC) of the PEG-PLLA micelles was determined at various temperatures (5-45 degrees C) using a dye absorption technique involving fluorescence spectrophotometry with pyrene as a probe to monitor the change in the polarity of the microenvironment in the micelle. An increase in the molecular weight of the hydrophobic block decreases the CMC. The partition coefficients of pyrene between the micellar and aqueous phases range from 0.68 x 10(4 )to 1.76 x 10(4), depending on the PLLA content in the block co-polymers. An Arrhenius plot of ln(CMC) versus 1/T exhibited an almost constant CMC at low temperatures (<35 degrees C), followed by an increase of the CMC at higher temperatures (>35 degrees C). The increase of the CMC with temperature indicates the increase of the mobility of the hydrophobic PLLA core. These results were confirmed by 1H-NMR measurements. The micelle size and size distribution were determined by dynamic light scattering (DLS), and were in the range of 78-92 nm. A spherical micelle shape was confirmed by transmission electron microscopy. These results indicate that the CMC and the thermal characteristics of the core-forming segment of the block co-polymer play an important role in the properties of the polymer micelles used for drug delivery.     

Viscosity of aqueous and alkaline solutions of poly(ethylene oxide)

Viscosity measurements over a wide range of temperature were made on aqueous solutions of poly(ethylene oxide) samples of different molar mass and of low polydispersity. Above ca. 308 K the Mark-Houwink exponent decreases and tends to a value of 0,50 at a lower critical solution temperature of 376 ± 2 K. The same value for this θ-temperature is derived also as that at which the slope of Stockmayer-Fixman plots tends to zero. At 298 K the unperturbed dimensions [〈r²〉₀/M]^1/2 = 0,089 nm · g^?1/2 · mol^1/2 and their temperature coefficient d ln 〈r²〉₀/dT ≈ ? 1,5 (±0,5) · 10^?3 K^?1. In aq. KOH the intrinsic viscosity [η] is virtually uninfluenced by pH at low-medium pH, but at high pH, [η] falls sharply. Viscosity and phase separation measurements yield θ-conditions in 1,24 M aq. KOH at 298 K. The derived polymer-water interaction parameters χ increase from 0,449 at 276 K to 0,493 at 358 K, but the enthaplic component χ_H is incapable of yielding a meaningful value for the solubility parameter δ₂ of the polymer in such a hydrogen-bonding system. The calculated value of χ₂ was 18,9 (kJ · dm^?3)^1/2.     

Ethylene chlorohydrin formation in radiation- and ethylene oxide-sterilized poly(vinyl chloride)

Published reports on the formation of ethylene chlorohydrin in ethylene oxide-sterilized poly(vinyl chloride) are contradictory. The present paper discusses parameters involved in the ethylene chlorohydrin formation, such as the stabilizer system, plasticizer content and thermal strain during manufacture. It is shown that ethylene chlorohydrin can be formed in ethylene oxide-sterilized poly(vinyl chloride) previously sterilized by irradiation, in amounts dramatically exceeding published ‘safe levels’.     

Factors affecting size and swelling of poly(ethylene glycol) microspheres formed in aqueous sodium sulfate solutions without surfactants

The LCST behavior of poly(ethylene glycol) (PEG) in aqueous sodium sulfate solutions was exploited to fabricate microspheres without the use of other monomers, polymers, surfactants or organic solvents. Reactive PEG derivatives underwent thermally induced phase separation to produce spherical PEG-rich domains that coarsened in size pending gelation, resulting in stable hydrogel microspheres between ≈1 and 100 microns in size. The time required to reach the gel point during the coarsening process and the extent of crosslinking after gelation both affected the final microsphere size and swelling ratio. The gel point could be varied by pre-reaction of the PEG derivatives below the cloud point, or by controlling pH and temperature above the cloud point. Pre-reaction brought the PEG derivatives closer to the gel point prior to phase separation, while the pH and temperature influenced the rate of reaction. Dynamic light scattering indicated a percolation-to-cluster transition about 3–5 min following phase separation. The mean radius of PEG-rich droplets subsequently increased with time to the 1/4th power until gelation. PEG microspheres produced by these methods with controlled sizes and densities may be useful for the production of modular scaffolds for tissue engineering.     

Chemical modification of poly(vinyl chloride) resin using poly(ethylene glycol) to improve blood compatibility

Poly(vinyl chloride) (PVC) was aminated by treating the resin with a concentrated aqueous solution of ethylenediamine. The aminated PVC was then reacted with hexamethylene diisocyanate to incorporate the isocyanate group onto the polymer backbone. The isocyanated PVC was further reacted with poly(ethylene glycol) (PEG) of molecular weight 600 Da. The modified polymer was characterized using infrared and X-ray photoelectron spectroscopy (XPS) and thermal analysis. Infrared and XPS spectra showed the incorporation of PEG onto PVC. The thermal stability of the modified polymer was found to be lowered by the incorporation of PEG. Contact angle measurements on the surface of polymer films cast from a tetrahydrofuran solution of the polymer demonstrated that the modified polymer gave rise to a significantly hydrophilic surface compared to unmodified PVC. The solid/water interfacial free energy of the modified surface was 3.9 ergs/cm(2) as opposed to 18.4 ergs/cm(2) for bare PVC surface. Static platelet adhesion studies using platelet-rich plasma showed significantly reduced platelet adhesion on the surface of the modified polymer compared to control PVC. The surface hydrophilicity of the films was remarkably retained even in the presence of up to 30 wt% concentration of the plasticizer di-(2-ethylhexyl phthalate). The study showed that bulk modification of PVC with PEG using appropriate chemistry can give rise to a polymer that possesses the anti-fouling property of PEG and such bulk modifications are less cumbersome compared to surface modifications on the finished product to impart anti-fouling properties to the PVC surface.