A. Ya. Polishchuk

The modeling of the simultaneous transport of solvent and low-molecular compounds in swelling polymers

Abstract Mathematical model has been developed in order to predict the behavior of systems consisting of hydrophylic polymer, water, and low-molecular compound. The model has taken into account the processes of swelling of polymers during water sorption. the existence of embedded form of drug in polymer matrix and some others processes. The dependencies of physico-chemical parameters on concentration of water, drug and on mechanical properties of poiymer were justified by corresponding experimental results. Different ratios of these parameters enable to predict the behavior of matrix systems for controlled release of drugs.

Transport of non-associated electrolytes in acrylamide hydrogels

Abstract Diffusion of non-associated electrolytes (LiCl and KCl) in different hydrogels has been studied to identify the mechanism of electrolyte interaction with the structure of hydrogels and its dependence on electrolyte concentration and thermodynamic features of the electrolyte. Hydrogel membranes have been prepared from acrylamide (AAm) using N,N′-methylene-bis-acrylamide (MBAAm) as the cross-linker. Properties of membranes have been altered varying the content of cross-linker. Properties of membranes have been altered varying the content of cross-linker. Integral diffusion coefficients of potassium chloride and lithium chloride in the hydrogel membranes ave been compared with mutual diffusion coefficients of those electrolytes in aqueous solutions. The study of electrolyte diffusion was supported by data on water solubility in hydrogels (degree of swelling, and sorption and desorption isotherms) showing dependence of electrolyte diffusion coefficient on water content inside polymer matrix. Thermodynamic study showed irreversible character of the sorption of solutes, probably due to acidic hydrolysis of amide groups of gels. The main features, which characterise properties of aqueous solution of strong electrolytes, remain in polymer matrix thus defining diffusion coefficients and other parameters representative of electrolyte transport in polyacrylamide hydrogels.

Thermal degradation studies of alternating copolymers: I—maleic anhydride-vinyl acetate

Abstract The thermal degradation of the alternating copolymer of maleic anhydride and vinyl acetate has been studied by thermal volatilisation analysis (TVA). An investigation of the decomposition products and a comprehensive analysis of the residues have been made using subambient TVA, IR spectroscopy, 1 H and 13 CNMR spectroscopy, the GC-MS technique and UV spectroscopy. On the basis of this evidence, a mechanism of degradation has been suggested. Under programmed heating at 10°C min −1 , two stages of breakdown, with rate maxima at 260 and 420°C, were observed. The products consisted of acetic acid, carbon dioxide, carbon monoxide, maleic anhydride and water. Acetic acid, carbon dioxide and traces of carbon monoxide were also observed in a detailed isothermal investigation at 205°C. It is suggested that, following the initial loss of acetic acid, structural rearrangements in the polymer chain can occur, with the formation of conjugated double bonds, so accounting for the colour of the partially degraded residues. Some hydroxyl groups are also formed. During degradation, insolubility develops, which has been attributed to reduction in the flexibility of the backbone and some intermolecular dehydration of OH groups. The interaction between the copolymer (or its residue) and water is discussed in relation to potential applications of this material.

Water ageing of smc composite materials. A tool for material characterisation

A methodological approach is developed to characterise the properties of polyester resin-glass fibre SMC composites. The methodology comprises kinetic analysis of water sorption in SMC materials, identification of chemical changes induced by water penetration and analysis of mechanical properties of the materials. The approach is based on a model which describes the specific water sorption response to physico-chemical properties of composite materials and evolution of these properties due to water ageing. The model, previously developed to describe water sorption in SMC materials, takes into account the hydrolysis, swelling and plasticisation, besides the alteration of mechanical properties of the material and changes in water solubility inside the material due to formation and leaching of low-molecular weight solutes. The model is applied here to deduce the relevant physical chemical properties of commercial materials.

Thermal degradation behaviour of some alternating copolymers

An overview is presented of the thermal degradation behaviour of a number of alternating copolymers, including maleic anhydride copolymers with vinyl acetate, isopropenyl acetate, allyl acetate, trans-stilbene and acenaphthylene, respectively, and diethyl maleate copolymers with vinyl and isopropenyl acetate. Mechanisms of degradation are considered. Several of these structurally regular copolymers show preferential side group decomposition in one of the two monomer units present in the chain, with the result that a new copolymer structure can be prepared by controlled partial degradation.

Sorption/diffusion behaviour of anionic surfactants in polyacrylamide hydrogels: from experiment to modelling

Abstract The sorption and diffusion processes of anionic surfactants with different chain length through polyacrylamide hydrogels with low swelling degree have been studied by electrical conductivity measurements. The multicomponent equilibrium equation has been used to model the sorption isotherms of different anionic surfactant in the hydrogels. Such isotherms show that initial rapid sorption of unimer surfactant into the membranes occurs, suggesting that non-freezing water can be involved in these interactions. In aqueous solution, at concentrations near and above the critical micelle concentration an anti-co-operative region is found. The diffusion coefficients of the anionic surfactants inside the hydrogel matrix show that the mobility of diffusing surfactant entities is dependent on cross-linker concentration and chain length. The Cukier hydrodynamic model and the free volume theory as modified by Peppas and Reinhart were applied to explain the dependence of the diffusion coefficients of surfactant on surfactant concentration inside the hydrogel. The hydrodynamic model was applied with success to the more hydrophilic surfactant, sodium 1-octanesulfonate, showing that the diffusion coefficients, D , increase when the resistance to hydrodynamic medium decreases; when the surfactant chain length increases (sodium dodecyl sulfate and sodium 1-hexadecane sulphonate) the variation of D with the free volume can only be understood considering the sieving effect produced by the surfactant inside gel.

Biodegradation of Polyolefins Biomedical Applications

Abstract Although polymer plastics find broad application in different areas of industry, and particularly in the medical industry, the behavior of these materials in biological media still requires better understanding. Biodegradation and biostability of polyolefins are reviewed with reference to the prediction of material durability, which requires permanent study of the stability of material properties.

Diffusion-activation laws for drug release from polymer matrices

Abstract This paper deals with investigations of simultaneous solvent and drug transport in three component systems (copolymers of N-vinylpyrrolidone-water-drug). A proposed mathematical model of transport processes in such systems has been confirmed by the experimental results. It has been shown that the water sorption velocity and the drug release mechanism depend on the hydrophilic/hydrophobic balance in the copolymer. For each investigated system, physicochemical parameters for the release process have been determined that enable the behaviour of these systems in practice to be predicted.

General Model of Transport of Water and Low-Molecular Weight Solute in Swelling Polymer

Abstract A mathematical model of the simultaneous transport of water and low molecular weight solute in a swelling polymer film has been generalized by consideration of the expansion of the film area and their effect on the parameters involved. The character of the kinetic curves for water uptake and solute desorption were examined as a function of (i) mobility of the low molecular weight compound, (ii) concentration and stress dependence of the diffusion coefficient of the solvent, and (iii) mechanical properties of the polymer (whose dependence on the concentration of water and solute has also been considered). The correlation of the expansion area of the water sorption curves was examined briefly, mostly as a check of the validity of the model.

Models of Simultaneous Transport of Water and Drugs in Hydrophilic Polymer Systems

Abstract Different models have been developed in order to predict the behavior of systems consisting of hydrophilic polymer, water, and drug. The first model deals with the so-called matrix system of controlled drug release and describes the simultaneous transport of water and drug in swelling glassy polymers. The dependencies of physical/chemical parameters on the concentation of water, drug and on the mechanical properties of the polymer are used for justification and prediction of corresponding experimental results. The method of calculating the physical/chemical parameters is based on an experimental investigation of the structure of the polymer and the diffusion-kinetic process. The main aim of the development of the other model is to predict the mechanism and velocity of drug release in “reservoir polymer systems” for which the sorption and diffusion properties of water transport through a polymer membrane are most important. The main steps of drug release have been shown, and various dependencies o...