Polymer-solvent Interaction Parameter Research Articles

Effect of the amount and type of the crosslinker on the swelling behavior of temperature-sensitive poly(N-tert-butylacrylamide-co-acrylamide) hydrogels

Temperature-sensitive poly(N-tert-butylacrylamide-co-acrylamide) [P(NTBA-co-AAm)] hydrogels were synthesized by free-radical copolymerization in a water–methanol mixture using three types of crosslinkers: 1,2-ethyleneglycol dimethacrylate, N,N-methylenebisacrylamide, and 1,3-butandiol dimethacrylate. These thermosensitive hydrogels were swollen to equilibrium in water at 20°C and examined by gravimetric measurements. The influence of type and content of crosslinkers on the swelling ratio, the polymer–solvent interaction parameter (χ), the average molecular mass between crosslinks \({\left( {\overline{M} _{c} } \right)},\) and the effective crosslinking density (νE) of the hydrogels were reported and discussed. The swelling process in water was found to be non-Fickian diffusion. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter for the hydrogels were determined by using the Flory–Rehner theory based on the phantom network model of swelling equilibrium. Negative values for ΔH and ΔS indicated that the hydrogels had a negative temperature-sensitive property in water; that is, swelling at a lower temperature and shrinking at a higher temperature. The temperature-reversibility and on–off switching properties of the P(NTBA-co-AAm) hydrogels may be considered as good candidates for designing novel drug-delivery systems.

PH-dependent swelling behavior and network parametes of ionic poly(N-t-butylacrylamide-co-acrylamide) hydrogels

Ionic poly(N-t-butylacrylamide-co-acrylamide) [P(TBA-co-AAm)] hydrogels were synthesized by the free-radical crosslinking copolymerization of N-t-butylacrylamide and acrylamide monomers in fixed amounts and the maleic acid (MA) comonomer in methanol in different amounts with N,N-methylene bis(acrylamide) as the crosslinker, ammonium persulfate as the initiator, and N,N,N′,N′-tetramethylenediamine as the activator. The swelling behavior of these hydrogels was analyzed in buffer solutions at various pHs. The polymer–solvent interaction parameter (χ) and the average molecular weight between crosslinks of the ionic P(TBA-co-AAm) hydrogels were calculated from swelling studies in buffer solutions at various pHs and were related to the MA content. The results indicated that the swelling behavior of the ionic P(TBA-co-AAm) hydrogels at different pHs agreed with the modified Flory–Rehner equation based on the affine network model and the ideal Donnan theory. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter for the hydrogels were also determined with the modified Flory–Rehner equation. The negative values for ΔH and ΔS indicated that the hydrogels had a negative temperature-sensitive property in water, that is, swelling at a lower temperature and shrinking at a higher temperature. The experimental swelling data of the hydrogels at different temperatures agreed with the modified Flory–Rehner approach based on the affine network model, which ensured that the sensitive dependence of the χ parameter on both the temperature and polymer concentration was taken into account. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1624–1630, 2006

Molecular thermodynamics for swelling of a mesoscopic ionomer gel in 1 : 1 salt solutions

For a microphase-separated diblock copolymer ionic gel swollen in salt solution, a molecular-thermodynamic model is based on the self-consistent field theory in the limit of strongly segregated copolymer subchains. The geometry of microdomains is described using the Milner generic wedge construction neglecting the packing frustration. A geometry-dependent generalized analytical solution for the linearized Poisson-Boltzmann equation is obtained. This generalized solution not only reduces to those known previously for planar, cylindrical and spherical geometries, but is also applicable to saddle-like structures. Thermodynamic functions are expressed analytically for gels of lamellar, bicontinuous, cylindrical and spherical morphologies. Molecules are characterized by chain composition, length, rigidity, degree of ionization, and by effective polymer-polymer and polymer-solvent interaction parameters. The model predicts equilibrium solvent uptakes and the equilibrium microdomain spacing for gels swollen in salt solutions. Results are given for details of the gel structure: distribution of mobile ions and polymer segments, and the electric potential across microdomains. Apart from effects obtained by coupling the classical Flory-Rehner theory with Donnan equilibria, viz. increased swelling with polyelectrolyte charge and shrinking of gel upon addition of salt, the model predicts the effects of microphase morphology on swelling.

Physicochemical characterization of poly( tert-butyl acrylate- b-methyl methacrylate) prepared with atom transfer radical polymerization by inverse gas chromatography

Poly( tert-butyl acrylate) (P tBuA) was synthesized by atom transfer radical polymerization (ATRP) using methyl-2-bromo propionate (MBP) as an initiator in bulk at 80 °C. The successive ATRP of methyl methacrylate in diphenyl ether at 80 °C using previously obtained P tBuA as a macroinitiator led to formation of poly( tert-butyl acrylate- b-methyl methacrylate) (poly( tBuA- b-MMA)). The synthesized macroinitiator and block copolymer have controlled molecular weight and low polydispersity ( M w/ M n<1.2). The block copolymer was characterized by gel permeation chromatography (GPC) and 1H NMR. The retention diagrams of poly( tBuA- b-MMA) for some aliphatic esters and aromatic hydrocarbons were obtained using inverse gas chromatography (IGC) technique. The glass transition temperatures, T gs of poly( tBuA- b-MMA) were determined by both differential scanning calorimeter (DSC) and IGC. It was observed that the block copolymer represents three T gs at 50, 75 and 100 °C by IGC although it represents only one T g at 71 °C by DSC. After the column was quenched from 180 to 0 °C, the T g at 100 °C shifted to 105 °C however others did not change. Specific retention volumes, V g 0 and the thermodynamical polymer–solvent interaction parameters such as Flory–Huggins, χ 12 ∞ , equation-of-state, χ 12 * and effective exchange energy, X eff were found for all studied solvents. Partial molar heat of sorption, Δ H ¯ 1 , sorp , partial molar heat of mixing, Δ H ¯ 1 ∞ and molar heat of vaporization, Δ H v, were determined. In addition, the solubility parameter of the corresponding block copolymer, δ 2 was determined as 11.0 (cal/cm 3) 1/2 at 25 °C.

Thermodynamic interactions of a copolyester of bisphenol A with terephthalic acid and isophthalic acid with some solvents

AbstractThe retention diagrams of n‐octane, n‐nonane, n‐decane, n‐butyl acetate, isobutyl acetate, and isoamyl acetate on the polyarylate Ardel D‐100, a copolyester of bisphenol A with terephthalic acid and isophthalic acid, were plotted at temperatures between 120 and 260°C by an inverse gas chromatography technique. The glass‐transition temperature of the copolymer was determined to be 190°C from the discontinuity of these diagrams. The retention diagrams of benzene, ethyl benzene, n‐propyl benzene, isopropyl benzene, and chlorobenzene were also plotted between 200 and 260°C. The specific retention volume, weight fraction activity coefficient, Flory–Huggins polymer–solvent interaction parameter, hard‐core polymer–solvent interaction parameter, and effective exchange energy parameter were determined for the studied solvents. The parameters suggest that the studied aromatic hydrocarbons and aliphatic esters are moderately good solvents and chlorobenzene is a very good solvent for this copolyester, but the n‐alkanes are very poor solvents. The solubility parameter of this copolymer was determined to be 11.6 (cal/cm3)1/2 at room temperature by extrapolation of the values of the solubility parameters from the studied temperatures to 25°C. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2365–2368, 2005

Solubility and diffusivity of solvents and nonsolvents in poly(methyl methacrylate co butyl methacrylate)

In this study, thermodynamic properties, namely retention volume, infinitely dilute weight fraction activity coefficient, Flory–Huggins interaction parameter, solubility parameter of the polymer, partition coefficient and diffusion coefficients of the various solvents in poly(methyl methacrylate co butyl methacrylate) (PMMA co BMA) at infinite dilution of the solvent have been determined by inverse gas chromatography (IGC). In this technique, a small amount of the solvent was injected into the capillary column and its retention time was measured and used to calculate several polymer–solvent interaction parameters which are mentioned above. The solvents used in this study were methanol, ethanol, propanol, butanol, methyl acetate, ethyl acetate, propyl acetate, dichloromethane, trichloromethane, acetone, methyl methacrylate, butyl methacrylate for PMMA co BMA. The thermodynamic results, obtained from the experiments, indicated that trichloromethane and dichloromethane were the most suitable solvents among all the solvents studied for PMMA co BMA. The partition ( K) and diffusion coefficients ( D p) of various solvents at infinite dilution of the solvent were calculated by using the model developed by Pawlisch et al. [C.A. Pawlisch, A. Macris, R.L. Laurence, Solute diffusion in polymers.1. The use of capillary column inverse gas chromatography, Macromolecules 20 (1987) 1564–1578]. The optimum K and D p values that best fit the data were found and the model predicted experimental data very well. Vrentas–Duda free volume theory was used to correlate the diffusion data and to investigate the effect of solvent size on diffusion process. The theory has shown to correlate diffusion data above the glass transition temperature very well for the PMMA-co-BMA–solvent system.

Determination of secondary transitions and thermodynamic interaction parameters of poly (ether imide) by inverse gas chromatography

The retention diagrams of poly(ether imide) for ethyl benzene, n-propyl benzene, isopropyl benzene, chloro benzene, n-butyl acetate, tert-butyl acetate, isoamyl acetate, n-nonane, n-decane, n-undecane, n-dodecane and n-tridecane were obtained by inverse gas chromatography technique. In this work, the slope changes on the diagram were assigned as secondary transitions. The secondary transition temperatures obtained by inverse gas chromatography technique are in good agreement with the ones obtained by thermally stimulated depolarization current in the literature. Specific retention volume, V g 0, the weight fraction activity coefficients of the solvents at infinite solution, Ω1∞, Flory-Huggins polymer-solvent interaction parameters,χ12∞, equation-of-state polymer-solvent interaction parameters,χ12*, effective exchange energy parameters, X eff were determined. Later, the partial molar heat of sorption, $\Delta\bar{H}_{1,sorp}$ and the partial molar heat of mixing, $\Delta\bar{H}_1^{\infty}$ were obtained. The solubility parameter of poly(ether imide), δ2 was determined as 10.7 (cal/cm3)1/2 by extrapolation of the δ2 values obtained by considering the free volume effects from studied temperature range to room temperature.

Determination of molecular parameters of NR/PU block copolymers by transport studies

The equilibrium swelling experiments of block copolymers based on natural rubber (NR) as soft segment and polyurethane (PU) derived from toluene diisocyanate (TDI) and 1,3-butane diol (1,3-BDO) as hard segment were performed in various solvents. Block copolymers with different NCO/OH ratio, viz., from 1.26 to 1.96 were employed in this study. The crosslink densities are found to vary with the NCO/OH ratio employed in the synthesis of the samples. The sorption behaviour is also found to vary with the NCO/OH ratio. The equilibrium swelling experiments have been used to determine the molecular parameters such as molecular mass between crosslinks, crosslink density, polymer–solvent interaction parameter, etc. The equilibrium swelling values were also used to calculate the solubility parameter values of the block copolymers.

A novel multiphysic model for simulation of swelling equilibrium of ionized thermal-stimulus responsive hydrogels

Abstract In this paper, a novel multiphysic mathematical model is developed for simulation of swelling equilibrium of ionized temperature sensitive hydrogels with the volume phase transition, and it is termed the multi-effect-coupling thermal-stimulus (MECtherm) model. This model consists of the steady-state Nernst–Planck equation, Poisson equation and swelling equilibrium governing equation based on the Flory’s mean field theory, in which two types of polymer–solvent interaction parameters, as the functions of temperature and polymer-network volume fraction, are specified with or without consideration of the hydrogen bond interaction. In order to examine the MECtherm model consisting of nonlinear partial differential equations, a meshless Hermite–Cloud method is used for numerical solution of one-dimensional swelling equilibrium of thermal-stimulus responsive hydrogels immersed in a bathing solution. The computed results are in very good agreements with experimental data for the variation of volume swelling ratio with temperature. The influences of the salt concentration and initial fixed-charge density are discussed in detail on the variations of volume swelling ratio of hydrogels, mobile ion concentrations and electric potential of both interior hydrogels and exterior bathing solution.

Enhancement of copolymerization of itaconic acid with N-vinyl 2-pyrrolidone by radiation in the presence of cross-linking agent

Enhancement of copolymerization of itaconic acid (IA) with N-vinyl 2-pyrrolidone (VP) by radiation in the presence of cross-linking agent was investigated. Hydrogels with varying IA content were prepared from the ternary systems N-vinyl 2-pyrrolidone/itaconic acid/water by irradiating with gamma-rays in the presence of a chemical cross-linker, ethylene glycol dimethacrylate (EGDMA) at ambient temperature. The incorporation of EGDMA into the ternary mixtures caused an increase in the amount of IA in the gel system up to a mole fraction of 13.7%. Hydrogels showed a typical pH response such as high pH swelling and low pH deswelling. Equilibrium volume swelling ratio at pH 7 was varied from 15–40 with changing the IA content in the gel system and irradiation dose. The equation recently modified by the authors for the determination of M ¯ c is observed to describe the swelling behaviour of P(VP/IA/EGDMA) networks containing relatively higher amount of charged units very well. In addition to the evaluation of M ¯ c from swelling data, the measurement of polymer solvent interaction parameter and the determination of the reaction yield of cross-links of the systems were examined.

The ratio of crystallinity and thermodynamical interactions of polycaprolactone with some aliphatic esters and aromatic solvents by inverse gas chromatography

The retention diagrams of benzene, toluene, ethyl benzene, chloro benzene, n-propyl benzene, isopropyl benzene, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate and isoamyl acetate on the polycaprolactone were plotted at temperatures between 70 and 140oC by inverse gas chromatography technique. Percent crystallinity of polycaprolactone were obtained at temperatures below melting point from the retention diagrams of benzene, toluene and ethyl benzene. It was concluded that the data obtained by inverse gas chromatography were comparable those of obtained by differential scanning calorimetry. Specific retention volume, Vgo, Flory-Huggins polymer-solvent interaction parameters, χ12∞, the weight fraction activity coefficients of the solvents at infinite dilution, Ω1∞, effective exchange energy parameters, Xeff were determined. Later, the partial molar heat of sorption, ΔH1,sorp and the partial molar heat of mixing, ΔH1∞ were obtained from the slope of the logarithm of specific retention volume, Ln Vgo versus 1/T plot and from the slope of the logarithm of the weight fraction activity coefficients, Ω1∞versus 1/T plot, respectively.

Radiation synthesis and characterization of poly( N, N-dimethylaminoethyl methacrylate-co- N-vinyl 2-pyrrolidone) hydrogels

In this study, radiation synthesis and characterization of swelling behavior and network structure of poly( N, N-dimethylaminoethyl methacrylate) (PDMAEMA), and poly( N, N-dimethylaminoethyl methacrylate-co- N-vinyl 2-pyrrolidone) (P(DMAEMA-co-VP)), hydrogels were investigated. PDMAEMA and P(DMAEMA-co-VP) hydrogels in the rod forms were prepared by irradiating the ternary mixtures of DMAEMA/VP/cross-linking agent, ethyleneglycol dimethacrylate (EGDMA), by gamma rays at ambient temperature. In composition ranges where the three components were completely miscible, water was also added to the ternary mixture to provide the formation of homogeneous polymerization and gelation. The influence of irradiation dose, comonomer, VP, and cross-linking agent, EGDMA, content on the total percentage gelation and monomer conversion were investigated. The effect of pH and temperature on the swelling behavior of hydrogels have also been examined. Hydrogels showed typical pH response and temperature responses, such as low-pH and low temperature swelling and high-pH and high temperature deswelling. Polymer–solvent interaction parameter ( χ) and enthalpy and entropy changes appearing in the χ parameter for the P(DMAEMA-co-VP)–water system were determined by using Flory–Rehner theory of swelling equilibrium. The negative values for Δ H and Δ S indicate that prepared pure PDMAEMA and P(DMAEMA-co-VP) hydrogels have lower critical solution temperature (LCST) and Flory–Rehner theory of swelling equilibrium provides a satisfactory agreement to the experimental swelling data of the hydrogels.

Swelling behaviors, tensile properties and thermodynamic studies of water sorption of 2-hydroxyethyl methacrylate/epoxy methacrylate copolymeric hydrogels

A series of copolymeric hydrogels based on 2-hydroxyethyl methacrylate (HEMA) and epoxy methacrylate (EMA) were synthesized by bulk polymerization. Swelling behaviors and tensile properties of hydrogels were studied. Dynamic swelling behaviors of copolymeric hydrogels indicate that the swelling process of these polymers follows Fickian behavior. The equilibrium water content (EWC) decreased and volume fraction of polymer in hydrogel ( ϕ 2) increased with EMA content increasing due to its hydrophobicity. The increase of ionic strength of swelling medium or temperature results in a decrease in EWC and an increase in values of ϕ 2. Young’s modulus and tensile strength of hydrogels, as well as effective crosslink density ( v e), increased as EMA content increased or ionic strength of swelling medium increased, attributing to increasing interaction between hydrophobic groups and polymer–polymer interaction with an increase in EMA content or in ionic strength. The polymer–solvent interaction parameter χ reflecting thermodynamic interaction was also studied. As EMA content, ionic strength of swelling medium or temperature increased, the values of χ increased. The values of χ and its two components χ H and χ S varied with increasing T. The negative values and trend of the enthalpy and entropy of dilution derived from values of χ S and χ H , could be explained on the basis of structuring of water through improved hydrogen bonding and hydrophobic interaction.

Swelling and network parameters of crosslinked thermoreversible hydrogels of poly( N-ethylacrylamide)

Samples of Poly( N-ethylacrylamide) (PEA) have been synthesized by free radical polymerization in water using N, N′-methylene bis-acrylamide (BIS) as crosslinker. Hydrogels obtained by swelling them in water, 15 wt% KCl and 1 wt% sodium dodecyl sulphate (SDS) were examined by gravimetric, dimensional and compression–strain measurements to afford values of swelling ratio, polymer–solvent interaction parameters, elastic moduli and effective crosslinking density ν e. Crosslinking inefficiency is evidenced by the low value (0.23) of ν e relative to the theoretical crosslinking density ν t based on the content of BIS in the synthesis. A small but finite extrapolated value of ν e at ν t = 0 is indicative of hydrophobic physical interactions. In water at 298 K increasing the content of BIS leads to a decrease in swelling and increases in values of elastic moduli and polymer–water interaction parameter. At a fixed content of BIS the values of ν e and the elastic moduli exhibit an unusual increase with temperature, the crosslinking thus being thermally reversible. It is proposed that this results from a balance between hydrophobic interaction and breakage of hydrophilic hydrogen bonding. Although KCl in the medium decreases the swelling compared with that in water, the opposite effect occurs on incorporation of SDS, which is assumed to confer some polyelectrolyte character to the PEA chains. The finding, that these two swelling media reduce the values of ν e and elastic moduli cf the value in water, has not been resolved satisfactorily.

Dilute solution properties of epoxy resins

Number-average molecular weights of fractions of epoxy resins were estimated by vapor-pressure osmometry and size exclusion chromatography coupled with multiple-angle light scattering. Potential reasons for differences between the two sets of data are examined. The molecular weight dependences of the intrinsic viscosity in tetrahydrofuran and chloroform are discussed in terms of theories which take into account the low-molecular weight character of poly(hydroxy ether) chains. The polymer-solvent interaction parameter is estimated. The impact of the presence of branched chains on the results of size exclusion chromatography is examined. It is shown that the universal calibration of size exclusion chromatographic columns by polystyrene is reliable at molecular weights above 2000 only.

Solvent molecular descriptors on poly( d, l-lactide- co-glycolide) particle size in emulsification–diffusion process

The size of poly( d, l-lactide- co-glycolide) (PLGA) nanoparticle was influenced by the thermodynamic parameters (after [Sung-Wook Choi, Hye-Young Kwon, Woo-Sik Kim, Jung-Hyun Kim, Colloids Surf. A Physicochem. Eng. Aspects 201 (2002) 283–289.]) such as mutual diffusion coefficients (exchange ratio, R) and solvent–polymer interaction parameters ( χ). However, this study introduces the concept of solvent molecular descriptors for elucidating the effect of solvent on the PLGA nanoparticle size in the emulsification–diffusion method. The most pronounced effects on the nanoparticle sizes have the empirical hydrophilicity index Hy, and the molecular descriptors such as the Randic shape descriptor. More rigor results that various molecular descriptors have on the PLGA nanoparticle size are obtained by the molecular descriptors that correspond to the 3D structure of molecules (3D MoRSE descriptors, directional WHIM indicies and the GETAWAY [Geometry, Topology and Atom-Weights Assembly] molecular descriptors). The derived experimental data correlated well with information available from other procedures, confirming that this new approach provides complementary insight into the thermodynamics and the molecular nature of the polymer nanoparticle formation in the solvent type of chemical environments.

Network structure and swelling–shrinking behaviors of pH‐sensitive poly(acrylamide‐co‐itaconic acid) hydrogels

AbstractpH‐sensitive poly(acrylamide‐co‐itaconic acid) [P(AAm/IA)] hydrogels were prepared by radiation induced copolymerization of acrylamide (AAm) and itaconic acid (IA) at various ratios. Swelling and shrinking behaviors of these hydrogels were found greatly dependent on the composition of the hydrogel and pH of the buffer solution. The basic structural parameters of the P(AAm/IA) networks such as the molecular weight between crosslinks (Mc) and polymer–solvent interaction parameter (χ) were also determined using the modified Flory‐Rehner equations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2586–2594, 2004

Effect of maleic acid content on network structure and swelling properties of poly(N‐isopropylacrylamide‐co‐maleic acid) polyelectrolyte hydrogels

AbstractHydrogels were prepared by γ‐ray–induced polymerization in aqueous solution of N‐isopropylacrylamide (NIPA) and of NIPA with three different charge densities, that is, maleic acid (MA) as a comonomer. The swelling behaviors of these hydrogels were analyzed in buffer solutions at various pH and temperature ranges. The equilibrium swelling ratios were relatively high and sensitive to pH and temperature. The polymer–solvent interaction parameter (χ) and the molecular weight between crosslinks (Mc) of P(NIPA/MA) polyelectrolyte hydrogels were calculated from swelling studies in buffer solutions at various pH values and related to MA content. A kinetic study of the absorption determined the transport mechanism as a non‐Fickian type diffusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 763–769, 2004

Thermal behavior and network structure of poly(N‐vinyl‐2‐pyrrolidone‐crotonic acid) hydrogels prepared by radiation‐induced polymerization

AbstractPoly(N‐vinyl‐2‐pyrrolidone‐crotonic acid) [P(VP/CrA)] hydrogels were prepared by irradiating the ternary mixture of VP/CrA and crosslinking agent ethylene glycol dimethacrylate (EGDMA) in water by γ rays at ambient temperature. Differential scanning calorimetry and thermogravimetric analysis were performed to evaluate the thermal properties of ionized networks and to establish if they showed thermal differences that could be related to the CrA content in the gel system. The volume swelling ratio of P(VP/CrA) hydrogels were investigated as a function of the pH in the immersing solution. The volume swelling ratio of these hydrogels increased with an increase in pH and a decrease CrA content in the hydrogel. The volume swelling ratio of the hydrogels was also evaluated using an equation, based on the Flory—Huggins thermodynamic theory, the phantom network theory of James–Guth and Donnan theory of swelling of weakly charged ionic gels for determination of the molecular weight between crosslinks $(\bar{M}_{{\rm c}})$ and the polymer–solvent interaction parameter (χ). Copyright © 2004 John Wiley &amp; Sons, Ltd.

Plasticized microporous poly(vinylidene fluoride) separators for lithium‐ion batteries. I. Swelling behavior of dense membranes with respect to a liquid electrolyte—Characterization of the swelling equilibrium

AbstractSome poly(vinylidene fluoride) (PVdF) microporous separators for lithium‐ion batteries, used in liquid organic electrolytes based on a mixture of carbonate solvents and lithium salt LiPF6, were characterized by the study of the swelling phenomena on dense PVdF membranes. We were interested in the evolution of the swelling ratios with respect to different parameters, such as the temperature, swelling solution composition, and salt concentration. To understand PVdF behavior in microporous membranes and, therefore, to have a means of predicting its behavior with different solvent mixtures, we correlated the swelling ratios in pure solvents and in solvent mixtures to the solvent–polymer interaction parameters and solvent–solvent interaction parameters. We attempted a parametric identification of swelling curves with a very simple Flory–Huggins model with relative success. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 532–543, 2004