Gordon-Taylor Equation Research Articles

Evaluating Stability of Vitamin C in Fortified Formula Using Water Activity and Glass Transition

Stability of vitamin C in fortified formula food at constant temperature, as affected by the water activity (aw ) and glass transition (Tg ), was investigated in an attempt to differentiate the effects of aw and Tg on the degradation reaction. Fortified formula samples, equilibrated at different moisture contents/water activity levels, were stored for more than 10 weeks at the room temperature, 23°C. The water activity and glass transition temperatures as a function of moisture content were determined for fortified formula to compare the two distinct criteria of food stability. The adsorption experiments, which were carried out at controlled water activities, at 23°C using an isopiestic method, were modeled using the GAB equation. The glass transition temperatures, which were measured by modulated differential scanning calorimeter, were modeled using the Gordon-Taylor equation. The loss of vitamin C followed a zero-order kinetic model. The vitamin C retention after storage of 73 days at water activities of 0.11 and 0.87 was 40 and 7%, respectively. The rate constants ranged from 5.8 to 10 mgd−1, depending on the water activities. The constants were correlated with water activities and glass transition temperatures. Results indicated that reactions rates correlated with both water activity and the glass transition temperatures. In the storage and processing of fortified food products, both the water activity and glass transition should be recognized as important criteria for gaining a better understanding of vitamin stability.

Multiple glass transitions and two step crystallization for the binary system of water and glycerol

Glass formation/crystallization phenomena were studied in water and glycerol mixtures using adiabatic calorimetry. The sample was cooled rapidly from room temperature and its thermal response was followed on heating from 80 to 300 K. The binary mixtures with the glycerol contents more than 55% (w/w) (19 mol%) yielded the homogeneous glassy states, consisting of randomly mixed water and glycerol molecules. Their glass transition temperatures showed the composition dependence of the Gordon–Taylor equation, and extrapolated exactly to that of pure water (135 K). The mixtures in the 0–55% (w/w) glycerol range crystallized partly on cooling and exhibited three anomalies in the temperature drift rate on heating. The first of these three is associated with the onset of reorientational motions of water molecules in the hexagonal ice which increases from 107 to 120 K on increasing the glycerol composition. The second is the composition independent temperature of 164 K that corresponds to the mixture with 76% (w/w) glycerol (38 mol%, known as the maximally freeze-concentrated solution), which is the mixture with the maximum composition of water that can be cooled without crystallization. The third is associated with the ice crystallization followed by ice dissolution in the range 185–202 K. In addition, the sample with 60% (w/w) glycerol composition (23 mol%) exhibited two distinguishable exothermic peaks on heating. The initial one is large and is attributed to crystallization into a novel two-dimensionally ordered structure of ice, and the second is due to the transformation of the layered structures into the hexagonal ice.

Isothermal crystallization kinetics in binary miscible blend of poly(ε‐caprolactone)/tetramethyl polycarbonate

AbstractThe crystallization kinetics of pure poly(ε‐caprolactone) (PCL) and its blends with bisphenol‐A tetramethyl polycarbonate (TMPC) was investigated isothermally as a function of composition and crystallization temperature (Tc) using differential scanning calorimetric (DSC) and polarized optical microscope techniques. Only a single glass‐transition temperature, Tg, was determined for each mixture indicating that this binary blend is miscible over the entire range of composition. The composition dependence of the Tg for this blend was well described by Gordon–Taylor equation with k = 1.8 (higher than unity) indicating strong intermolecular interaction between the two polymer components. The presence of a high Tg amorphous component (TMPC) had a strong influence on the crystallization kinetics of PCL in the blends. A substantial decrease in the crystallization kinetics was observed as the concentration of TMPC rose in the blends. The crystallization half‐time t0.5 increased monotonically with the crystallization temperature for all composition. At any crystallization temperature (Tc) the t0.5 of the blends are longer than the corresponding value for pure PCL. This behavior was attributed to the favorable thermodynamics interaction between PCL and TMPC which in turn led to a depression in the equilibrium melting point along with a simultaneous retardation in the crystallization of PC. The isothermal crystallization kinetics was analyzed on the basis of the Avrami equation. Linear behavior was held true for the augmentation of the radii of spherulites with time for all mixtures, regardless of the blend composition. However, the spherulites growth rate decreased exponentially with increasing the concentration of TMPC in the blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3307–3315, 2007

Solid dispersions of itraconazole and enteric polymers made by ultra-rapid freezing

The primary objective of the study is to investigate the influence of composition parameters including drug:polymer ratio and polymer type, and particle structure of enteric solid dispersions on the release of ITZ under sink and supersaturated dissolution conditions. Modulated differential scanning calorimetry (MDSC) was utilized to define the level of ITZ miscibility with each polymer. The compositions were completely miscible at 60% ITZ for both polymers and as high as 70% in HP-55. High potency composition glass transition temperatures ( T g) correlated with predicted T g's from the Gordon–Taylor equation, however, recrystallization exotherms revealed pure amorphous regions indicating that phase separation occurred during particle formation. Furthermore, in vitro studies including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), surface area analysis (BET), and dissolution were performed to determine differences between low potency (completely miscible) and high potency (partially miscible) compositions. Dissolution studies on low potency ITZ compositions revealed that miscibility plays an active role in ITZ release under sink conditions, and square root diffusion through the enteric polymer is observed. Supersaturated dissolution profiles revealed high potency compositions had maximum saturation levels ( C/ C e q max ) between 10.6- and 8-times equilibrium solubility, but had higher cumulative extents of supersaturation, compared to low potency compositions which had C/ C e q max values of 15–19.6. However, these low potency compositions rapidly precipitated leading to significantly lower AUCs ( p < 0.05). The change in the miscibility of the solid dispersion had a pronounced effect of drug release (sink) while differences in potency influenced supersaturated dissolution profiles.

The glass transition temperatures of sugar mixtures

We measured the glass transition temperatures of mono-, di-, and trisaccharide mixtures using differential scanning calorimeter (DSC) and analyzed these temperatures using the Gordon–Taylor equation. We found that the glass transition temperatures of monosaccharide–monosaccharide and disaccharide–disaccharide mixtures could be described by the conventional Gordon–Taylor equation. However, the glass transition temperatures of monosaccharide–disaccharide and monosaccharide–trisaccharide mixtures deviated from the conventional Gordon–Taylor equation and the amount of deviation in the monosaccharide–trisaccharide mixtures was larger than those in the monosaccharide–disaccharide mixtures. From these results, we conclude that the size and shape of the sugars play an important role in the glass transition temperature of the mixtures.

Miscibility and crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and methoxy poly(ethylene glycol) blends

AbstractPoly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHB‐HHx) and methoxy poly(ethylene glycol) (MPEG) blends were prepared using melt blending. The single glass transition temperature, Tg, between the Tgs of the two components and the negative χ value indicated that PHB‐HHx and MPEG formed miscible blends over the range of compositions studied. The Gordon–Taylor equation proved that there was an interaction between PHB‐HHx and MPEG in their blends. FTIR supported the presence of hydrogen bonding between the hydroxyl group of MPEG and the carbonyl group of PHB‐HHx. The spherulitic morphology and isothermal crystallization behavior of the miscible PHB‐HHx/MPEG blends were investigated at two crystallization temperatures (70 and 40 °C). At 70 °C, melting MPEG acted as a noncrystalline diluent that reduced the crystallization rate of the blends, while insoluble MPEG particles acted as a nucleating agent at 40 °C, enhancing the crystallization rate of the blends. However, no interspherulitic phase separation was observed at the two crystallization temperatures. The constant value of the Avrami exponent demonstrated that MPEG did not affect the three‐dimensional spherulitic growth mechanism of PHB‐HHx crystals in the blends, although the MPEG phase, such as the melting state or insoluble state, influenced the crystallization rate of the blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2852–2863, 2006

Non-isothermal crystallization kinetics of poly(trimethylene terephthalate)/poly(ethylene 2,6-naphthalate) blends

The glass-transition temperature and non-isothermal crystallization of poly(trimethylene terephthalate)/poly(ethylene 2,6-naphthalate) (PTT/PEN) blends were investigated by using differential scanning calorimeter (DSC). The results suggested that the binary blends showed different crystallization and melting behaviors due to their different component of PTT and PEN. All of the samples exhibited a single glass-transition temperature, indicating that the component PTT and PEN were miscible in amorphous phase. The value of T g predicted well by Gordon–Taylor equation decreased gradually with increasing of PTT content. The commonly used Avrami equation modified by Jeziorny, Ozawa theory and the method developed by Mo were used, respectively, to fit the primary stage of non-isothermal crystallization. The kinetic parameters suggested that the PTT content improved the crystallization of PEN in the binary blend. The crystallization growth dimension, crystallization rate and the degree of crystallinity of the blends were increased with the increasing content of PTT. The effective activation energy calculated by the advanced iso-conversional method developed by Vyazovkin also concluded that the value of E a depended not only on the system but also on temperature, that is, the binary blend with more PTT component had higher crystallization ability and the crystallization ability is increased with increasing temperature. The kinetic parameters U * and K g were also determined, respectively, by the Hoffman–Lauritzen theory.

Thermophysical properties of aqueous and frozen states of BSA/water/Tris systems

In the modelling and the optimization of pharmaceutical protein freeze–drying processes, thermophysical properties values of the formulation in frozen or in liquid states are necessary in order to determine the optimal operating conditions (temperature, pressure) of the two steps (sublimation, desorption) drying diagramme and the optimal storage conditions of the final freeze–dried product. The most important thermophysical properties of BSA/water/Tris system buffered with Tris–HCl (5%, w/w) at pH 7, a standard formulation largely used in industrial freeze–drying process of pharmaceutical proteins, are reported in this paper. The state diagram of this formulation was determined by modulated temperature differential scanning calorimetry (MTDSC) and, then the vitreous transition temperatures were interpreted as a function of water content by the Gordon–Taylor equation. The same technique was used to experimentally determine the heat capacity of the BSA/water frozen system. Moreover, the transient hot wire probe method was used to measure the thermal conductivity of the frozen system as a function of temperature. It proved that the thermal conductivity and the apparent heat capacity values for this dilute formulation were reasonably close to the values for the pure water/ice system. Sorption isotherms data were also measured by two different methods—the equilibrium with saturated salts solutions and also the controlled humidity oven. Water vapour sorption data were finally correlated by the three parameters Guggenheim, Anderson, De Boer (GAB) equation.

HyperDSC studies of amorphous polyvinylpyrrolidone in a model wet granulation system

Measurements of the properties of amorphous materials are very important to help in the understanding of how materials behave during manufacture, storage and use of medicines. However, there are few methods that are suited to the study of amorphous materials, especially if in multi-component systems or model formulations. The goal here was to explore the potential for the use of HyperDSC to study a model granulation system. It was found that the sensitivity of HyperDSC was such that the glass transition ( T g) of polyvinylpyrrolidone (PVP) could be detected in granules made with realistic levels of this binder. The measured T g in the granules, even after drying, was very different to that of PVP alone and to PVP in physical mixtures with lactose. It is argued that the granulation process has resulted in the dissolution of some lactose and that the amorphous binder holding the granules together is in fact a solid dispersion of PVP and lactose. Based on the standard Gordon–Taylor equation it was estimated that the solid dispersion contained 50% of PVP and lactose. Given that solid dispersions have a tendency to crystallise on storage, it could be expected that changes in the binder properties will occur with time after granulation. We believe that this is the first measurement of in situ properties of a binder in this way and opens the possibility of studies on formulated systems.

Forced and Natural Convective Drying of Trehalose/Water Thin Films: Implication in the Desiccation Preservation of Mammalian Cells

Trehalose is believed to offer desiccation protection to mammalian cells by forming stable glassy matrices. The goal of the current study was to explore the desiccation kinetics of thin films of trehalose-water solution under forced and natural convective conditions and to investigate the thermophysical state of mammalian cells at the bottom of the thin film. We developed a finite difference model based on the mass and energy conservation equations coupled to the water transport model from the cells. The boundary conditions were obtained from correlations or experimental measurements and the Gordon-Taylor equation was used to predict the glass transition temperature at every location. Results indicated that there are three distinct regimes for drying for both forced and natural convection, characterized by the slope of the moisture content plot as a function of time. Our results also indicate that the surface of the solution reached the glassy state in less than 10 min for the Reynolds (forced) numbers explored and approximately 30 min for some Rayleigh (natural convective) numbers; however, significant water was trapped at this instant. Larger drying force hastened quicker glass formation but trapped more water. The numerical model was capable of predicting the drying kinetics for the dilute region accurately, but deviated while predicting the other regimes. Based on these experimental validations of the model, the osmotic response of different cells located at the bottom of the solution with orders of magnitude difference in their membrane permeability (Lp) was predicted. The results suggested that extracellular glass formed around cells at the bottom of a trehalose-water solution by the propagation of glass into the solution; however it takes more than an order of magnitude time (approximately 7 min to >100 min for forced convective drying) to remove sufficient water to form glass around cells from the time when the first surface glass is formed. This is attributed to low diffusivity of water through the glass. In addition, the water transport from the glassy matrix could be either diffusion or Lp limited. For diffusion-limited transport, lowering the film thickness at the beginning of drying by half almost lowers the drying time by an order of magnitude. In summary, the optimal design of convective desiccation protocols requires accounting for the size of the cell, their membrane permeability (Lp) and the starting thickness of the solution.

Physical Stability of Amorphous Acetanilide Derivatives Improved by Polymer Excipients

Crystallization rates of drug-polymer solid dispersions prepared with acetaminophen (ACA) and p-aminoacetanilide (AAA) as model drugs, and polyvinylpyrrolidone and polyacrylic acid (PAA) as model polymers were measured in order to further examine the significance of drug-polymer interactions. The crystallization of AAA and ACA was inhibited by mixing those polymers. The most effective inhibition was observed with solid dispersions of AAA and PAA. The combination of AAA and PAA showed a markedly longer enthalpy relaxation time relative to drug alone as well as a higher T(g) than predicted by the Gordon-Taylor equation, indicating the existence of a strong interaction between the two components. These observations suggest that crystallization is effectively inhibited by combinations of drug and polymer that show a strong intermolecular interaction due to proton transfer between acidic and basic functional groups.

N,N-dicyclohexylcarbodiimide assisted synthesis and characterization of poly(vinyl alcohol- co-vinyl levulinate)

Poly(vinyl alcohol- co-vinyl levulinate) was synthesized by N,N-dicyclohexylcarbodiimide assisted esterification of poly(vinyl alcohol) with free levulinic acid using 4-pyrrolidino pyridine as a catalyst in N,N-dimethyl acetamide/lithium chloride solvent system in order to optimize the reaction condition. The vinyl levulinate content in the copolymer was attained up to 0.95. The 13C NMR dyad compositional analysis indicated the block character of the copolymer was 0.92, suggesting almost random poly(vinyl alcohol- co-vinyl levulinate) was formed. Glass transition temperature dependence on vinyl levulinate content of the copolymers fitted better into Gordon–Taylor equation as compared with Fox equation and the glass transition temperature of poly(vinyl levulinate) was given as 2.3 °C by the least regression method.

Thermal and crystallization characteristics of poly(trimethylene terephthalate)/poly(ethylene naphthalate) blends

Poly(trimethylene terephthalate) (PTT)/poly(ethylene naphthalate) (PEN) blends were miscible in the amorphous state in all of the blend compositions studied, as evidenced by a single, composition-dependent glass transition temperature ( T g) observed for each blend composition. The variation in the T g value with the blend composition was well predicted by the Gordon–Taylor equation, with the fitting parameter being 0.57. The cold-crystallization peak temperature decreased with increasing PTT content, while the melt-crystallization peak temperature decreased with increasing amount of the minor component. The subsequent melting behavior after both cold- and melt-crystallization exhibited melting point depression, in which the observed melting temperatures decreased with increasing amount of the minor component. During melt-crystallization, both components in the blends crystallized concurrently just to form their own crystals. The blend with 60% w/w of PTT exhibited the lowest total apparent degree of crystallinity.

Physicochemical evaluation of PVP–thiazide diuretic interactions in co-spray-dried composites—analysis of glass transition composition relationships

The aim of this study was to evaluate the possible interactions in the solid state between the thiazide diuretics: bendroflumethiazide (BFMT), hydroflumethiazide (HFMT) and hydrochlorothiazide (HCT) and polyvinylpyrrolidone (PVP) following processing. The glass transition temperatures ( T g s) of a range of binary co-spray-dried PVP–thiazide composites were determined and compared to the predictions of the Gordon–Taylor, Fox, Couchman–Karasz, Kwei and Schneider equations. The solid composites of the thiazide diuretics and PVP were prepared by a spray drying technique. Properties of composites were determined with the use of helium pycnometry and FTIR spectroscopy. For many systems studied the experimentally detected T g s exhibited large positive deviations when compared with the values predicted by the Gordon–Taylor, Fox and Couchman–Karasz equations. The data was better fitted by the Schneider equation consistent with a drug–polymer interaction. FTIR analysis revealed that strong hydrogen bonding between the sulphonamide groups of the thiazide diuretics and the PVP molecule was responsible for the increase in the T g s. Additionally, in the case of BFMT–PVP composites, an interaction between the phenyl group and polymer ring was apparent. Glass transition–composition behaviour for amorphous drug–PVP composites deviated from the predictions of the commonly used Gordon–Taylor equation. Deviations were consistent with interactions between the components in the amorphous mixtures. The Schneider equation may be successfully applied to fit the T g-composition profiles obtained, where other models fail to give good predictions.

Miscibility and intermolecular specific interactions in thermosetting blends of bisphenol S epoxy resin with poly(ethylene oxide)

AbstractThermosetting blends composed of phloroglucinol‐cured bisphenol S epoxy resin and poly(ethylene oxide) (PEO) were prepared via the in situ curing reaction of epoxy in the presence of PEO, which started from initially homogeneous mixtures of diglycidyl ether of bisphenol S, phloroglucinol, and PEO. The miscibility of the blends after and before the curing reaction was established on the basis of thermal analysis (differential scanning calorimetry). Single and composition‐dependent glass‐transition temperatures (Tg's) were observed for all the blend compositions after and before curing. The experimental Tg's could be explained well by the Gordon–Taylor equation. Fourier transform infrared spectroscopy indicated that there were competitive hydrogen‐bonding interactions in the binary thermosetting blends upon the addition of PEO to the system, which was involved with the intramolecular and intermolecular hydrogen‐bonding interactions, that is, OH···OS, OH···OH, and OH, versus ether oxygen atoms of PEO between crosslinked epoxy and PEO. On the basis of infrared spectroscopy results, it was judged that from weak to strong the strength of the hydrogen‐bonding interactions was in the following order: OH···OS, OH···OH, and OH versus ether oxygen atoms of PEO. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 359–367, 2005

A comparison of high speed differential scanning calorimetry (Hyper-DSC) and modulated differential scanning calorimetry to detect the glass transition of polyvinylpyrrolidone: the effect of water content and detection sensitivity in powder mixtures (a model formulation)

Differential scanning calorimetry is an established technique for the measurement of glass transition temperature (Tg). More recently modulated DSC has been used, a technique that allows the separation of the reversible Tg response from non-reversible events, allowing a more straightforward detection of glass transitions. However, even when using modulated DSC, the sensitivity is such that detecting glass transitions of amorphous components can be a challenge, particularly when the amorphous form is present at low levels. With Hyper-DSC the sample is ramped at a very fast scan-rate (up to 500°C/min). The rapid scan-rate can substantially enhance the sensitivity allowing small transitions to be detected more readily. The purpose of this study was to determine how much of an increase in sensitivity could be achieved whilst checking how results may be affected by the high scan rate. The Tg of PVP at various moisture contents was measured using both modulated and Hyper DSC. A comparison of the results demonstrated that the temperature of the Tg measured at the high scan rate was not significantly different from the temperature of the Tg obtained by modulated DSC. Also results for both techniques compared favourably with theoretical values calculated using the Gordon-Taylor equation. Additionally the size of the Tg was significantly larger when measured using Hyper-DSC. The increase in sensitivity was further demonstrated by measuring the Tg of PVP in a series of mixtures of PVP and lactose ranging from 5 up to 50% w/w PVP. Modulated DSC was only able to detect levels of 40% w/w PVP and above whereas Hyper-DSC was easily able to detect the Tg of PVP in all samples.

State Diagram of Date Flesh Using Differential Scanning Calorimetry (DSC)

The state diagram of date flesh was developed by measuring its freezing points, glass transition temperatures, maximal-freeze-concentration condition ( and ), and solute melting points (or decomposition temperature) by Differential Scanning Calorimetry (DSC). The freezing curve and glass transition lines were developed using Clausius-Clapeyron equation by incorporating concept of unfrozen water, and Gordon-Taylor equation, respectively. The developed state diagram of date flesh can be used in determining its stability during storage as a function of temperature and moisture content (such as, frozen and dried conditions) as well as in designing drying and freezing processes.

A Mechanistic Investigation of an Amorphous Pharmaceutical and Its Solid Dispersions, Part I: A Comparative Analysis by Thermally Stimulated Depolarization Current and Differential Scanning Calorimetry

To explore using thermally stimulated depolarization current (TSDC), in comparison to differential scanning calorimetry (DSC), for the characterization of molecular mobility of an amorphous pharmaceutical new chemical entity (LAB687), an amorphous polymer (PVPK-30), and their combination as solid dispersions at different % drug loadings. Amorphous drug was prepared by quenching from the melt. Solid dispersions containing 10-60% of drug in polymer were prepared by solvent evaporation method. Glass transition temperatures (Tg) were determined by DSC and TSDC. In comparison to a single T. obtained from DSC for the drug substance, TSDC shows two overlapping relaxations. Both peaks correspond to a-relaxations that are associated with the glass transition, with the second peak corresponding to the rigid fraction that is difficult to be detected by DSC because it is associated with only small changes in heat capacity. Two overlapping relaxations were also observed for the polymer vs. one Tg by DSC. The lower temperature relaxation is believed to be a beta-relaxation, whereas the higher temperature transition corresponds to an alpha-relaxation. For the solid dispersions, one single peak was obtained for each of the 20% and 30% dispersions in excellent agreement with the DSC results. However, at the 40% drug load, a small shoulder was observed by TSDC at the low temperature of the main peak. This shoulder becomes more pronounced and overlaps with the main peak as the drug load increases to 50% and 60%. Agreement between the Tg values calculated by the Gordon-Taylor equation and the DSC and TSDC experimental data, especially for the 20% and 30% drug loading, indicate ideal miscibility. At higher drug loads, only by TSDC was it possible to detect the saturation level of the drug in the polymer. TSDC proved to be very sensitive in detecting small reorientational motions in solids and in separating overlapping events with only slight differences in molecular motion exhibited as broad events in DSC. This allowed for detection of the rigid fraction of the amorphous drug, the sub-glass transition beta- relaxation in the polymer, and the limit of miscibility between the drug and the polymer in the solid dispersions.

Miscible blends of poly(vinyl phenyl ketone hydrogenated) and poly(styrene-co-4-vinylpyridine)

Miscibility behavior over a wide composition range was detected for polymer blends of poly(vinyl phenyl ketone hydrogenated) (PVPhKH) with poly(styrene-co-4-vinylpyridine) (PS-co-4VPy). Differential scanning calorimetry (DSC) and thermo mechanical analysis (TMA) reveal that each composition has only one glass transition temperature. The variation of the glass transition temperature with composition for PVPhKH/PS-co-4VPy miscible blends follows the Gordon–Taylor equation. FTIR analysis of this binary system indicates the existence of hydrogen bonding between pyridine ring of PS-co-4VPy and hydroxyl groups insert into PVPhKH. This specific interaction has a decisive influence in the phase behavior of PVPhKH/PS-co-4VPy blends.

STUDIES ON THE MISCIBILITY OF POLY(2-HYDROXYETHYLMETHACRYLATE) AND HYDRODY PROPYL METHYL CELLULOSE BLENDS

Miscibility characteristics of poly[2–hydroxyethylmethacrylate] (PHEMA) and hydroxy propyl methyl cellulose (HPMC) have been investigated by solution viscometry, ultrasonic and differential scanning calorimetric (DSC) methods. The interaction parameters were obtained using the viscosity data. Ultrasonic velocity and adiabatic compressibilities versus blend composition have been plotted and are found to be linear. Variation of glass transition temperature (Tg) with composition follows the Gordon-Taylor equation. Tg values have also been calculated from the Fox equation. The results obtained reveal that PHEMA forms a miscible blend with HPMC over the entire composition range.