Showing papers by "Nicholas A. Peppas published in 1987"
TL;DR: In this paper, an exponential relation M t /M ∞ = kt n may be used to describe the Fickian and non-Fickian release behavior of release systems which are prepared by incorporation of a drug in a hydrophilic, initially glassy polymer.
3,522 citations
TL;DR: In this paper, a simple exponential relation Mt/M∞ = ktn is introduced to describe the general solute release behavior of controlled release polymeric devices, where Mt is the fractional release, t is the release time, k is a constant, and n is the diffusional exponent characteristic of the release mechanism.
3,256 citations
Book•
31 Jan 1987
TL;DR: Hydrogels in medicine and pharmacy, Hydrogel-like properties, and their applications in pharmacy and medicine are investigated.
Abstract: Hydrogels in medicine and pharmacy , Hydrogels in medicine and pharmacy , کتابخانه مرکزی دانشگاه علوم پزشکی تهران
1,264 citations
TL;DR: In this article, a modified tensile tester in contact with bovine sublingual mucus, and the force-elongation behavior was measured up to the breakpoint was calculated and related to bioadhesive characteristics of the tablets.
235 citations
TL;DR: In this paper, a mathematical model was developed to describe the dissolution process of a glassy polymer by a thermodynamically compatible penetrant, which was verified by available experimental data from the fields of controlled release and micro-lithography.
188 citations
TL;DR: In this article, the pyridine transport mechanism was shown to be non-Fickian or Case-II transport, and that it was only slightly affected by the pretreatment of the coal samples.
Abstract: Dynamic swelling studies were performed on well-characterized coal particles treated in various ways. Pyridine was the penetrant and all studies were performed at 35°C. The transport behavior was compared for untreated, pyridine-extracted, oxidized and alkylated samples. Data analysis using an exponential equation of the penetrant uptake as a function of time and a relaxation-controlled analysis showed that the pyridine transport mechanism was non-Fickian or Case-II transport, and that it was only slightly affected by the pretreatment of the coal samples.
113 citations
TL;DR: In this article, the bioadhesive strength of the bond formed between surface-preswollen systems and the sublingual bovine mucus was determined by novel tensile experiments and it was found to be dependent on the poly( acrylic acid) content.
89 citations
TL;DR: In this article, a semi-empirical model for coal diffusion and case-II transport in thin coal slabs, spheres, and cylinders is presented, which can be used to define anomalous transport behavior in the macromolecular network structure of coal.
88 citations
TL;DR: In this paper, the temperature de transition vitreuse d'echantillons de charbon de differentes teneurs en carbone, par calorimetrie differentielle a balayage.
Abstract: Determination de la temperature de transition vitreuse d'echantillons de charbon de differentes teneurs en carbone, par calorimetrie differentielle a balayage. Les echantillons sont utilises tels quels ou extraits a la pyridine
71 citations
TL;DR: In this article, the effective macromolecular structure of ten coals was investigated by application of a modified Gaussian network equation to the results of equilibrium vapour-swelling studies using pyridine as the penetrant.
68 citations
TL;DR: In this article, spherical microparticles of EGDMA-crosslinked poly(2-hydroxyethyl methacrylate) were prepared by suspension polymerization and their dynamic and equilibrium swelling were studied in water and ethanol at 25 ° C. Controlled release studies of phenylephrin-HCl, dimenhydrinate and prednisolone indicated that the drug solubility affects the release behavior.
TL;DR: In this article, poly(ethylene oxides) and block copolymers of ethylene oxide and propylene oxide were crosslinked by diisocyanates and multifunctional branching agents to form water-swellable, partially crystalline networks.
TL;DR: In this paper, a constitutive relation is used to describe the effect of macromolecular relaxations on the rate of volume expansion as the polymer swells, and the penetrant fractional uptake, solute fractional release, sample dimensions, swelling front position, and instantaneous swelling interface number are determined and related to the nature of the swelling process.
Abstract: Penetrant transport through and solute release from continuously swelling polymers is viewed as a process associated with major structural changes in the polymer morphology. Changes in the diffusivities of penetrant and solute reflect a free volume mechanism for transport. The polymer is initially glassy with a uniform dispersion of solute. After the system is placed in contact with a thermodynamically good penetrant, a glassy/rubbery phase transition occurs at a well defined swelling interface. The Fickian equations with concentration-dependent diffusivities and moving boundaries are solved simultaneously in polymer-fixed coordinates. A constitutive relation is used to describe the effect of macromolecular relaxations on the rate of volume expansion as the polymer swells. The penetrant fractional uptake, solute fractional release, sample dimensions, swelling front position, and instantaneous swelling interface number are determined and related to the nature of the swelling process.
TL;DR: In this paper, the effect of the macromolecular relaxation time and characteristic diffusion time on the phenomenological and mechanistic behaviour of pyridine uptake in coal was investigated by varying the coal sample thickness.
TL;DR: In this article, the dynamic behavior of the bioadhesive strength is analyzed for novel controlled release systems containing poly (acrylic acid) and hydroxypropyl methylcellulose.
TL;DR: In this paper, poly(methyl methacrylate and co-maleic anhydride) were prepared by free-radical, bulk polymerization using 0.005 mole % benzoyl peroxide as an initiator at 50 °C for 24 h.
Abstract: Poly(methyl methacrylate) and poly(methyl methacrylate–co‐maleic anhydride) were prepared by free‐radical, bulk polymerization using 0.005 mole % benzoyl peroxide as an initiator at 50 °C for 24 h. The resulting transparent cylinders were cut in a lathe into disks of 14‐mm diameter and 2.2‐mm thickness. Samples were also prepared in the form of thin slabs of 14×2×1 mm3. Subsequently, they were irradiated by γ rays at the level of 2–12 Mrad and their molecular weight distribution was determined by gel permeation chromatography. Changes in their structure before and after irradiation were determined by infrared spectroscopy. Their sensitivity values Gs and solubility characteristics in various solvents were determined. Planar and radial dissolution studies were performed in pure methyl ethyl ketone or ethanol at 26 °C. The positions of the solvent/gel and gel/glassy fronts were followed as functions of time. The results were correlated with the pseudosteady‐state solutions of a new mathematical model incorp...
TL;DR: In this paper, the authors investigated the transport of liquid cyclohexane through well characterized, initially glassy, crosslinked polystyrene slabs, produced by bulk polymerization of styrene and divinyl benzene using benzoyl peroxide as an initiator at 90°C for 48 h.
Abstract: Transport of liquid cyclohexane through well characterized, initially glassy, crosslinked polystyrene slabs was investigated. The samples were produced by bulk polymerization of styrene and divinyl benzene using benzoyl peroxide as an initiator at 90°C for 48 h; they had initial crosslinking ratios, X, between 0.005 and 0.025 mol DVB/mol styrene, initial thickness of 0.25 mm to 1.80 mm, and the aspect ratio was maintained above 10 to achieve one-dimensional transport. The results of cyclohexane uptake as a function of time were used to elucidate the effects of degree of crosslinking and sample geometry on the mechanisms of penetrant transport. These results were interpreted in terms of relaxational and diffusional mechanisms.
TL;DR: In this article, a new model was derived to calculate the solute diffusion coefficient through heterogeneous membranes consisting of a crosslinked, swollen phase and an impermeable, crystalline phase.
Abstract: A new model is derived to calculate the solute diffusion coefficient through heterogeneous membranes consisting of a crosslinked, swollen phase and an impermeable, crystalline phase. The solute diffusion coefficient is shown to depend on various structural characteristics of the amorphous permeable phase and on the volume fraction of the impermeable phase.
TL;DR: In this article, crosslinked poly(2-hydroxyethyl methacrylate) were prepared by suspension polymerization and their crosslinked structure was determined by equilibrium and dynamic swelling experiments in water.
TL;DR: In this paper, a kinetic model was developed for the copolymerization/cross-linking reaction of a monovinyl and a divinyl monomer, which incorporates initiation, propagation, chain transfer and termination reactions.
TL;DR: In this article, the equilibrium swelling process and stress evolution of glassy polymer systems undergoing Case-II penetrant transport were examined using a rubber elasticity theory, and the coupling between stresses and penetrant concentration permitted calculation of equilibrium stress and concentration profiles.
TL;DR: In this article, a new kinetic model for free radical monomethacryl-dimethacryll monomer copolymerization/crosslinking reactions was developed, and the steps of initiation, propagation, crosslinking and termination were described.
TL;DR: Etude du transport dynamique du n-propylamine, n-butylamine and diethylamine sur des echantillons de charbons non traites et extraits a la pyridine as discussed by the authors.
Abstract: Etude du transport dynamique du n-propylamine, n-butylamine, diethylamine et dipropylamine sur des echantillons de charbons non traites et extraits a la pyridine
TL;DR: In this article, the macromolecular network structure of the organic phase of bituminous coals was investigated with equilibrium swelling experiments at 35° and 60°C, and it was determined that an oxygen-methylation technique led to cleavage of hydrogen bonds and significant increase of swelling.
Abstract: The macromolecular network structure of the organic phase of bituminous coals was investigated with equilibrium swelling experiments at 35° and 60°C. It was determined that an oxygen-methylation technique led to cleavage of hydrogen bonds and significant increase of swelling. Pyridine preextraction led to significant differences in swelling due to partial incorporation in the network structure.
TL;DR: Pyridine transport in 600-850-μm coal microparticles, pre-extracted with pyridine and redried, was studied as a function of time and temperature from 35 to 300 ° C as discussed by the authors.
TL;DR: In this article, it was shown that poly(methyl methacrylate-co-maleic anhydride is the best material for positive resist application based on a Gs value of 8 9 scissions per 100eV.
Abstract: Poly(methyl methacrylate), poly(methyl methacrylate-co-2-hydroxyethyl methacrylate), poly(methyl methacrylate-co-itaconic acid), poly(methyl methacrylate-co-maleic anhydride), poly(methacrylic acid-co-itaconic acid), poly(methacrylic acid-co-maleic anhydride), and poly(itaconic acid) were prepared by copolymerization of the appropriate amounts of the two monomers at 50°C for 24–40 h using benzoyl peroxide as initiator. Selected samples were γ-irradiated with a total dose ranging from 2 to 12 Mrad. The unexposed and degraded polymers were dissolved in tetrahydrofuran and their molecular weight distribution was determined by gel permeation chromatography. It was found that Mn decreased drastically with increasing irradiation dose. The presence of various functional groups in both unexposed and irradiated samples was confirmed by infrared spectroscopy. The copolymer thermodynamic compatibility with various solvents was evaluated on the basis of their fractional solubility parameters. The Gs values of these copolymers were determined using the gel permeation chromatography data. It was established that, among those studied, poly(methyl methacrylate-co-maleic anhydride) is the best material for positive resist application based on a Gs value of 8 9 scissions per 100eV.
TL;DR: In this paper, the disintegration of compacts in the presence of a solvent is described by the delamination of the compact and the rate of expansion of the detached layers using a new equation.
Abstract: Disintegration of compacts in the presence of a solvent is followed by measurement of the disintegration force development as a function of time. The process is described by the delamination of the compact and the rate of expansion of the detached layers using a new equation.