John Klier

Controlled release by using poly(methacrylic acid-g-ethylene glycol) hydrogels

Abstract Graft copolymers of poly (ethylene glycol) with poly(methacrylic acid) were prepared by reaction of poly(ethylene glycol) methacrylate macromonomer with methacrylic acid in the presence of tetraethylene glycol dimethacrylate as a crosslinking agent. The materials were swollen in aqueous solutions with the pH ranging from 1.5 to 12.0. Dynamic swelling studies were performed. The swelling rates were lowest in copolymer networks with 1:1 ratios of ethylene oxide to methacrylic acid. These results were attributed to the combined effects of diffusion and complex dissociation during swelling. Solute release studies were carried out to investigate the effect of pH and swelling on the release behavior. Lowest solute release rates were observed in complex-forming networks, verifying the relationship between complexation, swelling and solute permeability.

Polymerization reaction dynamics of ethylene glycol methacrylates and dimethacrylates by calorimetry

Abstract Profiles of reaction rate as a function of time were obtained for free radical crosslinking polymerizations of ethylene glycol methacrylates and dimethacrylates using differential scanning calorimetry. Copolymerizations of ethylene glycol monomethacrylates with small amounts of dimethacrylate crosslinking agents were studied in addition to homopolymerizations of dimethacrylates. In the former case, the effects of the crosslinking agent, initiator, solvent, and the pendent ethylene glycol chain length were investigated. Typically, a sharp increase in the reaction rate was observed which was attributed to autoacceleration. The time period before the onset of autoacceleration increased and the maximum reaction rate decreased as the solvent concentration or the pendent chain length were increased or the crosslinking agent concentration was decreased. These results were explained by an increase in the mobility of the growing polymer leading to a decrease in the magnitude of the gel effect. Studies of dimethacrylates yielded similar results for the effect of solvent. However, the maximum reaction rate increased when the number of repeating units between the methacrylate functionalities was increased from one to four, but decreased when the number of repeating units was increased from four to nine. Photopolymerization experiments indicated that radicals with significantly different lifetimes might be present in dimethacrylate homopolymerizations.

Solute and penetrant diffusion in swellable polymers. VIII: Influence of the swelling interface number on solute concentration profiles and release

Abstract Penetrant-activated solute release was modeled in polymers undergoing Case-II penetrant uptake. The rate of solute release can be nearly constant for systems with Case-II penetrant uptake behavior, depending on the values of solute diffusion coefficients and the functional form of concentration dependence. It is shown that swelling of a polymer slab can have a significant effect on solute release behavior.

Anomalous penetrant transport in glassy polymers: 4. Stresses in partially swollen polymers

Abstract The equilibrium swelling process and stress evolution of glassy polymer systems undergoing Case-II penetrant transport were examined using a rubber elasticity theory. Consideration of coupling between stresses and penetrant concentration permitted calculation of equilibrium stress and concentration profiles for a variety of molecular and geometric factors.

Anomalous penetrant transport in glassy polymers. III: Use of Raman spectroscopy to study penetrant transport

Summary Methylene chloride transport in copolymers of .poly(2-hydroxyethyl methaerylate-co-N-vinyl-2-pyrrolidone) was studied at 25 C using Raman microprobe spectroscopy. It is shown that the abrupt change of the penetrant concentration at the rubbery/glassy interface during swelling can be detected and followed to obtain useful information about the penetrant transport mechanisms in these copolymers.

Soluble chain fractions in hydrophilic polymer networks: origin and effect on dynamic uptake overshoots

Abstract The dynamic swelling behaviour of crosslinked poly(2-hydroxyethyl methacrylate) networks containing well characterized soluble fractions of poly(ethylene glycol) was studied. The mass uptake as a function of time exhibited a significant overshoot above the final equilibrium value. The magnitude and duration of the overshoot depended on the concentration and molecular weight of the soluble fraction, and was attributed to the presence of the soluble fraction. A statistical model was used to show that polymer networks formed by free-radical copolymerization and crosslinking reactions may contain a significant intrinsic soluble fraction made up of unreacted monomer and polymer chains that have not become incorporated into the gel. It is therefore suggested that this soluble fraction may contribute to swelling overshoot. The statistical model was used to relate the quantity and molecular weight of the intrinsic soluble fraction to the free-radial reaction parameters.