Issa Katime

Dual Drug Release of Triamterene and Aminophylline from Poly (N-Isopropylacrylamide) Hydrogels

We used temperature-sensitive poly(N- isopropylacrylamide) hydrogels as drug delivery systems, so changes in body temperature induced by pathogens could act like external stimuli to activate controlled release of the drugs incorporated in the hydrogel. In the distilled water combined release studies, we chose two model drugs: aminophylline and triamterene. The amount of drug released was measured by UV-Vis spectroscopy following the evolution of the absorption peaks of aminophylline (271 nm) and triamterene (365 nm). The maximum release time was greater for triamterene than for aminophylline at 37 oC, so these time-release profiles enabled the active ingredients to work over different periods of time. By increasing molar mass or solubility of the drug, we observed that the diffusion coefficient decreased. On the contrary, increasing hydrophobicity of the drug leads to a diffusion coefficient increase. The evolution of pore size distribution of hydrogels during loading and releasing was measured by quasi-elastic light scattering and by environmental electronic scanning microscope. When loading and releasing the drugs, the pore size of the hydrogel decreased and increased again without reaching the initial pore size of the hydrogel, respectively. We observed that the greater the concentration of drug loaded into the hydrogel, the greater the reduction in pore size.

Polymer co-solvent systems—I: Viscometric behaviour of poly(p-tert-butylphenyl methacrylate) in acetone/cyclohexane

Abstract The viscometric behaviour of poly(p-tert-butylphenyl methacrylate) in a binary mixture (acetone/cyclohexane) has been studied. This mixture presents a type of partial co-solvency (synergism) for this polymer: cyclohexane is a θ-solvent at 25° and acetone is very poor. The conformational parameter seems unaffected by the nature of this binary solvent mixture. The results are discussed in relation to the behaviour of the poly(p-tert-butylphenyl methacrylate) in some pure solvents, viz. acetone, cyclohexane and tetrahydrofuran. This viscometric behaviour is compared with that of polystyrene in the same mixture.

Micellization of triblock copolymers in a solvent selective for the middle block: Influence of the molar mass

The micellization thermodynamics and micelle structural parameters for polystyrene-b-poly(ethylene/butylene)b-polystyrene copolymers (SEBS) in n-octane were studied. This solvent is selective for the middle poly(ethylene/butylene) block of the copolymer. The copolymer samples have similar chemical composition and different molar mass. Standard thermodynamic functions of micellization (ΔG°, ΔH° and ΔS°) were determined by light scattering. All the functions showed more negative values for the SEBS copolymer with a larger molar mass. The structural parameters of micelles formed by different triblock copolymers were determined from static light scattering and viscosity measurements. Micelle molar mass, association number and viscometric hydrodynamic radius increase with the length of the copolymer chain for a constant copolymer composition; however, the radius of gyration decreases. Finally, the results found for SEBS micelles in n-octane are compared to those found for SEBS micelles in 4-methyl-2-pentanone. The different behaviour found supports the idea that the micelles of a triblock copolymer in a selective so vent of the middle block will show a shell formed by loops of the middle block in order that the two outer blocks go into the micelle core and even some poorly solvated outer blocks could be extended out of the micelle.

Polymer cosolvent system—II. Preferential adsorption of binary solvent acetone/cyclohexane by poly(p-tert-butylphenyl methacrylate)

Abstract The cosolvent system poly( p -tert butylphenyl methacrylate) (3)/acetone(1)/cyclohexane (2) has been studied at 298 K by light scattering, refractive index increment of dialysis equilibrium and viscometry. The preferential adsorption coefficient, λ∗, for the whole composition range of the binary mixture acetone (1)/cyclohexane(2) has been determined. The values have been compared with the theoretically calculated values. The results indicate that in this system it is necessary to take into account the tertiary interaction parameters χ 123 , χ 122 and χ 233 .

A study of the behaviour ofpoly(N-vinylcarbazole) in binary mixtures of tetrahydrofuran and poly(ethylene glycol) oligomers

In this paper we report studies onpoly( N -vinylcarbazole) (PNVK) in binary mixtures of THF (1) and poly(ethylene glycol) (2) obtained by viscometry and laser light scattering measurements. From these data, total and preferential solvation parameters were calculated over the whole binary mixture composition range studied. We have not found any inversion in the solvation. Inter- and intra-molecular interactions, K θ and B, were calculated using the Stockmayer-Fixman equation. Finally, we found that the compatibility between PNVK and PEG increases linearly as PEG molar mass increases.

Thermodynamics and Kinetics of Micellization, including Solubilization

Recent measurements carried out using surfactant selective electrodes constructed in this laboratory have shown that for aqueous solutions of anionic and cationic surfactants with a small amount of added salt (~ 10–4 mol dm-3) there is a significant decrease of the monomer surfactant concentration as the total concentration of the surfactant is increased in the micellar region. By carrying out simultaneous measurements using an electrode selective to the counterion it is also possible to evaluate the degree of micellar dissociation. We have considered the implications of these new data in relation to kinetic studies of monomer/micelle equilibria carried out using different relaxation techniques. As a result it has been shown that micellar parameters, which can be derived from kinetic studies, are extremely sensitive to changes in monomer surfactant concentration in the micellar region and also, to a lesser extent, to the degree of micellar dissociation. Kinetic and equilibrium measurements have also been extended to the investigation of cationic surfactants in formamide solutions. The authors gratefully acknowledge support of the SERC and Unilever Ltd.

Ptitsyn-Eizner λ parameter for syndiotactic poly(methyl methacrylate) in good solvents

Abstract We have calculated the λ parameter from the Ptitsyn-Eizner equation for syndiotactic poly(methyl methacrylate) in several good solvents (chloroform, acetone, ethyl and butyl acetate). We have analyzed the contributions of long and short range interactions to the λ parameter as a function of solvent quality.