No abstract

No abstract

No abstract

No abstract

The aim of this study was to assess the in vitro release kinetics of antituberculosis drug-loaded nanoparticles (NPs) using a “modified” cylindrical apparatus fitted with a regenerated cellulose membrane attached to a standard dissolution apparatus (modifiedcylinder method). The model drugs that were used were rifampicin (RIF) and moxifloxacin hydrochloride (MX). Gelatin and polybutyl cyanoacrylate (PBCA) NPs were evaluated as the nanocarriers, respectively. The dissolution and release kinetics of the drugs from loaded NPs were studied in different media using the modified cylinder method and dialysis bag technique was used as the control technique. The results showed that use of the modified cylinder method resulted in different release profiles associated with unique release mechanisms for the nanocarrier systems investigated. The modified cylinder method also permitted discrimination between forced and normal in vitro release of the model drugs from gelatin NPs in the presence or absence of enzymatic degradation. The use of dialysis bag technique resulted in an inability to differentiate between the mechanisms of drug release from the NPs in these cases. This approach offers an effective tool to investigate in vitro release of RIF and MX from NPs, which further indicate that this technique can be used for performance testing of nanosized carrier systems.

The dynamic mechanical properties of homogeneous copolymers of ethylene with 1‐butene, 1‐octene, and 1‐octadecene prepared by means of a vanadium‐based catalyst system have been determined. The 1‐butene copolymers show α′ and α transitions in the 20–60°C temperature range, whereas the 1‐octene and 1‐octadecene copolymers show single α transitions. The intensity of the β transition increases with comonomer content in 1‐butene and 1‐octene copolymers and also with the amount of interfacial material present. In ethylene‐1‐octadecene copolymers, this intensity is comparatively low, even though there is about 20% interfacial material present. The implications of these results with regard to the nature of interfacial material are discussed.

Random copolymers of ethylene with 1‐butene, 1‐octene, and 1‐octadecene have been prepared using a homogeneous vanadium‐based catalyst system. Comonomer contents determined by 13C‐NMR analysis of polymer solutions are in the range 1–10 mol%. Crystallinities were estimated by means of density measurements, x‐ray diffraction, differential scanning calorimetry, laser Raman spectroscopy, and CPMAS 13C‐NMR spectroscopy. The results are compared with those obtained for heterogeneous copolymers of ethylene containing 1–4 mol% 1‐butene. As the comonomer content is increased, the crystallinity decreases. The dimension perpendicular to the 110 plane in orthorhombic crystallites decreases linearly with crystallinity. This decrease in crystallite size is accompanied by an increase in the size of the orthorhombic unit cell. For copolymers containing large amounts of 1‐octene and 1‐octadecene, a second crystalline form appears. Differences in estimates of crystallinity are discussed in terms of looser packing in highly branched copolymers and the extent to which the second crystalline form participates in the phase structure.

SynopsisMelting points of copolymers of ethylene and 1-alkenes ranging from 1-butene to 1-octadecene have been determined. The copolymers were prepared by means of a homogeneous Et,Al,Cl,/VOCl, initiating system so that in individual samples, comonomer contents do not vary with molecular weight. Evidence is presented for a random distribution of comonomer units in the copolymers. Melting points determined by differential scanning calorimetry are essentially independent of branch length at low comonomer contents. At higher comonomer contents (5-9 mol% 1-alkene), melting points decrease in the order 1-butene > 1-octene > 1-octadecene copolymers. The weight fraction of ethylene sequences drops to iess than 60% in copolymers with 1-octadecene of high comonomer content and this results in a reduction in the crystallite thicknesses attained by these copolymers.