Crosslinked poly(ethylene oxide) for drug release systems

Three types of poly(ethylene oxide) (PEO)- based hydrogels have been synthesized and studied for drug release applications: γ-irradiated high molecular weight PEO, biodegradable polyether-polyester networks with malic acid as crosslinker of poly(ethylene glycol)s and amphiphilic PEO-based polyureas crosslinked with multifunctional isocyanates. Varying the length of the PEO chain and the type of the crosslinker, hydrogels with different swelling properties, loading capacities and release characteristics were obtained. A large number of pharmaceuticals (acebutolol. HCl, diclofenac. Na, procaine. HCl, phenobarbital.a, propranolol, etc.) were tested for a sustained release in different media (pH=1.2, 6.5, 7.4). Most of them # gave reasonable retarded release profiles for 8 hours when incorporated before the γ-irradiation crosslinking of PEO. While amphiphilic hydrogels were found to be suitable for hydrophobic solutes, the biodegradable PEO-based polyester ones affected predominantly the release of water-soluble drugs. No pH effect was found for the γ-irradiated PEO as a carrier in contrast to the strong pH dependence for the degradable polyester networks.     

Computer simulation of the liquid crystal formation in a semi-flexible polymer system

Molecular dynamic simulations are reported for system of semi-flexible linear rod-like molecules. The molecules are composed of N_c tangent soft spheres, connected by elastic springs. Rigidity is introduced by additional springs between all pairs of spheres along the molecule. The formation of only a nematic LC phase is shown for all systems with N_c = 8 and different flexibility. The effect of flexibility on the order parameter and the volume fraction at the LC phase transition is compared with theoretical predictions by Khokhlov-Semenov and with available simulation data. The dependence of the anisotropy of diffusion on chain flexibility in LC phase was studied. The polymer brushes consisting of flexible and semi-flexible (composed of linear rod-like segments) chains were simulated at different grafting densities. Height of brush, order parameter, distribution of density and chain ends in brush were obtained in both cases and compared with theoretical predictions.     

Structure,energy spectra and magnetic properties of poly(m-aniline)s

The energy spectra and magnetic properties of a large class of one-dimensional poly(m-aniline)s (PMA) and further model polymers are investigated theoretically. The band structure of those PMA's which are aza-analogs of the alternant non-classical (non-Kekulé) hydrocarbons (polymers) is characterized by a wide gap in which there is a narrow half-filled band (HFB). The different contributions to the effective spin exchange between the unpaired electrons in the HFB: Coulomb (Hund), kinetic and indirect exchange interactions are calculated. While it has been shown earlier that PMA exhibits a net spin exchange of ferromagnetic nature, this approach enables a detailed understanding of the influence of substituents on the nitrogen centers and changes in the aromatic bridging unit. The ferromagnetic nature of the spin coupling in the singly bridged PMA models therebye prevails independent of the structural changes. The HFB width of those PMA's which are derivatives (aza-analogs) of ladder-type non-alternant hydrocarbons is very large and the Wannier functions are delocalized. For this group of polymers the delocalized, non-magnetic state is favored and, therefore, they may be good candidates for testing electrical conduction.     

Nickel Poisoning of a Cracking Catalyst Unravelled by Single‐Particle X‐ray Fluorescence‐Diffraction‐Absorption Tomography

Ni contamination from crude oil in the fluid catalytic cracking (FCC) process is one of the primary sources of catalyst deactivation, thereby promoting dehydrogenation–hydrogenation and speeding up coke growth. Herein, single‐particle X‐ray fluorescence, diffraction and absorption (μXRF‐μXRD‐μXAS) tomography is used in combination with confocal fluorescence microscopy (CFM) after thiophene staining to spatially resolve Ni interaction with catalyst components and study zeolite degradation, including the processes of dealumination and Brønsted acid sites distribution changes. The comparison between a Ni‐lean particle, exposed to hydrotreated feedstock, and a Ni‐rich one, exposed to non‐hydrotreated feedstock, reveals a preferential interaction of Ni, found in co‐localization with Fe, with the γ‐Al₂O₃ matrix, leading to the formation of spinel‐type hotspots. Although both particles show similar surface zeolite degradation, the Ni‐rich particle displays higher dealumination and a clear Brønsted acidity drop.