Thermoplastic elastomers: structural and morphological aspects of ether-esteramide copolymers

Polyesteramide 6NT6 (I)-polytetramethylene ether glycol (II) copolymers, pptd. from dil. soln. were studied by small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) with variation of the II content. A comparison of the structural characteristics of these materials was made with those of I, which consists of -CO-p-C6H4CONH(CH2)6NHCO-p-C6H4CO2(CH2)6O- units. Chain folding is assumed as the crystn. mechanism for the low-II content copolymers, with possible inclusion of polyether segments within the I crystal lattice. WAXS data support the view of a weakening of the I cryst. packing in the equatorial planes as the reason for broadening of the diffraction peaks, for changes in their relative intensities, and for the increase in the equatorial interplanar distances in the high-II content samples. The annealing behavior was investigated

Different aspects of solvent engineering in lipase catalysed esterifications

A microbial lipase from Pseudomonas sp., immobilized on an ACR-silica gel, has been used as catalyst for esterification reactions in organic solvents which were largely different in some fundamental physico-chemical characteristics. The results obtained were compared with the same reactions carried out in supercritical carbon dioxide. Significant variations in conversion values as function of log Pmow of the solvent (dielectric constants and Hildebrand solubility parameters not providing consistent results) seem to demonstrate the importance of the enzyme-water content on the mechanism of action as in terms of conformations arrangements as well as in terms of substrates partition equilibrium with the polar matrix. Differently, the conversions and enantioselectivity of the reactions in the supercritical fluid, always higher than in organic solvents, could be attributed to the specific properties of the medium in terms of low viscosity and surface pressure values and higher diffusivity of substrates in the supercritical phase