A series of segmented polyurethanes was prepared from the new commercial product KRASOL LBH (linear liquid polybutadiene terminated with secondary hydroxy groups), aromatic diisocyanates, and an aliphatic low-molecular-weight diol. Three types of networks were prepared, with the nature of the crosslinks varied from purely chemical to physical, with a continuous transition to "combined" networks containing both crosslink types. Potassium 2-ethyl hexanoate was used as a catalyst of the in situ formation of trifunctional isocyanurate groups (by cyclotrimerization of isocyanate groups). It was confirmed that mechanical, thermal, and swelling properties are considerably influenced by the ratio of chemical to physical crosslink concentration. The best balance of stressstrain properties was obtained for "combined" networks at a NCO-OH molar ratio of 1.10 when only a few chemical crosslinks are present in predominantly physically crosslinked networks. The presence of thermally stable isocyanurate groups mainly influences the storage shear modulus at elevated temperatures. Small-angle X-ray scattering confirmed the two-phase structure of polyurethanes with a periodicity of 6 -8 nm.
Two poly(amino acid) systems were studied: (a) poly[N5‐(2‐hydroxyethyl)‐L‐glutamine] (PHEG) derivatives prepared by NCA polymerization; (b) poly‐α,β‐[N‐(2‐hydroxyethyl)‐DL‐aspartamide] (PHEA) derivatives prepared by thermal polycondensation of aspartic acid to racemic polysuccinimide followed by chemical modification reactions. The degradation of polymers by isolated enzymes and homogenate of kidney tissue was studied in vitro and the effect of polymer structure on the rate of degradation and the size of degradation products was evaluated. A PHEA derivative (modified by tyramine residues in 9.6 % of side chains) was accumulated in the lysosomes of kidney cells of rats and the molecular‐weight distribution of the polymer retained inside the lysosomes of living cells and that of the polymer excreted into urine was analysed by a high‐sensitivity size‐exclusion chromatography using the fluorescence and radioactive labelling. While PHEG derivatives were degraded by isolated mammalian enzymes and a tissue homogenate, no significant degradation of PHEA and derivatives was observed, either in vitro, with isolated enzymes and homogenate or in vivo, under a long‐term exposure to the lysosomal enzymes in living cells.
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