Bioabbaubare, amorphe Copolyesterurethannetzwerke mit Formgedächtniseigenschaften

Sustainable Shape-Memory Polyurethane from Abietic Acid: Superior Mechanical Properties and Shape Recovery with Tunable Transition Temperatures

A new chemical architecture from abietic acid, consisting of a cycloaliphatic unsaturated terminal diisocyanate (AADI) structure, is synthesized and fully characterized. The AADI is then used to construct an amorphous and biocompatible shape-memory polyurethane (SMPU) network system with adjustable cross-linking densities over a wide range. The SMPU network exhibits good shape-memory properties with a shape fixing rate of greater than 98 % and a shape recovery rate of 95 %. In vitro hydrolytic biodegradation weight loss ratio of SMPUs reaches 71 % within eight weeks. The physical properties of these SMPUs are comparable to those reported for SMPUs obtained from commercially available petroleum-derived diisocyanates. This is the first time that multiple SMPU networks based on abietic acid have been reported. These environmentally-friendly SMPUs display a wide range of physicomechanical properties with promising hydrolytic degradability, showing good potential for practical application.

Why Are BINOL-Based Monophosphites Such Efficient Ligands in Rh-Catalyzed Asymmetric Olefin Hydrogenation?

Whereas recent synthetic studies concerning Rh-catalyzed olefin hydrogenation based on BINOL-derived monodentate phosphites have resulted in an efficient and economically attractive preparative method, very little is known concerning the source of the unexpectedly high levels of enantioselectivity (ee often 90-99%). The present mechanistic study, which includes the NMR characterization of the precatalysts, kinetic measurements with focus on nonlinear effects, and DFT calculations, constitutes a first step in understanding this hydrogenation system. The two most important features which have emerged from these efforts are the following: (1) two monodentate P-ligands are attached to rhodium, and (2) the lock-and-key mechanism holds, in which the thermodynamics of Rh/olefin complexation with formation of the major and minor diastereomeric intermediates dictates the stereochemical outcome. The major diastereomer leads to the favored enantiomeric product, which is opposite to the state of affairs in classical Rh-catalyzed olefin hydrogenation based on chiral chelating diphosphines (anti lock-and-key mechanism as proposed by Halpern).