Poly(phosphorodiamidate)s by Olefin Metathesis Polymerization with Precise Degradation

Degradable polymers are a currently growing field of research for biomedical and materials science applications. The majority of such compounds are based on polyesters and polyamides. In contrast, their phosphorus‐containing counterparts are much less studied, in spite of their potential precise degradation profile and biocompatibility. Herein, the first library of poly(phosphorodiamidate)s (PPDAs) with two P?N bonds forming the polymer backbone and a pendant P?OR group is prepared through acyclic diene metathesis polymerization. They are designed to vary in their hydrophilicity and are compared with the structural analogues poly(phosphoester)s (PPEs) with respect to their thermal properties and degradation profiles. The degradation of PPDAs can be controlled precisely by the pH: under acidic conditions the P?N linkages in the polymer backbone are cleaved, whereas under basic conditions the pendant ester is cleaved selectively and almost no backbone degradation occurs. The PPDAs exhibit distinctively higher thermal stability (from thermogravimetric analysis (TGA)) and higher glass transition and/or melting temperatures (from differential scanning calorimetry (DSC)) compared with analogous PPEs. This renders this exotic class of phosphorus‐containing polymers as highly promising for the development of future drug carriers or tissue engineering scaffolds.     

Local and non‐local ductile damage and failure modelling at large deformation with applications to engineering

The numerical analysis of ductile damage and failure in engineering materials is often based on the micromechanical model of Gurson [1]. Numerical studies in the context of the finite‐element method demonstrate that, as with other such types of local damage models, the numerical simulation of the initiation and propagation of damage zones is strongly mesh‐dependent and thus unreliable. The numerical problems concern the global load‐displacement response as well as the onset, size and orientation of damage zones. From a mathematical point of view, this problem is caused by the loss of ellipticity of the set of partial di.erential equations determining the (rate of) deformation field. One possible way to overcome these problems with and shortcomings of the local modelling is the application of so‐called non‐local damage models. In particular, these are based on the introduction of a gradient type evolution equation of the damage variable regarding the spatial distribution of damage. In this work, we investigate the (material) stability behaviour of local Gurson‐based damage modelling and a gradient‐extension of this modelling at large deformation in order to be able to model the width and other physical aspects of the localization of the damage and failure process in metallic materials.     

ChemInform Abstract: The Extended Stability Range of Phosphorus Allotropes.

A complete stability range of known and new crystalline allotropes of phosphorus including recently discovered tubular modifications and not‐yet‐known crystal structures of [P₁₂] nanorods, and not‐yet‐isolated [P₁₄] nanorods is given using quantum chemical DFT calculations.