Arylene ether phosphine oxide homopolymers were prepared via nucleophilic aromatic substitution polycondensations of bis(4-ftuorophenyl)phenyl (or methyl) phosphine oxide with various aromatic bisphenols in the presence of a weak base and an aprotic dipolar solvent. These thermoplastic materials with Tg values in the range of about 200°C-285°C showed 5% weight loss in air around 500°C with substantial amounts of char yield at 800°C, which was related to their excellent' self-extinguishing characteristics relative to other engineering thermoplastics. Additionally, the presence of phosphorus in the char after such high temperature heating implied that these materials should also be resistant to aggressive oxygen plasma environments. Indeed, these systems showed extremely low amounts of etching in oxygen plasma when compared with other engineering polymers. The presence of phosphorus residues after either burning or etching with oxygen plasma could play crucial roles in areas of commercial importance and aerospace applications.

No abstract

An experimental demonstration has been given of the initiation of a vortex‐forming instability in sheets of charge by perturbations in the shape of the sheet. The net motion of charge along the sheet wherever the sheet is bent is shown to be related to displacement of the potential minimum in the sheet. These results suggest the existence of an instability in current sheets which also produces vortex forms. There is evidence that both of these instabilities result in the formation of vortexes in the aurora.

No abstract

No abstract