The application of microwave irradiation in polymer syntheses and modifications is of continuously growing interest and has received significant international interest since the beginning of the millennium. Preceded by a review that was published 6 years ago, the present paper summarizes the most recent trends in this research area. Radical as well as step-growth and ring-opening polymerizations will be addressed; furthermore, the evolution from microwave-assisted polymerizations to microwave-assisted material fabrication will be described on the examples of polymeranalogous reactions, polymer/metal composites and bio-based materials.

In this work, the effect of surface roughness and cleaning procedures on reactivity during priming with hexamethyldisilazane is described for four silicon substrates frequently used in semiconductor technology, namely thermally grown SiO 2 , argon implanted tetraorthosilicate SiO 2 , polysilicon, and amorphous silicon. Surface energy and roughness were determined by static contact angle measurements and atomic force microscopy. The surface roughness of the silicon substrates increased in the order: thermally grown SiO 2 , argon implanted tetraorthosilicate SiO 2 , polysilicon, and amorphous silicon. It was found not to be substantially affected by standard cleaning procedures. The surface energy of all silicon samples decreased with increasing hexamethyldisilazane vapor exposure at 90°C, and the extent of the decrease corresponded to the surface roughness. Furthermore, a promoting effect on the silylation reaction by an argon implantation process was determined. A correlation between the surface morphology of different silicon materials and reactivity in the silylation reaction with hexamethyldisilazane could be established.

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The inventory of the single-crystal X-ray structures of aliphatic and aromatic 2-oxazolines, namely 2-nonyl-2-oxazoline, 2,2tetramethylenebis(2-oxazoline) and 2-phenyl-2-oxazoline, reveals significant delocalization of π -electrons along the N-C-O segment. The delocalization of π -electrons is stabilized by inductive and resonance contributions of the side-chains; in 2phenyl-2-oxazoline, also π-arene interactions between the benzene ring and the C-N and the C-O bond stabilize the crystalline phase. This delocalization gives a partial negative charge to the nitrogen atom and a partial positive charge to the oxygen atom. The partial negative charge of the nitrogen atom makes this atom the exclusive reaction partner also for highly reactive non-selective cations, which explains the regioselectivity of electrophilic attacks in cationic ring-opening polymerizations. Scheme 1. Representation of the preparation of 2-oxazolines from the reaction of nitriles with ethanol-2-amines.2-amino-2-oxazolines, where π -electron delocalization could neither be separated from the involvement of the S and N heteroatoms nor attributed to the C-N-O segment itself. 31 -33 In the example of β-keto oxazolines, which were crystallized as enaminones, πelectron delocalization involving the C-O bond was observed, but again could not be referred to the tautomeric 2-oxazolines. 34 The key incentive of this work was to determine the crystal structure of 2-oxazolines bearing aliphatic and aromatic heteroatom-free substituents, in order to elucidate the contribution of the π-electron delocalization to the binding situation in 2-oxazoline rings.

Anhydrous thallium hydrogen L-glutamate [Tl(L-GluH)] crystallizes from water (space group P2(1)) with a layer structure in which the thallium ions are penta- and hexacoordinated exclusively by the oxygen atoms of the γ-carboxylate group of the hydrogen L-glutamate anions to form a two-dimensional coordination polymer. The thallium-oxygen layer is composed of Tl(2)O(2) and TlCO(2) quadrangles and is only 3 Å high. Only one hemisphere of the thallium ions participates in coordination, indicative of the presence of the 6s(2) lone pair of electrons. The thallium-oxygen assemblies are shielded by the hydrogen l-glutamate anions. Only the carbon atom of the α-carboxylate group deviates from the plane spanned by the thallium ions, the γ-carboxylate groups and the proton bearing carbon atoms, which are in trans conformation. Given the abundance of L-glutamic and L-aspartic acid in biological systems on the one hand and the high toxicity of thallium on the other hand, it is worth mentioning that the dominant structural motifs in the crystal structure of [Tl(L-GluH)] strongly resemble their corresponding analogues in the crystalline phase of [K(L-AspH)(H(2)O)(2)].