Conical parametric scattering of a single extraordinary beam in BaTiO3 crystal

In this paper, the parametric scattering of a single extraordinary polarized beam of laser in BaTiO₃ photorefractive crystal has been investigated experimentally and theoretically. The resulting pattern consists of beam fanning, isotropic ring, and anisotropic one. Among all parts of scattering pattern, isotropic ring has not been studied as much as beam fanning and anisotropic ring, and there still are some differences in reports about it. Therefore, the study has mainly focused on this part. In this experimental configuration, isotropic ring is just visible in positive angles although the other parts of parametric scattering pattern can be visible from behind and in front of the crystal. In addition to steady state pattern in forward and backward directions, its transient behavior with the rotation of crystal has been studied. The results of experiments have been analyzed carefully, and their theoretical explanations have been presented based on the standard theory of parametric scattering in photorefractive crystals. It has been shown that this configuration corresponds to the so called parametric B-process scattering.     

Laboratoriumsapparate

Ohne Zusammenfassung     

Crossover in dynamics of polymeric liquids: Back to Tll?

Light scattering spectra of two polymers, polyisobutylene (PIB) and polystyrene (PS), were analyzed in the broad frequency range at temperatures above the glass transition (T_g ). At high temperatures, the spectra followed the qualitative scenario suggested by mode‐coupling theory (MCT) of the glass transition. The crossover temperature (T_c ) was defined to be approximately 1.35 T_g in PIB and approximately 1.15 T_g in PS. At lower temperatures (T < T_c ), the light scattering spectra deviated strongly from the idealized MCT scenario. Different signs of the dynamic transition around T_c are discussed. The difference between the suggested interpretation and an old idea of the liquid–liquid transition in polymeric liquids is stressed: we describe the transition as purely dynamic in nature. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2785–2790, 2000     

The cyclodimerisation of 3-methyl-2-butenenitrile

3-Methyl-2-butenenitrile (1) cyclodimerised on treatment with lithium diisopropylamide in dimethoxyethane at temperatures between ?78°C and 0°C to 3-amino-4-cyano-1,5,5-trimethyl-1,3-cyclohexadiene (2) the structure of which was established by acid hydrolysis to the known 4-cyano-1,5,5-trimethyl-1-cyclohexene-3-one (3).     

Conditions for deuterium exchange mediated by iridium complexes formed in situ

A series of iridium-based complexes formed in situ, containing pyridine, phosphines, triphenylarsine, triphenylstibine, and triphenylamine as ligands, has been screened for ability to mediate ortho-exchange of hydrogen in a series of model substrates. Improved incorporation into a number of substrate classes has been achieved. The electronic properties and number of ligands at the metal centre are instrumental in determining which catalysts are best suited to exchange in any given substrate.     

Recent advances in the anionic synthesis of chain-end functionalized polymers

Recent results for the preparation of chain-end functionalized polymers using alkyllithium-initiated anionic polymerization are described. Termination with 4-chloro-1,1,1-trimethoxybutane has been used to prepare trimethoxy ortho ester (carboxyl)-functionalized polymers. Functionalization with the oxiranes, glycidoxypropyltrimethoxysilane, 3,4-epoxy-1-butene and 1,1,1-trifluoro-2,3-epoxypropane, has been investigated to prepare trimethoxysilyl-functionalized polymers, 1,3-diene-functionalized macro monomers and trifluoromethyl-functionalized polymers, respectively. Secondary amine-functionalized polymers have been prepared by termination with N-(benzylidene)methylamine and also using an N-benzyl tertiary amine-functionalized alkyllithium initiator followed by hydrogenolysis of the benzyl group.