Synthesis of di-and triblock-copolymers of vinylic monomers in the presence of high molecular weight nitroxyl radicals formed in situ from N-tert-butyl-C-phenylnitrone

High molecular weight nitroxyl radicals formed directly in polymerization system (in situ) from N-tert-buiyl-C-phenylnitrone are efficient agents for the chain growth control and allow one to perform synthesis of di- and triblock-copolymers based on a number of vinylic monomers (styrene, methyl methacrylate, N-vinylpyrrolidone, and butyl acrylate) under more mild temperature regimes than their low molecular weight analogs. The macromolecular structures synthesized are characterized by GPC, NMR and IR spectroscopy, and MALDI TOF MS method.     

The structure of rare earth pyrosilicates

Summary An investigation of vibrational spectra of europium pyrosilicate with small additions of other rare earth metals and binary systems (R, R)₂Si₂O₇ confirms the assumption as to the change in the coordination state of cations and the reason for the existence of three structural types of rare earth metal pyrosilicates.The authors are deeply grateful to F. Ya. Galakhov for providing the specimens of silicates of the system (Y_1–x,Erx)₂Si₂O₇.     

Homotopy Theory of A∞ Ring Spectra and Applications to MU-Modules

We give a definition of a derivation of an A ring spectrum and relate this notion to topological Hochschild cohomology. Strict multiplicative structure is introduced into Postnikov towers and generalized Adams towers of A -ring spectra. An obstruction theory for lifting multiplicative maps is constructed. The developed techniques are then applied to show that a broad class of complex-oriented spectra admit structures of MU-algebras where MU is the complex cobordism spectrum. Various computations of topological derivations and topological Hochschild cohomology are made.     

Effect of Molecular Weight on Photoinduced Birefringence in a Chiral Liquid Crystalline Azodye Polymer

Summary: The evolution of the photoinduced birefringence in thin films of narrow polymer fractions is studied and compared with the behavior of the non‐fractionated polymer. The Δn_ind value decreases by increasing the degree of polymerization ( ) within the oligomeric range but becomes independent of molecular weight starting from a of ≈70. Thermal pretreatment of the films results in higher photoinduced birefringence. The films show good stability of the photorecording.

Birefringence induced after 10 min, Δn_ind(600) and its growth rate at the same moment versus molecular weight.