Irreversible helix rearrangement from Cis‐transoid to Cis‐cisoid in poly(p‐n‐hexyloxyphenylacetylene) induced by heat‐treatment in solid phase

Polymerization of p‐n‐hexyloxyphenylacetylene (pHPA) by using a [Rh(norbornadine)Cl]₂‐triethylamine catalyst was carried out at room temperature to afford stereoregular helical poly(p‐n‐hexyloxyphenylacetylene)s (PpHPAs). When ethanol and n‐hexane were used as polymerization solvents, a bright yellow PpHPAs, poly( Y ) with M_n = 8.5 × 10⁴ and its purple red polymer, poly( R ) with M_n = 5.3 × 10⁴ were obtained in 95% yields and 84% yields, respectively. Diffuse reflective UV–vis spectra of poly( Y ) and poly( R ) in solid phase showed different broad absorption peaks at 445 and 575 nm, respectively. X‐Ray diffraction patterns of poly( Y ) and poly( R ) showed typical columnar structures assignable to cis‐transoid and cis‐cisoid structures, respectively, which were also supported by molecule mechanics calculation. Poly( Y ) was irreversibly transformed to a reddish‐black polymer, poly( Y‐B ), which columnar diameter was nearly the same as that of poly( R ). Further, poly( Y ) showed an exothermic peak in the differential scanning calorimetry trace at 80 °C for 1 h in N₂ gas. Thus, these findings suggest a thermally irreversible rearrangement from an unstable cis‐transoid form, poly( Y ) with a stretched cis‐transoid helix to a stable cis‐cisoid form, poly( R ), with a contracted cis‐cisoid helix in the solid phase to give poly( Y → B ) with the cis‐cisoid form. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Production of core/shell polystyrene/poly(3,5-xylidine) composite particles by chemical oxidative seeded dispersion polymerization

Micron-sized monodispersed polystyrene (PS)/poly(3,5-xylidine) (PXy) composite particles were produced by chemical oxidative seeded dispersion polymerization of 3,5-xylidine at 20 °C with 1.6-μm-sized monodispersed PS seed particles in HCl aqueous solution, the pH of which was always kept at 2.5 with a pH stat. The composite particles produced consisted of a PS core and a PXy shell. Received: 16 December 1998 Accepted in revised form: 25 March 1999     

Anionic polymerization of methacrylates by samarium (III) enolate on networked polystyrene: Effects of its sterically confined environment on polymerization behavior

Anionic polymerization of methacrylates under sterically confined environment in a spherical beads‐shaped networked polystyrene (NwPS) matrix is described. The initiator used herein is a samarium (Sm) (III) enolate, which was formed by treatment of 2‐bromoisobutylate immobilized in the side chain of NwPS with Sm (II) iodide. By using this NwPS‐bound initiator, polymerization of a series of methacrylates (=solid‐supported polymerization) was studied to find its two aspects: (1) In the early stages, the rate constant for each methacrylate was comparable to that for its conventional solution‐phase polymerization using a Sm (III) enolate, suggesting that methacrylate can be efficiently supplied to the propagating end by its free permeation without any interference by the networked structure of the matrix. (2) After the early stages, the rate constant decreased remarkably, implying that permeation of methacrylate was sterically interfered by the formed poly(methacrylate) that filled the confined space in NwPS, as supported by a SEM image of the resulting beads, of which pores were filled with the formed polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1510–1521, 2009     

New Magneto-Optical Effect in Co-Doped CuGeO3

We report the anomalous effect of the polarization dependence of electron paramagnetic resonance absorption in CuGeO₃ doped with 2% of Co. While the resonance line of Cu²⁺ chains is independent of the microwave polarization in the Faraday geometry, the resonant mode of Co impurity exhibits a strong polarization dependence for all directions of the external magnetic field. Possible reasons of such behavior are discussed. Authors' address: Alexey V. Semeno, Department of Low-Temperature and Cryogenic Engineering, A. M. Prokhorov General Physics Institute, Russian Academy of Sciences, Vavilov ulitsa 38, Moscow 119991, Russian Federation     

Dissipative crystallization of aqueous solutions of hydroxypropyl cellulose

Drying dissipative structures of aqueous solutions of hydroxypropyl cellulose, their viscosities of 2 wt.% solutions ranging from 2 to 2,000 mPa.s were studied on a cover glass, a watch glass, and a Petri glass dish. The thickness profile of the dried film shows the coexistence of a low round hill and a high broad ring on a cover glass. The broad ring size increased as molecular weight and/or concentration of the polymers increased on a cover glass and a watch glass. Microscopic drying crystal patterns of HPC changed as a function of the distance from the film center, which is one of the typical results of the dissipative crystallization. Rod-like microscopic drying patterns originated in the cholesteric liquid crystalline structures were observed. The rods oriented mainly parallel and in some case perpendicularly to the radial direction of the dried film except the central area, where the rods distributed at random. These orientation effects were significant for low molecular weight samples and in a watch glass.     

Dissipative crystallization of sodium salt of deoxyribonucleic acid

Drying patterns of aqueous solutions of sodium salt of deoxyribonucleic acid (NaDNA) were studied on a cover glass, a watch glass, and a Petri glass dish at room temperature. Orientation of the rod-like single crystals of NaDNA molecules in the radial direction was observed especially at low polymer concentrations. The ratios of the size of the broad ring against initial size of the liquid on a cover glass and a watch glass were very small between 0.05 and 0.1 compared with those of the typical polyelectrolytes. Main cause is the compact conformation of NaDNA forming single or double stranded helix structures in the dried film. Microscopic drying patterns were long rods accompanied with the many short rods especially on a cover glass. Thick and short rods and dendritic crystals were fogrmed at the inward and outward areas of the dried films, respectively, on a watch glass and a Petri glass dish. Rod-like and dendritic crystals resembled the distorted hedrite and/or spherulite structures. Dissipative crystallization such as the orientation and accumulation of the single crystals of NaDNA were observed and the importance of the convectional and sedimentation processes was demonstrated during the course of crystallization.