Rheo-Optical Studies of Liquid Crystalline Solutions of Helical Polypeptides

The shear dependence of structures of liquid crystalline solutions of Poly-γ-benzyl-l-glutamate PBLG in m-cresol was examined in a polarizing microscope using a specially constructed shearing stage and stroboscopic illumination. Three different textures were observed depending on shear rate. The shear rates at which the texture changes occurred correlated well with the changes in sign of the first normal stress difference reported earlier.^1,2 The region of negative first normal stress difference corresponded to a texture consisting of striations perpendicular to shear.

The transverse striations were also observed to develop over a period of seconds or minutes after cessation of shear at rates within the first positive region of N ₁, These striations could be fixed in a dried film by using a volatile helicogenic solvent (1,4-dioxane).

A speculative model is proposed to account for the rheological observations in Refs.^1,2 and the rheo-optical observations reported herein.     

Living carbocationic copolymerization of isobutylene with styrene

The carbocationic copolymerization of isobutylene (IB) and styrene (St), initiated by 2‐chloro‐2,4,4‐trimethylpentane/TiCl₄ in 60/40 (v/v) methyl chloride/hexane at ?90 °C, was investigated. At a low total concentration (0.5 mol/L), slow initiation and rapid monomer conversion were observed. At a high total comonomer concentration (3 mol/L), living conditions (a linear semilogarithmic rate and M_n–conversion plots) were found, provided that the St concentration was above a critical value ([St]₀ ～ 0.6 mol/L). The breadth of the molecular weight distribution decreased with increasing IB concentration in the feed, reaching M_w/M_n ～ 1.1. St homopolymerization was also living at a high total concentration, yielding polystyrene with M_n = 82,000 g/mol, the highest molecular weight ever achieved in carbocationic St polymerization. An analysis of this system by both the traditional gravimetric–NMR copolymer composition method and FTIR demonstrated penultimate effects. IB enrichment was found in the copolymers at all feed compositions, with very little drift at a high total concentration and above the critical St concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1778–1787, 2007     

Lyapunov Pairs in Semilinear Differential Problems with State-Dependent Impulses

Set-Valued and Variational Analysis - The paper deals with semilinear differential inclusions with state-dependent impulses in Banach spaces. Defining a suitable Banach space in which all the...     

The existence of viable trajectories in state-dependent impulsive systems

Suitable topological tools for studying the existence of viable and periodic viable trajectories in state-dependent impulsive differential equations and inclusions are provided. Some results based on the Wa?ewski retract method are applied. The techniques presented in the paper are illustrated with several examples.     

Toward a Bioartificial Pancreas: Diffusion of Insulin and IgG Across Immunoprotective Membranes with Controlled Hydrophilic Channel Diameters

Research continued toward a bioartificial pancreas (BAP). Our BAPs consist of a perforated nitinol scaffold coated with reinforced amphiphilic conetwork membranes and contain live pancreatic islets. The membranes are assemblages of cocontinuous hydrophobic domains and hydrophilic channels whose diameters were varied by the MW of hydrophilic segments between crosslinks (M_c,HI = 32, 44, and 74 kg · mol^?1). We studied the diffusion rate of insulin, BSA, and IgG across the membrane of the BAP in the absence of islets. Membranes of M_c,HI = 74 kg · mol^?1 showed rapid insulin and BSA transport and negligible IgG diffusion. BAPs containing ≈300 mouse islets showed appropriate response upon glucose challenge in vitro. The BAP implanted into diabetic mice reduced hyperglycemia and maintained islet viability for at least 4 d.