Water‐soluble acrylamide copolymers. VIII. Preparation and characterization of polyacrylamide‐co‐N‐t‐butylacrylamide

The preparation of a series of copolymers of N‐t‐butylacrylamide (NTBAM) with acrylamide (AM) is reported. The insolubility of NTBAM in water led to the testing of methanol, t‐butanol, and mixtures of these solvents with water to obtain effective copolymerization. Several of these polymerizations produced nonhomogeneous product mixtures. Samples of the components were separated and characterized by photoacoustic Fourier transform infrared spectroscopy and ¹³C NMR spectroscopy. Hydrodynamic volumes of the products were obtained from solution‐viscosity measurements, gel permeation chromatography, and multi‐angle laser light scattering methods. The NTBAM‐co‐AM copolymers had degrees of polymerization and molecular weights in the 4.1–5.9 × 10⁴ monomer units and 3.25–4.5 × 10⁶ g/mol range, respectively. They contained from 15 to 36 mol % NTBAM. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 1960–1977, 2001     

Polyisobutylene‐based polyurethanes. V. Oxidative‐hydrolytic stability and biocompatibility

The oxidative/hydrolytic stability of polyurethanes (PUs) containing exclusively polyisobutylene (PIB), or mixed PIB/polytetramethylene oxide (PTMO), or mixed PIB/polyhexamethylene carbonate (PC) soft segments was investigated. The tensile strengths and elongations of various PUs were determined before and after agitating in 35% HNO₃ or 20% H₂O₂/0.1 M CoCl₂ solutions and retentions were quantified. The presence of PIB imparts significant oxidative/hydrolytic resistance. The tensile strength and elongation of PUs containing 70% PIB, or those of mixed PIB/PC soft segments with 50% PIB, remained essentially unchanged upon exposure to HNO₃; in contrast, PUs containing mixed PIB/PTMO soft segments with 50% PIB underwent significant degradation. The tensile strength of PUs with mixed PIB/PC (60/10%) soft segment increased after exposure to HNO₃, most likely because of oxidative crosslinking of PC segments. PIB/PTMO‐ and PIB/PC‐based PUs and commercially available PUs (Elast‐Eon® and Carbothane®) were exposed to H₂O₂/CoCl₂ solutions for up to 14 weeks. Although the experimental PIB/PC‐based PUs exhibited negligible change in mechanical properties and no surface damage, Elast‐Eon® and Carbothane® showed significant surface damage. PIB‐based polyureas and Bionate® were implanted in rats for 4 weeks in vivo, and their biocompatibility was investigated. The biocompatibility of PIB‐based materials was superior to Bionate®. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2194–2203, 2010     

Strain‐induced crystallization and strength of elastomers. I. cis‐1,4‐polybutadiene

Crosslinked samples of cis‐1,4‐polybutadiene (BR) were crystallized at low temperatures and then slowly melted. From volume changes and differential scanning calorimetry measurements, the degree of crystallization in the unstrained state was estimated to be about 20%, much lower than for natural rubber (NR). Crystallization and melting were followed in stretched samples by corresponding changes in tensile stress. Crystallization was faster at higher strains, and the melting temperature was raised significantly on stretching but less than for NR, and the decrease in stress on crystallizing was smaller. Measurements of tensile strength were made over a wide temperature range and showed a marked drop with heating to temperatures of 40–60 °C, falling to values of only 1–2 MPa. A similar drop in strength occurred in NR vulcanizates at high temperatures and was attributed to failure to crystallize on stretching (A. G. Thomas & J. M. Whittle, Rubber Chem Technol 1970, 43, 222; A. N. Gent, S. Kawahara & J. Zhao, Rubber Chem Technol 1998, 71, 668). At ambient temperatures, where strain‐induced crystallization occurred, the strength of BR samples was only about one‐half of that of similar NR materials. This was attributed to less strain‐induced crystallinity in BR (verified by X‐ray studies), paralleling the lower amount developed at low temperatures. We speculate that the higher density of molecular entanglements in BR than in NR prevents BR from crystallizing to the same degree as NR. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 811–817, 2001     

Azulene‐substituted pyridines and pyridinium salts. Synthesis and structure. 1. Azulene‐substituted pyridines

4‐Azulen‐1‐yl substituted 2,6‐dimethyl‐and 2,6‐diphenyl‐pyridines are obtained in good yields from the reaction of corresponding 4‐azulen‐1‐yl‐pyranylium salts and ammonium acetate in ethanol or starting from 4‐chloro‐2,6‐diphenyl‐pyranylium salts in two steps: reaction with azulenes followed by in situ treatment with ammonium acetate. The effect of substitution at the 3‐position of the heterocycle was taken into account. The structure assignment was accomplished with NMR and uv‐vis spectra.     

Azulene‐substituted pyridines and pyridinium salts. Synthesis and structure. 2. Azulene‐substituted pyridinium salts

4‐Azulen‐1‐yl substituted 2,6‐dimethyl‐and 2,6‐diphenyl‐pyridinium salts are obtained in yields between 50 % and 100 % in the reaction of corresponding 4‐azulen‐1‐yl‐pyranylim salts and various amines. The effects of amine structure and of substitution in the heterocycle or at azulene moieties on the synthesis have been investigated. The uv‐vis and NMR spectra of reaction products are examined and discussed in correlation with their structure.