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. VIII. Polyurethanes with ‐O‐S‐PIB‐S‐O‐ soft segments

We describe the synthesis, characterization, and select properties of a novel polyurethane (PU) prepared using a new polyisobutylene diol, HO‐CH₂CH₂‐S‐PIB‐S‐CH₂CH₂‐OH, soft segment and conventional hard segments. The diol is synthesized by terminal functionalization of ally‐telechelic PIB followed by low‐cost thiol‐ene click chemistry. Properties of ‐S‐ containing PU (PIB_S‐PU) containing 72.5% PIB were investigated and compared to similar PUs made with HO‐PIB‐OH (PIB_O‐PU). Hydrolytic resistance was studied by contact with phosphate‐buffered saline, oxidative resistance by immersing in concentrated HNO₃, and metal ion oxidation resistance by exposure to CoCl₂/H₂O₂. Hydrolytic and oxidative resistances of PIB_S‐PU and PIB_O‐PU are similar and superior to a commercial PDMS‐based PU, Elast‐Eon? E2A. According to ¹H NMR spectroscopy the ‐S‐ in PIB_S‐PUs remained unchanged upon treatment with HNO₃, however, oxidized mainly to ‐SO₂‐ by CoCl₂/H₂O_2. Static mechanical properties of PIB_S‐PU and PIB_O‐PU are similar, except creep resistance of PIB_S‐PU is surprisingly superior. The thermal stability of PIB_S‐PUs is ～15 °C higher than that of PIB_O‐PU. FTIR spectroscopy indicates H bonded S atoms (N‐H…S) between soft and hard segments, which noticeably affect properties. DSC and XRD studies suggest random low‐periodicity crystals dispersed within a soft matrix. Energy dispersive X‐ray spectroscopy–scanning electron microscopy indicates homogeneous distribution of S atoms on PIB_S‐PU surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1119–1131     

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