1,3,5‐Triamino‐1,3,5‐trideoxy‐cis‐inositol,a Ligand with a Remarkable Versatility for Metal Ions. Part XIII

The two neutral complexes [Re(CO)₃(H₋₁taci)] ( 1 ) and [ReO₃(H₋₁taci)] ( 2 ) (taci=1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol) were synthesized from the conventional Re^I and Re^VII precursors (Et₄N)₂[ReBr₃(CO)₃] and [ReO₃(OSnMe₃)]. The crystal structures of 1 and 2 , which were determined by single crystal X‐ray analysis, are virtually isomorphous. Both compounds crystallize in the orthorhombic space group Pnma, Z=4; 1 : a=14.806(3), b=8.466(2), c=9.781(2) Å, 2 : a=13.050(2), b=8.732(1), c=9.061(1) Å. In both complexes, the monodeprotonated H₋₁taci ligand is bonded to the Re center in an N,O,N‐coordination mode. The resulting molecular C_s symmetry is retained in the crystal structure and confirmed by IR spectroscopy of solid‐state samples. The observed binding mode of the ligand is discussed in terms of steric and electronic effects.     

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     

Epoxy‐functionalized,low‐glass‐transition‐temperature latex. II. Interdiffusion versus crosslinking in the presence of a diamine

This article describes the results of experiments examining the competition between the polymer diffusion rate and the crosslinking rate in low‐glass‐transition‐temperature, epoxy‐containing latex films in the presence of a diamine. We examined films formed from donor‐ and acceptor‐labeled poly(butyl acrylate‐co‐methyl methacrylate‐co‐glycidyl methacrylate) copolymer latex and studied the influence of several parameters on the growth rate of gel content and the rate of polymer diffusion. These factors include the molecular weight of the latex polymer, the presence or absence of a diamine crosslinking agent, and the cure protocol. The results were compared to the predictions of a recent theory of the competition between crosslinking and polymer diffusion across interfaces. In the initially formed films, polymer diffusion occurs more rapidly than the chemical reaction rate. Therefore, these films fall into the fast‐diffusion category of this model. In our system (unlike in the model), the latex polymer has a broad distribution of molecular weights and a distribution of diffusivities. The shortest chains contribute to the early time diffusion that we measure. At later stages of our experiment, slower diffusing species contribute to the signal that we measure. The diffusion time decreases substantially, and we observe a crossover to a regime in which the chemical reaction dominates. The increases in chain branching and gel formation bring polymer diffusion to a halt. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4098–4116, 2002     

Titanium‐Catalyzed Norbornene Oligomerization. Isolation of a Crystalline Heptamer with a 2,3‐exo‐Disyndiotactic Structure

Summary: Norbornene (NB) was oligomerized at 0 °C using AlEt₂Cl‐TiCl₄ at a monomer/titanium molar ratio of about 11. The oligomerization product consists of a fraction soluble in diethyl ether, amorphous by X‐ray examination, and of a crystalline fraction, insoluble in diethyl ether. The crystalline fraction was shown by powder X‐ray diffraction to consist of a NB heptamer. Single‐crystal X‐ray analysis indicated that the heptamer had a stereoregular 2,3‐exo‐disyndiotactic structure. The heptamer adopts a strained, highly irregular, folded conformation in the crystalline state. Structural differences with respect to NB oligomers obtained with zirconocene catalysts are discussed.

A view of the molecular structure of the crystalline NB heptamer.