Sorbitol–POSS Interactions on Development of Isotactic Polypropylene Composites

This study investigates the nature of interactions between the molecules of polyhedral oligomeric silsesquioxane (POSS) containing silanol functionalities (silanol–POSS) and di(benzylidene)sorbitol (DBS) encountered in the development of nanocomposite fibers from the compounds of POSS, DBS, and isotactic polypropylene (iPP). The interactions were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and oscillatory shear rheology. Mass and NMR spectrometry revealed that the molecules of silanol–POSS and DBS formed several amorphous noncovalent molecular complexes promoted by hydrogen bonding. More abundant complex formation was observed with silanol–POSS molecules carrying four silanol groups and phenyl substitutions. Such complex formation deterred fibrillation of DBS when the compounds of iPP, DBS, and silanol–POSS were cooled from homogeneous melt states. It was also revealed that POSS–DBS complexes were of much lower viscosity than iPP

Group 13 Superacid Adducts of [PCl₂N]₃

Irrespective of the order of the addition of reagents, the reactions of [PCl₂N]₃ with MX₃ (MX₃ = AlCl₃, AlBr₃, GaCl₃) in the presence of water or gaseous HX give the air- and light-sensitive superacid adducts [PCl₂N]₃·HMX₄. The reactions are quantitative when HX is used. These reactions illustrate a Lewis acid/Brønsted acid dichotomy in which Lewis acid chemistry can become Brønsted acid chemistry in the presence of adventitious water or HX. The crystal structures of all three [PCl₂N]₃·HMX₄ adducts show that protonation weakens the two P–N bonds that flank the protonated nitrogen atom. Variable-temperature NMR studies indicate that exchange in solution occurs in [PCl₂N]₃·HMX₄, even at lower temperatures than those for [PCl₂N]₃·MX₃. The fragility of [PCl₂N]₃·HMX₄ at or near room temperature and in the presence of light suggests that such adducts are not involved directly as intermediates in the high-temperature ring-opening polymerization (ROP) of [PCl₂N]₃ to give [PCl₂N]_n. Attempts to catalyze or initiate the ROP of [PCl₂N]₃ with the addition of [PCl₂N]₃·HMX₄ at room temperature or at 70 °C were not successful

Group 13 Superacid Adducts of [PCl₂N]₃

Irrespective of the order of the addition of reagents, the reactions of [PCl₂N]₃ with MX₃ (MX₃ = AlCl₃, AlBr₃, GaCl₃) in the presence of water or gaseous HX give the air- and light-sensitive superacid adducts [PCl₂N]₃·HMX₄. The reactions are quantitative when HX is used. These reactions illustrate a Lewis acid/Brønsted acid dichotomy in which Lewis acid chemistry can become Brønsted acid chemistry in the presence of adventitious water or HX. The crystal structures of all three [PCl₂N]₃·HMX₄ adducts show that protonation weakens the two P–N bonds that flank the protonated nitrogen atom. Variable-temperature NMR studies indicate that exchange in solution occurs in [PCl₂N]₃·HMX₄, even at lower temperatures than those for [PCl₂N]₃·MX₃. The fragility of [PCl₂N]₃·HMX₄ at or near room temperature and in the presence of light suggests that such adducts are not involved directly as intermediates in the high-temperature ring-opening polymerization (ROP) of [PCl₂N]₃ to give [PCl₂N]_n. Attempts to catalyze or initiate the ROP of [PCl₂N]₃ with the addition of [PCl₂N]₃·HMX₄ at room temperature or at 70 °C were not successful

Structure and Conformation of the Medium-Sized Chlorophosphazene Rings

Medium-sized cyclic oligomeric phosphazenes [PCl₂N]_<i>m</i> (where <i>m</i> = 5–9) that were prepared from the reaction of PCl₅ and NH₄Cl in refluxing chlorobenzene have been isolated by a combination of sublimation/extraction and column chromatography from the predominant products [PCl₂N]₃ and [PCl₂N]₄. The medium-sized rings [PCl₂N]_<i>m</i> have been characterized by electrospray ionization–mass spectroscopy (ESI-MS), their ³¹P chemical shifts have been reassigned, and their T₁ relaxation times have been obtained. Crystallographic data has been recollected for [PCl₂N]₅, and the crystal structures of [PCl₂N]₆, and [PCl₂N]₈ are reported. Halogen-bonding interactions were observed in all the crystal structures of cyclic [PCl₂N]_<i>m</i> (<i>m</i> = 3–5, 6, 8). The crystal structures of [P­(OPh)₂N]₇ and [P­(OPh)₂N]₈, which are derivatives of the respective [PCl₂N]_<i>m</i>, are also reported. Comparisons of the intermolecular forces and torsion angles of [PCl₂N]₈ and [P­(OPh)₂N]₈ with those of three other octameric rings are described. The comparisons show that chlorophosphazenes should not be considered prototypical, in terms of solid-state structure, because of the strong influence of halogen bonding