Synthesis and physical properties of highly branched perfluorinated polymers from AB and AB2 monomers

Highly branched perfluorinated aromatic polyether copolymers were prepared from the polycondensation of the AB₂ monomer, 3,5‐bis[(pentafluorobenzyl)oxy]benzyl alcohol with a variety of fluoroaryl and alkyl bromide AB comonomers. The structures and comonomer distribution of the resulting polymers were characterized in detail. ¹H NMR data from kinetic trials illustrated that perfluoroaryl AB comonomer distribution correlated to AB comonomer sterics. ¹⁹F NMR data revealed that fluorinated AB monomers and 3‐bromo‐1‐propanol AB monomers were distributed within the AB₂ polymer backbone, while longer alkyl bromide AB monomers, 6‐bromo‐1‐hexanol, were mostly distributed along hyperbranched polymer chain ends. In general, as AB comonomer incorporation increased for nonsterically hindered copolymers, thermal decomposition onset increased and glass transition temperatures decreased. The combined data demonstrated the effect of comonomer distribution and sterics on physical properties of AB₂‐based polymer systems. The resulting materials were used to cast thin polymer films for measurement of contact angle, which were shown to be directly related to comonomer content. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1880–1894     

Chemical Composition and Microstructure of Plasma-Nitrided Aluminium

 Detailed examinations were made by AES depth profiling, SEM, TEM and electron diffraction to get information about the relation between treatment conditions and the state of plasma-nitrided aluminium. The chemical composition and the elemental depth distribution were proofed to be depending on gas phase mixture, pressure and temperature during plasma treatment. The admixture of hydrogen during presputtering for surface cleaning and during nitriding results both in an improved nitriding behaviour and in a reduction of the formation of conical-shaped particles at the surface. The microstructure of the nitride layer isn’t depending on tested process conditions significantly. Surface and interface between layer and substrate are roughly in a scale of a few ten nanometers owing to sputtering effects. The main phase inside the layer is nanocrystalline AlN of the known hexagonal modification. In addition, some crystallites of remaining aluminium are present as a second phase. In contrast to nitrogen-implanted aluminium no preferred lattice orientation of the AlN phase was evident.     

Membrane preparation from hyperbranched perfluorinated polymers

In this research, membrane formation with hyperbranched perfluorinated polymers (HBFP) was investigated. To create a tough membrane, HBFP was blended and crosslinked with a tougher linear polymer. Blending only or crosslinking only was not sufficient to create a tough membrane, but combining blending with crosslinking was successful. Miscibility, phase separation, and thermal and mechanical properties were evaluated for a variety of systems. By using a toughening linear polymer with lower polarity, reduced phase separation and improved mechanical properties were seen. Overall, imidazole‐containing HBFPs produced the clearest and toughest blends. These new hyperbranched ionomers and copolymers are strong candidates for future use in anhydrous proton exchange membranes. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 961–972     

Cooperative effects in restricted rotations of aryl groups in 2,4,6,8-tetraary-3,7-diazabicyclo[3.3.1]nonanes and related systems

The free energies, enthalpies and entropies of activation for the rotation of the aryl groups in the N,N′-dimethyl and N,N′-dichloro derivatives of rel-(2R,4S,6S,8R)-2,4,6,8-tetrakisaryl-3,7-diazabicyclo[3.3.1]nonanes have been determined and compared with related tricyclic systems which cannot undergo chair-to-boat conformational changes. It is concluded on the basis of the large, negative value of ΔS³ for rotation of the 2(4) aryl group that this rotational process is correlated with rotation of the 8(6) aryl group. The 8(6) aryl group can however rotate independently of the 2(4)-aryl group. The usefulness of the entropies of activation as a criterion for cooperative rotation of groups is briefly discussed.     

Lifting of the degeneracy in semibullvalenes by remote and direct substituents: a quantitative study using variable-temperature carbon-13 NMR spectroscopy

A series of six 1,5-(ethylmethyl)semibullvalenes (1a <==> 1a', 2 <==> 2', 3 <==>3') and two 4(2)-substituted semibullvalenes (4 <==> 4'), each undergoing Cope equilibria between nondegenerate valence tautomers, was investigated by carbon-13 NMR spectroscopy at a range of temperatures in several different solvents. Gompper's treatment of substituent perturbation was extended, specifically accounting for the effects of the substituents on chemical shifts, to allow the determination of the thermodynamic parameters for these skewed equilibria. These new treatments were used to determine the population difference (f - f ') between the valence tautomers and the perturbation thermodynamic quantities DeltaH(P), DeltaS(P), and DeltaG(P). The slow-exchange limit was reached for the parent 1,5-(ethylmethyl)semibullvalenes 3a <==> 3a' from which it was established that the preferred valence tautomer is 3a with the ethyl group on the cyclopropane ring. Despite considerable effort, the slow-exchange limit could not be reached in any of our other remotely substituted semibullvalenes. Provided that the ethyl group always prefers the cyclopropyl position as in 3a, the 1-ethyl-5-methylsemibullvalenes 1a, 2, and 3 are more stable by DeltaH(P) = 0.7-1.7 kJ mol(-1) than their valence tautomers 1a', 2', and 3'. In the directly substituted semibullvalenes (4 left harpoon ovet right harpoon 4'), the preferred valence tautomers 4a and 4b have the bromine atom or the nitrile group on the vinyl position (C(4)) rather than on the cyclopropane ring (C(2)) and are more stable than 4a' and 4b' by DeltaH(P) = 4.8 and 7.0 kJ mol(-1), respectively.