Click construction of spiro- and bridged-quatrefoil polymer topologies with kyklo-telechelics having an azide group.
Unprecedented tetracyclic polymer topologies with spiro- and a bridged-type quatrefoil forms are effectively constructed through an alkyne-azide, click-linking reaction by employing a kyklo-telechelic poly(tetrahydrofuran), poly(THF), precursor having an azide group, obtained through an electrostatic self-assembly and covalent fixation (ESA-CF) process, and complementary tetrafunctional alkyne reagents of either a pentaerythritol derivative or a four-armed star telechelic polymer precursor.
Modular construction of macrocycle-based topological polymers via high-efficient thiol chemistry
Modular and precise construction of topological polymers with structural complexity is a prerequisite to understand the structure-property relationships of functional non-linear macromolecules. In this article, several examples of well-defined topological polymers are prepared by using two kinds of functionalized cyclic polymeric precursors via different high-efficient thiol-related chemistries. Firstly, multifunctional atom transfer radical polymerization (ATRP) initiators bearing alkyne and disulfide groups were elaborately prepared. Well-defined thiol-containing monocyclic and fused-bicyclic polymers via ATRP and Cu-catalyzed azide–alkyne cycloaddition (CuAAC) ring closure were then synthesized. Finally, by the utilization of thiol-containing monocyclic or fused-dicyclic polymers as building blocks, several kinds of macromolecules with tadpole-, spiro-shaped, fused-dicyclic tadpole and other topologies were successfully constructed via a modular mode. This study expands the scope of available macrocycle-based topological polymers and facilitates further diverse development of even more complex non-linear macromolecules via modular synthetic methodology.
Nuclear spin-lattice relaxation in transition metal compounds with local tetragonal symmetry.
We report on the various contributions to the total spin-lattice relaxation rate in metallic materials with local tetragonal symmetry. The analytical formulae are given in the tight-binding approximation. The calculations show the relation between various partial electron densities of states and corresponding contributions to the relaxation rates. The presented formulae can be used to compare theoretically calculated electron band structure parameters with those obtained from NMR spin-lattice relaxation time measurements.