Solid-State NMR Investigations of Molecular Dynamics in Polyphenylene Dendrimers: Evidence of Dense-Shell Packing

Autor:	Kay Saalwächter, Michael Wind, Uwe-Martin Wiesler, Hans Wolfgang Spiess, Klaus Müllen
Rok vydání:	2002
Předmět:	Range (particle radiation) Polymers and Plastics Chemistry Organic Chemistry Shell (structure) Activation energy Inorganic Chemistry Molecular dynamics Nuclear magnetic resonance Solid-state nuclear magnetic resonance Chemical physics Dendrimer Materials Chemistry Surface modification Spinning
Zdroj:	Macromolecules. 35:10071-10086
ISSN:	1520-5835 0024-9297
DOI:	10.1021/ma021283d
Popis:	We present solid-state NMR investigations of a series of shape-persistent polyphenylene dendrimers of generation 1−4 with different surface functionalization. Using a combination of traditional static and more advanced magic-angle spinning (MAS) exchange techniques for the elucidation of slow dynamics as well as fast-MAS recoupling techniques for the quantification of dynamic averaging in the megahertz range, we derive a clear picture of the complex molecular dynamics in these systems. Fast processes in the megahertz regime are shown to be restricted to fast vibrations of terminal phenyl rings with amplitudes of up to 40° at most, with a 5−30% fraction of rings performing larger-amplitude motions. Slow processes on the time scale of milliseconds to seconds are also restricted to terminal and doubly para-substituted phenyl rings. This type of motion is characterized by a two-site jump with a mean reorientation angle of 24° and a mean apparent activation energy of 34 kJ/mol and is presumably a concerted pro...
Databáze:	OpenAIRE
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