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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 9: Crystallization and Self Assembly II
CPP 9.7: Vortrag
Montag, 22. März 2010, 15:30–15:45, H48
Local and Collective Motions in Polyolefins with Precise Alkyl Branches: a Solid State NMR Study — •Robert Graf1, Yuying Wei2, Kenneth B. Wagener2, and Hans Wolfgang Spiess1 — 1Max-Planck-Institut für Polymerforschung, Mainz, Germany — 2University of Florida,Gainesville, Florida (USA)
In linear polymers, such as polyethylene (PE), chain branches change the local mobility and have pronounced effects on the mechanical properties, such as processablity and drawability. In many previous studies, the irregular distribution of the branching sites along the main chain caused an uncertainty of the branching influence on morphology, chain dynamics, as well as other physical properties. Here results from investigations of dynamic processes in crystalline regions of PE samples with regular spaced methyl branches. By deuteration of the methyl branches, the molecular dynamics of the defect site can be studied selectively via 2H NMR methods, whereas molecular reorientations of the polymer chain between the branching sites can be monitored separately via 13C chemical shift anisotropy measurements. Combining these results with studies of local conformations, a twist motion can be identified, which is localized at the branching sites for a spacing of more than twenty CH2 units between subsequent branching points. In methyl branched PE samples with shorter spacing, a collective dynamic process can emerge from this twist motion, which ultimately leads to the formation of a rotator phase.