Molecular dynamics of polymers by means of NMR field cycling relaxometry

The molecular dynamics of polymer melts and networks with molecular weight well above the critical value were studied based on a power law dependence of the NMR spin-lattice relaxation time (T1) as a function of the Larmor frequency, predicted by Kimmich and Fatkullin, which were developed from the renormalized Rouse formalism. Three different regions of power laws explaining the relaxation dispersion for the chain mode dynamics of polymer melts can be distinguished and have been observed experimentally over a range of molecular weights and temperatures for several types of polymer melts. In these studies, the T1 relaxation dispersions of polymer melts and networks were obtained over a wide range of frequencies and temperatures employing NMR field cycling relaxometry, and WLF master curves were reconstructed to describe the dispersion over more than nine orders of magnitude. Influences of chemical and physical constraints on the relaxation dispersion of polymers were investigated. This included the introduction of chemical cross-links and filler particles to produce elastomers, for which further constraints were imposed by mechanical deformation. As an alternative means to affect molecular mobility, investigations were also carried out for polystyrene-polybutadiene (PS-PB) copolymers. In all cases, the T1 relaxation dispersions directly reflect the molecular dynamics which were altered in different ways by the inflicted restrictions. Moreover, solvent induced molecular mobility in both polymer melts and networks were studied and additional experiments measuring the transverse relaxation rate and the dipolar coupling strength via double quantum encoding were conducted. The polymer networks used in these studies were natural rubber, butadiene rubber, and polydimethylsiloxane rubber samples. The results obtained here are interpreted based on the molecular dynamics described for the polyisoprene (PI), polybutadiene (PB), and polydimethylsiloxane (PDMS) melts of higher molecular weight (Mw > Mc), where only the physical entanglements are present. In terms of field cycling relaxometry, the power-law relations, which describe the chain mode dynamics for the polymer melts, were used to analyze the experimentally obtained data. The results obtained from the PI melts were somewhat different from those of the other polymers and, therefore, partially deuterated PI melts were investigated employing proton and deuteron experiments to elucidate whether the chemical structure or the intermolecular interaction play the significant role for this particular behavior.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2005

Author dc:creator

• Kariyo, Sobiroh

Contributors dc:contributor

• Stapf, Siegfried

• info:eu-repo/classification/ddc/540
• Chemie
• Polymerschmelze
• Polymeres Netzwerk
• Molekularbewegung
• Field-cycling
• NMR
• Relaxometry
• Elastomers
• Molecular Dynamics

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-121613%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:59868