Intra- and inter-chain fluctuations in entangled polymer melts in bulk andconfined to pore channels

It is known that topological restraints by "chain entanglements" severely a ffect chain dynamics in polymer melts. In this field-cycling NMR relaxometr y and fringe-field NMR diffusometry study, melts of linear polymers in bulk and confined to pores in a solid matrix are compared. The diameter of the pore channels was 10 nm. It is shown that the dynamics of chains in bulk dr amatically deviate from those observed under pore constraints. In the latte r case, one of the most indicative signatures of the reptation model is ver ified 28 years after its prediction by de Gennes: The frequency and molecul ar mass dependencies of the spin-lattice relaxation time obey the power law T-1 proportional to M-0 nu(3/4) on a time scale shorter than the longest R ouse relaxation time tau(R). The mean squared segment displacement in the p ores was also found to be compatible to the reptation law < r(2) >proportio nal to M(-1/2)t(1/2) predicted for tau(R) < t < tau(d), where tau(d) is the so-called disengagement time. Contrary to these findings, bulk melts of en tangled polymers show frequency and molecular mass dependencies significant ly different from what one expects on the basis of the reptation model. The data can however be described with the aid of the renormalized Rouse theor y.