From a simple liquid to a polymer melt: NMR relaxometry study of polybutadiene.
We utilize NMR field cycling relaxometry to study the crossover from glassy dynamics (t approximately > tau alpha) through Rouse to reptation behavior in a series of monodisperse polybutadienes with molecular weights M=355 to 817,000 g/mol. We separate characteristic polymer dynamics from the total spectrum dominated by glassy dynamics. The polymer dynamics show typical Rouse relaxation features that grow with M and saturate at high M. Comparing to Rouse theory, we determine the Rouse unit size MR approximately = 500 and entanglement weight Me approximately = 2000; the Rouse spectrum saturates at Mmax approximately = 4000. The local order parameter S approximately 0.11 is relatively large, indicating noticeable local packing already in the Rouse regime. The M dependence of the glass transition temperature Tg, obtained from dielectric relaxation spectra, shows distinctive kinks at MR and Me.
Kariyo
S
S
Experimentalphysik II, Universität Bayreuth, D-95440 Bayreuth, Germany.
Gainaru
C
C
Schick
H
H
Brodin
A
A
Novikov
V N
VN
Rössler
E A
EA