The relationship between melt viscosity ή0 and molecular weight M for entangled linear polymers is accurately described by a power law,ή0 α M3.4, up to M/Me~ 150, where Meis the entanglement molecular weight. We have sought here to test the range of validity of that law by measurements on polymers with M/Meas large as practically possible. Anionic polymerization was used to prepare a series of narrow distribution polybutadienes with low vinyl content and molecular weights ranging from 1 × 103to 1.65 × 107(0.5 < M/M&< 8000). Several linear viscoelastic techniques were used to determine viscosities ranging from 1 × 10° P to 2 × 1012P. Significant departures from the 3.4 power law were found beyond M/Me~ 200. The results are consistent with an approach to M3dependence as suggested by reptation theory, but the scatter is too large to allow a definite conclusion. The apparent ή0/M3asymptote is within a factor of 2 of a prediction based on reptation theory, modified by the contributions of tube renewal. Additionally, a comparison was made of the monomeric friction coefficient obtained from viscosities at low molecular weight and from transition responses at high molecular weight. Values of the modulus shift factor bTwere obtained for an unusually wide range of temperatures and are briefly discussed.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry