Rheological Properties of Linear and Branched Polyisoprene

W. W. Graessley, T. Masuda, E. L. Hoovers, Nikolaos Hadjichristidis

Research output: Contribution to journalArticlepeer-review

119 Scopus citations

Abstract

Viscosity η and first normal stress N1 have been measured as functions of shear rate γ for solutions of linear, four-arm star, and six-arm star polyisoprenes, all with narrow molecular weight distributions. Concentrations in tetradecane ranged from 0.02 g/ml to 0.33 g/ml; molecular weights ranged from 35 000 to 2 000 000. All measurements were made at 25 °C in a Weissenberg Rheogoniometer. The effects of branching on zero shear viscosity t)o, steady state compliance Je0, the characteristic shear rate (marking the onset of shear rate dependence in η) γ0, and the shape of the η vs. γ master curve were determined. At low concentrations and molecular weights the values of η0 and Je0 were lower for the branched samples, while at high concentrations and molecular weights the reverse became true and substantial enhancements in η and Je0 were found. On the other hand, the product η0Je0γ0 was essentially the same for all samples irrespective of concentration, molecular weight, or branching, and the form of the master curve appeared to be independent of branching. Enhancement factors were determined and compared with results reported by Kraus and Gruver on star-branched polybutadienes. Data on viscosity enhancement for the two polymers reduced to essentially the same curve when correlated in terms of Φ5/6(ΦMb/Mc), Φ being the volume fraction of polymer, Mb the molecular weight of the branches, and Mc the characteristic molecular weight for entanglement in the respective undiluted linear polymers. The form of this correlating parameter was arrived at by considerations on the effect of long branches on macromolecular mobility in entangling systems. The interpretation of enhancement in η0 and Je0 in relation to the spectrum of relaxation times and their practical effects on η vs. γ behavior are discussed.

Original languageEnglish (US)
Pages (from-to)127-141
Number of pages15
JournalMacromolecules
Volume9
Issue number1
DOIs
StatePublished - Jan 1 1976

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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