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Rheologica Acta

, Volume 33, Issue 3, pp 220–237 | Cite as

The effect of entanglements on the rheological behavior of polybutadiene critical gels

  • M. E. De Rosa
  • H. H. Winter
Original Contribution

Abstract

We investigated the stress relaxation behavior of critical gels originating from six nearly monodisperse, highly entangled polybutadiene melts of different molecular weight from 18000 to 97 000 g/mole. The polymers were vulcanized by a hydrosilation reaction which takes place nearly exclusively at the pendant 1,2-vinyl sites distributed randomly along the polybutadiene chain. The BSW spectrum represents the relaxation of the initial uncrosslinked precursor. A characteristic parameter is the longest relaxation time of the precursor. Crosslinking increases this longest time even further. Surprisingly, the relaxation spectrum of the precursor is not altered much by the crosslinking except for an additional long time behavior. At the gel point (critical gel), this long time behavior is self-similar. It follows the typical power law as described by the Chambon-Winter gel equation, G(t) = Stn, in the terminal zone. The critical relaxation exponent was found to be close to n = 0.5 over a range of stoichiometric ratios and for all precursor molecular weights analyzed. A new scaling relationship was found between the gel stiffness, S, and the precursor molecular weight of the form: S ∼ M w zn , where exponent z from the zero shear viscosity-molecular weight relationship, η0M w z , is commonly found to be z = 3.3 – 3.6.

Key words

Gelation critical gel entanglement relaxation time spectrum 

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Copyright information

© Steinkopff-Verlag 1994

Authors and Affiliations

  • M. E. De Rosa
    • 1
  • H. H. Winter
    • 1
    • 2
  1. 1.Polymer Science and Engineering DepartmentUniversity of MassachusettsAmherstUSA
  2. 2.Dept. Chemical Engineering DepartmentUniversity of MassachusettsAmherstUSA

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