THE SMALL-STRAIN MODULI OF ELASTOMERIC NETWORKS HAVING HIGH FUNCTIONALITY CROSS LINKS AND THE CONSTRAINED JUNCTION THEORY


IBRAHIM SHARAF M. A.

JOURNAL OF MACROMOLECULAR SCIENCE-PURE AND APPLIED CHEMISTRY, ss.83-92, 1993 (SCI İndekslerine Giren Dergi) identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası:
  • Basım Tarihi: 1993
  • Dergi Adı: JOURNAL OF MACROMOLECULAR SCIENCE-PURE AND APPLIED CHEMISTRY
  • Sayfa Sayıları: ss.83-92

Özet

Poly(dimethylsiloxane) networks of high cross-link functionality and high extents of reaction have been prepared by end-linking vinyl-terminated chains with multifunctional poly(methylhydrosiloxane) chains. At small strains, these networks had elongation moduli that significantly exceeded the values predicted by the Flory-Erman theory. In a revised analysis, the segments between cross links along the junction precursor molecule are considered as short network chains, thus contributing to the modulus in a system that essentially has a bimodal distribution of both network chain lengths and cross-link functionalities. Relevant here is the fact that as the degree of chemical cross-linking increased, an unmistakable transition in values of the modulus is observed between the two extremes of deformation, namely the affine and phantom limits. As expected, this would be the case where the constraints on the fluctuation of junctions vanish at higher degrees of cross-linking because the mutual interspersion of chains is less when the chains are shorter, even in the small-strain region. Calculations based on recognition of such short chains give results in much better agreement with experiment.