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Viscoelastic response of model epoxy networks in the glass transition region
Author(s) -
Gerard J. F.,
Galy J.,
Pascault J. P.,
Cukierman S.,
Halary J. L.
Publication year - 1991
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760310813
Subject(s) - glass transition , viscoelasticity , materials science , epoxy , prepolymer , dynamic mechanical analysis , composite material , volume fraction , volume (thermodynamics) , superposition principle , thermodynamics , polymer chemistry , polymer , physics , quantum mechanics , polyurethane
Six epoxy networks with various structures built up from a diepoxy prepolymer, DGEBA, and three different diamines or mixtures of a monoamine and a diamine were studied by dynamic mechanical analysis in the glass transition region. The systems were designed in order to investigate the dependence of glass transition T g on both crosslink density and network chain flexibility. The time (frequency)—temperature superposition principle (WLF equation) was used to determine the viscoelastic coefficients C g 1 and C 2 gwhich are related to some free volume characteristics on the molecular scale. C g 1 , related to the free volume fraction available at T g depends mainly on crosslink density, even though the product C g 1 C 2 g , related to the free volume expansion coefficient, is dependent on both chain flexibility and crosslink density. Thus, viscoelastic properties determined over large temperature and frequency ranges are shown to yield more precise information on epoxy network structure than the simple analysis of glass transition temperature.