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Cure of epoxy novolacs with aromatic diamines. I. Vitrification, gelation, and reaction kinetics
Author(s) -
Oyanguren P. A.,
Williams R. J. J.
Publication year - 1993
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1993.070470806
Subject(s) - stoichiometry , epoxy , differential scanning calorimetry , amine gas treating , activation energy , glass transition , polymer chemistry , kinetics , reaction rate constant , materials science , vitrification , reactivity (psychology) , chemistry , polymer , organic chemistry , composite material , thermodynamics , medicine , physics , alternative medicine , pathology , quantum mechanics , andrology
The cure reaction of a commercial epoxidized novolac with 4,4' diaminodiphenylsulfone (DDS) was studied at constant cure temperatures in the range 120–270°C, as well as at constant heating rates (differential scanning calorimetry, DSC). Stoichiometric formulations did not attain complete conversion due to the presence of topological restrictions. The limiting conversion was x max = 0.8. Samples containing an amine excess (≥ 20%) could be completely reacted, whereas this was not possible for formulations containing an epoxy excess. Samples containing a 20% amine excess showed the maximum value of the glass transition temperature ( T g 230°C). Cure took place by epoxy‐amine hydrogen reactions catalyzed by (OH) groups. A reactivity ratio of secondary to primary amine hydrogens equal to 0.2 was found. The activation energy was E = 61 kJ/mol, as arising from T g versus time shift factors and time to gel measurements. A unique relationship between T g and x could be obtained. Gelation took place at x gel = 0.45 and the maximum T g for the stoichiometric system was T g max = 215°C for x = 0.8. A conversion versus temperature transformation diagram was used to represent conditions where gelation, vitrification, degradation, and topological limitations took place. © 1993 John Wiley & Sons, Inc.