Curing of epoxy resins. I. Statistics of curing of diepoxides with diamines

Abstract

The curing of epoxy resins with amine curing agents has been statistically treated as irreversible alternating polyaddition with the aid of the theory of cascade processes for cases when the polymerization of epoxy groups and cyclization are negligible. The coefficients of vectorial generating functions are obtained by solving kinetic differential equations. The solution has been carried out for the reaction of diepoxide with diamine with an independent reactivity of epoxy groups in diepoxide and amino groups in diamine, but with a different reactivity of hydrogen atoms in the primary and secondary amino group. Relationships have been derived for changes in the molecular weight averages, in the sol and gel fractions and their composition, and in the concentration of elastically active network chains as a function of conversion. The conditions for the gel point have been determined. The structural parameters depend on the ratio of the rate constants of hydrogen atoms in the primary and secondary amino group, k2/k1 = r, and on the stoichiometric ratio of functionalities. In a stoichiometrically equivalent system the critical conversion at the gel point increases from 1/2 for r → oo up to (1/2) (51/2 – 1) for r → 0. The critical stoichiometric ratio for gel formation at full conversion of (epoxide) functionalities in deficiency is < 3 or > 3 for r < 1 or r > 1, respectively.

Thiol−Yne Photopolymerizations: Novel Mechanism, Kinetics, and Step-Growth Formation of Highly Cross-Linked Networks

“…Dušek, however, demonstrated deviation from the gel-point conversion predicted by the FS equation for the step-growth mechanism where consecutive additions to a polymerizable moiety are of unequal reactivity. (31) Systems in which the rate of initial addition is faster than the subsequent addition (i.e., k P,2 / k P,1 < 1) have a higher gel-point conversion than predicted by the FS equation; the opposite trend is observed when the rate of the subsequent addition exceeds that of the initial (i.e., k P,2 / k P,1 > 1). Thus, the observed rate constant ratio for PETMP/DDY (i.e., k P,2 / k P,1 ∼ 3) indicates that a gel-point conversion somewhat lower than the Flory−Stockmayer prediction will occur; however, as k P,2 / k P,1 is still of the same order of magnitude, the deviation from this prediction is likely small.…”

Viscoelastic Properties for Sol-Gel Transition

“…The classification of the diamine unit shown here is similar to that of Dušek et al(Dušek, 1975). However, its use to define the gel point is different.…”

Hetero‐Functional Polymers with Alternating Hydroxyl and Epoxy Groups Synthesized by Thiol‐yne Click (co)Polymerization

“…In nature, thiol‐yne click polymerization allows consecutive addition of two thiols occur with the alkyne as the mechanism of the epoxy‐amine addition, giving rise to a step‐growth polymerization . As dithiols and alkynes go into the polythioether alternately, the available hydroxyl and epoxy groups correspondingly arrange along the macromolecular main chain .…”