The role of tertiary amines as internal catalysts for disulfide exchange in covalent adaptable networks

Abstract

Here we explore true effects of internal tertiary amines on the bond exchange properties of cross-linked network with a disulfide exchange mechanism. The creep and stress relaxation data are first...

Vanillin-Based Epoxy Vitrimers: Looking at the Cystamine Hardener from a Different Perspective

“…Indeed, while both materials exhibit a 50 °C difference in Tg, all stress relaxation experiments were conducted at Tg + 60 °C; therefore, the influence of Tg should be limited. This unexpected phenomenon can be ascribed to the difference of reactivity and stability of the generated radicals (aliphatic vs aromatic) toward disulfides and/or concomitant mechanism with base-catalyzed thiolate anion-mediated exchanges. , This feature is more deeply investigated in the section dealing with 4AFD and cystamine mixtures and will be the focus of a dedicated study with model reactions and DFT calculations.…”

“…In addition, the faster exchanges evidenced above for aliphatic disulfides in combination with recently reported base-catalyzed thiolate anion-mediated exchanges should not be neglected. 50 , 51 The in situ formation of tertiary aliphatic or aniline amine within the network (i.e., arising from the reaction between amine or aniline with epoxy) with different basicity can also act as an internal catalyst. In summary, the underlying mechanism of disulfide exchanges is certainly more complex than anticipated with strong dependency on intrinsic parameters.…”

Trapping bond exchange phenomenon revealed for off-stoichiometry cross-linking of phase-separated vitrimer-like materials

“…4 represents the relaxation spectra for the three samples at temperatures ranging from 130 to 160 °C. To discuss the relaxation rate difference, the spectra were fitted with the Kohlrausch–Williams–Watts (KWW) function, 29,30 according to eqn (5), to estimate the first-order average relaxation time 〈 τ 〉 on the basis of eqn (6), in which Γ represents the gamma function. 31 …”

Combination of Fluorine and Tertiary Amine Activation in Catalyst-Free Thia-Michael Covalent Adaptable Networks

“…In this case, the catalyst needed for the exchange reaction to occur is covalently bonded to the network, preventing any leaching. This strategy has been used to develop CANs based on transesterification, ,− silyl ether exchange, − or disulfide exchange, where the reactions are internally catalyzed by tertiary or secondary amines. In the case of transesterification vitrimers, the insertion of a tertiary amine was relatively simple as this functionality is already present in commercially available multifunctional epoxides or can easily be obtained by epoxy/amine reaction.…”