Thermosetting material by a thermo responsive cross-linking using retroDiels–Alder and, in situ, Thia-Michael reactions

Abstract

The aim of this study was to prepare new responsive polymers using an original thermal cross-linking reaction. The retroDiels–Alder reaction coupled, in situ, to a Michael addition allows the synthesis of materials with tailored properties. The syntheses of three different maleimides, one solid and two liquids, from Jeffamines® are presented. These maleimides have been blocked using Diels–Alder reaction and the concept of unprotection has been tested and proven by 1H NMR. Versatile polythiols (n⩾2) have been used as reactants in the Thia-Michael addition of free or blocked maleimides. Twelve materials have been synthesized, six with free maleimides and six with blocked maleimides, and the efficiencies of various formulations were examined only few seconds (<120s) are necessary at room temperature (20–25°C) with free maleimides to obtain a cross-linked material. On the contrary when the maleimide is blocked the stability at room temperature increases up to seven days and the cross-linking reaction only occurs by curing at 110°C. The cross-linked materials have glass transition temperatures ranging from −50°C to −7°C and very good thermal stabilities (up to 350°C).