Introduction of Photolatent Bases for Locally Controlling Dynamic Exchange Reactions in Thermo-Activated Vitrimers

Abstract

Vitrimers exhibit a covalently crosslinked network structure, as is characteristic of classic thermosetting polymers. However, they are capable of rearranging their network topology by thermo-activated associative exchange reactions when the topology freezing transition temperature (T_v ) is exceeded. Despite the vast number of developed vitrimers, there is a serious lack of methods that enable a (spatially) controlled onset of these rearrangement reactions above T_v . Herein, we highlight the localized release of the efficient transesterification catalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) by the UV-induced cleavage of a photolatent base within a covalently crosslinked thiol-epoxy network. Demonstrated with stress relaxation measurements conducted well above the network's T_v , only the controlled release of TBD facilitates the immediate onset of transesterification in terms of a viscoelastic flow. Moreover, the spatially resolved UV-mediated photoactivation of vitrimeric properties is confirmed by permanent shape changes induced locally in the material.

Keywords: materials science; photochemistry; photolatent base; polymers; vitrimer.