Shape memory, reprocessable and photothermal networks of polyurethane with silyl ether bonds and croconaine segments

Abstract

Organic dyes were integrated into networks of polyurethane (PU) in the form of croconaine segments, in order to bestow photothermal properties on the materials. In addition, the PU networks were crosslinked with polysilsesquioxane (PSSQ) so that the materials can be reprocessed (or self-healing) via the metathesis of silyl ether bonds under catalysis. Toward this end, we synthesized a novel diol bearing croconaine moiety, which was used as one of chain extenders and a series of linear PU telechelics with dihydroxyl termini were synthesized. The α,ω-dihydroxyl PU telechelics were then allowed to react with 3-isocyanatopropyltriethoxysilane to gain α,ω-ditriethoxysilane PU telechelics. Through sol-gel process, α,ω-ditriethoxysilane PU telechelics readily underwent crosslinking with PSSQ as the crosslinkages. The crosslinking of PU was in marked contrast to traditional crosslinking of PU with multifunctional ols (or amines) as the crosslinkers. Owing to the crosslinking, shape memory properties were bestowed on the organic-inorganic PU networks. Thanks to the metathesis of silyl ether bonds under catalysis, the organic-inorganic PU networks were reprocessable (or recyclable). Benefiting from the built-in of dye segments, the PU networks significantly displayed excellent photothermal conversion properties. By leveraging the photothermal properties, the shape shifting of the PU networks can be triggered via the irradiation under infrared laser and in a non-contact fashion. In addition, the PU networks were capable of displaying the light-triggered self-healing properties. Thanks to these excellent properties, we demonstrated a successful application of the PU networks a soft robot.