Triggered Crosslinking of Main-Chain Enediyne Polyurethanes via Bergman-Cyclization.

Crosslinking chemistries have been occupying a significant position in polymer modification, being of particular importance when triggered in response to external stimuli. We here use enediyne (EDY) moieties, known to undergo a pericyclic Bergman cyclization (BC), for a triggered crosslinking of polyurethanes (PU). We place diamino-EDYs, where the distance between the enyne-moieties is known to be critical to induce a BC, as main-chain structural elements in isophorone-based PUs to observe a reinforcement upon heating, compression, or stretching. A 7-day compression under room temperature results in a ∼ 69% activation of the Bergman cyclization, together with the observation of an increase in tensile strength by 62% after 25 stretching cycles. We further prove the occurrence of BC by the decreased exothermic values in differential scanning calorimetry (DSC), together with characteristic peaks of the formed benzene moieties via IR spectroscopy. Purely heat-induced crosslinking contributes to 191% of the maximum tensile strength in comparison to the virgin PU. The BC herein forms an excellent crosslinking strategy, triggered by heat or force in PU-materials. This article is protected by copyright. All rights reserved.