Suppressive Photochromism and Promotive Mechanochromism of Rhodamine Mechanophore by the Strategy of Poly(methyl acrylate)/Polyurethane Interpenetrating Polymer Network
Xin Cheng, Huan Hu, Lijuan Bu, Yu Wu, Zhimin Ma, Zhiyong Ma, Zhiyong Ma, Zhiyong Ma
Abstract
As molecular design and the structure–property relationships of photochemical molecules established in the literature serve as a convenient reference for mechanophore exploration, many typical mechanophores suffer undesired responses to UV light or even sunlight in bulk polymers. We developed a strategy of a poly(methyl acrylate)/polyurethane (PMA/PU) interpenetrating polymer network (IPN) to suppress the photochromic property of the mechanophore and promote its mechanochromic property. A widely used rhodamine mechanophore (Rh-2OH) was first incorporated into polyurethane (P1). Then P1 was swollen in methyl acrylate and photopolymerized to prepare a PMA 2.8 /PU IPN (P2). Different from photo/force-responsive P1, P2 selectively responded to force because the low free volume in IPN greatly hinders photoisomerization of the rhodamine spirolactam, suggesting that a simple IPN strategy successfully resolves the giant problem of nonselective response to photo/force for photochromic mechanophores. Moreover, PMA/PU IPN enhanced the mechanical property, resulting in a higher mechanochemical activation ratio than PU, and the prestretching effect of PMA/PU IPN promoted the force sensitivity of rhodamine mechanophores significantly. We believe that the strategy can be applied to other mechanophores, promoting their application in more complicated environments.