A Stress-Responsive Shape Memory Polymer via Chemical Grafting Functionalized Cinnamoyl-Based Mechanophore

Abstract

Due to the intrinsic mechanochemical characteristics, shape memory polymers (SMPs) with multifunctionalities are highly desirable for structural applications. The capability of self-sensing for early damage has been extensively investigated. The general fabrication technique for feature incorporation is to blend stress-responsive additives directly; however, this approach usually leads to performance tradeoffs. Here, we have developed a method to attach a cinnamoyl-based mechanophore to the backbone of the SMP matrix via a chemical grafting technique. We have varied weight ratios of mechanophore, which exerts its amine functionality to mingle with Jeaffmine D230 forming an advanced crosslinker and allowing for the fabrication of a stress-responsive polymeric network inside an SMP matrix. Dynamic mechanical analysis (DMA) and quasi-static tensile tests were performed to characterize the mechanical and thermal properties of SMP thermoset samples and investigate the optimal weight ratio. Meanwhile, the rubber elasticity plateau is utilized to calculate the crosslinking densities for the SMP samples. The storage moduli and glass transition temperatures of SMP-based thermoset samples were slightly reduced with the lower weight ratio of mechanophore on 5 wt.% and 7.5 wt.%. With increasing mechanophore loading weight to 9 wt.%, the storage modulus and glass transition temperatures of baseline SMP improved by 9.0 % and 15.7 %, respectively. Interestingly, increasing the weight ratio of mechanophore to 10 wt.% and 12.5 wt.% caused the property reduction again. This could be attributed to the over-saturation from self-polymerization or unreacted mechanophore affecting the SMP matrix negatively. Quasi-static tensile tests were performed while the instrument is coupled with in situ fluorescence detection setup to monitor the self-sensing capabilities under given loading conditions.