Probing Mechanical Activation of Covalent Chemistry in Crosslinked Polymer Gels

Toughness, the measure of how much energy a material can absorb before rupture, is an important property of materials. It has been demonstrated that the toughness of a single polymer chain of gem-dihalocyclopropane (gDHC) functionalized polybutadiene (PB) is increased dramatically over PB alone, due to the mechanically triggered electrocyclic ring opening reaction of gDHC into 2,3-dibromoalkenes. This thesis explores whether this molecular mechanical property can also be manifested in bulk material properties. Crosslinked gem-dichlorocyclopropane (gDCC) embedded PB polymers were swollen in various solvents, and the resulting gels were mechanically deformed under tensile stress. Young's modulus and fracture toughness were compared among PBs with gDCC incorporated in the backbones and/or crosslinking positions. The results showed that the incorporation of gDCC does not measurably increase the fracture toughness of the crosslinked polymer gels. Neither NMR nor FT-IR characterization of the post-test samples revealed detectable activation of the gDCC in the crosslinked PB. Further experiments will be focused on optimizing the polymer structure and testing methods to more effectively transfer the macroscopic force to the mechanophore in the material and continuing exploring the correlation between molecular responses and changes in macroscopic properties.