Photo-induced topological self-reorganization and self-growth of polymer based on dynamic reversible aromatic pinacol units

Abstract

Crosslinked polyurethane containing aromatic pinacol units as novel reversible C–C bonds provider is synthesized. For the first time, photo-induced topological self-reorganization through the reversible C–C bonds leads to the transformation of micro-phase separation structure, realizing improvement of the tensile strength and failure strain from 23 MPa to 34 MPa and from 1205% to 1695%, respectively. In contrast, mechanical properties of the reference sample without pinacol moieties decrease sharply after the same UV irradiation. Internal structural variations are analyzed in detail by equilibrium swelling experiment, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), small angle neutron scattering (SANS) and positron annihilation lifetime spectroscopy (PALS). Moreover, the carbon radicals generated from homolysis of the aromatic pinacol are found to be able to further initiate polymerization of vinyl monomers, which helps to achieve crack healing, surface self-growth and formation of semi-interpenetrating polymer networks. This kind of macromolecular initiator-embedded polymer could re-initiate polymerization when the surface arrays are wiped away to expose the fresh underlying aromatic pinacol units. It is believed that the outcomes may enrich and expand the applications of dynamic covalent polymers.