Topology-Enabled Simultaneous Enhancement of Mechanical and Healable Properties in Glassy Polymeric Materials Using Larger POSS

Mechanically robust yet healable glassy polymeric materials (HGPMs) are poised for use as next-generation structural and protective materials. However, achieving such materials remains a great challenge due to the inherent conflict between good mechanical properties and adequate molecular mobility required for healing. Herein, we investigate the variations of network topology in HGPMs, leading to simultaneously enhanced mechanical and healable properties. The materials (T8-UPy8, T10-UPy10, and T12-UPy12) are fabricated by combining multiple hydrogen bonds with T8, T10, and T12 polyhedral oligomeric silsesquioxanes (POSSs), respectively, which have identical chemical components yet distinct topologies. It is found that the topological effects arising from the POSS cage size and/or symmetry strongly affect the materials' elastic modulus (E), glass transition temperature (Tg), and healing temperature (Th). Notably, T10-UPy10 and T12-UPy12 exhibit lower Tg (59.5 and 65.4 °C) and Th (65 and 70 °C) yet higher E (5.0 and 6.0 GPa) compared to those of T8-UPy8. Elaborate comparisons underscore the instrumental contribution of larger POSS-based topological structures, revealing that the larger POSSs contribute to higher molecular mobility with tighter internal framework structures. Meanwhile, these materials possess high pencil hardness, transparency, and exceptional flexibility, making them well-suited for robust flexible protective coatings. This work highlights the significance of the topology, particularly a larger POSS, for fabricating advanced HGPMs.