We review the state-of-the-art in the molecular design and processing of low density organic-inorganic hybrids at the extreme limits of molecular-scale confinement. A particular focus is provided on unique mechanical and molecular behavior that can be achieved in the limit of such intimate molecular mixing and confinement. We show that molecular hybrids can have marked asymmetric elastic and thermal expansion properties that are inherently related to terminal chemical groups in confinement. We describe a new nanoscale design principle using hyperconnected molecular architectures to achieve remarkable mechanical properties controlled by designing connectivity into the intrinsic molecular structure in innovative ways. We probe the mechanical and fracture properties of hybrids in the extreme limits of molecular confinement, where a stiff inorganic matrix phase confines polymer chains to dimensions far smaller than their bulk radius of gyration. Finally, we describe a synthesis strategy which involves the infiltration of individual polyimide precursors into a nanoscale porous network where imidization reactions under such confinement increase the molecular backbone stiffness. We find that polyimide oligomers can then undergo crosslinking reactions even in such molecular-scale confinement, increasing the molecular weight of the organic phase and toughening the nanocomposite through a confinement-induced energy dissipation mechanism. This work demonstrates that the confinement-induced molecular bridging mechanism can be extended to thermoset polymers with multifunctional properties, such as excellent thermo-oxidative stability and high service temperatures (&gt; 350 °C).

Molecular design and engineering of hybrids at the extreme limits of molecular-scale confinement

2019 Spring National Meeting

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