Entanglements between polymer chains are responsible for the strength and toughness of polymeric materials. When the chains are too short to form entanglements, the polymer becomes weak and brittle. Here we show that molecular bridging of oligomers in molecular-scale confinement can dramatically toughen materials even when intermolecular entanglements are completely absent. We describe the fabrication of nanocomposite materials that confine oligomer chains to molecular-scale dimensions and demonstrate that partially confined unentangled oligomers can toughen materials far beyond rule-of-mixtures estimates. We also characterize how partially confined oligomers affect the kinetics of nanocomposite cracking in moist environments and show that the presence of a backfilled oligomeric phase within a nanoporous organosilicate matrix leads to atomistic crack path meandering in which the failure path is preferentially located within the matrix phase.
Keywords: fracture toughness; nanocomposites; polymer confinement; polymer entanglements; porous materials.