Mechanical Reinforcement of Polycarbonate Composites through Molecular Recognition with a Cyclodextrin Dimer

Polymer additives are widely used to tailor the mechanical, thermal, and processing properties of polymers; however, their interactions with polymer chains are generally nonspecific and difficult to regulate at the molecular level. Naturally derived cyclodextrin (CD) derivatives are promising alternatives to conventional petroleum-based additives because their well-defined cavities enable selective and reversible host–guest recognition. Here, we developed a reinforcement strategy for polycarbonate (PC) using a triacetylated β-cyclodextrin dimer (TAcβCD-dimer) as a bifunctional supramolecular additive. The TAcβCD-dimer was incorporated into adamantane-modified PC (Ad-PC), in which adamantane side groups act as guests for CD cavities. Nuclear Overhauser effect spectroscopy confirmed host–guest complexation, supporting intermolecular association between Ad-PC and TAcβCD-dimer. Tensile testing showed that TAcβCD-dimer addition increased both Young’s modulus and yield stress of Ad-PC, whereas no comparable systematic reinforcement was observed for phenyl-modified PC (Ph-PC) containing TAcβCD-dimer or for Ad-PC containing monomeric triacetylated β-cyclodextrin (TAcβCD-dimer). These comparisons suggest that strong host–guest interactions together with the dimeric architecture play a major role in the observed reinforcement. Morphological analyses revealed a heterogeneous sea–island structure in which TAcβCD-dimer-enriched, relatively stiff domains were dispersed in a softer matrix. During tensile deformation, voids and craze-like damage preferentially developed within the island domains rather than at the phase boundaries, indicating that the heterogeneous morphology influences the deformation and fracture processes. Although the individual contributions of molecular association and morphology could not be quantitatively decoupled, the enhancement in Young’s modulus and yield stress is primarily associated with host–guest-mediated intermolecular association, while the heterogeneous morphology contributes to the characteristic damage behavior. This study demonstrates a molecular-recognition-based strategy for reinforcing glassy polymers using naturally derived supramolecular additives.