We have synthesized and analyzed the mechanical/structural characteristics of a polyester containing 21 wt % of a triptycene monomer and compared it to a reference polyester homologue wherein benzene replaces the triptycene residue. Solvent-cast films and tension heat-treated (THT) films were investigated by tensile deformation and wide-angle X-ray scattering. The addition of triptycene units increases the T g and, contrary to what is typically observed, also increases the ductility of film samples. In comparison to the solvent-cast non-triptycene polyester films, the triptycene polyester films displayed a nearly 3-fold increase in Young's modulus, an approximately 3-fold increase in strength, and a more than 20-fold increase in strain to failure. THT films of the triptycene polyester exhibited a modulus more than 7 times that of the non-triptycene as-cast polyester and strength greater than 14 times higher for roughly the same strain to failure. This unusually beneficial mechanical behavior is primarily attributed to the ability of individual triptycene units to express what has been termed as “internal molecular free volume” (IMFV). We suggest that the triptycene polymers adopt favorable conformations that minimize the IMFV, and the resultant assembly introduces two mechanisms for the enhancement of tensile mechanical properties:  molecular threading and molecular interlocking.

The incorporation of pendant iptycene units into polyesters creates a novel polymer‐chain contour resembling “molecular barbed wire.” These types of units contain a unique structural property called the internal molecular‐free volume (IMFV) and have been shown to induce steric interactions between polymer chains through the minimization of the IMFV. This process creates a sterically interconnected polymer‐chain network with high ductility because of two new mechanisms: molecular threading and molecular interlocking. The ability for these mechanisms to enhance the mechanical properties of polyesters is robust across concentration and processing conditions. The size, shape, and concentration of these pendant units affect the mechanical behavior, and results indicate that the larger units do not necessarily produce superior tensile properties. However, the molecular‐barbed‐wire architecture consistently produces enhanced mechanical properties compared to the reference polyester. The particular stress–strain response can be tailored by minute changes to the periphery of the iptycene unit.

We have synthesized polyester systems containing pendant iptycene units and compared their mechanical/structural properties to a homologous reference polymer wherein benzene replaces iptycene units. Iptycenes have unique structural properties called internal molecular free volume (IMFV). The incorporation of iptycene into polyester backbones results in a polymer chain contour resembling “molecular barbed wire.” The contribution of iptycene to the mechanical properties of polyesters is significant and robust across concentration and processing conditions. The triptycene polyester films displayed a nearly 3-fold increase in Young's modulus, an approximately 3-fold increase in strength, and a more than 20-fold increase in strain to failure. We proposed that the presence of triptycene introduces two mechanisms for the enhancement of tensile mechanical properties: molecular threading and molecular interlocking.