Molecular barbed wire: Threading and interlocking for the mechanical reinforcement of polymers

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.