Elastomer Mechanics of Cross-linked Ring-Linear Polymer Blends

Recent studies have demonstrated the distinctive physical properties of non-concatenated ring polymers, such as the softness and stretchability of cross-linked ring polymers. Nevertheless, synthesizing ring polymers with high purity has remained demanding in polymer chemistry. A blend of ring and linear polymers occurs more readily in experiments and brings blend composition as a new parameter for the designing of ring-polymer-based materials. Large-scale molecular simulations are performed to investigate the elastomer mechanics of cross-linked polymer blends. The tensile stress σ as a function of the stretch ratio λ in a uniaxial tensile test is calculated for varying volume fractions Φ_R of ring polymers. As Φ_R increases, both the network shear modulus G and the maximum stretch ratio λ_p before the network failure do not change much until a large Φ_R^c, beyond which G decreases while λ_p increases towards their respective values for the super-soft and super-stretchable pure ring elastomer. Meanwhile, the network strength as characterized by the peak stress σ_p depends on Φ_R non-monotonically, exhibiting a maximum around Φ_R^c before decreasing towards the value of the pure ring elastomer. Further analysis of the topology reveals that the threading of rings by linear chains plays a crucial role in the structure-property relationship for the dependencies of G, λ_p, and σ_p on Φ_R.