Influence of Hydroxyl Group Concentration on Mechanical Properties and Impact Resistance of ROMP Copolymers

Ring-opening metathesis polymerization (ROMP) produced homopolymers and copolymers of 5-ethylidene-2-norbornene (ENB) and 5-methanol-2-norbornene (NBOH), and this provided a platform to explore the influence of monomer polarity and noncovalent interactions on the mechanical and high velocity impact performance. The tensile yield, mode-I fracture, and high velocity impact behavior displayed a strong dependence on the hydroxyl-containing NBOH content when compounding effects (such as degree of undercooling and polymer topology) are considered. Specifically, the high velocity impact performance systematically increased with increasing hydroxyl groups and tracked well with the increase in yield stress, implying the failure mechanism was yield stress dominated. Positron annihilation lifetime spectroscopy (PALS) data revealed a decrease in the pore volume with increasing NBOH content, giving insight into the increases in density and the positive deviation of the glass transition temperature (Tg) from a simple rule-of-mixtures average. Collectively, these data illustrate a strong correlation between the noncovalent interactions on the nanoscale and macroscopic properties, demonstrating that polarity and noncovalent interactions are a critical design parameter in formulating polymer materials for protection applications.