Oil additives demonstrate dual effects on thermal and mechanical properties of cross-linked hydroxy-DCPD thermosets

Ring opening metathesis polymerization (ROMP) derived poly-dicyclopentadiene (poly-DCPD) materials enjoy high impact strength, and high chemical resistance. They offer control over the thermomechanical properties of the resulting cross-linked polymers, depending on initiator type and loading, the curing method and the monomer's chemical structure. Herein, we report on an additional method to tune properties of novel thermoset polymers obtained by ROMP by using blended mixtures containing 1-hydroxy-dicyclopentadiene (DCPD-OH) and four different oil additives, silicone oil (SO), mineral oil (MO), jojoba oil (JO) and linseed oil (LO). Various parameters such as curing behavior, glass transition temperatures (T_g), cross-link densities and mechanical properties were studied. Accordingly, all the polymeric blends are amorphous, display higher T_g than that of the parent poly-DCPD-OH and retained their thermal stability. T_g values increased with a rise in the oil content until phase segregation in the polymeric films was dominant. This trend was also manifested by a gradual increase in the calculated cross-linking density values. Tensile analysis of polymeric blends with the highest cross-linking density values revealed that, although the films gained strength, they also showed reduced plastic strain compared to the parent poly-DCPD-OH. This behavior is explained by the divergent interplay between the plasticizing effects and the cross-linking density in thermoset composites.