Stiffness Tuning and Ductility Enhancement of Semicrystalline Polymers by Incorporating Miscible Noncrystallizable Blocks

High Resolution Image Download MS PowerPoint Slide The mechanical behavior of hydrogenated poly(norbornene- b -substituted norbornene) diblock copolymers was investigated, where the substituted norbornene blocks are intimately mixed within the amorphous layer between hydrogenated polynorbornene (N) crystallites. In particular, hydrogenated poly(norbornene- b -norbornyl norbornene) diblock copolymers were studied; hydrogenated poly(norbornyl norbornene) homopolymers are glassy at room temperature. Enhancement of both yield stress and Young’s modulus was found at an enrichment of just 20 wt % glassy (G) block in the amorphous layer. Surprisingly, these N-G diblocks exhibit improved toughness over N homopolymers, with a nearly 4× decrease in minimum tie molecule fraction for ductility compared to quenched N homopolymers. Enhanced ductility is observed whether the substituted norbornene block is glassy or rubbery, as was demonstrated with a hydrogenated poly(norbornene- b -hexylnorbornene) diblock copolymer (N-R). These materials’ strain-hardening moduli reveal that the amorphous block promotes ductility by reducing disentanglement of tie molecules during drawing.