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Published on: June 20, 2019
Stiffness Tuning and Ductility Enhancement of Semicrystalline Polymers by Incorporating Miscible Noncrystallizable
Katherine M Gunter1, Richard A Register1
1Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey08544-5263, United States.
Abstract:
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.
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