**Unexpected Ductility in Semiflexible Polymer Glasses with Entanglement
Length Equal to their Kuhn Length**

JD Dietz and K Nan and RS Hoy, PHYSICAL REVIEW LETTERS, 129, 127801 (2022).

DOI: 10.1103/PhysRevLett.129.127801

Semiflexible polymer glasses (SPGs), including those formed by the recently synthesized semiflexible conjugated polymers, are expected to be brittle because classical formulas for their craze extension ratio lambda(craze) and fracture stretch lambda(frac )predict that systems with N-e = C-infinity have lambda(craze) = lambda(frac) = 1 and hence cannot be deformed to large strains. Using molecular dynamics simulations, we show that in fact such glasses can form stable crazes with lambda(craze) ? N-e(1/4) ? C-infinity(1/4) , and that they fracture at lambda(frac )= (3N(e) (1/2 )- 2)(1/2 )? (3C(infinity)(1/2 )- 2)(1/2). We argue that the classical formulas for lambda(craze) and lambda(frac) fail to describe SPGs' mechanical response because they do not account for Kuhn segments' ability to stretch during deformation.

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