INS2-0217
Tie Chains and Ductility in Semicrystalline Polymers
Topic
S2. High-End Characterization/Polymer Physics/Properties
When and Where
Sep 30, 2026
15:50 - 16:15
Room 103
Session Chairs
Sheng LI
Presenter(s)
Richard Register (Princeton University)
Co-Author(s)
Abstract
Semicrystalline polymers of low glass transition temperature, such as polyethylene (PE) and hydrogenated polynorbornene (hPN), can be either brittle or ductile depending on how well stress can be transmitted between crystallites—such as via tie molecules (TMs), chains that directly bridge the intercrystalline amorphous layer. TM content will increase with increasing molecular weight (M), or with the fraction of high-M chains in a disperse polymer; it will also increase with decreasing intercrystallite repeat spacing d, which can be manipulated through thermal history and the incorporation of comonomer. We have examined the failure mode of model narrow-distribution linear PEs and hPNs, where d is varied through both crystallization history (either quenching or slowly cooling) and the incorporation of short branches (at variable levels) that are unable to enter the crystals. For a given (co)polymer composition and thermal history, a rather sharp brittle-to-ductile transition (BDT) is observed with increasing M, at a value MBDT. However, when looking across thermal histories and comonomer contents, MBDT does not correspond to a particular numerical value of the tie molecule fraction (P), calculated by the Huang-Brown approach. Rather, PBDT increases strongly as crystal thickness decreases, with both PE and hPN showing similar dependences. We trace this unanticipated dependence to the loss of TMs during drawing, with polymers having thinner initial crystals losing a larger fraction of their TMs. This postulate is confirmed by measurements of the post-draw strain-hardening modulus, which reflects the content of TMs remaining after the material has necked and drawn. These insights provide guidance for the molecular design of ductile and easily processible polymers (via molecular weight distribution and branch content), and how those desirable characteristics can be preserved through rounds of mechanical recycling.
