Comparing Morphological Evolution during Tensile Deformation of Two Precise Polyethylenes via 2D Fitting of in Situ X-ray Scattering

Some types of precise polyethylenes, or linear polyethylenes containing precisely periodic functional groups, exhibit significant strain hardening under tensile deformation. Here we perform in situ X-ray scattering during tensile deformation of two precise polyethylenes: one with pendant carboxylic acid groups every 21st carbon (p21AA) and another with pendant imidazolium bromide groups every 15th carbon (p15ImBr). p21AA exhibits significant strain hardening and its layered structure orients with the layer normal along the tensile axis, while p15ImBr does not exhibit strain hardening and its layer normal orients perpendicular to the tensile axis. Quantitative evaluation of the 2D fiber patterns shows that p21AA undergoes a morphological transition, from a semicrystalline structure to a nanofibrillar structure, while the morphology of p15ImBr reorients and the chain folding structure is preserved. This suggests that fibrillization plays an important role in the strain hardening mechanism.