Effects of chain architecture on the mechanical response of glassy/semicrystalline block copolymers: CEC versus CECEC lamellae

In this work, we investigated the effects of molecular architecture on the mechanical response of glassy/semicrystalline block copolymers. Poly(cyclohexylethylene) (C) comprises the glassy blocks while the semicrystalline blocks are poly(ethylene) (E). This research specifically compared the mechanical response of lamellar structured triblock CEC and pentablock CECEC copolymers. General material response was measured and a detailed analysis of the microstructure was performed. The triblock and pentablock copolymers were investigated in the multi-grained and single-grained state; the single-grained samples were created by the application of an oscillatory shear field that induced long-range lamellar orientation. Mechanical testing of the single-grained specimens enabled us to isolate the effects of the morphological structure on the physical properties of these materials. Additionally, this work helps us to understand the effects of processing induced orientation of the lamellae on the final mechanical properties of block copolymers.; Basic tensile tests were carried out to determine the yield stress, elastic modulus and strain-to-failure. Small angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) were utilized to image the changes in the lamellar structure resulting from the various processing conditions and mechanical tests the samples underwent. In addition, specimens were subjected to SAXS at select stages of the deformation process. This enabled us to monitor changes in alignment and/or breakup of the lamellae as a function of strain-induced plastic deformation.