Extraction of intrinsic effects of glassy domain cross-linking on the tensile properties of ABA block copolymer elastomers via photo cross-linking approach

Abstract

Chemical or physical cross-links into the A glassy domains have been reported to enhance mechanical properties for glassy-b-soft-b-glassy ABA triblock copolymer-based elastomers. However, no reports dealt with the pure effects of the domain cross-linking, since the cross-linking processes inevitably altered the morphological characteristics. This study extracts the intrinsic effects of domain cross-linking on the tensile properties based on the ABA triblock copolymer with the A blocks cross-linked via photo cross-linking without heat and cross-linker molecules. Differential scanning calorimetry, viscoelasticity measurements, and small-angle X-ray scattering (SAXS) with a model function analyses were used to confirm preservation of the segmental dynamics of the B block and the morphology of the self-assembled structure after cross-linking, which are all important for a fair discussion. Tensile properties were then investigated by simple elongation and cyclic tests, revealing that the domain cross-linking enhanced the stress in the small deformation region and the recovery property primarily. These changes of the tensile properties were discussed in terms of the deformation resistance of the micro-phase separated structure based on the SAXS data under elongation. The superiority or inferiority of cross-linking the end block domains or middle block strands for mechanical property enhancement was interpreted based on the observed difference between the neat and cross-linked samples. In the last section, effects of domain photo cross-linking for the different morphologies were also examined. Throughout the article, this study can provide new and essential knowledge of the mechanical properties of block copolymer-based materials, and some valuable hints for further modification of the physical properties of these materials.