Effect of Block Immiscibility on Strain-Induced Microphase Segregation and Crystallization of Model Block Copolymer Elastomers

• Published in: Macromolecules 2018-08, Vol.51 (15), p.5685-5693
• Main Authors: Nowak, Christian, Escobedo, Fernando A
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.8b00965

Main-chain liquid crystalline elastomers (LCE) of ABA block copolymer chains are simulated using a polymer bead–spring model to understand how their sawtooth tensile behavior is affected by changes in the degree of immiscibility between the A and B block as parametrized by χN, playing a role akin to reciprocal temperature. It is found that the toughness, namely, the energy absorbed under uniaxial extension, increases with χN, but its behavior depends upon a threshold value of χN that marks the emergence of crystalline domains. Below the threshold, the toughness increases slowly with χN and has an irregular dependence on composition, while above it the toughness increases more rapidly with χN and depends on the volume fraction of the minority block. These trends differ from those found in a previous analysis of LCEs [ Nowak, C. ; Escobedo, F. A. Tuning the Sawtooth Tensile Response and Toughness of Multiblock Copolymer Diamond Networks. Macromolecules 2016, 49 (17), 6711−6721 ] where the toughness was found to increase linearly with χN and always be the largest for the equimolar block composition. The uniaxial deformation behavior of un-cross-linked block copolymer chains is also studied to show that block immiscibility is insufficient to engender a sawtooth tensile response and that it can only emerge with the further confluence of appropriate network topology and chain semiflexibility.