Order-disorder transitions and mesophase stability in asymmetric “soft-nature” diblock copolymers

Block copolymers (BCPs) are essential in nanotechnology due to their ability to self-assemble into well-defined nanostructures. In the context of structured liquids, a fundamental understanding of microphase behavior is key to the rational design of advanced soft-matter materials. This study investigates the phase behavior of viscoelastic poly(butadiene)-block-poly(dimethylsiloxane) (PB 1 , 2 - b -PDMS) copolymers, where PB segments exhibit 100% 1,2-microstructure. We focus on how molecular parameters—such as block asymmetry, degree of polymerization, and segregation strength—govern the resulting morphology. In-situ small-angle X-ray scattering was employed to monitor real-time, temperature-dependent order–order and order–disorder transitions (ODT). Copolymers with low molecular weight values exhibited gradual loss of order, while intermediate ones underwent sharp ODT and high molecular weight systems preserved long-range order and structural orientation across wider temperature ranges. In all sequences the morphological behavior was impacted by the PDMS content. These findings provide new insight into the thermotropic self-assembly behavior of low-modulus, nanostructured BCPs and highlight their potential in applications such as soft lithography, flexible electronics, and neurointerfaces. • Thermotropic behavior of nanostructured liquids • Well-defined viscoelastic copolymers through anionic polymerization • Order-disorder transition due to asymmetric fluctuations