Topological Effect on Order-Disorder Transition of Self-Assembled High-χ Block Copolymers

This work aims to systematically examine the topological effect on the self-assembly of high-χ block copolymers. Symmetric polystyrene-block-polydimethylsiloxane (PS-b-PDMS) block copolymers (BCPs) with different topologies including diblock, 3-arm star-block, and 4-arm star-block possessing various molecular weights are synthesized to investigate the topological effect on the temperature of order-disorder transition (T_ODT) through temperature-resolved small-angle X-ray scattering experiments. Apparent increase on the T_ODT can be identified with the increase of arm number of the BCPs with equivalent arm length. On the basis of self-consistent field theory, the Flory-Huggins interaction parameters (χ) can be determined from the regression of the measured T_ODT. With the invariant of the enthalpic contribution of interaction parameter (χ_H) for the block copolymers, there is a significant variation on the entropic contribution of interaction parameter (χ_S) as the arm number increases, reflecting the topology effect on the entropic penalty of chain packings. Accordingly, the topology might effectively alter the χ value due to the dependence of χ_S on the arm number, in line with the theoretical prediction.