Temperature-Sensitive Micro- and Macrophase Separation of Hydrogen-Bonded Polystyrene-Polydimethylsiloxane Blends

Supramolecular block copolymers have attracted considerable attention due to their unique capabilities for responding to external stimuli by altering their degree of association and correspondingly their self-assembled structures. Although hydrogen bonding (H-bonding) interactions that can be dissociated and re-associated with changes in temperature have been widely combined with polymer blend systems, the case of H-bonded polymer blends with multiple single-point H-bonds between strands that are of sufficient length to microphase separate remains largely unexplored. Herein, phenol (Ph) and pyridine (Py) as a strong single-point H-bonding pair were attached as pendants to polystyrene (PS) and polydimethylsiloxane (PDMS) chains, respectively. The tendency for PS and PDMS to phase-separate competes with the attraction between Ph and Py units. The number of H-bonding groups per chain was systematically tuned, leading to a transition in the low-temperature state from macrophase- to microphase-separated as the number of H-bonding groups increased. Broad small-angle X-ray scattering (SAXS) patterns for blends with ≥20 H-bonding groups (Ph or Py) per (PS or PDMS) chain indicate the formation of disordered nanostructures. Interestingly, for the highest number of H-bonding groups (an average of 36 per chain), a reversible change in domain spacing, from 8 to 35 nm with increasing temperature from room temperature to 190 °C was observed due to progressive dissociation of H-bonds. Gravimetric analysis and SAXS after etching of the PDMS phase indicated percolation of both PDMS and PS phases, suggesting that this architecture offers a simple and highly tunable route to form cocontinuous polymer nanostructures.