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

Supramolecular block copolymers have attracted considerableattentiondue to their unique capabilities for responding to external stimuliby altering their degree of association and correspondingly theirself-assembled structures. Although hydrogen bonding (H-bonding) interactionsthat can be dissociated and re-associated with changes in temperaturehave been widely combined with polymer blend systems, the case ofH-bonded polymer blends with multiple single-point H-bonds betweenstrands that are of sufficient length to microphase separate remainslargely unexplored. Herein, phenol (Ph) and pyridine (Py) as a strongsingle-point H-bonding pair were attached as pendants to polystyrene(PS) and polydimethylsiloxane (PDMS) chains, respectively. The tendencyfor PS and PDMS to phase-separate competes with the attraction betweenPh and Py units. The number of H-bonding groups per chain was systematicallytuned, 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 & GE;20 H-bonding groups (Ph or Py) per (PS or PDMS) chain indicatethe formation of disordered nanostructures. Interestingly, for thehighest number of H-bonding groups (an average of 36 per chain), areversible change in domain spacing, from 8 to 35 nm with increasingtemperature from room temperature to 190 & DEG;C was observed dueto progressive dissociation of H-bonds. Gravimetric analysis and SAXSafter etching of the PDMS phase indicated percolation of both PDMSand PS phases, suggesting that this architecture offers a simple andhighly tunable route to form cocontinuous polymer nanostructures.