Order-Order Transition in a Rod-Coil Diblock Copolymer Induced by Supercritical CO2

We synthesized a series of well-defined rod-coil block copolymers (BCPs), poly(dimethylsiloxane)-b-poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene) (PDMS-b-PMPCS), containing a CO2-philic block PDMS, and we studied their phase structures in bulk and after treatment with supercritical CO2 (scCO(2)) using small-angle X-ray scattering. The nanostructure of the BCP changed from lamellae (LAM) to hexagonally packed cylinders (HEX) when the volume friction Of PDMS (f(PDMS)) decreased to similar to 18%. Although the glass transition temperature (T-g) of the PMPCS block in scCO(2) could not he measured directly in Our experiment, it significantly decreased in scCO(2) at 110 bar. as estimated from SAXS results. More significantly, we observed a HEX-LAM order-order transition induced by scCO(2) in a HEX-Structured BCP which was located close to the HEX-LAM phase boundary in the BCP phase diagram under our experimental conditions. The OOT could be attributed to increases in both the volume fraction of HIP coil block and the effective interaction parameter. The lamellar structure was fixed by the rigid-rod-like block during depressurization. It was stable below the high T-g of the rod block and could change back to the original HEX structure by thermal annealing above the T-g of the rod block. For other BCP's which were located far away from the HEX-LAM phase boundary, the structures did not change; but the periodic sizes increased following scCO(2) treatment.Polymer ScienceSCI(E)EI16ARTICLE82900-29074