Self-Assembly of an Ultrahigh-χ Block Copolymer with Versatile Etch Selectivity

We report the successful synthesis of previously inaccessible poly(3-hydroxystyrene)-block-poly-(dimethylsiloxane) (P3HS-b-PDMS) block copolymers (BCPs) with varying volume fractions, molecular weights, and narrow dispersities by sequential living anionic polymerization. The chemical structure and molecular weight were fully characterized by H-1 NMR and gel permeation chromatography. The BCP phase behavior was investigated using small-angle X-ray scattering (SAXS) and transmission electron microscopy. Temperature-resolved SAXS measurements from symmetric disordered sample were used to determine the interaction parameter (chi) using mean-field theory. The results provide an estimate for interaction parameter, chi(HS/DMS) (T) = 33.491/T + 0.3126, with an upper bound value of 0.39 at 150 degrees C. The calculated, chi for P3HS-b-PDMS is approximately 4 times higher than that observed in a commonly studied high-chi system, PS-b-PDMS. The ultrahigh interaction parameter observed here affords the formation of well-ordered materials at remarkably low molecular weight. The presence of both PDMS and P3HS provides significant versatility in terms of etch selectivity, while the hydroxystyrene domain offers additional functionality as it can be exploited for immobilizing functional organic moieties.