Synthesis and thin-film self-assembly of cylinder-forming high- χ block copolymers
Cylinder-forming Polystyrene-block-polycarbonate (PS-b-PC) high-χ block copolymers (BCP) were developed to extend the scaling beyond the most widely used BCP, poly(styrene-b-poly(methyl methacrylate) (PS-b-PMMA). In this work, two PC-containing BCPs, poly(styrene-b-trimethylene carbonate (PS-b-PTMC) and poly(styrene-b-methyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate) (PS-b-PMTC-Me) were synthesized using ring opening polymerization (ROP) of the cyclic carbonyl monomers from hydroxy-functional polystyrene (PS-OH) with diazabicyclo[5.4.0]undec-7-ene (DBU) as the base catalyst. Resulting BCPs were purified by fractionating in methanol:acetonitrile (MeOH:MeCN) solvent mixture to afford clean BCPs that are needed for thin-film applications. Thin-film morphologies and the orientation of the purified BCPs were determined using atomic force microscopy (AFM) analysis by coating the BCP solution on neutral underlayer modified substrates followed by short thermal annealing. It was observed that while the PS-b-PTMC domains oriented parallel to the surface, the PS-b-PMTC-Me BCP domains oriented perpendicular to the surface at similar thermal annealing temperatures without the use of topcoat or additives.