Polar aprotic solvents disrupt interblock hydrogen bonding and induce microphase separation in double hydrophilic block copolymers of PEGMA and PAAMPSA

The disruption of interblock hydrogen bonding to induce microphase separation of the double hydrophilic block copolymer (DHBC) in the solid state, by solvent casting the block copolymer with polar aprotic solvents was demonstrated. Films of DHBC that contained poly-(oligoethylene oxide methyl ether methactylate) (PEGMA), and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAMPSA) were cast with four different solvents, methanol, water, dimethylformamide (DMF), and dimethyl sufoxide (DMSO). It was observed that PEGMA/PAAMPSA formed a single-phase, homogenous melt when cast from methanol and water, while solvent casting PEGMA/PAAMPSA from DMSO and DMF yielded highly ordered microphase-seperated structures. DMSO and DMF are polar aprotic solvents, with the high basicities that allow these solvents to readily accept hydrogen bonds from the sulphonic acid groups of PAAMPSA. Using DMSO and DMF as casting solvents thus enabled the disruption of interblock hydrogen bonding that would otherwise be present in PEGMA/PAAMPSA.