Side Chain Dipole Orientation and Its Effect on Microphase Separation: Experiment and Simulation via Structural Isomer Variation

Abstract

We use experiments and molecular dynamics simulations in an investigation of structural isomer–property relationships in block copolymers (BCPs) that allow us to isolate the effects of dipole orientation on microphase separation and χ. We combine anionic polymerization of a single parent BCP with post-polymerization thiol-epoxy “click” chemistry with a series of structural isomers of fluorinated thiophenols to synthesize structural isomeric BCPs (SI-BCPs). The resulting SI-BCPs possess identical molecular weight and dispersity, such that only the isomerism can affect microphase separation. Domain periodicity of the SI-BCPs is measured with small angle X-ray scattering, from which χ is estimated. The value of χ for each SI-BCP shows a significant dependence on the position of fluorine atoms on the phenyl ring of the thiophenol. Simulation results show a strong correlation between the dipole moment orientation of the appended thiol and χ, which is also observed in simulations of a BCP of the structural isomers poly(2-vinylpyridine) and poly(4-vinylpyridine). This work illustrates a little-known facet of the structure–property relationship of BCP materials and provides another tool for the molecular engineering of BCPs.