MICELLES FORMED BY A MODEL HYDROGEN-BONDING BLOCK-COPOLYMER

A nearly monodisperse polystyrene-block-poly(p-hydroxystyrene) copolymer (PS-PSOH) was synthesized by combining protected group chemistry with high-vacuum anionic polymerization. The molecular weight of both blocks was 1.0 x 10(4). Our objective was to study the effect of hydrogen bonding on micelle formation in block copolymer solutions. The self-hydrogen-bonding capability of the hydroxystyrene moieties is well established. Light scattering experiments were conducted on dilute solutions of PS-PSOH in tetrahydrofuran (THF), a common solvent for both blocks, and toluene, a selective solvent for the polystyrene block. Dynamic light scattering (DLS) measurements indicated that the block copolymer was molecularly dispersed (or nearly so) in THF with a hydrodynamic radius R(h) = 3.8 nm. However, large aggregates with R(h) = 76 nm were observed by DLS in toluene solutions. Static light scattering (SLS) measurements on the PS-PSOH/toluene solutions confirmed the presence of large aggregates with aggregation numbers of 10(4) chains/micelle. The micellar structure was determined by enforcing simultaneous consistency with both SLS and DLS measurements. A rodlike structure, 300 nm in length and 40 nm in diameter, is consistent with both measurements.