Photoinitiated Synthesis of Mixed Polymer Brushes of Polystyrene and Poly(methyl methacrylate)

Abstract

We describe the synthesis of mixed, or binary, polymer brushes containing polystyrene (PS) and poly(methyl methacrylate) (PMMA). These films were synthesized by a grafting-from (GF) strategy from gold substrates that were coated with a bis-thiol free radical photoinitiator, similar to 2,2‘-azobis(isobutyronitrile) (AIBN). The PS layer was 70 nm thick for all substrates, and the PMMA was varied up to 700 nm. The number-average molecular weight (Mn) of the ungrafted polymers was determined by gel permeation chromatography (GPC) and multiangle light scattering (MALS); the Mn for bulk PS and PMMA was ∼57 000 and ∼515 000 Da, respectively. The air/liquid interface was probed by static water contact angles (θ) and X-ray photoelectron spectroscopy (XPS). We found that both θ and the oxygen concentration varied depending on whether the substrate was immersed in a nonselective solvent (tetrahydrofuran) or selective solvent for PS (cyclohexane) or PMMA (isobutanol). The morphology was monitored by atomic force micr...