Synthesis and surface characterization of well-defined amphiphilic block copolymers composed of polydimethylsiloxane and poly[oligo(ethylene glycol) methacrylate]

Abstract

A series of amphiphilic polydimethylsiloxane-b-poly[tri(ethylene glycol) methyl ether methacrylate] (PDMS-b-PM3) diblock copolymers were prepared with varying PM3 compositions. The well-defined PDMS-b-PM3 was synthesized by using a coupling reaction between the living PM3 and ω-benzyl bromide-functionalized PDMS. The obtained polymers had narrow molecular weight distributions (M_w/M_n ≤ 1.08) and predictable molecular weights. The bulk-state self-assembly of the polymers was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) measurements. The microphase separated morphologies in these amphiphilic block copolymers varied from the PDMS-cylinder to lamellar, even if the molecular fraction of the PM3 was progressively reduced from 70 wt% to 17 wt%. We also performed the detailed surface structural characterization of the amphiphilic PDMS-b-PM3 thin-films by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and static water contact angle measurement. Based on these structural analyses, we proposed that the block copolymer self-assembled into a cylinder-like nanostructure at the top of thin film surface without any tedious annealing method in the case of the block copolymer possessing high PM3 content (≥70 wt%).