Synthesis, Characterization, and Surface Structures of Styrene—2-Vinylpyridine—Butadiene Three-Block Polymers

For the purpose of studying morphologies of ultra-thin adsorbed layers, novel polystyrenepoly(2-vinylpyridine)–polybutadiene (PS-PVP-PB) three-block polymers were synthesized with a multistep coupling method. First, end-chlorinated PS-PVP-Cl diblock precursors were made via termination of living PS-PVP⁻ anions with a large excess of p-xylylene dichloride (XDC). Those PS-PVP-Cl precursors were precipitated in heptane under vacuum to reduce substantially the amount of unreacted XDC left with them and then were allowed to be coupled with PB precursors having diphenylethylene (DPE) anion ends. The desired 1:1 coupling of the PS-PVP-C1 and PB-DPE⁻ precursors was successfully achieved, and the PS-PVP-PB three-block polymers were obtained after fractionation. Preliminary surface measurements were carried out for ultra-thin, adsorbed layers of some of those PS-PVP-PB polymers. Those layers were prepared on mica, and were examined in their as-dried state without any heat treatment. X-ray photoelectron spectroscopy and contact angle measurements revealed that the PVP blocks were located at the bottom of the layers while the PS and PB blocks were at the top. Surface profiles of the top layers were examined with an atomic force microscope (AFM), and nodules of height ≅ 1 nm and width ≅ 20–50 nm were observed. Similar nodules were found for an adsorbed layer of a PS-PVP diblock polymer, but not for a PB-PVP layer. This result suggested that the nodules for the PS-PVP-PB layers were the domains of the PS blocks. Mechanisms of the nodule formation as well as the location of the PB blocks in the PS-PVP-PB adsorbed layers are discussed.