Fabrication of Patterned High-Density Polymer Graft Surfaces. 1. Amplification of Phase-Separated Morphology of Organosilane Blend Monolayer by Surface-Initiated Atom Transfer Radical Polymerization

• Published in: Macromolecules Vol. 35; no. 4; pp. 1412 - 1418
• Main Authors: Ejaz, Muhammad, Yamamoto, Shinpei, Tsujii, Yoshinobu, Fukuda, Takeshi
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 12.02.2002
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymerization; Preparation, kinetics, thermodynamics, mechanism and catalysts; Patterning; Surface reaction; Graft copolymers; Atom transfer polymerization; Living polymer; Methyl methacrylate polymer; Organic silane; Surface topography; Experimental study; Sulfonyl halide; Mixed monolayer; Free radical polymerization; Langmuir Blodgett layer; Wafer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma010371f

Patterned films of a low-polydispersity polymer densely end-grafted on a silicon substrate were fabricated for the first time by the combined use of the Langmuir−Blodgett (LB) and the surface-initiated atom transfer radical polymerization (ATRP) techniques:  a blend monolayer of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CTS:  ATRP initiator) and n-octadecyltrimethoxysilane (OTS:  noninitiator) was immobilized on a silicon wafer by the LB technique, and then the ATRP of methyl methacrylate was carried out on the modified wafer in the presence of the Cu/ligand complexes. Atomic force microscopic studies revealed that the CTS/OTS blend was immiscible and phase-separated into two monolayer phases:  most OTS molecules aggregate with each other, forming a condensed-type monolayer domain with CTS molecules excluded from there almost perfectly, and the remaining OTS molecules are incorporated in the matrix region. This 2-dimensionally phase-separated structure was successfully amplified by the controlled growth of a high-density graft layer only on the matrix phase of CTS as a main component. The amplification by the ATRP technique was characterized by a sharp boundary between the grafted and ungrafted domains; as a measure of the spatial resolution, the boundary sharpness Δw was evaluated to be ca. 100 nm. The domain size in the phase-separated structure was independent of the mole fraction of CTS, while it could be changed by changing the pH of the subphase water:  namely, the higher was the pH, the larger was the domain size. It was deduced that a change in pH of the subphase water gave rise to a change in the hydrolysis rate of the methoxysilyl groups into silanol groups and hence a change in the rate of condensation of the silanol groups into domains.