Polymer Brush Growth by Surface-Initiated Ring-Opening Polymerization from a Cross-Linked Polymer Thin Film

Abstract

Modification of a surface with polymer brushes has emerged as an effective approach to tune the properties of a substrate. Brushes grown from an inimer-containing cross-linkable polymer coating provide significant advantages compared to other “grafting-from” methods, such as improved stability, increased grafting density, and the potential to control the grafting density. So far, the inimer coating method has only been applied for surface-initiated controlled radical polymerizations. In this work, an approach is presented for the fabrication of a stable cross-linked ultra-thin polymer coating containing hydroxyl groups which serve as initiating sites for surface-initiated ring-opening polymerization (SI-ROP). The polymers used for the fabrication of the coatings consist of 2-((tetrahydro-2H-pyran-2-yl)oxy)ethyl methacrylate (THPEMA), a small fraction of a cross-linkable unit, and a diluent styrene. Three coatings with varying THPEMA and styrene content are fabricated, and poly(dimethyl siloxane) (PDMS) and poly(caprolactone) (PCL) brushes are grown by SI-ROP of hexamethylcyclotrisiloxane (D₃), and ε-caprolactone respectively. The brushes are characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), static contact angle measurements, ellipsometry and size exclusion chromatography (SEC). The results demonstrate a well-controlled ROP of D₃ and ability to control grafting density by tuning the THPEMA content of the coatings.