Surface-initiated, ring-opening polymerization of p-dioxanone from gold and silicon oxide surfaces

A polymeric thin film of a biodegradable poly(p-dioxanone) (PPDX) was grown from flat solid surfaces by a combination of formation of self-assembled monolayers terminating in hydroxyl groups and surface-initiated, ring-opening polymerization (ROP) of p-dioxanone (PDX). Tin(II) octoate [Sn(Oct) ₂] was used as a catalyst, and gold and silicon oxide surfaces were chosen as model surfaces. A molecularly-ordered film (self-assembled monolayer, SAM) was formed by immersing gold and silicon oxide substrates in a solution of alkanethiolates and in a solution of triethoxysilanes, respectively. The polymerization was achieved by heating a mixture of Sn(Oct)₂, PDX, and the SAM-coated substrate in anhydrous toluene for 24 h at 55°C (for a gold substrate) or 70°C (for a silicon oxide substrate). The characteristic IR peaks of PPDX (C-H stretching at ∼2923 cm^-1 and the CO ester at ∼1748 cm^-1) were observed in polarized infrared external reflectance spectroscopy (PIERS) spectra, indicating the presence of a PPDX film on the gold and silicon oxide surfaces. The average thickness of the PPDX film was measured to be 90 nm on the gold substrate and 46 nm on the silicon oxide substrate by ellipsometry. The PPDX films were further characterized by X-ray photoelectron spectroscopy (XPS), contact angle measurement, and atomic force microscopy (AFM).