Tuning the properties of surface-anchored polymer networks by varying the concentration of thermally-activated crosslinker, annealing time, and temperature in a one-pot reaction*

We investigate the properties of surface-anchored polymer networks created via one-pot synthesis using thermally active 6-azidosulfonylhexyltriethoxy silane (6-ASHTES).  6-ASHTES is a bi-functional gelator that undergoes crosslinking and surface-anchoring reactions when annealed above 100°C.  We employ a polyvinylpyrrolidone (PVP) with different molecular weights (10 - 1,300 kDa) as a model system to examine the effect of 6-ASHTES concentration, annealing time, and annealing temperatures on gel formation.  A thin film of PVP/6-ASHTES mixture is deposited on a clean silicon wafer and annealed to form network layers.  Spectroscopic ellipsometry measures the film thickness of the crosslinked layers from which the gel fraction and swelling ratio are determined.  The gel fraction of PVP in the network can be “dialed in” by varying the annealing time, temperature, and concentration of 6-ASHTES in the PVP/6-ASHTES mixture.  We use a simple Monte Carlo simulation model to describe crosslinking as a function of crosslinker concentration, reaction rate, reaction time, and polymer length.  The trends obtained from the model simulations are in qualitative agreement with the experimental data.