(16f) Temperature and pH Response of a Series of Amino Methacrylate Polymer Brushes by In-Situ Spectroscopic Ellipsometry Measurements
Stimuli responsive polymers have potential in a wide range of applications, from nanometer-scale drug delivery to flow control in microfluidic devices. Surface-confined atom transfer radical polymerization (ATRP) or single electron transfer living radical polymerization (SET-LRP) has been used to synthesize a series of surface-grafted poly(amino methacrylates) from silicon substrates modified with silane self assembled monolayers (SAMs). Synthesis and characterization of the following polymers will be described in this presentation: poly(2-dimethylamino) ethyl methacrylate (PDMAEMA), poly(2-dimethylamino)ethyl acrylate (PDMAEA), poly(2-diethylamino ethyl methacrylate) (PDEAEMA), and poly(2-(tert-butylaminoethyl methacrylate) (PTBAEMA). These poly(amino (meth)acrylate) brushes can show combined pH and temperature dependent changes in the grafted polymer layer thickness. The optical constants of a polymer grafted to a reflective substrate can be measured using spectroscopic ellipsometry. As the polymer layer expands/contracts in response to an external condition, the optical constants for the polymer change and can be modeled to provide a very precise resolution of the layer thickness changes. In-situ spectroscopic ellipsometery studies were performed using a liquid cell attachment with temperature control to collect dynamic and equilibrium data. Multilayer models were generated based on a Cauchy dispersion model that accounted for the for the polymer, initiator, and silane layers. Modeling the ellipsometry data collected at different solution temperatures and pH levels allowed for determination of percent thickness change, maximum and minimum thickness, and response rates as a function of temperature and time.