Growth and Structure of Multifunctional Polymer Brushes from Ultra-thin Coatings

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NON-TECHNICAL SUMMARY:Polymer brushes are long stringy molecules that are chemically bonded to a surface to form dense, thin coatings that drastically change the properties of the surface. These coatings guide the behavior of cells for regenerative medicine, promote biocompatibility in implant devices, resist deposition of micro-organisms on ship hulls, or control flow of electricity in microelectronic devices. The structure of the polymer brushes provides the needed mechanical strength to form a stable coating and their chemistry provides the right functionality to interface/communicate between the substrate and the environment. This research program will develop new synthetic methodologies to make these polymer brushes and develop materials characterization techniques to promote a molecular-level understanding of the resulting structures. This methodology has the potential to be of broad impact since the chemistry is simple enough to be adapted by the coatings industries. The research program will serve to inspire and involve undergraduate students in polymer science and engineering research, by working with the PI and graduate student mentors through the REU program. K-12 educational modules developed through this research will be disseminated nationally by the PI and the graduate students by partnering with UW-Madison Institute for Chemical Education (ICE). Through the Women in Science and Engineering (WISE) Residential Program the PI will engage in mentoring underrepresented students to create a supportive environment by coordinating information, research and activities for and about women in the sciences and engineering.TECHNICAL SUMMARY: The research program will study the synthesis of a single-component crosslinked coating to grow homopolymers and mixed polymer brushes with excellent control over homogeneity of grafting sites, dispersities, chemical functionalities, graft to graft distance, ability to grow low to high molecular weights, and with stability to thermal annealing conditions. The growth of polymer brushes from these coatings is fundamentally different from growth from traditional self-assembled monolayers. A key aspect of this research will be to develop a mechanistic understanding of the growth process by combining depth profiling and angle resolved X-ray photoelectron spectroscopy (ARXPS) studies. The stratification effect as well as brush growth kinetics will be studied as a function of crosslink density and coating thickness by embedding specific elemental markers in the brush (Br and N). Combination of ARXPS, Atomic force microscopy and 3D tomography will provide useful morphological information on these polymer brushes. The brushes grown from these coatings will be floated off from the substrate as "polymer carpets" and 3D morphological insight obtained by 3D tomography. Melt self-consistent field theory (SCFT) predictions of phase diagrams for mixed polymer brushes are based on the assumption that the grafting densities are uniform. So far experimental means for meeting these assumptions have lagged behind. Using the unique chemistry for growth of well-defined brushes and the characterization methods developed in this proposal the SCFT predictions will be tested. Furthermore the simplicity of the chemistry is expected to allow arbitrary changes in composition to tune surface properties by incorporating appropriate comonomers. For these reasons the methodology developed here has the potential to have major impact by highly simplifying the way polymer brushes are grown.