Reactions of Functional Polymers at Organic Interfaces

Columbia University, New York NY

Investigators

Abstract

TECHNICAL SUMMARY: Interfacial reactions involving polymers are far more complex than reactions involving small molecule reactants because of the broad range of variables that can affect their molecular structure and behavior at interfaces. While interfacial reactions are a part of many polymer applications, a fundamental understanding of the parameters affecting them is generally lacking. The scientific goal of the proposed research plan is therefore to provide a fundamental and quantitative understanding of the factors that influence the reactions of polymers at organic interfaces. The achievement of this goal is the deliverable of this project: a fundamental basis for both the molecular design of polymer interfacial reactions and for the subsequent control of the interfacial properties they bring about. Two model reaction systems have been selected for study to represent the wide variety of reactions that may be encountered in practice: . a "standard" reaction between a functional polymer and an organic surface containing a complementary functional group . a photografting reaction between a polymer in contact with an organic surface, one of which contains a photoactive group capable of grafting the polymer to the surface. The functional polymers required for the research will be prepared by atom transfer radical polymerization. The proposed research investigates how interfacial reactions are influenced by factors such as: solvent quality and concentration, including neat polymers; molecular weight; areal density of functional groups; location of functional groups along the polymer backbone; the nature of the surface interaction parameter, state of the polymer (i.e., glassy or rubbery), conditions of the photochemical reaction and reaction time. The organic interfaces employed will be prepared on either silicon wafers or gold-coated wafers in order to enable characterization of the reactions by a barrage of techniques including: x-ray photoelectron spectroscopy, grazing incidence reflection infrared, ellipsometry, contact angle, MALDI-TOF mass spectrometry, fluorescence spectroscopy and gel permeation chromatography. The research program also includes validation of a new concept, covalent layer-by-layer assembly, in which multiple polymer layers are successively built up on an organic substrate wherein each layer is covalently bound to the previous layer. NON-TECHNICAL SUMMARY: The nature of how long chain molecules react at interphases is an important underlying aspect of many applications involving polymers and biomacromolecules. Such reactions are used to control surface properties of materials and coatings such as adhesion and wettability, are employed to make magnetic nanoparticles soluble in water for potential use as magnetic resonance imaging contrast enhancement agents, and are used in the fabrication of biosensors wherein DNA, proteins, antibodies and antigens are chemically bound to substrates to form diagnostic microarrays. The proposed research program will provide a scientific basis for the design of such reactions and their optimization for use in these applications. This enabling technology will play an important role in the manufacturing of inexpensive DNA sequencing chips, clothing that can filter out harmful pathogens and rapid diagnostics that can identify dangerous pathogens and antigens. The proposed research will also have a broad impact on research and education through a number of programs: the training of undergraduate and graduate researchers, hosting of a summer high school chemistry teacher researching interfacial reactions and with that teacher, the development of modules on polymer chemistry suitable for use in his classes. The P.I. will also continue his outreach efforts to Columbia University undergraduate students at large through his activities as a Professor in Residence, living amongst the students in a dormitory and hosting informal dinners with undergraduates and a special guest talking on a topic related to the series theme "Society and Technology".