In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Craig Hawker of the University of California at Santa Barbara will develop strategies for utilizing ketene chemistry as a synthetic tool for creating modular polymer and soft materials. The approach is to discover reaction conditions for the low temperature, quantitative generation of ketenes from Meldrum's acid and its derivatives. The precursor moieties would then be placed at the side chains, chain ends and interiors of polymers and on surfaces in order to explore the modular chemical functionalization of such substrates, exploiting the rich chemistry of ketenes. The broader impacts involve advancing teaching, training and learning through the development of a course on communication and presentation design, organizing an ACS Symposium on "click" chemistry approaches to polymer and materials synthesis, and funding local minority undergraduate students to attend the Dow Foundation Lecture Series.
This work will expand the repertoire of chemistry that can be used to create new polymers and materials. The results of these studies could have many important long term impacts on a variety of applications and industries in which polymeric materials are important, including fine chemicals, coatings, electronics, and biotechnology.
Through advances in controlled polymerization techniques and reliable post-functionalization methods, a team of polymer chemists at the University of California, Santa Barbara have developed the tools necessary to create materials of almost infinite variety and architecture. This ability to produce robust and functional materials with well-defined structures and multiple, individually accessible functional groups is best exemplified in the UCSB work on crosslinked films. Crosslinked films are widely used in applications ranging from microelectronic devices to coatings for food containers and medical devices. In all cases, the starting materials are soluble and processable organic polymers/small molecules and generally, covalent crosslinking of polymeric assemblies is brought about by the application of heat or light. This generates highly reactive groups along the polymer chains, however these traditional strategies suffer from a general lack of control of the crosslinking chemistry as well as the fleeting nature of the reactive species that precludes secondary chemistry. The UCSB researchers have addressed both of these issues by exquisite control of chemical reactivity to effect both crosslinking and subsequent functionalization of polymer films by mild heating. This results in exacting control of the crosslink density as well as the density of the residual stable functional groups available for subsequent, step-wise functionalization. This methodology was exploited to develop a strategy for the independent and orthogonal triple-functionalization of crosslinked polymer thin-films through microcontact printing, showing great promise in low-cost diagnostic devices. A number of important additional challenges in materials science require not only access to new functional polymers as described above, but also triggered, on-demand properties and performance. The power of such temporal and spatial control of polymerization can be found in Nature, where the production of proteins, nucleic acids, and polysaccharides helps regulate multicomponent systems and maintain homeostasis. Building on the above concepts of control and efficient reactions, UCSB researchers have added significantly to the existing strategies for temporal control of polymerizations through external stimuli. Their recent work with light as a common and easily manipulated external stimuli illustrates the considerable potential for this emerging field and provides a coherent vision and set of criteria for pursuing future strategies for regulating controlled polymerizations.
