Polymeric Materials: Science and Engineering Division

2006 ACS Applied Polymer Science Award in Honor of Christopher K. Ober

Professor Christopher K. Ober, the Francis Norwood Bard Professor of Materials Engineering at Cornell University, is the 2006 recipient of the ACS award in Applied Polymer Science.  Chris has carried out significant research in several major areas of applied polymer research during his professional career. Following a Ph.D degree from the University of Massachusetts in 1982, Chris spent several years at the Xerox Research Center of Canada before joining the Department of Materials Science and Engineering at Cornell.  His global research interests involve the clever design and synthesis of novel polymers and their characterization using a variety of innovative techniques. While a graduate student, Chris made significant contributions to the development of the field of liquid crystalline polymers. At Xerox he earned several corporate research awards revolving around his invention of dispersion polymerization of large monodisperse polymer microspheres as part of his work on xerographic printing materials. These microsphere polymerization methods were successfully transferred to the development-scale manufacture of xerographic toners and ink-jet inks.  This work has had a lasting and major impact on the field of dispersion polymerization.  Since joining Cornell in 1986, Chris has established a successful polymer research group with emphasis on the synthesis, processing and characterization of functional polymers with tailored molecular architectures for predefined properties. His activities include the detailed evaluation of polymer behavior for the design of superior macromolecular materials using synchrotron based characterization methods, and the development of new controlled architecture polymers using synthetic tools such as anionic and living radical polymerization. Of special interest has been material systems that undergo “bottoms-up” self-organization/assembly including liquid crystalline polymers and block copolymers and “top down” lithographic processing.   Environmentally friendly materials and processes are a recent focus of his group.  He is an author on more than 250 publications, 250 invited presentations, more than 30 patents, and has graduated ~25 Ph.D. students.

Much of Ober’s recent activity has focused on photolithography, and in particular fluorinated photopolymers. Working with major semiconductor manufacturers and resist companies, his group has tackled the problem of water developable, 157 nm radiation transparent photoresists by inventing a variety of photopatternable fluoropolymers and it is here that he has had his greatest impact on polymer science.  These resist materials became the first “test” resist for a new generation of lithographic tools that could be patterned to form features as small as 100 nm. This work required the invention of several new families of water-soluble fluoropolymers and the successful study of the absorbance behavior of polymers under 157 nm irradiation. Ober and his group demonstrated the important role that certain fluorocarbinol functions have in altering absorbance properties at these short wavelengths opening up new paths for theoretical study. Ober recently published the first paper to appear in a major journal to describe a functioning 157 nm resist.

To overcome the problem of the poor solubility of fluoropolymers and problems associated with pattern collapse in aqueous developers, Ober has also pioneered the use of supercritical CO2 as an environmentally friendly, lithographic developer. Not only are the environmental aspects important, but also this experimental process holds the prospects for creating microelectronics much smaller than now possible because of the low viscosity and low surface tension of this solvent. Ober was awarded the 2000 SRC/SSA/International Sematech (ISMT) award for research in manufacturing and environment, safety and health for part of this work. These surface stable “resists” have been shown to have resolution below 100 nm and to form topographically controlled ultrahydrophobic surfaces with contact angles greater than 150°, a truly non-wetting, water repellent surface. More recently Ober has explored molecular glass photoresists for next generation lithographies.

Fluorinated polymers while well known for their low surface energy properties are less appreciated for their ability to exhibit liquid crystalline properties, a characteristic that Ober and his group have exploited to make fluoropolymers with remarkably low surface energies. Using innovative molecular design, Ober has incorporated semifluorinated LC segments into polymers to produce materials that resist surface reconstruction due to the thermodynamic barrier to rearrangement presented by the mesophase. The extremely high surface-ordering present in these semifluorinated LC polymers has been proven using Near Edge X-ray Absorption Fine Structure (NEXAFS), AFM and other techniques. These materials are part of Ober’s efforts in the study of environmentally friendly materials as they make excellent coatings that resist biofouling in a marine environment without the need for toxic substances. Protective films made of these liquid crystalline fluoropolymers are undergoing testing by the Navy for marine coatings and are presently among the more successful non-toxic coatings so far developed.

Another environmental problem is the accumulation of large quantities of used printed circuit boards from used computers. Building on his studies of photopolymers, Ober also examined the effect of inserting the same weak links into thermosets as an aid in recycling epoxy based composites. These thermosets have now been identified as providing a “rework” function to thermosets, that is, the thermoset network can be induced to break down by modest heating.  This completely new class of thermosets is proving to be of great interest to the microelectronics industry where adhesives that are robust under normal use can be removed under specific conditions. His fundamental study of the breakdown mechanism was instrumental in understanding the process and designing new materials to exploit this behavior.  These “reworkable” materials are being commercialized for use by the computer and telecommunications industries as adhesives for microchips that permit reprocessing of defective materials.  These polymers are expected to first find use in cell phone manufacture. This combination of careful science mixed with technical relevance is creating great interest in industry for Ober’s research. Finally, this work combined with efforts on the creation of supercritical CO2 processable photopolymers earned Ober’s student, Dr. Shu Yang, the 2001 Unilever Award for Outstanding Graduate Thesis in the Polymer Field.

Harnessing molecular level self-organizing processes and directing that assembly on nanometer length scales will be essential if many of the anticipated goals of biotechnology and nanotechnology are to be achieved. Ober has shown that the competition between the mesophase and phase separation leads to the formation of new microphase structures and to the ability to use the microstructure to manipulate mesophase behavior and orientation. The convergence of self-assembly and photolithographic processes is an area of intense research in his group. These fundamental studies are expected to have future impact on applications in photonics, nanotechnology and biotechnology.

Ober’s professional activities include his continuing role as Associate Editor of Macromolecules and as a member of the editorial boards of Journal of Macromolecular Science, Polymers for Advanced Technologies, and Polymer Bulletin. He has been active in PMSE, serving as the division chair in 2000 and continues his service today as a member of the Long-Range Planning Committee and as the division's Alternate Councilor. Ober serves as a member of the Advisory Council of the Max-Planck Institute for Polymer Research, Mainz, Germany. He served as Director of the Department of Materials Science & Engineering from 2000-2003. He is presently vice president of the IUPAC Polymer Division.

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