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| UNC-CH Collaborators |
| Edward Samulski |
| Ashby Group Research Projects | |
| General Overview | |
| The
synthetic and materials design capability in the Ashby group allows
for unique approaches to address the continued need for new materials
with advanced properties. In line with these priorities, the research
explores a broad range of topics from polymer/quasicrystal composites
to functionalized elastomers to the newest interest, functionalized
aliphatic biomaterials. The first project in the group, the design,
fabrication and study of polymer quasicrystal composites is an exciting,
growing area. Our group was the first to produce these unique composites
that combine the low surface energy, high hardness, high scratch
resistance, and high thermal stability of quasicrystals with the
well-known processing techniques of polymeric matrices. The work
was highlighted on the cover of the U.S. Department of Energy’s,
DOE This Month in August of 2000. Since that time, the group has
shown in 5 papers and a filed patent that these composites do have
a unique combination of high strength and hardness comparable to
ceramic-filled composites, but with minimal abrasion to other surfaces. The second project in the group addresses a materials problem with a synthetic methodology approach, further highlighting the flexibility in new materials design in the Ashby group. A lack of functional group versatility, poor processing, difficult synthetic techniques, molecular weight limitations, poor film-forming ability are a few of the problems which have plagued poly(paraphenylene)-based materials. The Ashby group has utilized metal-catalyzed coupling reactions to overcome many of these obstacles and lead to new materials that have a unique combination of properties including flame retardance, excellent insulating ability, film-forming ability, and water and organic solvent resistance. Potential uses for these new materials in separations membranes, electronics, structural materials, and fuel cells led to the filing of a patent application that issued in 2003. In addition, seven articles in this area have been published by the group. Finally, the group seeks to design and prepare new materials using functionalized diene-based monomers. This research opens the door to the formation of polymers to be used as adhesives, elastomers, blend compatibilizers coatings, etc. The work is the topic of three issued patents and numerous papers. In addition, the most recent work in the group utilizes many of these compounds to synthesize new functionalized biomaterials with target applications in drug delivery and gene therapy. The ability to attach targeting groups, cell fusion promoters, mechanical property-enhancing groups, etc. would significantly advance performance. |
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| Polymer Quasicrystal Composites | |
New polymer-quasiscrystal materials with the unique combination of super high hardness and extraordinarily low abrasion are being developed. Quasicrystals, first discovered in 1982 by Dan Shechtman are complex metal alloys that are most comparable to ceramic particulate fillers in polymer composites. The unique properties of the bulk quasicrystal material include low surface energy compared to most metals, low wettability in contact with most aqueous solutions, low coefficients of friction, high hardness, low thermal conductivity, and high softening temperatures. The major drawback in quasicrystal applications is the brittle nature of the materials and the high temperature thermal spray coating techniques used in processing. By combining polymers with quasicrystals in a composite, quasicrystals are easily processed and simultaneously their unique, low abrasion and high hardness properties are introduced into the composite. The excellent wear properties point to a variety of applications including biomaterials. Recently, it was determined what polyethylene-quasicrystal materials
meet the two key requirements for biological utility, namely that
they do not cause cell damage or death and that the tested cells
do not significantly adhere to the material surface. The potential
increase in the lifetime of joint replacements, as well as in other
low wear mechanical part applications, is tremendous. |
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| High Performance Polymers via Nickel Catalysis | |
Many
of the barriers for the synthesis of high performance polymers are
understood, but difficult to resolve. For example, the properties
of a material are often directly linked to its rigidity, crystallinity
or functionality. Hence, design of a material with a high use temperature
and other desired properties often simultaneously gives a polymer
that is difficult to synthesize and to process. In order to address
these kinds of issues in high performance polymers, we have explored
new materials and synthetic methods. Our efforts focus on a nickel-catalyzed
reaction that is a facile and is a feasible route to carbon-carbon
bond formation. It has provided a low temperature, mild reaction
to produce a variety of poly(p-phenylene) analogues. For example,
the fluorinated derivatives of the polymer (2) shown below are being
synthesized. The initial materials (2) has an excellent combination
of properties. It is flame retardant, water resistant, very thermally
stable, clear, colorless, and forms flexible films.  In addition to the fluorinated materials, a variety of functionalized poly(p-phenylene) materials have been made using new synthetic methodologies designed in the group. These alternative routes have led to efficient ways to produce several new materials including polar functionalized polybenzophenones, and rod-coil-rod materials. "Fluorinated Aromatic Monomers and Their Polymerization by Nickel Catalyzed Coupling”, Issued 2/03, Patent No. 6,515,101 "A series of New High-Performance Materials Based on Poly(4'-fluorophenyl-bis(4-phenyl)phosphine oxide)”, Rusch-Salazar, L.; Sheares Ashby, V. J. Polym. Sci., Pt. A 2003, 41(14), 2277. "Novel Poly(paraphenylene)s via Nucleophilic Aromatic Substitution of Poly(4’fluoro-2,5-diphenylsulfone)”, Bloom, P.; Sheares, V.V. Macromolecules 2001, 34, 1627. "Synthesis of Poly(p-phenylene) Macromonomers and Multiblock Copolymers”, Bloom, P.D.; Sheares, V.V. J. Polym. Sci., Polym. Chem. Ed. 2001, 39, 3505. "Bilayer Nanocomposite Molecular Coatings from Elastomeric/Rigid Polymers: Fabrication, Morphology and Micromechanical Properties”, Luzinov, I.; Julthongpiput, D.; Bloom, P.D.; Sheares, V.V.; Tsukruk, V.V. Macromol. Symp. 2001, 166, 227. "Synthesis and Characterization of Poly[[1,1’-biphenyl]-4,4’-diyl[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]]”, Havelka, P.A.; Sheares, V.V. Macromolecules 1999, 32, 6418. "Alkyl-Substituted Poly(2,5-benzophenone)s Synthesized via Ni(0)-Catalyzed Coupling of Aromatic Dichlorides and Their Miscible Blends”, Pasquale, A.J.; Sheares, V.V. J. Polym. Sci., Polym. Chem. Ed. 1998, 36, 2611. "Novel Poly[3-(p-substituted)benzoyl-2,5-thiophenes] via Nickel(0)-Catalyzed Coupling Polymerization”, Wang, J.; Vonhof, T.; Sheares, V.V. Macromolecules 1998, 31, 6769. |
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| Polar, Functionalized Diene-Based Polymers | |
As with the above described materials, our interest in the field of functionalized dienes stems from the possibility of creating systems that combine the unique properties of a functional group and those of a high molecular weight polymer. Because the structures of most dienes have been limited to carbon, hydrogen and halogens, the properties of the resulting polymers have also been limited. The approach that we have taken in this area is to synthesize polar functionalized monomers. The increased polarity alters a number of properties including adhesion, solubility, permeability, etc. In addition, the polar functionality can be used as a reactive site for further polymerization and for the creation of a variety of polymeric structures. Polarity also changes the reactivity of the monomers and the ratio of the geometric isomers in the final polymers, depending upon the initiating system and upon the polymerization conditions. As a result, the thermal and mechanical properties will also be affected. Our study has
included a number of different functional groups including amines,
nitriles, esters, acids and alcohols. These groups were targeted
with specific properties in mind. For example, small molecule amine
additives (3) are known to increase adhesion in polymers to certain
surfaces and are often used in materials like styrene-butadiene
rubber. The diester (5) is a means of introducing acid functionality,
and therefore water solubility, into the materials via post-polymerization
modification. One of the newest projects in the group takes advantage
of these materials to produce polar, functionalized, biomaterials. |
Department of Chemistry
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Last Updated:
January 16, 2007
© 2006 University of North Carolina at Chapel Hill Content Manager: chemcontent@unc.edu |