Among the research directed by our group, Dennis Smith also holds many positions in the professional community:

• Co-founder, Tetramer Technologies, LLC
  
• Associate Director, COMSET
• Editor, Polymer Bulletin, Springer Journal of Polymer Science (2007 -
• Chair, ACS Division of Polymer Chemistry (Elected 2007- 
• Editorial Board, Polymers for Advanced Technologies, Wiley Journal (2006-
• Editorial Board, High Performance Polymers, Sage Journal (1998-
• Organizer and Chair, “FLUOROPOLYMER 2000-2008”, ACS Conference (2000-2008)
  

• PFCB - the cyclopolymerization of trifluorovinyl monomers to polymers containing the perfluorocyclobutane linkage.
• PLA - the improvement and optimization of renewable resource/biodegradable polymers based on polylactic acid derivatives.
• BODA - the thermal polymerization of bis-ortho-diynylarene monomers to polyarlyene thermosets.

Low-attenuation waveguides based on the propagation of long-range surface plasmon polaritons (LRSPPs) along thin Au stripes embedded in low absorption perfluorocyclobutane (PFCB) polymer are presented. A new low in propagation loss of <2:0 dB=cm was achieved for a 4 μm wide waveguide by optimizing the cladding material and fabrication process. The coupling efficiency between the LRSPP waveguide and the optical fiber is studied theoretically and experimentally for different widths of Au stripes and various cladding thicknesses. Lower coupling loss is found when the cladding thickness is close to the mode diameter of the butt-coupled fiber. Based on the 2D distribution of SPP modes calculated by a finite-difference mode solver, a symmetric structure of multilayer claddings with different refractive indices is proposed to optimize device insertion loss

Read more about this work at Applied Optics 2008, 47, No. 21, 3892-3900.

New fluorinated arylene vinylene ether (FAVE) polymers were prepared by a facile, metal-free condensation polymerization of fluorene, phenylenevinylene, dithiophene, or thiadiazole chromophore-containing bisphenols with bis(trifluorovinyloxy)biphenyl. The addition of chromophores encapsulated into the polymers were prepared in good yields and characterized by 1H and 19F NMR and GPC. Thermal analysis by differential scanning calorimetry (DSC) confirmed the polymers are entirely amorphous and are easy to solution process, producing optically transparent, flexible films. Thermal gravimetric analysis (TGA) showed they possess high thermal stability with decomposition temperatures of 340-387 °C and 308-443 °C in nitrogen and air, respectively.

Chromophore inclusion was confirmed by ultraviolet-visible (UV-vis) spectroscopy, which demonstrated tailorable photoluminescence (PL) in both the solution and the solid state by selective substitution of the chromophore. Polymer thin film PL studies revealed notable red-shifts compared with polymer solutions presumably attributable to aggregation in the solid state. Solution quantum yields of the polymers were comparable to those reported for the single chromophores used in this study.

Read more about this work at Macromolecules 2008, 41, 7490-7496 .

A difluorovinylene aromatic ether polymer (P1) incorporating periodic 5,5'-distyryl-2,2'-bipyridyl units as metal chelating chromophores was prepared by a transition metal-free step-growth polymerization. P1 displays strong ionochromic and ionoluminescent effects in response to transition metals. Although significant emission quenching is observed upon exposure to most transition metal ions, bathochromically shifted emission is observed upon addition of divalent d¹⁰ ions (Zn²⁺, Cd²⁺ and Hg²⁺). A selective 10-fold increase in integrated emission intensity is observed upon addition of Zn²⁺ to P1. The Zn²⁺-P1 metallopolymer acts as a ratiometric fluorescent indicator selective for fluoride anions, and the Cu²⁺-P1 metallopolymer exhibits a striking turn-on fluorescence response (>100-fold increase in integrated intensity) selective for cyanide and fluoride anions.

Read more about this work at J. Mater. Chem. 2008, 18, 1970-1976.

Post functionalization of aryl ether perfluorocyclobutyl (PFCB) polymers with fluoroalkyl side chains was accomplished with Umemoto's FITS reagents. The fluoroalkylated PFCB polymers (20 % functionalized) showed increases in both hydrophobicity and oleophobicity. Static contact angle for hexadecane was increased after fluoroalkylation from 0° to greater than 30° for the two PFCB polymers tested. Increased oil repellency makes these materials potential candidates for various coatings applications.

Read more about this at Polym. Bulletin 2008, 60, 343-349. 

The synthesis and characterization of solution processable, semi-fluorinated perfluorocyclobutyl (PFCB) aryl ether polymers possessing covalently bound pendant polyhedral oligomeric silsesquioxanes (POSS) cages were achieved. The synthesis of POSS aryl trifluorovinyl ether (TFVE) monomers were accomplished by the condensation of commercial monosilanolalkyl-POSS with TFVE-functionalized chlorosilane. POSS TFVE monomers were elucidated by ¹H, ¹⁹F, ¹³C, and ²⁹Si NMR spectroscopy, ATR-FTIR analysis, and elemental (C, H, and F) combustion analysis. Bulk thermal copolymerization of POSS TFVE monomers afforded random and block PFCB aryl ether copolymers functionalized with various POSS loadings. Quantitative monomer conversion was monitored by ¹⁹F NMR, which produced copolymer number-average molecular weights (M_n) of (19.5-24.9) x 10³ (in CHCl₃ using polystyrene as standard) determined by gel permeation chromatography (GPC). Thermal properties of POSS PFCB aryl ether copolymers were evaluated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Transmission electron microscopy (TEM) analysis of spin cast optically transparent, flexible POSS PFCB aryl ether copolymer films revealed the presence of 5-20 nm-sized POSS agglomerates. Optical profilometer analysis of spin and drop cast film surfaces exhibited a modest increase in surface roughness of POSS PFCB aryl ether copolymers as compared to PFCB aryl ether homopolymers without POSS inclusion. The POSS copolymers exhibited a modest increase in hydrophobicity as measured by static water contact angle analysis. Synthesis, characterization, thermal analysis, and unique surface features of POSS PFCB aryl ether copolymers are discussed.

Structure of PFCB POSS pendant copolymer and scheme of static water contact angle due to increased surface roughness.

Read more about this work at Macromolecules 2007, 40, 9517-9522.

Versatile intermediates 4-bromo(trifluorovinyloxy)benzene or 4-trifluorovinyloxyphenylboronic acid pinacol ester undergo a one step Suzuki coupling reaction with commercial aryl diboronic acids or aryl dibromides and afforded three new aryl trifluorovinyl ether chromophore monomers. The structures of these monomers were confirmed by ¹H, ¹⁹F and ¹³C NMR spectroscopy and elemental (C, H and N) combustion analysis. The monomers were readily polymerized via thermal [2 + 2] cyclopolymerization to form chromophore containing PFCB polymers with high molecular weights (M_n = 16,700 - 22,000), superb thermal stability T_d > 450 °C, and excellent processability. Photoluminescence studies reveal that the fluorinated ether linkage has no effect on lumiphore emission wavelength or solution quantum yields. Copolymerization affords a facile route to tailored emission from a linear polymeric system that includes a broad range of the visible spectrum. The properties of these polymers were analyzed by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), gel permeation chromatography (GPC), and absorbance and photoluminescence spectroscopy.

Solid-state PL overlay (max excitation) of copolymers P1-P5 as thin films (left) and photographs of mixed chromophore PFCB networks (right) (1 cm diameter) at 0.15 wt % total chromophore under ambient light (a), 254 nm light (b), and 365 nm light (c) and 7.5 wt % total chromophore under ambient light (d), and 365 nm light (e).

Read more about this at Macromolecules 2007, 40, 9378-9383.

A novel approach to property enhancement of poly(L-lactic acid) (PLLA) through the use of perfluoropolyether (PFPE) enchainment was achieved. Segmented copolymers (FluoroPLA) exhibit tailored surface properties with reasonably high molecular weights and low polydispersities compared to PLLA alone using standard ring-opening polymerization procedures in the presence of tin catalysts. Low loadings of PFPE content (ca. 1-5 wt %) decreases surface energies compared to PLLA from 35 to 38 to 15-18 mN/m², similar to values reported for poly(tetrafluoroethylene). Ultimate strain studies of FluoroPLA fibers and films have shown a dramatic increase (>300 % elongation) over PLLA. This new class of polymer may further expand the use of renewable resources in a variety of applications such as flame retardants, chemical resistant fibers and/or fabrics with tailorable surface energies and wetting properties.

Schematic illustration of L-lactide ring opening polymerization (ROP) with and without PFPE macroinitiator and illustration of resulting surface effects.

Read more about this at Macromolecules 2007, 40, 9354 - 9360.

First introduced by Dow in the early 1990's, perfluorocyclobutyl (PFCB) aryl ether polymers remain of interest to the academic community as well as industry.  An invited review highlighting nearly the past twenty years of PFCB aryl ether polymer research and directed applications has now been published. 

Read more about this review in J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 5705-5721 .  This work was featured on the cover of the journal in the December 2007 issue. 

In collaboration with Drs. Joseph M. Mabry and Ashwani Vij from the Air Force Research Lab, Edwards AFB, CA, we have prepared a new class of fluorinated POSS (F-POSS) materials possessing both a high degree of water and oil repellency. By controlling the degree of fluorine and architecture of the corner cap (R_f) substitution, we were able to tune the materials to exhibit desired wetting and melting properties. We plan to use these materials as drop-in modifiers for composite blends with PFCB aryl ether polymers to enhance mechanical and surface energy properties.

Synthesis of fluorinated POSS nanostructures.

Read more about this work in Chem. Commun. 2007, 4992-4994 . This article was featured on the cover of the December 2007 issue of Chemical Communications.

Dupont’s Nafion has served as a platform for development of perfluorosulfonic acid ionomer based proton exchange membranes (PEMs).  However, degradation of conductivity and mechanical properties above 110°C (the glass transition temperature) for Nafion is problematic for high temperature fuel cells, particularly for automotive applications.  In addition to its high cost, alternative materials for PEMs are of intense research in academic as well as industrial labs.

Our group has recently developed a new semi-fluorinated perfluorocyclobutyl (PFCB) aryl ether containing polymer in high yield via the condensation of a commercial bisphenol T and bis(trifluorovinyloxyether)biphenyl producing transparent, flexible films.  The polymer system exhibited a high degree of thermal stability and processability.  The sulfonated analogue showed the highest degree of sulfonation at 27% from ion-exchange chromatography, producing a conductivity of 0.011 S/cm at 100% relative humidity (RH).

Sulfonated FAVE Polymer

More information on this work has been recently published as an invited article in High Performance Polymers 2007, 19, 581.

POSS endcapped PFCB copolymers have been recently prepared producing optically transparent, solution processable materials with enhanced physical properties.  This effort was done in collaboration with Dr. Joseph M. Mabry (Air Force Research Laboratory Edwards AFB, CA) for the development of hydro- and oleophobic coatings. Trifluorovinyl aryl ether (TFVE) POSS monomers serve as chain terminators to control polymer molecular weight thermal [2+2] cyclodimerization. Three distinct TFVE POSS monomers were synthesized using a corner-capping methodology with cyclopentyl, iso-butyl, and trifluoropropyl moieties installed on the apex of each silicon atom. Incorporation of POSS into the PFCB polymer serves as a plasticizer by lowering glass transition temperature (T_g) and was shown to increase the thermal stability of the copolymers compared with the PFCB homopolymers with no POSS incorporation.

Read more about this work in Polymer 2007, 48, 4637-4645.

The thermal cyclopolymerization of three trifluorovinyl aromatic ether monomers 1,1,1-tris (4-trifluorovinyloxyphenyl)ethane (1), 4,4'-bis(4-trifluorovinyloxy)biphenyl (2) and 2,2-bis(4-trifluorovinyloxyphenyl)-1,1,1,3,3,3-hexafluoropropane (3) were monitored in situ using time-resolved electron paramagnetic resonance (EPR) spectroscopy over a temperature range of 150–210 ^◦C. The signals observed during the early stages of perfluorocyclobutyl (PFCB) polymer production suggest the formation of a triplet state corresponding to the proposed biradical intermediate with a strong dipole–dipole interaction. A doublet splitting shows the presence of hyperfine coupling due to fluorine. The characterization of radical species formed during the polymerization of monomer 1 using model compounds and polymerization kinetics of monomer 2 are also presented.

Read more at Polym. Int. 2007, 56, 1142-1146.

Bis-ortho-diynylarene (BODA) monomers, prepared from common bisphenols in three high yielding steps, undergo free-radical-mediated thermal polymerization via an initial Bergman cyclo-rearrangement. Polymerization is carried out at 210 °C in solution or neat with large pre-vitrification melt windows (4–5 h) to form branched oligomers containing reactive pendant and terminal aryldiynes. Melt- and solution-processable oligomers with weight-average molecular weight M_w = 3000–24 000 g mol^–1 can be coated as a thin film or molded using soft lithography techniques. Subsequent curing to 450 °C affords network polymers with no detectable glass transition temperatures below 400 °C and thermal stability ranging from 0.5–1.5 % h^–1 isothermal weight loss measured at 450 °C under nitrogen. Heating to 900–1000
°C gives semi-conductive glassy carbon in high yield. BODA monomer synthesis, network characterization and kinetics, processability, thin-film photoluminescence, and thermal properties were characterized.

X-ray single-crystal structures of the three forms of monomer 1 (2,2-Bis-(3,4-di(phenylethynyl)phenyl)-1,1,1,3,3,3-hexafluoropropane).

Read more at Adv. Funct. Mater. 2007, 17, 1237-1246.