The pure enantiomers of D -C as well as a third constitutional isomer of this higher fullerene were produced by a retro-Bingel reaction on the first organic derivatives of C (see scheme). These derivatives were synthesized by Bingel cyclopropenation of C , separated, and unambiguously structurally characterized.
For adequate transparency we have selected hexafluoroisopropanol as an acid group and an ␣-trifluoromethylacrylic moiety as a repeat unit of our 157 nm resist polymers. The hexafluoroalcohol group is bound to norbornene or styrene. Four platforms are currently available to us: ͑1͒ all-acrylic, ͑2͒ all-alicyclic, ͑3͒ acrylic-alicyclic, and ͑4͒ acrylic-aromatic systems. While the all-alicyclic ͑all-norbornene͒ polymers are synthesized by transition-metal-initiated addition polymerization, all other polymers involving ␣-trifluoromethylacrylic monomers are prepared by conventional radical copolymerization. Characterization of the polymers and preliminary lithographic evaluation are reported.
The novel mixed bis-adducts of C60, (+/-)-4-(+/-)-8 and 9, with a bis(ethoxycarbonyl)methano addend (Bingel addend) and a second addend ([1,2]benzeno, but[2]eno, methaniminomethano, or diarylmethano) bridging 6,6-closed bonds of the carbon sphere were synthesized in two-step reactions. Each bis-adduct was exhaustively electrolyzed at the potential of the second fullerene-centered reduction step, resulting in the selective removal of the Bingel addend (retro-Bingel reaction) to produce the corresponding mono-adducts, which were isolated in yields of over 60%. These results open up the possibility of using the Bingel addend as a temporary protecting and directing group in the construction of multiple adducts of C60 with unusual addition patterns. The Bingel-type mono-adduct of C70 10 and the constitutionally isomeric bis-adducts 11, (+/-)-12, and (+/-)-13 were also included in this investigation. A large difference in the electrochemical behavior between C70 bis-adducts and the corresponding C60 derivatives was observed. Thus, the intramolecular "walk-on-the-sphere" isomerization which occurs readily with Bingel-type bis-adducts of C60 under the conditions of two-electron controlled potential electrolysis (CPE) is only a minor reaction pathway in the series of C70 derivatives. The latter preferentially undergo retro-Bingel reaction.
Unexpectedly good UV transmittance at 157 nm of poly(norbornene sulfone) bearing a pendant hexafluoroisopropanol functionality has prompted us to employ this fluoroalcohol as an acid group for the design of chemical amplification resists for use in 157 nm lithography. The backbone structures to which the hexafluoroalcohol group is attached are polynorbornene and polystyrene. Furthermore, our discovery that poly(methyl a-trifluoromethylacrylate) is adequately transparent at 157 nm has led us to incorporate the a-trifluoromethylacrylic unit in the polymer backbone by radical copolymerization with styrenes and norbomenes. Thus, four platforms are currently available to us in preparation of 157 nm resist polymers; 1) all-acrylic, 2) all-norbornene, 3) acrylic-norbomene, and 4) acrylic-styrenic systems.
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