Polyhydroxylated C 60 As An Hypercross-Linking Agent
- PDF / 270,519 Bytes
- 4 Pages / 414.72 x 648 pts Page_size
- 41 Downloads / 146 Views
ABSTRACT Polyhydroxylated fullerene derivatives (fullerenols) were utilized as an efficient hypercross-linking agent for the synthesis of elastic poly(tetramethylene oxide)-based polyurethane networks with excellent thermal mechanical properties. Polyhydroxylated fullerenes were synthesized from the hydrolysis of polycyclosulfated fullerene derivatives in the presence of water at 85-90 °C or in aqueous NaOH solution at ambient temperature. Fullerene molecules possessing unusual conjugated molecular orbitals are susceptible to chemical reactions with a variety of nucleophilic, electrophilic, organo-radical, enophilic and halogenation reagents. 1-4 These extensively explored functionalization chemistry become essential means in the design of multiple-step synthetic pathways for the preparation of fullerene derived functional intermediates. That interested chemists in exploring the utility of functional fullerenes derivatives in molecular and polymeric materials applications. Polar fullerene derivatives, such as water-soluble fullerenols 5,6 containing multiple hydroxy functional groups, have been prepared primarily by a sequence of reactions initiated by either the electrophilic reagent 7 ,8 or the oxidative nucleophilic reagent. 9 A feasible synthetic methodology using the former reagent involved the electrophilic attack of cationic nitronium ions on olefinic moieties of fullerene molecules, forming the carbocationic nitronium-C60 intermediate, prior to the replacement of resulting nitro addends by weak nucleophiles. The latter reagent was used to initiate the direct one-electron oxidation of fullerene molecules in strong acids, followed by the nucleophilic attack of the counter anion on the resulting carbocationic C60 radical in the reaction medium. Fullerenol synthesized by these two independent approaches showed distinguishable difference in its molecular structure and stability in acid. The electrophilic synthesis was frequently complicated by the proposed fullerene-oxide rearrangement as a part of the overall reaction mechanism that resulted in the formation of hemiketal substructure in the fullerene cage skeleton in addition to hydroxy addends. 10 Whereas the stepwise oxidative nucleophilic synthesis afforded polycyclosulfated C60 derivatives 9 as highly hydrolyzable 1' precursors. This reaction process involved no fullerene-oxide intermediates. Therefore, immediate hydrolysis of polycyclosulfated C60 derivatives gave the corresponding fullerenols 1, containing no hemiketal and enol-ether structures. Owing to plural reactive hydroxy functions covalently attached and randomly distributed on the molecular surface of the C60 cage, fullerenols have the capability to create high-density cross-linking in the fabrication of polymer matrix, or composite materials. 331 Mat. Res. Soc. Symp. Proc. Vol. 359 01995 Materials Research Society
Here we report the use of polyhydroxylated C60 derivatives as reagents for the high-density crosslinking of polyether-based polyurethane, forming polymer networks which exhibit excell
Data Loading...
