Semimetallic Transport in Nanocomposites Derived from Grafting of Linear and Hyperbranched Poly(phenylene sulfide)s onto the Surface of Functionalized Multi-Walled Carbon Nanotubes

Abstract

The semimetallic conductive nanocomposites, linear or hyperbranched poly(phenylene sulfide) (PPS) grafted multiwalled carbon nanotubes (MWNT), were successfully prepared by two-step reaction sequences. MWNT were first functionalized with 4-chlorobenzoic acid in poly(phosphoric acid) (PPA)/phosphorus phentoxide (P2O5) medium in a “direct” Friedel−Crafts acylation reaction to afford 4-chlorobenzoyl-functionalized MWNT (CB-MWNT). A subsequent nucleophilic substitution reaction between CB-MWNT and 4-chlorobenzenethiol as an AB monomer or 3,5-dichlorobenzenethiol as an AB2 monomer was conducted to graft the linear PPS (LPPS) or hyperbranched PPS (HPPS) in NMP/toluene in the presence of sodium carbonate to afford LPPS grafted MWNT (LPPS-g-MWNT) or HPPS grafted MWNT (HPPS-g-MWNT), respectively. The covalent attachment of corresponding polymers onto the surface of MWNT was indirectly confirmed by a model study. The structures of polymer-grafted nanocomposites were clearly discernible from those of the samples prepared by solution-blending of LPPS and CB-MWNT. The dispersability and melt-processability of nanocomposites were enhanced by the grafting of PPS polymers. Thus, the nanocomposite specimens could be easily compression molded. Without chemical doping, the measured surface conductivities of as-prepared LPPS-g-MWNT and HPPS-g-MWNT molded samples were in the semimetallic transport region at 11.76 and 3.56 S/cm, respectively