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Keywords:

  • single-walled carbon nanotubes;
  • polystyrene;
  • composite;
  • TEMPO

Abstract

Single-walled carbon nanotubes (SWCNTs) dispersed in N-methylpyrrolidone (NMP) were functionalized by addition of polystyryl radicals from 2,2,6,6-tetramethyl-1-piperidinyloxy-ended polystyrene (SWCNT-g-PS). The amount of polystyrene grafted to the nanotubes was in the range 20-25 wt% irrespective of polystyrene number-average molecular weight ranging from 2270 to 49 500 g mol−1. In Raman spectra the ratios of D-band to G-band intensity were similar for all of the polystyrene-grafted samples and for the starting SWCNTs. Numerous near-infrared electronic transitions of the SWCNTs were retained after polymer grafting. Transmission electron microscopy images showed bundles of SWCNT-g-PS of various diameters with some of the polystyrene clumped on the bundle surfaces. Composites of SWCNT-g-PS in a commercial-grade polystyrene were prepared by precipitation of mixtures of the components from NMP into water, i.e. the coagulation method of preparation. Electrical conductivities of the composites were about 10−15 S cm−1 and showed no percolation threshold with increasing SWCNT content. The glass transition temperature (Tg) of the composites increased at low filler loadings and remained constant with further nanotube addition irrespective of the length and number of grafted polystyrene chains. The change of heat capacity (ΔCp) at Tg decreased with increasing amount of SWCNT-g-PS of 2850 g mol−1, but ΔCp changed very little with the amount of SWCNT-g-PS of higher molecular weight. The expected monotonic decrease in ΔCp coupled with the plateau behavior of Tg suggests there is a limit to the amount that Tg of the matrix polymer can increase with increasing amount of nanotube filler. Copyright © 2012 Society of Chemical Industry