Abstract
Anionic surface-initiated polymerization of ethylene oxide and styrene has been performed using
multiwalled carbon nanotubes (MWNTs) functionalized with anionic initiators. The surface of MWNTs
was modified via covalent attachment of precursor anions such as 4-hydroxyethyl benzocyclobutene (BCBEO) and 1-benzocyclobutene-1′-phenylethylene (BCB-PE) through Diels-Alder cycloaddition at 235
°C. Surface-functionalized MWNTs-g-(BCB-EO)n and MWNTs-g-(BCB-PE)n with 23 and 54 wt %
precursor initiators, respectively, were used for the polymerizations. Alkoxide anion on the surface of
MWNTs-g-(BCB-EO)n was generated through reaction with potassium triphenylmethane for the
polymerization of ethylene oxide in tetrahydrofuran and phenyl substituted alkyllithium was generated
from the surface of MWNTs-g-(BCB-PE)n using sec-butyllithium for the polymerization of styrene in
benzene. In both cases, the initiation was found to be very slow because of the heterogeneous reaction
medium. However, the MWNTs gradually dispersed in the reaction medium during the polymerization.
A pale green color was noticed in the case of ethylene oxide polymerization and the color of initiator as
well as the propagating anions was not discernible visually in styrene polymerization. Polymer grafted
nanocomposites, MWNTs-g-(BCB-PEO)n and MWNTs-g-(BCB-PS)n containing a very high percentage
of hairy polymer with a small fraction of MWNTs (<1 wt %) were obtained. The conversion of ethylene
oxide and the weight percent of PEO on the surface of the MWNTs increased with increasing reaction
time indicating a controlled polymerization. The polymer-grafted MWNTs were characterized using FTIR,
1H NMR, Raman spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and
transmission electron microscopy (TEM). Size exclusion chromatography of the polymer grafted MWNTs
revealed broad molecular weight distributions (1.3 < Mw/Mn < 1.8) indicating the presence of different
sizes of polymer nanocomposites. The TEM images showed the presence of thick layers of polymer up
to 30 nm around the MWNTs. The living nature of the growing polystyryllithium was used to produce
diblock copolymer grafts using sequential polymerization of isoprene on the surface of MWNTs.