Polystyrene-grafted multiwalled carbon nanotubes (PS-g-MWNTs) with a hairy-rod nanostructure were synthesized by the in situ free-radical polymerization of styrene in the presence of multiwalled carbon nanotubes (MWNTs) terminated with vinyl groups. To quantitatively study the molecular weight and composition of polystyrene (PS) chains in PS-g-MWNTs, PS-g-MWNTs were fully defunctionalized. by hydrolysis. The results showed that 1 of every 100 carbon atoms in MWNTs was functionalized at the tips and outer walls of the carbon nanotubes and grafted by PS with a weight-average molecular weight of 9800 g/mol; therefore, a uniform thin layer (ca. 8-10 nm) of a PS shell was formed on the outer wall of MWNTs. PS-g-MWNTs were soluble in dimethylformamide and tetrahydrofuran. The thermal stability and glass-transition temperature of PS in PS-g-MWNTs were obviously increased. Nanopins were formed on the glass substrates by the self-assembly of PS-g-MWNTs, and the dewetting effect between the glass substrate and PS chains covered MWNTs during the evaporation of the solution. Both the length and diameter of the nanopins increased with the solution concentration. When PS-g-MWNTs were compression-molded, MWNTs were dispersed uniformly in the PS matrix and formed good networks, such as circlelike and starlike structures, because of the entanglements of hairy PS chains on MWNTs. (c) 2006 Wiley Periodicals, Inc.