A new soluble multiwalled carbon nanotubes (MWNTs) covalently functionalized with conjugated polymer PCBF, in which the wt % of MWNTs is approximately calculated as 7.3%, and the average thickness of PCBF covalently grafted onto MWNTs is 10.4 nm, was synthesized by an amidation reaction. In contrast to the starting polymer PCBF-NH2, grafting of PCBF onto MWNTs led to a 0.3 eV red-shift of the N1s XPS peak at 399.7 eV assigning to N in the unreacted NH2 moieties in the resulting copolymer structure and an appearance of new peak at 402 eV corresponding to N bound to the carbonyl C (i.e., NH-C=0). Unlike PCBF-NH2, which only displayed a weak optical limiting response at 532 nm, Z-scan for MWNT-PCBF exhibited a much broader reduction in transmission and a scattering accompanying on the focus of the lens at both 532 and 1064 nm, indicating a prominent broadband optical limiting response. The thermally induced nonlinear scattering is responsible for the optical limiting. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 101-109, 2011