Multiwall carbon nanotubes (MWCNTs) have been functionalized via addition of undecyl (C-11-) radicals generated by thermal decomposition of lauroyl peroxide. The functionalized MWCNTs (C-11-MWCNTs) were characterized by Raman, IR spectroscopy, and thermogravimetric analysis (TGA). Isotactic polypropylene (iPP) and syndiotactic Polypropylene (sPP) nanocomposites containing both purified and alkyl-functionalized MWCNTs have been synthesized via in situ polymerization Method with the use of C-2- and C-s-symmetry zirconocenes activated by MAO in liquid propylene medium. The effect of incorporating, C-11-MWCNTs on Structural, electrical. and mechanical properties of the polypropylene-based nanocomposites has been studied. Analysis of electrical properties in the microwave range elucidates interfacial transformations ill the composites induced by MWCNT functionalization and evaluates relative aspect ratios for the filler particles in different systems. The synthesized materials demonstrate improved filler dispersion and mechanical characteristics as a result of nanotube chemical functionalization. The MWCNT functionalization leads to markedly improved nanocomposite plasticity and noticeable enhancement of sPP tensile modulus.