Isotactic and blend of iso-tactic: syndio-tactic (70:30) polypropylene (PP) matrices based melt-mixed PP/MWNT nanocomposites are comparatively evaluated with regard to morphological, rheological and mechanical properties. Relatively increased mean free space lengths (If) between nanotubes in syndiotactic blended PP/MWNT nanocomposites with its manifestations on the rheological percolation up to a higher extent of MWNT loading (phi(c) similar to 1.4 x 10(-3) in isotactic to phi(c) similar to 6.1 x 10(-3) in iso-syndio blend) visa-vis enhanced normalized (similar to four-times) tensile failure strain has been observed. The rheological percolation confirming the formation of a mechanically responsive network structure was ascertained following the power-law relationship between storage modulus and critical volume fraction. Construction of van-Gurp Palmen plot indicated a transition in the rheological response attributed to the network morphology getting shifted to higher concentration of MWNT in the syndio-modified than the iso-unmodified nanocomposites. Constitutive modeling of complex viscosity response of the nanocomposites functionally demonstrated the percolation and relaxation dynamics of polymer chains. The T-g remained affected more by the polymer-nanotube entanglements in iso-syndio than in iso-only system. The increase in strain at break has been attributed to an overall reduction in crystallinity in the syndio-modified PP/MWNT nanocomposites. (C) 2014 Published by Elsevier B.V.