Polypropylene (PP) and its derivatives, poly(5-hexen-1-ol-co-propylene) (PPOH) and poly(1-hexene-co-propylene) (PPH), were comprehensively investigated by means of wide-angle X-ray diffraction, dynamic mechanical analysis (DMA), H-1 pulsed nuclear magnetic resonance (NMR), infrared (IR), and positron annihilation lifetime (PAL) techniques. The deduced nanoscopic amorphous structure was discussed in comparison with the mechanical properties such as tensile strength. Introducing polar hexenol and nonpolar hexene comonomers into PP chains resulted 0.33 in a significant reduction of the crystallinity for both the derivatives, which failed to explain the anomalous higher tensile strength of PPOH. The long decay T-2 observation from NMR indicated a lower chain mobility in the amorphous region of PPOH compared to PPH, consistent with the DMA analysis, providing a higher glass transition temperature for the former polymer. The PAL and IR results signified reduced free volume size along with hydrogen bond formation in the amorphous region of PPOH, illustrating an essential role of the nanoscopic amorphous structure in the superior mechanical strength of PPOH compared to the other polymers.