Molecular and Thermal Characterization of a Nearly Perfect Isotactic Poly(propylene)

The structure formation upon cooling of the quiescent melt of a nearly defect-free isotactic poly(propylene) (iPP) homopolymer is investigated in this study. This iPP, having a molecular weight of 1 × 10⁶ g mol^-1 and a narrow molecular weight distribution, has been produced with a C2 symmetric hafnocene complex. Information about the crystallization kinetics is collected in a broad range of cooling rates. Standard differential scanning calorimetry is used for cooling rates in the range 3-100 C min^-1 and FSC is employed to analyze the solidification process at cooling rates larger than 100 C s^-1. The near absence of regio- and stereo-defects allows this iPP to crystallize at significantly high temperatures and to form crystals at cooling rates higher than commonly observed for standard Ziegler-Natta iPP. The data reveal that the iPP homopolymer with close-to-perfect stereo-regularity form crystals at high cooling rates as, e.g., α-nucleated iPP. The defect-free polymer chain allows the formation of relatively thick lamellar crystals which resulted in a relatively high tensile modulus of 2088 ± 8 MPa. A nearly defect-free isotactic poly(propylene) (iPP) homopolymer is produced with a C2 symmetric hafnocene complex. The near absence of regio- and stereo-defects allows this iPP to crystallize at significantly high temperatures and to form crystals at cooling rates higher than commonly observed for standard Ziegler-Natta iPP.