Tailoring Mechanical Properties of Isotactic Polypropylene Via Crystallization of the Mesophase and Control of Stereodefects Concentration

A strategy to tailor the properties of isotactic polypropylene, based on the combination of the crystallization of the mesophase and the control of the molecular structure and concentration of stereodefects via polymerization with metallocene catalysts, is presented. The mechanical properties can be modulated through the conventional slow crystallization from the melt in the α and γ forms, depending on the concentration of stereodefects, or the crystallization of the mesophase by melt quenching. The most stereoirregular sample with rr concentration of 11% shows elastic behavior either when it is slowly crystallized in the γ form or when it is crystallized in the meso morphic form, but with remarkable differences in the values of the modulus and tensile strength.