Thermoplastic Elastomers from Binary Blends of Syndiotactic Polypropylenes with Different Stereoregularity

A study of the structure and properties of binary blends of syndiotactic polypropylene (sPP) having different degrees of stereoregularity and synthesized by different metallocene catalysts, is reported. Three series of binary blends have been prepared by mixing a more stereoregular and crystalline sample sPP1, with concentration of fully syndiotactic pentads rrrr of 78%, with low stereoregular and poorly crystalline samples samPP1 and samPP2 having [rrrr] = 54.6 and 45.8%, respectively, and a nearly atactic fully amorphous sample amPP with [rrrr] = 26.5%. All blends show outstanding elastomeric properties with rigidity and tensile strength that can be tailored by opportunely changing the stereoregularity of the components and blend composition. A continuous change of properties with composition is observed, from those of high-modulus thermoplastic elastomers for blends having high concentration of the most syndiotactic sample sPP1, to those of low-strength elastomers for blends with high content of the less syndiotactic component.