Rheological and thermal properties of elastomeric polypropylene

The properties of elastomeric polypropylene synthesized from an unbridged metallocene catalyst are investigated by mechanical rheometry, differential scanning calorimetry, and optical depolarization. The material is compositionally heterogeneous in tacticity, and its behavior is compared to that of its solvent fractions. The behavior of elastomeric polypropylene is also compared with tacticity-matched atactic/isotactic homopolymer blends. For T below T-m, mechanical rheometry shows that elastomeric polypropylene forms a more constrained network than tacticity-matched homopolymer blends. Differential scanning calorimetry reveals that the elastomeric samples crystallize at a lower temperature than blends composed of the same isotactic content. Depolarization studies show similar transitions but reveal the presence of an additional slower time scale involved with crystallizing the elastomeric sample. Data are consistent with the presumed atactic/isotactic multiblock microstructure of elastomeric polypropylene.