Unveiling the role played by crystal morphology in crystalline elastomers based on syndiotactic polypropylene.

Syndiotactic polypropylene (sPP) synthesized with stereoselective metallocene catalysts is an interesting material combining mechanical properties characteristic of semicrystalline polymers, such as high mechanical resistance and stiffness, and typical of elastomers such as ductility and elasticity. In contrast with the classic elasticity, sPP-based materials show elastic behavior notwithstanding the high crystallinity, thanks to the polymorphic transformations occurring in the crystalline phase during stretching and relaxation, that allowed defining these materials as crystalline elastomers. However, the role played by the crystal morphology in terms of shape, size and organization of the crystals in the amorphous matrix need to be investigated to understand the origin of the elastic behaviour observed in stereoregular samples crystallized in the mesomorphic form of sPP and in stereoirregular sPP samples, where no polymorphic transitions accountable for the elastic recovery occur.