Tailoring Properties of Polypropylene through Crystallization in the Presence of Polymeric Nucleating Agents.

In this communication, we present a strategy for the addition of polymeric nucleating agents for the crystallization of isotactic polypropylene (iPP) that guarantees a perfect fine dispersion of nucleating particles within the entire mass of the polymer, with consequent their high efficiency even at very low concentrations. The Ziegler-Natta catalyst particles are coated by a thin skin of poly(trimethylallylsilane) (PTMAS) or poly(vinylcyclohexane) (PVCH) that will act as nucleating agents, by prepolymerization of the corresponding monomers. PVCH shows higher nucleation efficiency than PTMAS with greater increase of crystallization temperature by standard cooling from the melt. Both polymeric nucleating agents affect the crystal morphology greatly reducing the size of shperulites. This in turn affects the mechanical properties improving ductility and flexibility. The presence of the nucleating agent accelerates the crystallization of iPP and affords crystallization of the α form even upon fast crystallization by quenching the melt, condition that generally produces crystallization of the mesomorphic form of iPP. Crystals of α form so obtained show a nodular morphology and absence of spherulitic superstructure. This novel iPP material is characterized by outstanding and unexpected properties of high mechanical strength and modulus and contemporarily high ductility, flexibility and good transparency due to the nodular morphology of α form.