Component Stress−Strain Behavior and Small-Angle Neutron Scattering Investigation of Stereoblock Elastomeric Polypropylene

Abstract

Elastomeric polypropylene (ePP) produced from unbridged 2-arylindene metallocene catalysts was studied by uniaxial tensile and small-angle neutron scattering (SANS) techniques. The ePP can be separated into the following: a low tacticity fraction soluble in ether (ES), an intermediate tacticity fraction soluble in heptane (HS), and a high tacticity fraction insoluble in heptane (HI). Tensile properties of ePP were compared to its solvent fractions, and the role of each solvent fraction residing within ePP was investigated by blending 5 wt % deuterated fraction with ePP. The tensile properties of each fraction vary considerably, exhibiting properties from a weak gum elastomer for ES, to a semicrystalline thermoplastic for HI. The intermediate tacticity HS fraction exhibits elastic properties similar to the parent elastomer (ePP). In the melt at 160 °C, SANS shows that all deuterated fractions are homogeneously mixed with ePP. Slow cooling from the melt to 25 °C causes the low tacticity fraction to preferentially segregate in amorphous domains due to different crystallization temperatures and kinetics although, despite its low crystallinity (≤2%), the low tacticity fraction can cocrystallize with the matrix. The dES-ePP shows little or no relaxation when held under strain and recovers readily upon the release of stress. The high tacticity component (dHI-ePP) retains its plastic properties in the blend.