The properties of three elastomeric stereoblock polypropylene (PP) samples made with unbridged 2-phenylindene zirconocene catalysts were investigated. One of the characteristics of these catalysts is the ability to control the structure and properties of the polypropylenes by manipulation of the reaction conditions. Samples PP1 and PP2 were prepared to have similar tacticities (as indicated by IR and NMR spectroscopy) yet different molecular weights. The molecular weight of PP2 is approximately half the molecular weight of PP1. Sample PP3 has a molecular weight similar that of PP2 but is lower in isotactic pentad content. All three samples were separated into fractions that differ in their solubilities in boiling ether and heptane. The fractionation appeared to be governed by tacticity and molecular weight. Thermal analysis by differential scanning calorimetry showed very broad melting endotherms. The broadness of the transitions and the relatively large standard deviations calculated for the enthalpy of fusion are indicative of a multiphase material. X-ray powder diffraction patterns of the three samples and their fractions (except the ether-soluble fractions) all showed characteristic peaks of the R crystalline phase. The heptane-insoluble fractions of both PP1 and PP2 also exhibited γ-phase reflection, whereas in the heptane-soluble fractions, that reflection is less evident. Tensile tests performed on PP1 and PP2 yielded a similar tensile modulus for the two, indicating similar degrees of crystallinity. PP1 exhibited better recovery properties, as measured in tests at 100% and 300% elongation.

The effects of replacing one of the 2-phenylindenyl-type ligands in bis(2-phenylindenyl)zirconium dichloride, (2-PhInd)2ZrCl2 (7), a catalyst precursor for the production of elastomeric polypropylene (ELPP-7), with a cyclopentadienyl-type ligand have been studied. The mixed-ring compounds:  (pentamethylcyclopentadienyl)(2-phenylindenyl)zirconium dichloride, Cp*(2-PhInd)ZrCl2, (8), (pentamethylcyclopentadienyl)(1-methyl-2-phenylindenyl)zirconium dichloride, Cp*(1-Me-2-PhInd)ZrCl2 (9), and (cyclopentadienyl)(2-phenylindenyl)zirconium dichloride, Cp(2-PhInd)ZrCl2 (10), have been synthesized through the reaction of the corresponding lithium indenide with C5R5ZrCl3 (8 and 9:  R = CH3; 10:  R = H). Crystal structures have been determined for complexes 8 and 9. The behavior of the catalysts derived from complexes 8, 9, and 10 upon their activation by methylaluminoxane (MAO) for ethylene and propylene polymerization has been studied. Of all mixed-ring catalysts only 8/MAO produces elastomeric polypropylene (ELPP-8) with properties consistent with a stereoblock microstructure. The stereosequence distributions in ELPP-8 determined from 13C NMR spectra are very similar to those in elastomeric polypropylene generated with 7/MAO under comparable conditions. However, the melting points and IR indices of 8/MAO-derived samples are significantly lower than for samples of ELPP-7 with similar isotacticity which may be attributable to shorter isotactic block lengths in ELPP-8. At the same time, comparison of 8/MAO to another metallocene system capable of producing elastomeric polypropylene rac-MeHC(Me4Cp)(Ind)TiCl2/MAO, 1/MAO, described by Chien reveals significant similarities both in the catalyst symmetry and properties of generated polypropylene. The increase of isotacticity of ELPP-8 with propylene pressure similar to the trend observed for ELPP-7 favors the two-state mechanism of stereoblock formation with 8/MAO.

SYNOPSISInterfacially compatibilized immiscible blends with an isotactic polypropylene matrix ( P P ) and dispersed polyamide-66 (PA) were prepared by extrusion with anhydride-grafted isotactic PP compatibilizers, one of high-anhydride content (HAC, 2.7 wt % grafted maleic anhydride) and one of low-anhydride content (LAC, 0.2 wt % anhydride). On a weight basis, HAC was more efficient than LAC in dispersing PA to submicron domains, but on a total weight % anhydride basis, both compatibilizers were equally efficient. Both compatibilizers imparted similar tensile strength improvement compared to an uncompatibilized blend. Maximum fracture strain was obtained at similar total anhydride content, but much higher maximum fracture strain was achieved with LAC than with HAC. Good adhesion in an 11.25 wt % LAC blend was seen at the microscale as fibrillar ligaments connecting PA particles to the drawn PP matrix. Interfacial failure was observed in a lower fracture strain composition, 11.25 wt % HAC.

SYNOPSISTwo anhydride-grafted isotactic polypropylene ( PP ) compatibilizers, HAC or high-anhydride compatibilizer (2.7 w t % grafted maleic anhydride) and LAC or low-anhydride compatibilizer (0.2 w t % anhydride), were compared in PP-rich blends with polyamide-66 (25 wt % ) . A previous article demonstrated that LAC imparted a much higher fracture strain than did HAC at similar anhydride concentrations. The present study shows that LAC is capable of cocrystallization with PP. HAC does not cocrystallize, but crystallizes as a second phase in binary PP/HAC blends studied by DSC and hot-stage microscopy. A cocrystallization model is proposed to explain the higher fracture strain of PP/LAC/PA blends. A separate phase crystallization model is proposed for PP/HAC/PA blends. The models are supported by peel tests, which demonstrate greater adhesion of PP with LAC than with HAC.

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.