Binary mixtures of 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS) within the melt of polypropylene (PP) were studied at DMDBS contents of 0.4 and 1.0 wt %. DMDBS serves as a nucleating agent in PP crystallization by formation of a nanofibrillar network. The kinetics of the DMDBS solidification process within the PP melt and the ensuing nanofibrillar structure were studied by in situ small-angle X-ray scattering (SAXS) analysis combined with imaging by electron microscopy. The dynamic lag of the fibrillar structure formation kinetics and its temperature dependence indicate a nucleation and growth mechanism, controlled by the rate of nucleation. Investigation of the fibrillar structure by electron microscopy indicates a complex structure in which long and thin fibrils (less than 100 nm in cross-section) are composed of thinner nanofibrils (less than 10 nm in cross-section).

The activity of amine bis(phenolate) Ti dibenzyl complexes in 1-hexene polymerization catalysis as a function of the phenolate substituents was investigated. Two series of Ti complexes carrying either a dimethylamino or a methoxy sidearm donor were prepared and characterized. In each series, the substituents on the phenolate rings were either alkyl groups of varying bulk or electron-withdrawing chloro groups. When activated with a suitable Lewis acid, all precatalysts have shown reactivity toward 1-hexene. Different structure−activity trends were observed in the two series:  The activity of the catalysts of the “OMe” series was low to moderate and was almost independent of the phenolate substituents. In contrast, the activity of the “NMe2” catalysts had a strong dependence on both the steric and electronic character of the phenolate substituents, ranging from mild to highly active. The difference in polymerization activity trends between the two series may be traced back to their different tendency toward misinsertions. A “NMe2”-Ti complex having Cl groups in the ortho, para positions of the phenolate rings led to the most active catalyst and to a remarkably high-M w polymer (>4 000 000) obtained within 1 h of polymerization at RT. The characterization of this ultrahigh-M w atactic poly(1-hexene) by means of oscillatory rheometry and stress relaxation experiments indicated typical elastomeric behavior at RT.

Chiral Salan ligands were found to wrap in a highly diastereoselective manner around zirconium leading to C2-symmetric complexes of predetermined chirality at the metal. These complexes led to active polymerization of higher olefins, their activity and isospecific induction depending on the nature of the phenolate substituents.