Armenag H. Dekmezian

Synthesis of Long-Chain Branched Propylene Polymers via Macromonomer Incorporation

Long-chain branched (LCB) poly(propylene)s (PP) are synthesized by the incorporation of pre-formed, vinyl-terminated macromonomers using metallocene catalysts. LCB-PP polymers made with isotactic PP macromonomers are characterized by means of multi-angle laser light scattering and extensional viscosimetry. The LCB polymers exhibit enhanced melt properties, such as strain hardening and shear thinning. These properties are critical in many polymer fabrication processes, such as thermoforming, blow molding and foaming.

Synthesis of vinyl‐terminated isotactic poly(propylene)

Isotactic poly(propylene)s with 60–80% vinyl chain-end selectivity were synthesized with metallocene catalysts. Some of these vinyl-terminated poly(propylene)s are highly stereoregular (mmmm pentads up to 95%) and have high crystalline melting points in the range of 140–150°C. Chain-end analysis using 13C NMR indicates the vinyl chain-ends in the polymer are most likely formed through β-methyl elimination in the chain termination step.

Long chain branch polymer chain dimensions: application of topology to the Zimm–Stockmayer model

Abstract An explicit topological approach to the dimensions of LCB polymers is presented. It is based on the Wiener number, a topological descriptor which is shown in this study to be related to the topological radius of the macromolecule, the mean-square radius of gyration, the g -ratio, and the intrinsic viscosity within the Rouse–Zimm range. The new theory enables the treatment of the highly complex hyperbranched polymers, which are difficult to handle by the classical theory of Zimm and Stockmayer. The agreement with the measured g -values of model polyethylenes, synthesized by Hadjichristidis et al., is fairly good for star-like polymers and satisfactory for pom–pom type of structures, whereas for crowded comb-type species the calculated g -values are underpredicted. Extension of the approach is shown to cyclic structures for which the Kirchhoff number replaces the Wiener number.