Correlations Between Chain Branching, Morphology Development and Polymer Properties of Polyethenes

Molecular architectures of polyethenes, in particular short and long chain branching, were varied over a very wide range by means of either metallocene-catalyzed ethene/1-olefin copolymerization or Ni- and Pd-catalyzed migration/insertion-type ethene homopolymerization. While short chain branches affected melting, glass transition, and blend compatibility, long chain branching represented the key to improved melt processability. Both the number of short and long chain branches depended upon the ligand Substitution pattern of dimethylsilylene-bridged bisindenyl complexes. The degree of branching increased with Variation of the substitution in 4-position, i.e., 4-napthyl > 4-phenyl > benzannelation. Variation of the 1-butene content of ethene/1-butene (EB) copolymers gave control of morphology development and properties of isotactic polypropene (iPP) blends with EB. Highly flexible, single-phase as well as stiff and tough two-phase iPP/EB (70 wt.-%/30 wt.-%) blends were obtained. Rheological studies on ethene/1-eicosene model polyethene revealed the presence of a positive comonomer effect with respect to molar catalyst activity, molecular weight, and long-chain branching. A new family of thermoplastic elastomers based upon highly branched polyethene was prepared via Pd-catalyzed ethene copolymerization with 2,2,6,6-tetramethyl-piperidineoxy (TEMPO)-functionalized 1-olefin as macromonomers to produce macroinitiators for the initiation of the controlled free radical graft copolymerization of styrene onto highly branched polyethenes. The Variation of the polystyrene block length gave control on nanophase Separation of the resulting branched polyethene - graft - polystyrene.