Abstract
The value of long chain branching (LCB) in polyethylene (PE) has long been known. Even though low density PE (LDPE) is generally inferior to linear low density PE (LLDPE) in most of the physical properties (e. g., toughness), it still has a large share of the market due to its greater processability. This rheological behavior that leads to the enhanced processability of LDPE is attributed to the presence of long branches. By 'long' we mean here a branch with a molecular weight at least greater than the entanglement molecular weight, M sub e , which for PE is around 1000 g/mol exp 2 . The characterization of LCB in polymers is in general quite difficult. In the work described herein we have taken advantage of the ability to produce saturated hydrocarbon polymers with precisely controlled branching structures through the saturation of anionically synthesized polydienes. We describe the application of well-developed strategies to prepare branched polybutadienes and by hydrogenation the corresponding polyethylenes. The range of structures includes stars, combs, and pom-pom architectures. We show here how the variation of LCB type and level can have large impact on flow behavior.