KSC Seminar: Precisely Branched Polyethylene: Effect of Alkyl Branch Size on Nanoscale Morphology
Speaker: Dr. Ingo Lieberwirth
Max Planck Institute for Polymer Research, Mainz, Germany
Date & Time: Wednesday May 24th, 2017 at 3pm
Venue: Building 5, level 5, room 5220
Light refreshments will be provided.
Abstract: Morphological characterization is reported for a series of precisely branched polyethylene structures, the branch being placed on every 21st or 39th carbon and varying in size from methyl to pentadecyl group and additionally with the introduction of phosphate and phosphonate groups. The morphology and physical properties of the crytallized polymer were investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Methyl branching significantly reduces the melting point and single crystal lamellae thickness. On the other hand, all further branches from ethyl to pentadecyl produce polymers that have similar melting points and single crystal lamellar thickness.
A polyethylene with methyl-branches at precisely every 38th unit (PE-38-Me) will incorporate the methyl defects into the lamellar crystals upon crystallization. Structural analysis reveals for this kind of defect-loaded polymer crystal, that the packing perpendicular to the main chain axis is of orthorhombic PE type with a 14% increase of lattice parameters a and b. The appearance of the (00l) spots, on the other hand, gives rise to assume a much higher disorder of crystal structure in direction of the molecular backbone.
Furthermore, we examined precision polyphosphoesters (PPE), with a phosphate or phosphonate group in the polymer chain. From TEM and X-ray examinations, we can show, that the phosphate groups are expelled from the crystal, sitting on the basal surface of the polymer crystal lamellae. Biography: