KSC Seminar: Precisely Branched Polyethylene: Effect of Alkyl Branch Size on Nanoscale Morphology

Speaker: Dr. Ingo Lieberwirth

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 21^st or 39^th 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 38^th 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.

Ingo Lieberwirth studied physics at the University of Dortmund. He obtained his diploma in 1997 with a thesis on selected metallization of polymer surfaces under the supervision of Prof. J. Petermann. During this work he came into contact with electron microscopy of polymers for the first time. In 2001 he finished his PhD at the Technical University of Eindhoven in the group of Prof. P. Lemstra on orientation induced crystallization of semi-crystalline polymers. Subsequently he joined the group of Prof. Wegner at the MPI-P. In 2006 he became head of the electron microscopy group at the MPI-P and he is vice-speaker of the electron microscopy center Mainz (EMZM). Besides his work in electron microscopy, his research activities comprise polymer controlled crystallization of anorganic minerals, structure formation of self assembled polyelectrolytes in aqueous solution, interaction of nanoparticles with the cell membrane, visualization of the protein corona and crystallization of precision polymers. Ingo Lieberwirth is the co-author of over 130 peer review research articles with an h-index of 35.