Blocking the Intercalation of Cyclic Poly(ethylene oxide)s into Graphite Oxide for Separation Performance

Macrocyclic polymers (polymers having more than 20 atoms in a ring structure), have been the center of research attraction, particularly over the last decade. Much of this interest can be attributed to unique physical properties: such as reduced melt viscosity, reduced entanglement and increased glass transition temperature at medium-low molecular weight, most of which can be traced to the absence of end groups in their topologies. Advances in this field have led to the development of graphite oxide-based materials. Technically, graphite oxide is a layered material derived from graphite and is basically composed of carbon, oxygen, and hydrogen. To date, the structural composition of graphite oxide has remained a contentious issue amongst various scientists and scholars. Existing literature reports of two feasible models for establishing the structural composition of graphite oxide; both of which still call for further improvement.

Essentially, in these types of models, one ought to understand the type of interactions between the graphite oxide functional groups and intercalant species. On this basis, scientists from the Materials Physics Center in Spain: Professor Fabienne Barroso-Bujans and Professor Angel Alegria, in collaboration with Professor Jürgen Allgaier at the Jülich Centre for Neutron Science and Institute for Complex Systems, Forschungszentrum Jülich GmbH, in Germany investigated the intercalation kinetics of cyclic poly(ethylene oxide) (CPEO) into graphite oxide from the melt and of their linear PEO (LPEO) analogues. Their motivation was based on the background knowledge on the cyclic topology influence on many physical properties of polymers. Their work is currently published in the research journal, Macromolecules.

In their approach, the research team performed kinetic measurements of the melt intercalation of CPEO and LPEO by monitoring the reduction of melting peak areas of PEO after the isothermal annealing of mixtures of PEO and graphite oxide-based structures at 80 °C and the subsequent cooling of samples on a DSC capsule. This experimental approach is based on the suppression of polymer thermal transitions (crystallization and melting) that the intercalated polymer phase experiences under extreme two-dimensional confinement.

The authors reported that the intercalation rate was faster for LPEO than for CPEO, although the differences were not big. More so, the team demonstrated that by pillaring the graphite oxide structure with 1 wt % of 1,6-hexanediamine, the topological sensitivity of the intercalation of CPEO and LPEO was dramatically enhanced. Remarkably, their results were supported by complimentary X-ray diffraction (XRD) and time-resolved Fourier transform infrared (FTIR) spectroscopy data.

In summary, the study assessed the role of poly (ethylene oxide) (PEO) topology in the melt intercalation in graphite oxide- based materials. Their results suggested that it is possible to restrict the intercalation of cyclic PEO into partially pillared graphite oxide, whilst allowing the linear analogue to diffuse through the graphite oxide interlayer space. In a statement to Advances in Engineering, Professor Professor Fabienne Barroso-Bujans emphasized that the aforementioned finding could potentially be the basis for developing new methods of purification of cyclic polymers.