Poly(ethylene oxide) Melt Intercalation in Graphite Oxide: Sensitivity to Topology, Cyclic versus Linear Chains

The role of poly(ethylene oxide) (PEO) topology in the melt intercalation in graphite oxide (GO)-based materials is investigated. The intercalation of PEO in GO leads to changes in the GO interlayer space and to the suppression of polymer thermal transitions (crystallization and glass transition). Herein, we perform kinetic measurements of the melt intercalation of cyclic and linear PEO (CPEO and LPEO) with M-n = 2-20 kg/mol in different GO-based structures by monitoring the reduction of melting peak areas of PEO. We demonstrate that high sensitivity to PEO topology can be achieved using GO partially pillared with 1,6-hexanediamine. Using only 1 wt % of pillars, the rate constants of cyclic PEO become up to a 100 times smaller than that of linear chains of similar molecular weight. This enormous difference in the intercalation kinetics of topologically different PEO chains cannot be achieved in nonpillared GO, where the rate constants of cyclic PEO presented values that were only up to 4 times smaller than that of their linear analogues. The dramatic reduction in the intercalation rate for CPEO in the presence of pillars indicates that topological constraints (formation of squeezed structures with double folded strand conformations) are the most important factors affecting the melt intercalation kinetics. The results suggest that it is possible to restrict the intercalation of cyclic PEO into partially pillared GO, whilst allowing the linear analogue to diffuse through the GO interlayer space. This important finding could be the basis for developing new methods of purification of cyclic polymers.