Topological effects by cyclic polymers are enhanced in the confinement of a flat surface: a research team led by Dr. Edmondo M. Benetti have demonstrated that cyclic polyoxazoline brushes provide higher steric stabilization with respect to their linear analogues, and display super-lubricious behavior in water.
The cyclic polymer topology strongly alter the interfacial, physico-chemical properties of polymer brushes, when compared to the linear counterparts. In this study, we especially concentrated on poly-2-ethyl-2-oxazoline (PEOXA) cyclic and linear grafts assembled on titanium oxide surfaces by “grafting-to” technique. The smaller hydrodynamic radius of ring PEOXAs favours the formation of denser brushes with respect to linear analogues. Denser and more compact cyclic brushes generate a steric barrier that surpasses the typical entropic shield by a linear brush. This phenomenon, translates into an improved resistance towards biological contamination from different protein mixtures. Moreover, the enhancement of steric stabilization coupled to the intrinsic absence of chain ends by cyclic brushes, produce surfaces displaying a super-lubricating character when they are sheared against each other. All these topological effects pave the way for the application of cyclic brushes for surface functionalization, enabling the modulation of physico-chemical properties that could be just marginally tuned by applying linear grafts.
Morgese, G., Trachsel, L., Romio, M., Divandari, M., Ramakrishna, S. N. and Benetti, E. M. (2016), Topological Polymer Chemistry Enters Surface Science: Linear versus Cyclic Polymer Brushes. Angew. Chem. Int. Ed. doi:10.1002/anie.201607309