Determination of the persistence length of helical and non-helical polypeptoids in solution

Control over the shape of a polymer chain is desirable from a materials perspective because polymer stiffness is directly related to chain characteristics such as liquid crystallinity and entanglement, which in turn are related to mechanical properties. However, the relationship between main chain helicity in novel biologically derived and inspired polymers and chain stiffness (persistence length) is relatively poorly understood. Polypeptoids, or poly(N-substituted glycines), constitute a modular, biomimetic system that enables precise tuning of chain sequence and are therefore a good model system for understanding the interrelationship between monomer structure, helicity, and persistence length. The incorporation of bulky chiral monomers is known to cause main chain helicity in polypeptoids. Here, we show that helical polypeptoid chains have a flexibility nearly identical to an analogous random coil polypeptoid as observed via small angle neutron scattering (SANS). Additionally, our findings show that polypeptoids with aromatic phenyl side chains are inherently flexible with persistence lengths ranging from 0.5 to 1 nm.