Polypeptoids featuring N-substituted polyglycine backbones are structural mimics of polypeptides (Figure 1). Because of N-substitution, polypeptoids do not have extensive hydrogen bonding and main chain stereogenic centers, in contrast to polypeptides. As a result, polypeptoids are proteolytically stable, soluble in a variety of common solvents, and thermally processable in a way that is similar to conventional thermoplastics. Polypeptoids have attracted recent attention due to potential materials applications in biotechnology (e.g., drug delivery, smart coating, and bioseparation). While much progress has been made regarding understanding the physicochemical properties of polypeptoids, how they behave under nanoconfinement or near interfaces are limited. Dewetting of polymer films often poses an obstacle in the design of thin film devices, such organic photovoltaics, antifouling coatings and biosensors. In this study, linear and cyclic polypeptoids i.e., poly(N-decyl glycine) (PNDG) thin films with similar DPn have been prepared on silicon substrates and subjected to thermal annealing at T &gt;&gt; Tm. It was found that cyclic PNDG films were far more stable against dewetting as compared to their linear counterparts. To unveil the role of interfacial structures, the cyclic and linear PNDG films were leached with a good solvent and the residue films (i.e., adsorbed nanolayers) were characterized by a combination of X-ray reflectivity (XRR) and grazing incidence wide angle scattering (GIWAXS). The cyclic PNDG films were found to have a much thicker adsorbed nanolayer than the linear counterparts, which likely play a significant role in stabilizing the film at the adsorbed polymer-free polymer melt interface. These findings suggest that the chain cyclization can be used as an effective approach for improving the thermal stability of polypeptoid thin films on solid surfaces, which may also be applicable to other crystallizable polymer systems bearing long alkyl side chains.

Enhanced thermal stability of cyclic polypeptoid thin films: Role of interfacially adsorbed chains

2019 Fall National Meeting

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