The secondary structures of PEG-functionalized random copolymers derived from (R)- and (S)- families of alkyne polycarbodiimides

A series of helical rigid-rod (R)- and (S)-polycarbodiimides having PEG2K, 10K, and 20K groups attached to aromatic or aliphatic side chains have been successfully synthesized from the respective alkyne polycarbodiimide precursors using the CuI-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The AFM, TEM and SEM studies of this series revealed the formation of different types of aggregated morphologies, i.e., micro- and nanospheres, fiber-like crystallites, and porous aggregates, which can be tailored with the hydrophilic PEG segments in the polymer structure. In general, heavily PEGylated scaffolds comprising approximate to 44 ethylene oxide segments are prone to form round-shaped secondary structures, especially in the bulk, as evident by SEM measurements. AFM data suggested that spherical aggregates are the preferred motifs in a wide range of concentrations. Moreover, polycarbodiimide-graft-PEG(2K) random copolymers were shown to efficiently suspend SWCNTs in water, leading to novel neutral photoluminescent nanocomposite materials. Overall, these extensive self-assembly studies on various polycarbodiimide platforms featuring a hydrophobic rigid rod main chain and a flexible hydrophilic periphery may provide a basic layout for prospective biomedical applications, such as controlled drug delivery and enhanced dispersibility properties of SWCNTs.