Folding Polymers with Pendant Hydrogen Bonding Motifs in Water: The Effect of Polymer Length and Concentration on the Shape and Size of Single-Chain Polymeric Nanoparticles

A set of random copolymers based on a benzene-1,3,5-tricarboxamide functional methacrylate (BTAMA) and oligoethylene glycol methacrylate (oEGMA) with different degrees of polymerization (DP, from 110 to 450) and a 10 mol % loading of BTAMA were prepared using RAFT polymerizations. The pendant BTA units encode for the formation of helical aggregates via 3-fold hydrogen bonding while the oligoethylene glycol side chains provide solubility in water. The copolymers were characterized with size exclusion chromatography, 1H NMR spectroscopy, circular dichroism spectroscopy, light scattering, and small angle neutron and X-ray scattering. In dilute aqueous solutions, the copolymers fold intramolecularly and form single chain polymeric nanoparticles (SCPNs) in water. Variable temperature CD spectroscopy showed that the cooling curves are independent of the chain length, indicating a lack of cooperativity in the folding of these copolymers. Scattering studies revealed that the SCPNs have an asymmetric shape. An increase in DP results in an increase of the aspect ratio, while the cross-sectional diameter remains the same at around 3 nm. The elongated shape of the SCPN is proposed to account for the noncooperative folding observed using CD spectroscopy, as such a shape results in a constant local BTA concentration as the copolymer increases in length.