The Intramolecular Self-Assembly of Statistical Copolymers in Aqueous Solution to Form Anisotropic Single-Chain Nanoparticles with Tunable Aspect Ratio

Natural single-chain nanoparticles (SCNPs) such as proteins have inspired research into the formation and application of synthetic SCNPs. Although the latter can mimic general aspects of the self-assembly behavior of their biological counterparts, these systems remain relatively understudied. In this respect, a systematic series of amphiphilic statistical copolymers (ASC) of different molecular weights, with a hydrophilic comonomer (methacrylic acid) and varying hydrophobic comonomer to encompass methacrylates of different hydrophobicity, are synthesized. Small-angle X-ray scattering studies confirmed that SCNPs are achieved for each copolymer series when dispersed in basified water at 1% w/w. When the aggregation number of the ASC nanoparticles is close to unity the particle shape elongates resulting in a larger particle surface area to volume ratio, allowing more hydrophilic groups to locate on the particle surface tending to keep the particle surface charge density (PSC) constant. Thus, within a series, particle elongation increases with copolymer molecular weight. Structural parameters of SCNPs formed by ASCs composed of hydrophobic components with low partition coefficients are well consistent with predictions obtained from the PSC model. These results highlight the main parameters, namely molecular weight and acid content, responsible for the SCNP formation and provide insight into how specific particle morphology can be targeted.