Molecular weight effect on the structural detail and chain characteristics of 33-armed star polystyrene

In this study, synchrotron X-ray scattering and quantitative data analysis were performed on a series of 33-armed polystyrenes with four different arm molecular weights in cyclohexane (CHX, Θ solvent) and tetrahydrofuran (THF, good solvent). The quantitative scattering analysis was successfully done, providing molecular structure details and their responses to the solvent change. Each star system is confirmed to be prepared in a very narrow unimodal size distribution; the distribution is slightly broadened with increasing the arm molecular weight. It has an oblate ellipsoid shape, which is composed of two phases, a denser and smaller core and a less dense and thicker fuzzy shell; the ellipsoidicity ranges in 0.56–0.62. The core and shell phases are enlarged and thickened respectively by the arm molecular weight increases. Both the phases are further expanded in THF. Interestingly, the THF-induced expansion is predominant in the core against the fuzzy shell with a Gaussian like density gradient. Overall, the 33-armed star polystyrenes in various molecular weights are quite unique in the structural details and performance in solvent changes, which would be beneficial for advanced applications in various technological areas including smart deliveries of desired molecules (drug, gene, imaging agent, etc.). [Display omitted] •Thirty-three armed star polystyrene reveals oblate ellipsoidal shape in solution.•Oblate ellipsoid consists of a dense core and a less dense fuzzy shell.•Structural parameters are increased with increasing arm molecular weight.•Molecular size is enlarged by solvent change to good solvent from theta solvent.•Good solvent induced molecular expansion is driven mainly by the core expansion.