Characterization of well-defined PHEMA-based bottlebrushes with controlled chain length and grafting density

Bottlebrushes with controlled horizontal- and vertical-axis scales, which have a high density of graft chains on their main chains, are useful as a nanomaterial. The properties of bottlebrushes depend on the polymer-type, -chain length, and grafting density. We fabricate well-defined bottlebrushes based on poly(2-hydroxyethyl methacrylate) (PHEMA) using the grafting from method. Macroinitiators with different compositions of an atom transfer radical polymerization (ATRP) initiator group are prepared, and two bottlebrushes are consequently synthesized by ATRP of HEMA with the macroinitiator: a concentrated bottlebrush with graft chains on the repeating units and a semi-dilute bottlebrush with graft chains on approximately 10%. The hydrodynamic and gyration radii of the concentrated- and semi-dilute bottlebrushes are Rh = 9.2 nm (R-g = 24.9 nm) and R-h = 69.1 nm (R-g = 130 nm), respectively. The shape factors (R-g/R-h) of these bottlebrushes indicate both solid-rods. The virial coefficient of semi-dilute bottlebrush, calculated from static light scattering measurements, is higher than that of concentrated bottlebrush, owing to the flexibility and solvation structure. The grafting density play a more prominent role than the graft-chain length in the excluded volume effect of the bottlebrush. These results provide useful insights for the construction of polymethacrylate-based bottlebrushes with specific hydrodynamic properties.