Dimensional characterizations from rod stars to brushes of polymers with a low degree of polymerization

Dimensional characterizations from rod stars to brushes (PSt-g-HIC-32) with a relatively low degree of polymerization of the main chain have been studied in tetrahydrofuran (THF) at 25 °C by employing synchrotron radiation small-angle X-ray scattering, static and dynamic light scatterings, and viscosity measurements. The rod stars and brushes consist of a flexible linear polystyrene (PSt) main chain and 32 n-hexyl isocyanate (HIC) units in each side chain. Eight PSt-g-HIC-32 samples with a weightaverage degree of polymerization (N_M) of 11-495 of the main chain and a narrow molecular weight distribution (M_w/M_n) of 1.08-1.17 were prepared using a recycling preparative size-exclusion chromatography (SEC) system. The mean-square radius of gyration (〈S²〉), hydrodynamic radius (R_H), and intrinsic viscosity ([η]) of the stars and brushes were tabulated. The absolute calibration curve obtained in SEC analysis, scattering form factor, and ρ (==〈S²〉^1/2/R_H) parameter indicated a continuous change in the shape from the rod star to rod brush on increasing the aspect ratio of the main chain to the side chain. The N_M dependences of 〈S²〉, R_H, and [η] were consistently and quantitatively described using the current theories based on a wormlike (sphero-) cylinder model by taking into account the effective protruding effects of the side chains near the ends of the main chain.