SAXS and SANS characterization of gelable polystyrene-b-poly(acryloxy propyl triethoxysilane) (PS-b-PAPTES) diblock copolymer micelles before and after hydrolysis–condensation

Abstract

Diblock copolymers of styrene and gelable acryloxy propyl triethoxysilane (APTES) were successfully prepared through Nitroxide-Mediated Polymerization (NMP). Their micellar behaviour in dioxane–methanol solutions was investigated by Small Angle X-ray Scattering (SAXS) and Neutron Scattering (SANS) measurements. The micelles were found to be spherical whatever the copolymer composition with a PS core size varying from 13.5 nm to 37.8 nm depending on the PS chain length and the swelling ratio. The thickness of the PAPTES corona increased from 6.0 nm to 10.8 nm when increasing the PAPTES polymerization degree from 91 to 336. Two micellar structural regimes were identified, depending on the chain length of the PAPTES soluble block. For PAPTES polymerization degrees higher than 100, the PS core radius in dried state R_DC can be consistently described by a scaling relationship R_DC α (N_PS^0.34N_PAPTES^−0.069) and the aggregation number N_agg obeys the relationship N_agg α (N_PS^0.021N_PAPTES^−0.21), consistent with previous studies. For polymerization degrees of the soluble block lower than 100, it was shown that R_DC and N_agg do not follow the expected scaling relationships with higher values of N_agg, possibly due to complete chain incorporation in the micelle core. After the cross-linking process, a decrease of the hydrodynamic diameter of 1.6 to 4.7 nm was observed. This is mainly due to the corona shrinkage, the aggregation number and the core radius being directly dependent of the parent non-crosslinked micelles.