Hollow mesoporous organosilica nanospheres templated with flower-like micelles of pentablock copolymers

We present a facile preparation of hollow mesoporous organosilica nanospheres with well-defined, uniform mesopores by controlling the morphology of pentablock copolymer templates under acidic conditions. The CBABC type poly(lactic acid-co-glycolic acid)-b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(lactic acid-co-glycolic acid) (PLGA-b-PEO-b-PPO-b-PEO-b-PLGA) pentablock copolymers were synthesized via a step-growth and ring-opening polymerization method using Pluronic F68 and F108 as macro-initiators. Two kinds of pentablock copolymers, (LA₄₅GA₁₂)EO₇₅PO₃₀EO₇₅(LA₄₅GA₁₂) and (LA₂₈GA₉)EO₁₄₁PO₅₄ EO₁₄₁(LA₂₈GA₉), were used as single soft templates to prepare mesoporous ethane-silica and benzene-silica hollow nanospheres by sol-gel chemistry in acidic aqueous solutions. The inner cavity diameter was controlled up to ∼20 nm by varying acidity and the chain length of the hydrophobic PLGA block without using additional swelling agents. The evolution of hollow nanospheres could be explained by single flower-like micelle template mechanism and the variation of morphology of pentablock copolymers upon solution acidity. Moreover, the amine-functionalized hollow benzene-silica nanospheres showed high carbon dioxide adsorption at ambient conditions. The hollow organosilica nanospheres were characterized by small-angle X-ray scattering, nitrogen adsorption-desorption, solid-state ¹³C- and ²⁹Si nuclear magnetic resonance, and scanning and transmission electron microscopy and so on.