Synthesis via RAFT Polymerization of Tadpole-Shaped Organic/Inorganic Hybrid Poly(acrylic acid) Containing Polyhedral Oligomeric Silsesquioxane (POSS) and Their Self-assembly in Water

Tadpole-shaped inorganic/organic hybrid poly( tert -butyl acrylate) was prepared by RAFT polymerization of tert -butyl acrylate ( t BA) using a POSS-containing chain transfer agent (CTA). The polymerization kinetics showed a pseudofirst-order behavior with a short induction period; the number-average molecular weights linearly increase with conversion. In conjunction with low polydispersity (PDI < 1.3), this confirms a controlled polymerization. POSS-P t BA was further hydrolyzed into amphiphilic, tadpole-shaped poly(acrylic acid) (POSS-PAA). The self-assembly behavior of POSS-PAA in aqueous solution at pH = 8.5 was investigated by transmission electron microscopy (TEM) as well as static and dynamic light scattering (SLS and DLS). The results show that POSS-PAA self-assembles in water into rather large aggregates where the POSS moieties are dispersed in the particle. The size (average radius ≈ 60 nm by DLS) is nearly independent of the chain length of PAA. The aggregates are pH-responsive, contracting when decreasing pH from 8.5 to 4.