Preparation of nano-TiO2/polyurethane emulsions via in situ RAFT polymerization

Stable nano-TiO2/polyurethane (PU) emulsions were prepared via in situ reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of 2-hydroxyethyl acrylate (HEA)-capped PU macromonomer, using azobisisobutyronitrile (AIBN) as a radical initiator and 2-{[(butylsulfanyl)carbonothioyl]sulfanyl} propanoic acid (BCSPA) anchored onto TiO2 nanoparticles (TiO2-BCSPA) as a RAFT agent. When the molar ratio of AIBN to TiO2-BCSPA was changed from 1:3 to 1:10, the polydispersity index (PDI) of polymers in the emulsions decreased from 1.83 to 1.06, due to more effective RAFT polymerization in the emulsions. The TiO2 nanofillers were well-dispersed throughout the polymer films. The tensile strengths of the nanocomposite films were significantly enhanced due to coordination bonding between the TiO2 nanofillers and the –COOH end groups of the polymers, as evidenced by the FT-IR spectral data.