Effect of Graft Chain Length and Structure Design on Temperature-Sensitive Hairy Particles

Poly( N -isopropylacrylamide) (PNIPAM) chain-grafted particle was prepared to obtain a thermosensitive microsphere. The graft polymerization of NIPAM was carried out by the controlled radical polymerization technique using an iniferter. A photosensitive iniferter was used to conduct the graft polymerization under an ambient condition (at room temperature in water). The particle diameter increased linearly with the conversion. The controllability of this reaction was examined by adding a free initiator species to the medium, and it was found that the polydispersity indices of PNIPAM generated by iniferter-control polymerization were 1.3−2.1 where number-average molecular weights were 64 000−319 000. The graft chain length affected the thermosensitivity, and the longer graft chain brought an abrupt change in diameter around 33 °C. When a small amount of acrylic acid was incorporated into the graft polymer, the particle worked as an adsorbent of protein, and its adsorbability could be controlled by the temperature. The structure design by means of controlling monomer unit distribution in the graft polymer resulted in an improvement of the protein collection.