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SANS and DLS Study of Tacticity Effects on Hydrophobicity and Phase Separation of Poly( N -isopropylacrylamide)

2013; American Chemical Society; Volume: 46; Issue: 15 Linguagem: Inglês

10.1021/ma401349v

1520-5835

Kengo Nishi, Takashi Hiroi, Kei Hashimoto, Kenta Fujii, Young‐Soo Han, Tae‐Hwan Kim, Yukiteru Katsumoto, Mitsuhiro Shibayama,

Electrostatics and Colloid Interactions

The tacticity effect on phase separation process of poly(N-isopropylacrylamide) (PNiPAM) aqueous solutions was investigated by dynamic light scattering (DLS) and small angle neutron scattering (SANS) measurements. SANS measurement revealed that hydrophobicity of PNiPAM consisting of meso- and racemo-isomers increased with increasing the meso-content. This result is in accordance with the result of the previous experimental and simulation study on NiPAM dimers (DNiPAM) and trimers (TNiPAM) [Katsumoto, Y.; J. Phys. Chem. B 2010, 114, 13312−13318, and Autieri, E.; J. Phys. Chem. B 2011, 115, 5827–5839]; i.e., meso-diad is more hydrophobic than racemo-diad. In addition, a series of scattering experiments revealed that the ratio of meso-diad does not affect the static structure or the shrinking behavior of a single chain, but strongly affects the aggregation behavior. The PNiPAMs with low meso-content suddenly associate around the phase separation temperature, while that of the high meso-content gradually aggregate with increasing temperature. We propose that phase transition behavior of PNiPAM aqueous solutions can be controlled by changing the stereoregularity of the polymer chain.