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Self-Association of a Thermosensitive Amphiphilic Block Copolymer Poly(N‑isopropylacrylamide)‑b‑poly(N‑vinyl-2-pyrrolidone) in Aqueous Solution upon Heating

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posted on 08.01.2013, 00:00 by Takahiro Sato, Kohei Tanaka, Akiko Toyokura, Rika Mori, Rintaro Takahashi, Ken Terao, Shin-ichi Yusa
The self-association behavior of a thermosensitive amphiphilic block copolymer, poly­(N-isopropylacrylamide)-b-poly­(N-vinyl-2-pyrrolidone) (PNIPAM-b-PNVP) in water upon heating was investigated by static and dynamic light scattering (SLS and DLS), small-angle X-ray scattering (SAXS), and pulsed field gradient NMR (PFG-NMR). Combining SLS and DLS with SAXS and PFG-NMR, we conclude that above 40 °C, the unimer or a few arms star micelle of the copolymer coexists with large spherical particles of uniform density, which should be regarded as concentrated-phase droplets produced by a liquid–liquid phase separation. The spherical particles of PNIPAM-b-PNVP samples with the PNIPAM content less than 0.32 became smaller with increasing temperature. This temperature dependence was explained in terms of the packing parameter for amphiphiles.

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