title: Amphiphilic telechelic poly(N-isopropylacrylamide) in water: from micelles to gels.
abstract: We report the first study of aqueous solutions (0.025 gL(-1) to 46 gL(-1)) of a telechelic poly(N-isopropylacrylamide) with octadecyl termini (C(18)-PNIPAM-C(18), M(w): 37000, 320 NIPAM units, M(w)/ M(n)=1.07) obtained by reversible addition-fragmentation chain transfer (RAFT) free radical polymerization of N-isopropylacrylamide. Static and dynamic light scattering measurements and fluorescence spectroscopy, using 8-anilino-1-naphthalenesulfonic acid (ANS) as probe, yielded the concentration dependence of the size and aggregation number of C(18)-PNIPAM-C(18) micelles in cold ( 20( degrees )C) dilute aqueous solutions. Concentrated solutions ( c>20 gL(-1)) form transient gels exhibiting an oscillatory shear behavior that can be approximated by a single-relaxation Maxwellian model. Aqueous solutions of C(18)-PNIPAM-C(18) undergo a phase transition upon heating to 31.5( degrees )C as determined by microcalorimetry. The heat-induced phase separation of dilute (0.025 gL(-1)) C(18)-PNIPAM-C(18) solutions yields a fluid that is colloidally stable at temperatures higher than 33( degrees )C. The overall results are consistent with a model assuming the formation of flowerlike micelles in the dilute regime and a network of micelles connected by telechelic chains in the concentrated regime.
authors.affiliation: Department of Chemistry and Faculty of Pharmacy, University of Montreal, Succursale Centre Ville, CP 6128, H3C 3J7 Montreal, QC, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Kujawa
authors.forename: H
authors.initials: H
authors.lastname: Watanabe
authors.forename: F
authors.initials: F
authors.lastname: Tanaka
authors.forename: F M
authors.initials: FM
authors.lastname: Winnik