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Switching the conformational behaviour of poly( N ‐isopropyl acrylamide)
Author(s) -
Rimmer Stephen,
Soutar Ian,
Swanson Linda
Publication year - 2009
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.2537
Subject(s) - lower critical solution temperature , phosphorescence , aqueous solution , intersystem crossing , copolymer , polymer chemistry , materials science , molar mass , photochemistry , chemistry , polymer , fluorescence , organic chemistry , singlet state , physics , quantum mechanics , nuclear physics , excited state
In this review we present data highlighting the power and versatility of luminescence spectroscopy in the study of the conformational behaviour of poly( N ‐isopropyl acrylamide) (PNIPAM). PNIPAM shows a lower critical solution temperature (LCST) in aqueous solution at 32 °C. Fluorescence time‐resolved anisotropy measurements (TRAMS) have confirmed that a conformational change occurs from an expanded open chain to a globular structure at the LCST, which forms the basis of phase separation observed for semi‐dilute concentrations. The coiled conformation can solubilise low‐molar‐mass species as revealed by the spectral profile of pyrene and is extremely protective: intersystem crossing to the triplet manifold can be enhanced by use of a heavy‐atom promoter (bromostyrene) copolymerised with NIPAM and trace levels of acenaphthylene allowing generation of phosphorescence at temperatures as high as 50 °C in aqueous solution. Manipulation of the conformational switch of PNIPAM is possible via simple free radical copolymerisation. However, a reduction in the magnitude of the transition occurs, which has an impact on the solubilisation properties of the resultant copolymers. Alternative strategies are suggested to overcome this problem: synthesis of graft copolymers allows fine‐tuning of the thermal response whilst maintaining the magnitude of the transition as revealed by TRAMS. Copyright © 2009 Society of Chemical Industry