Temperature Response of Aqueous Solutions of Pyrene End-Labeled Poly(N-isopropyl acrylamide)s Probed by Steady-State and Time-Resolved Fluorescence

Abstract

Aqueous solutions of a series of monodisperse poly(N‐isopropylacrylamide)s end‐labeled with n‐butyl‐1‐pyrene at one or both chain ends (Pyn‐PNIPAMs with n = 1 or 2) were studied by turbidimetry, light scattering, and fluorescence. For a given polymer concentration and heating rate, the cloud point (Tc) of an aqueous Pyn‐PNIPAM solution, determined by turbidimetry, was found to increase with the number‐average molecular weight (Mn) of the polymer. The steady‐state fluorescence spectra and time‐resolved fluorescence decays of Pyn‐PNIPAM aqueous solutions were analyzed and all parameters retrieved from these analyses were found to be affected as the solution temperature passed through Tc, the solution cloud point, and Tm, the temperature where dehydration of PNIPAM occurred. The trends obtained by fluorescence to characterize the aqueous Pyn‐PNIPAM solutions as a function of temperature were found to be consistent with the model proposed for telechelic PNIPAM by Koga et al. in 2006.