Temperature‐Induced Phase Transition in Aqueous Solutions of Poly(N‐isopropylacrylamide)‐Based Block Copolymer

Abstract

SummaryTemperature‐induced phase transition in D2O solutions of the poly(ethylene oxide)(PEO)‐b‐poly(N‐isopropylacrylamide)(PNIPAm) block copolymer was investigated and compared with the LCST transition of the PNIPAm homopolymer. We confirmed that the temperature behavior of solutions of the PEO‐b‐PNIPAm in NMR spectra is in accord with existence of micelles where immobilized PNIPAm blocks form rather compact core and mobile PEO blocks form a shell of micelles. By combination of NMR and IR spectroscopy, and DSC we have found that the phase transition and globular structures of the PNIPAm component are significantly affected by the presence of the PEO block. E.g., at temperatures above the phase transition the degree of dehydration of PNIPAm segments (CO groups) is two times larger in the block copolymer in comparison with the neat PNIPAm. 2D NOESY spectra revealed certain conformation changes in the solution of the PEO‐b‐PNIPAm block copolymer already in the pretransition region.