Thermoresponsive behavior of block copolymers of PEO and PNIPAm with different architecture in aqueous solutions: A study by NMR, FTIR, DSC and quantum-chemical calculations

Abstract

Temperature behavior of D2O solutions of thermoresponsive diblock poly(ethylene oxide) (PEO)-b-poly(N-isopropylacrylamide) (PNIPAm) copolymers and Y-shape triblock PEO-b-(PNIPAm)2 copolymers was investigated and compared with the phase transition of the PNIPAm homopolymer by combination of NMR and ATR FTIR spectroscopy, DSC and model quantum-chemical calculations. It is shown that the phase transition and structures of PNIPAm component (forming micellar cores) are significantly affected not only by the presence of the PEO block but also by copolymer architecture. Both these factors affect energetics of the phase transition, influence of the polymer concentration and behavior of bound water at elevated temperatures. They also affect the degree of dehydration of PNIPAm segments (CO groups) at temperatures above the phase transition which is higher for block copolymers (especially for the diblock) in comparison with PNIPAm homopolymer. NOESY NMR spectra likewise revealed influence of the architecture of the block copolymer on its conformational behavior in the pretransition region.