Temperature‐Induced Phase Transition Characterization of Responsive Polymer Brushes Grafted onto Nanoparticles

Abstract

Temperature‐induced phase transition parameters of responsive free polymer and brushes onto nanoparticles are measured using high‐resolution magic‐angle sample spinning (HRMAS) NMR spectroscopy. To this purpose, a two‐state statistical model of temperature dependence of thermodynamic observables is developed and applied to obtain parameters which characterize the process of temperature‐induced phase transition of stimuli‐sensitive polymers. In this investigation the thermodynamic observable is the integral intensity of the 1H HRMAS NMR spectrum peaks and the derived thermodynamic parameters are transition temperature and transition entropy. This approach is applied to investigate the dependence of temperature‐induced coil‐to‐globule transition of poly(N‐isopropylacrylamide), (PNIPAm), asymmetric end functionalized with benzyl and thiol groups (Bn–PNIPAm–SH) on molecular weight in the range 3600–30 000 g mol–1 in aqueous solutions. The characteristics of the phase transition represented by transition temperature, and transition entropy are compared to that of Bn–PNIPAm–SH brushes onto gold nanorods in the same range of molecular weight. The method used for measuring the characteristics of phase transition is based on transverse magnetization relaxation (T2) spin‐echo enhance editing of the integral intensities of the 1H HRMAS NMR spectra. This NMR observable reflects changes in transverse relaxation times as an indicative of the polymer chains conformations and dynamics reached in the process of temperature‐induced phase transition. image