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Quantification of the stimuli-responsive phase transition in polymers is topical and important for the understanding and development of novel stimuli-responsive materials. The temperature-induced phase transition of poly( N-isopropylacrylamide) (PNIPAm) with one thiol end group depends on the confinement-free polymer or polymer brush-on the molecular weight and on the nature of the second end. This paper describes the synthesis of heterotelechelic PNIPAm of different molecular weights with a thiol end group-that specifically binds to gold nanorods and a hydrophilic NIPAm end group by reversible addition-fragmentation chain-transfer polymerization. Proton high-resolution magic angle sample spinning NMR spectra are used as an indicator of the polymer chain conformations. The characteristics of phase transition given by the transition temperature, entropy, and width of transition are obtained by a two-state model. The dependence of thermodynamic parameters on molecular weight is compared for hydrophilic and hydrophobic end functional-free polymers and brushes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The investigation of the coacervation (self-aggregation) behavior of biomicrogels which can potentially be used as drug carriers is an important topic, because self-aggregation can not only cause loss of activity, but also toxicity and immunogenicity. To study this effect microgels from elastin-like recombinamer are synthesized using miniemulsion technique. The existence of coacervation for such microgels, at different concentrations and temperatures, is studied and proved by cryo-field emission scanning clectron microscopy (cryo-FESEM), cryo-transmission electron microscopy (cryo-TEM), and by a novel 1H high-resolution magic angle sample spinning (HRMAS), nuclear magnetic resonance (NMR) spectroscopy, and relaxometry methods. The findings by 1H HRMAS NMR spectroscopy and relaxometry show simultaneous processes of volume phase temperature transition and coacervation with different sensitivity for hydrophobic and hydrophilic amino acid side-chains in the microgel. The coacervation process is more evidential by the behavior of glycine α-CH2, 1H NMR peak as compared to the proline β -CH2. [ABSTRACT FROM AUTHOR]