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Author: Demco, Dan Eugen × Author: Möller, Martin × End date: 2019 × Start date: 2010 × DDC: 540 ×

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    Thermodynamic Parameters of Temperature-Induced Phase Transition for Brushes onto Nanoparticles: Hydrophilic versus Hydrophobic End-Groups Functionalization
    (Weinheim : Wiley-VCH, 2017) Schweizerhof, Sjören; Demco, Dan Eugen; Mourran, Ahmed; Keul, Helmut; Fechete, Radu; Möller, Martin
    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.
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    Polymers Diffusivity Encoded by Stimuli-Induced Phase Transition: Theory and Application to Poly(N-Isopropylacrylamide) with Hydrophilic and Hydrophobic End Groups
    (Weinheim : Wiley-VCH, 2018) Schweizerhof, Sjören; Demco, Dan Eugen; Mourran, Ahmed; Fechete, Radu; Möller, Martin
    The self-diffusion of various nano-objects investigated by high-resolution nuclear magnetic resonance diffusometry proves to be an efficient method for the characterization of dynamics, aggregation kinetic, and matrix morphology. This study investigates how the two-state model and Boltzmann function approach can be used for the evaluation of the thermodynamic parameters of temperature-induced phase transition encoded in polymer diffusivity. The characteristics of the phase transition given by the transition temperature, change of entropy, and width of transition are obtained for poly(N-isopropylacrylamide) (PNIPAm) linear polymers with hydrophilic and hydrophobic end-group functionalization. The effect of end groups upon the polymer diffusivity is investigated as a function of molecular weight (M n), from which fractal dimensions and hydrodynamic drag coefficients are obtained. The PNIPAm diffusivity is affected strongly by the end groups, and it is reflected in the hydrodynamic radius dependence upon molecular weight that obeys different power-law relations. In this study, the synthesis of α-ω-heterotelechelic PNIPAm of different molecular weights with a thiol end group and a hydrophilic NIPAm-like as well as a hydrophobic benzyl end group are described by reversible addition–fragmentation chain-transfer polymerization.