Macromolecular Chemistry and Physics · 2016 · 15 citations · 21 references
Natural SciencesChemistryMaterials SciencePhysical ChemistryPolymer ChemistryPolymer MaterialsPolymer CharacterizationPolymer Phase BehaviorPolymer Physical ChemistryPolymer PhysicsPolymer StructurePolymer ThermodynamicsBlock Copolymer MicellesCritical Solution TemperatureCritical TemperatureLower Critical Solution TemperatureNuclear Overhauser Effect SpectroscopyPolymer Concentration DependencePolymer Concentration EffectsPolymer Molecular Characteristics
Temperature behavior of D2O solutions of poly(ethylene oxide) (PEO)114-block-poly(N-isopropylacrylamide) (PNIPAm)109 is characterized by NMR methods. At temperatures above the lower critical solution temperature (LCST) transition of PNIPAm component, 1H NMR spectra are consistent with existence of micelles where immobilized PNIPAm blocks form rather compact core and mobile PEO blocks form a shell of micelles. The transition of PNIPAm component shifts toward lower temperatures with increasing polymer concentration. 2D nuclear Overhauser effect spectroscopy spectra which can provide information on proton groups in close spatial contact (<0.5 nm) show an increase in intensity of cross-peaks between PEO protons and main chain CH and CH2 protons, and isopropyl CH protons of PNIPAm units after increasing the temperature from 292.7 to 301.6 K. The fact that this change occurs at temperature, which is still below the LCST transition of PNIPAm component evidences certain conformation changes in the PEO-b-PNIPAm block copolymer already in the pretransition region.
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Thermal analysis of the volume phase transition with N-isopropylacrylamide gels
Katsuto Otake, Hiroshi Inomata, Mikio Konno et al. · Macromolecules · 1990 · 740 citations