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Thermoresponsive Properties of Poly(N-vinylcaprolactam)-Poly(ethylene oxide) Aqueous Systems: Solutions and Block Copolymer Networks
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2001
Year
EngineeringResponsive PolymersChemistrySoft MatterChemical EngineeringPolymer MaterialPolymer TechnologyBlock Copolymer NetworksPhase SeparationThermosensitive PolyThermoresponsive PropertiesPolymer ChemistryEthylene OxideMaterials SciencePolymer EngineeringPhysical ChemistryPolymer SolutionPolymer SciencePolymer Property
Two- and three-dimensional phase diagrams have been constructed for thermosensitive poly(N-vinylcaprolactam)-poly(ethylene oxide) (PVCL-PEO) aqueous systems. Both solutions and swollen block copolymer networks have been investigated to elucidate the effect of the copolymer content and crosslinking density on their temperatures of phase separation (Tph.s.). The introduction of hydrophilic PEO into an aqueous solution of PVCL decreases its Tph.s.. This suggests that the strength of the hydrogen bonds within the thermoresponsive PVCL-water system is weakened by the introduction of PEO that also interacts with water. Based on the DSC investigation of the swollen networks, it was found that the influence of PEO on the phase behavior of weakly crosslinked networks is comparable with that of PVCL-PEO-H2O solutions. For networks with a higher degree of crosslinking, the presence of the crosslinks is of major importance for the explanation of the Tph.s. location. This detailed phase analysis led to the proposal of an irregular water distribution in these swollen networks.