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Energetics of Cooperative Transitions of N ‐Vinylcaprolactam Polymers in Aqueous Solutions
Author(s) -
Dubovik Alexander S.,
Makhaeva Elena E.,
Grinberg Valerij Ya.,
Khokhlov Alexei R.
Publication year - 2005
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200400554
Subject(s) - aqueous solution , enthalpy , chemistry , polymer , heat capacity , phase transition , phase (matter) , methacrylic acid , thermodynamics , transition temperature , sodium sulfate , poly(methacrylic acid) , atmospheric temperature range , polymer chemistry , analytical chemistry (journal) , copolymer , chromatography , sodium , organic chemistry , physics , superconductivity , quantum mechanics
Summary: Phase and conformational behavior of poly( N ‐vinylcaprolactam) was studied as a function of polymer concentration, concentration of NaCl, and concentration of sodium dodecyl sulfate (SDS). Precise measurements of the partial heat capacity of the polymer were first carried out within the temperature range 10–125 °C. Thermodynamic parameters of the phase separation transition (transition temperature, enthalpy, and heat capacity increment) do not change with variations in polymer concentration. In the presence of salt the transition temperature decreases, the enthalpy increases, and the heat capacity increment does not vary significantly. Beginning with the SDS concentration of 0.005 M , the phase separation is suppressed and the heat capacity peak splits into two peaks. Upon further increase in surfactant concentration the amplitude of the low‐temperature peak increases while that of the high‐temperature peak vanishes. Phase separation transition in aqueous solutions of N ‐vinylcaprolactam‐methacrylic acid copolymers of different compositions were studied at different polymer concentrations and pH (4–12). The transition parameters do not depend on polymer concentration and pH.“Macroglobule” formed spontaneously as a result of the phase separation of a poly( N ‐vinylcaprolactam) solution.