Distribution of Phenols in Thermoresponsive Hydrogels

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• 作者：Katalin Kosik ; Erzsé ; bet Wilk ; Erik Geissler ; Krisztina L&aacute ; szló
• 刊名：Macromolecules
• 出版年：2007
• 出版时间：March 20, 2007
• 年：2007
• 卷：40
• 期：6
• 页码：2141 - 2147
• 全文大小：164K
• 年卷期：v.40,no.6(March 20, 2007)
• ISSN：1520-5835

文摘

The effect of three hydrotropic molecules, phenol, resorcinol and phloroglucinol, on thethermodynamic equilibrium and the dynamics of poly(N-isopropylacrylamide) (PNIPA) hydrogels is reported.With increasing hydroxyl number of this molecular sequence both the depression of the temperature and thewidth of the volume phase transition (VPT) increase, reflecting the nonuniform distribution of these moleculesinside the gel. Small-angle X-ray scattering detects no notable change in the local structure of the polymer chainsin the presence of phenol. Dynamic light scattering observations, however, show that phloroglucinol, unlike phenoland resorcinol, produces a small but significant decrease in the mobility of the polymer in the solvent. Isothermalmicrocalorimetry reveals an anomalous increase in the exothermic enthalpy of mixing just below the transition,both with phenol and phloroglucinol, which indicates a pretransition state in the gel in which the aromatic moleculespartly replace the bound water. This finding is corroborated by small-angle neutron scattering measurementsunder contrast matched conditions showing that at low phenol concentration the aromatic molecules are uniformlydispersed in the solvent, but in pretransition conditions a sparsely populated layer of phenol forms close to thepolymer chains.