Synthesis and Characterization of Thermal- and pH-Sensitive Polyurethane Hydrogels with Different Transition Temperature
A series of novel thermal- and pH-sensitive polyurethane (PU) hydrogels with different transition temperatures were successfully synthesized via a three-step polymerization using polyethylene glycol (PEG), 4,4'-diphenylmethane diisocyanate (MDI), dimethylol propionic acid (DMPA) and trimethylolpropane (TMP). Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were employed to characterize the basic properties of the PU hydrogels. The swelling tests were simultaneously used to measure the thermal- and pH-sensitive properties of the PU hydrogels. FTIR analysis demonstrated that the PEG (the temperature-sensitive component) and –COOH groups (the pH-sensitive component) were successfully introduced into the PU molecule chains. SEM study indicated that the PU hydrogels possessed a honeycomb structure, while the DSC and XRD analysis revealed that the PEG crystallization in the PU hydrogels were still retained and the onset of transition temperature for the PU hydrogels appeared at 15.8 °C, 23.6 °C, 33.4 °C, 36.5 °C and 38.3 °C, respectively. In addition, the swelling tests showed the thermal- and pH-sensitive properties for all the PU hydrogels. Concretely, when temperature was increased from 15 °C to 25 °C, the equilibrium swelling ratio (ESR) for the hydrogels 1 and 2 showed an obvious decrease and the other three PU hydrogels showed significant decrease when the temperature was increased from 35 °C to 45 °C. Moreover, the ESR increased sharply when the pH value was increased from 4.0 to 7.0. With their thermaland pH-sensitive properties, the synthesized PU hydrogels have potential for use in many fields, such as biomaterials, molecular imprinting materials, adsorbing materials and so on.
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Document Type: Short Communication
Publication date: August 1, 2016
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