Synthesis and Characterization of Thermal-and pH-Sensitive Polyurethane Hydrogels
Three types of thermal-and pH-sensitive polyurethane (PU) hydrogels were successfully synthesized via three-step polymerization using polyethylene glycol (PEG),4,4'-diphenylmethane diisocyanate (MDI),2-ethyl-2-(hydroxymethyl)-1,3-propanediol (TMP) as main raw materials and 1,4-butanediol (BDO),Nmethyldiethanolamine (MDEA),dimethylolpropionic acid (DMPA) as chain extenders.FT-IR,DSC,XRD,swelling tests,swelling-deswelling tests were used to characterize the structures and properties of the PU hydrogels.FT-IR analysis demonstrate that the thermal-sensitive component (PEG) and pH-sensitive functional groups (-N(CH3)-and-COOH) are successfully incorporated into the PU hydrogels.DSC and XRD analysis reveal that the PEG crystallization in the PU hydrogels is still retained and the phase transition temperatures of the PU hydrogels appeare at 55 ℃,60 ℃ and 64 ℃,respectively.In addition,the swelling tests show the thermal-and pH-sensitive properties for all PU hydrogels.Concretely,when the temperature increases from 45 ℃ to 60 ℃,the equilibrium swelling ratio (ESR) for the PU hydrogels shows an obvious decrease.Moreover,the ESR for hydrogel (b) sharp decreases from 12.9 to 10.0 in the pH range from 8.5 to 11.5,while the ESR for hydrogel (c) significantly increases from 11.5 to 15.5 in the pH range from 4.0 to 7.0,both of them showing pH-sensitive property.The swelling-deswelling cycles show that Hydrogel (b) and Hydrogel (c) possess good reversibility and stability.
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