Ultrasensitive pH-Induced Water Solubility Switch Using UCST Polymers

作者：Zhang, Hu; Guo, Shengwei; Fan, Weizheng; Zhao, Yue^*

来源：Macromolecules, 2016, 49(4): 1424-1433.

DOI：10.1021/acs.macromol.5b02522

• CRITICAL SOLUTION TEMPERATURE
• UREIDO-DERIVATIZED POLYMERS
• BLOCK-COPOLYMER MICELLES
• COIL-TO-GLOBULE
• THERMORESPONSIVE PROPERTIES
• AQUEOUS-SOLUTIONS
• REVERSIBLE UCST
• TRANSITION
• LCST
• BEHAVIOR

For some thermosensitive polymers, the absence of an upper critical solution temperature (UCST) in water in an accessible temperature range (say, 5-90 degrees C) can be attributed to the influence of charged groups in the polymer structure. This property was exploited in the present study to achieve ultrasensitive pH-induced water solubility switch of UCST polymers in physiological medium. By incorporating either acrylic acid (AAc) or 4-vinylpyridine (4VP) comonomer units in the random copolymer of acrylamide and acrylonitrile (P(AAm-co-AN-co-AAc) or P(AAm-co-AN-co-4VP)), the pH induced shift of UCST was investigated by monitoring the solution cloud point. The results revealed an unusually large shift of the cloud point upon pH variation over a small range. In particular, one P(AAm-co-AN-co-4VP) sample exhibited a cloud point drop from 72 degrees C at pH 4.75 to 15 degrees C at pH 4.50 (i.e., 57 K shift over 0.25 pH units), and its transition from soluble to insoluble state at room temperature was visually observable over a pH change as little as 0.05 unit. Using this sample as macromolecular chain transfer agent to polymerize dimethylacrylamide (DMA) through RAFT, an ABA-type triblock copolymer of P(AAm-coAN-co-4VP)-b-PDMA-b-P(AAm-co-AN-co-4VP) was obtained, and it showed an even larger cloud point switch from 71 to 10 degrees C with pH decreasing from 4.75 to 4.50. Consequently, the micelle formed by this block copolymer was stable at 37 degrees C with pH from 7.00 down to 4.75 but abruptly dissolved at pH 4.50 due to the water solubility switch. This study demonstrates a new UCST polymer-based approach to polymer assemblies that can sense a very small pH change by undergoing straightforward water solubility switch.

• 出版日期2016-2-23
• 单位北方民族大学