Tuning of Thermo-Triggered Gel-to-Sol Transition of Aqueous Solution of Multi-Responsive Diblock Copolymer Poly(methoxytri(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethoxydi(ethy

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• 作者：Naixiong Jin ; Jeremiah W. Woodcock ; Chenming Xue ; Thomas G. O鈥橪enick ; Xueguang Jiang ; Shi Jin ; Mark D. Dadmun ; Bin Zhao
• 刊名：Macromolecules
• 出版年：2011
• 出版时间：May 10, 2011
• 年：2011
• 卷：44
• 期：9
• 页码：3556-3566
• 全文大小：1099K
• 年卷期：v.44,no.9(May 10, 2011)
• ISSN：1520-5835

文摘

This article reports on the synthesis of a hydrophilic diblock copolymer composed of two distinct thermosensitive polymers with one block containing a small amount of carboxylic acid groups, poly(methoxytri(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethoxydi(ethylene glycol) acrylate) (P(TEGMA-co-AA)-b-PDEGEA), and the study of thermo-induced sol鈭抔el鈭抯ol transitions of its moderately concentrated aqueous solutions at various pH values. The diblock copolymer was obtained by the removal of tert-butyl groups of P(TEGMA-co-tert-butyl acrylate)-b-PDEGEA, which was synthesized by reversible addition鈭抐ragmentation chain transfer polymerization. PTEGMA and PDEGEA are thermosensitive polymers with lower critical solution temperatures (LCSTs) of 58 and 9 掳C, respectively, in water. The incorporation of a small amount of carboxylic acid groups into PTEGMA allowed the LCST of the P(TEGMA-co-AA) block to be tuned by changing the solution pH. We found that a 20 wt % aqueous solution of P(TEGMA-co-AA)-b-PDEGEA with pH of 3.11 (measured at 0 掳C) underwent multiple phase transitions upon heating, from a clear, free-flowing liquid (<19 掳C) to a clear, free-standing gel (19 to 39 掳C), to a clear, free-flowing hot liquid (40 to 55 掳C), and to a cloudy mixture (鈮?6 掳C). With the increase of pH, the gel-to-sol transition (T_gel鈭抯ol) and the clouding temperature (T_clouding) of the sample shifted to higher values, while the sol-to-gel transition temperature (T_sol鈭抔el) remained the same. These transitions and the tunability of T_gel鈭抯ol stemmed from the thermosensitive properties of the two blocks of the diblock copolymer and the pH dependence of the LCST of P(TEGMA-co-AA), which was confirmed by differential scanning calorimetry and dynamic light scattering studies. Using the vial inversion test method, we further mapped out the C-shaped sol鈭抔el phase diagrams of (PTEGMA-co-AA)-b-PDEGEA in water in the moderate concentration range at three different pH values (3.11, 4.49, and 5.25, all measured at 0 掳C). While the lower temperature boundaries overlapped, the upper temperature boundary shifted upward and the critical gelation concentration decreased with the increase of pH. In contrast, the sol鈭抔el phase diagram of PTEGMA-b-PDEGEA, which contained no pH-responsive groups, showed no changes in T_sol鈭抔el, T_gel鈭抯ol, and T_clouding with pH.