Effect of Molecular Structure on Thermoresponsive Behaviors of Pyrrolidone-Based Water-Soluble Polymers

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• 作者：Jun Sun ; Yifeng Peng ; Ying Chen ; Yu Liu ; Junjie Deng ; Lican Lu ; Yuanli Cai
• 刊名：Macromolecules
• 出版年：2010
• 出版时间：May 11, 2010
• 年：2010
• 卷：43
• 期：9
• 页码：4041-4049
• 全文大小：1061K
• 年卷期：v.43,no.9(May 11, 2010)
• ISSN：1520-5835

文摘

This paper describes the molecular structure dependent thermoresponsive behaviors of pyrrolidone-based water-soluble polymers. A series of well-defined poly[N-(2-methacryloyloxyethyl)pyrrolidone] (PNMEP), poly[N-(3-acryloyloxypropyl)pyrrolidone] (PNAPP), and poly[N-(3-methacryloyloxypropyl)pyrrolidone] (PNMPP) were synthesized via visible light activating RAFT polymerization at 25 °C. Kinetic studies indicate a rapid and well-controlled behavior of this polymerization. Gel permeation chromatography (GPC) and ¹H NMR analysis confirm their intact molecular structure, well-defined molecular weight, and narrow distribution. Laser light scattering and temperature-variable ¹H NMR analyses demonstrate that the cloud point of a PNMEP sample at a degree of polymerization (DP) of 96 is 1.5 °C lower than that of PNAPP at a DP = 104. Additional backbone methyl groups in PNMPP lead to a dramatic cloud point lowering, e.g., cloud point of PNMPP at a DP = 100 is 37 °C lower than that of PNAPP at a DP = 104. This is contrary to what was observed in poly(N-isopropylacrylamide) (PNIPA) and its polymethacrylamide analogues. These pyrrolidone-based polymers show a dramatic solvent isotopic effect that is different from that of PNIPA; e.g., the cloud point of PNMEP at a DP = 237 is 8.5 °C lower in D₂O than in H₂O. Increasing polymer chain length or hydrophobicity may suppress this solvent isotopic effect. This phase transition is correlated to Hofmeister series but more sensitive than PNIPA. Na₂CO₃ dramatically lowers cloud point, while NaI significantly improves cloud point, up to full dissolution in H₂O at 95 °C. The solvent isotopic effect in NaCl or Na₂CO₃ solution is the same as what observed in solution absent of salt. Upon heating D₂O solution of PNMEP, the polymer first forms the hydrated irregular colloidal aggregates near the cloud point, the phase transition occurs at the fully hydrated state at cloud point, and further heating leads to the dehydration and separation from D₂O. However, in NaCl solution, the dehydration of PNMEP occurs subsequently from apolar backbones, spacers, and finally pyrrolidone groups.