Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.
Langmuir. 2011 Mar 1;27(5):2019-27. doi: 10.1021/la1044706. Epub 2010 Dec 28.
This article describes the temperature-induced phase transfer behavior of a series of thermosensitive polymer brush-grafted particles between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). Six samples were made by surface-initiated atom transfer radical polymerization: silica particles grafted with poly(methoxypoly(ethylene glycol) methacrylate) (PPEGMMA) with two different molecular weights, poly(methoxytri(ethylene glycol) methacrylate) (PTEGMMA), poly(methoxydi(ethylene glycol) methacrylate) (PDEGMMA), and two copolymers of PEGMMA and TEGMMA with different compositions (P(PEGMMA-co-TEGMMA)-82 and P(PEGMMA-co-TEGMMA)-74). The cloud points of free PPEGMMA with M(n,SEC) of 23 and 40 kDa, P(PEGMMA-co-TEGMMA)-82, P(PEGMMA-co-TEGMMA)-74, and PTEGMMA in [EMIM][TFSI]-saturated water were 95, 94, 80, 72, and 43 °C, respectively. PDEGMMA was not soluble in the ionic liquid-saturated water. PPEGMMA brush-grafted particles moved spontaneously and completely from water to the [EMIM][TFSI] phase upon heating at 80 °C. When cooled to 22 °C, all particles returned to the water layer. From UV-vis absorbance measurements, the transfer temperature (T(tr)) of PPEGMMA-grafted particles from water to the ionic liquid was 42 °C. Thermodynamic analysis showed that the particle transfer was an entropically driven process. P(PEGMMA-co-TEGMMA)-82, P(PEGMMA-co-TEGMMA)-74, and PTEGMMA brush-grafted particles also underwent reversible and quantitative transfer between the two phases upon heating at 70 °C and cooling at 0 °C; their transfer temperatures from water to [EMIM][TFSI] were 36, 30, and 16 °C, respectively. T(tr) was a linear function of the cloud point of the corresponding free polymer in ionic liquid-saturated water. In contrast, PDEGMMA-grafted particles moved spontaneously to the ionic liquid layer upon heating but did not return to water even after prolonged stirring at 0 °C.
本文描述了一系列温敏聚合物刷接枝粒子在水和疏水性离子液体 1-乙基-3-甲基咪唑双(三氟甲基磺酰基)亚胺([EMIM][TFSI])之间的温度诱导相转移行为。通过表面引发原子转移自由基聚合制备了 6 个样品：接枝有两种不同分子量的聚甲氧基聚(乙二醇)甲基丙烯酸酯(PPEGMMA)、聚甲氧基三(乙二醇)甲基丙烯酸酯(PTEGMMA)、聚甲氧基二(乙二醇)甲基丙烯酸酯(PDEGMMA)和两种 PEGMMA 和 TEGMMA 组成的共聚物(P(PEGMMA-co-TEGMMA)-82 和 P(PEGMMA-co-TEGMMA)-74)的二氧化硅粒子。在[EMIM][TFSI]饱和水中，游离 PPEGMMA 的分子量(SEC)为 23 和 40 kDa、P(PEGMMA-co-TEGMMA)-82、P(PEGMMA-co-TEGMMA)-74 和 PTEGMMA 的浊点分别为 95、94、80、72 和 43°C，而 PDEGMMA 在离子液体饱和水中不溶解。PPEGMMA 刷接枝粒子在 80°C加热时自发且完全从水中转移到[EMIM][TFSI]相。当冷却至 22°C 时，所有粒子都返回水层。从紫外-可见吸收测量中，可以看出 PPEGMMA 接枝粒子从水到离子液体的转移温度(T(tr))为 42°C。热力学分析表明，粒子转移是一个熵驱动的过程。P(PEGMMA-co-TEGMMA)-82、P(PEGMMA-co-TEGMMA)-74 和 PTEGMMA 刷接枝粒子在 70°C 加热和 0°C 冷却时也在两相之间发生可逆和定量转移；它们从水到[EMIM][TFSI]的转移温度分别为 36、30 和 16°C。T(tr)是与离子液体饱和水中相应游离聚合物浊点的线性函数。相比之下，PDEGMMA 接枝粒子在加热时自发地移动到离子液体层，但即使在 0°C 长时间搅拌后也不会返回水相。
