MICELLIZATION OF POLY(ETHYLENE OXIDE)-POLY(PROPYLENE OXIDE)-POLY(ETHYLENE OXIDE) TRIBLOCK COPOLYMERS IN AQUEOUS-SOLUTIONS - THERMODYNAMICS OF COPOLYMER ASSOCIATION
MICELLIZATION OF POLY(ETHYLENE OXIDE)-POLY(PROPYLENE OXIDE)-POLY(ETHYLENE OXIDE) TRIBLOCK COPOLYMERS IN AQUEOUS-SOLUTIONS - THERMODYNAMICS OF COPOLYMER ASSOCIATION
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DOI：
10.1021/ma00087a009
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发表时间：
1994-04-25
期刊：
影响因子：
5.5
通讯作者：
HATTON, TA
中科院分区：
文献类型：
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作者：
ALEXANDRIDIS, P;HOLZWARTH, JF;HATTON, TA
用染料增溶法测定了12种聚环氧乙烷-聚环氧丙烷-聚环氧乙烷(PEO-PPO-PEO)嵌段共聚物的临界胶束温度(CMT)和临界胶束浓度(CMC)值，其相对分子质量(2900-14600)和PPO/PEO比值(0.19-1.79)范围较大。发现一个封闭的缔合模型可以很好地描述大多数Pluronics的共聚胶束化过程，并用于获得胶束化的标准自由能(DELTAG度)、热(DELTAH度)和熵(DELTAS度)。结果表明，胶束化过程是由熵驱动的，具有吸热胶束化热。Pluronics的疏水部分PPO是胶束形成的原因，显然是由于水与PPO之间的氢键随着温度的升高而减弱。Pluronics的CMC对温度和头基(PEO)大小的依赖关系与低相对分子质量的非离子表面活性剂C(I)E(J)类似，温度的影响在Pluronics中更为明显。将PEO-PPO-PEO嵌段共聚物与PPO-PEO-PPO嵌段共聚物和PEO-PPO无规共聚物进行了比较，试图探讨分子结构对胶束形成的影响。在PPO-PEO-PPO嵌段共聚物水溶液中，随着温度的升高，在浊点附近没有观察到胶束。
The critical micellization temperature (cmt) and critical micellization concentration (cmc) values of 12 Pluronic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers, covering a wide range of molecular weights (2900-14 600) and PPO/PEO ratios (0.19-1.79), were determined employing a dye solubilization method. A closed association model was found to describe adequately the copolymer micellization process for the majority of the Pluronics and used to obtain the standard free energies (DELTAG-degrees), enthalpies (DELTAH-degrees), and entropies (DELTAS-degrees) of micellization. It was determined that the micellization process is entropy-driven and has an endothermic micellization enthalpy. The hydrophobic part of the Pluronics, PPO, was responsible for the micellization, apparently due to diminishing hydrogen bonding between water and PPO with increasing temperature. The cmc dependence on temperature and size of headgroup (PEO) of Pluronics follows a similar trend with lower molecular weight C(i)E(j) nonionic surfactants, the effect of temperature being more pronounced with the Pluronics. The PEO-PPO-PEO block copolymers were compared to PPO-PEO-PPO block and PEO-PPO random copolymers, in an attempt to probe the effect of molecular architecture in the formation of micelles. No micelles were observed in aqueous PPO-PEO-PPO block copolymer solutions with increasing temperature, up to the cloud point.