Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52056 Aachen, Germany.
Phys Chem Chem Phys. 2014 Mar 14;16(10):4917-32. doi: 10.1039/c3cp54707h.
The influence of architecture on polymer interactions is investigated and differences between branched and linear copolymers are found. A comprehensive picture is drawn with the help of a fluorescence approach (using pyrene and 4HP as probe molecules) together with IR or NMR spectroscopy and X-ray/light scattering measurements. Five key aspects are addressed: (1) synergistic intramolecular complexation within miktoarm stars. The proximity of thermoresponsive poly(propylene oxide) (PPO) and poly(dimethylaminoethyl methacrylate) (PDMAEMA) within a miktoarm star leads to complexation between these weakly interacting partners. Consequently, the original properties of the constituents are lost, showing hydrophobic domains even at low temperatures, at which all homopolymers are water soluble. (2) Unimolecular micelles for miktoarm stars. The star does not exhibit intermolecular self-assembly in a large temperature range, showing unimers up to 55 °C. This behavior was traced back to a reduced interfacial tension between the PPO-PDMAEMA complex and water (PDMAEMA acts as a "microsurfactant"). (3) Unimolecular to multimolecular micelle transition for stars. The otherwise stable unimolecular micelles self-assemble above 55 °C. This aggregation is not driven by PPO segregation, but by collapse of residual PDMAEMA. This leads to micrometer-sized multilamellar vesicles stabilized by poly(ethylene oxide) (PEO). (4) Prevention of pronounced complexation within diblock copolymers. In contrast to the star copolymers, PPO and PDMAEMA adapt rather their homopolymer behavior within the diblock copolymers. Then they show their immanent LCST properties, as PDMAEMA turns insoluble at elevated temperatures, whereas PPO becomes hydrophobic below room temperature. (5) Two-step micellization for diblock copolymers. Upon heating of linear copolymers, the dehydration of PPO is followed by self-assembly into spherical micelles. An intermediate prevalence of unimolecular micelles is revealed in a small temperature window between PPO collapse and self-assembly of PEO-b-PPO. Also for PPO-b-PDMAEMA, PPO segregation prevails after initial weak complexation, leading to micelles with a PPO core. Considerable amounts of water are entrapped within the collapsed PDMAEMA domains above 55 °C (skin effect), preventing PPO-PDMAEMA complexation within precipitating PPO-b-PDMAEMA. Further, collapsed PDMAEMA is rather polar as sensed by pyrene and 4HP. In summary, advanced macromolecular architectures can lead to an unprecedented intramolecular self-assembly behavior, where internal complexation prevents intermolecular aggregation.
研究了聚合物相互作用受结构的影响，发现支化和线性共聚物之间存在差异。利用荧光法（使用芘和 4HP 作为探针分子）结合 IR 或 NMR 光谱以及 X 射线/光散射测量，得出了一个全面的结果。文中提到了五个关键方面：（1）星型嵌段共聚物中协同的分子内络合作用。在星型嵌段共聚物中，温敏性聚（环氧丙烷）（PPO）和聚（二甲氨基乙基甲基丙烯酸酯）（PDMAEMA）之间的接近导致这些弱相互作用的聚合物之间发生络合。结果是，原来的聚合物失去了自身的特性，即使在所有均聚物都溶于水的低温下，也表现出疏水性。（2）星型嵌段共聚物的单分子胶束。在很大的温度范围内，星型嵌段共聚物不会发生分子间自组装，直至 55°C 时仍呈现单分子状态。这种行为可以归因于 PPO-PDMAEMA 复合物与水之间的界面张力降低（PDMAEMA 充当“胶束微表面活性剂”）。（3）星型嵌段共聚物向多分子胶束的转变。否则，稳定的单分子胶束在 55°C 以上自组装。这种聚集不是由 PPO 分离引起的，而是由剩余 PDMAEMA 的坍塌引起的。这导致由聚（氧化乙烯）（PEO）稳定的微米级多层囊泡。（4）二嵌段共聚物中显著络合作用的抑制。与星型嵌段共聚物相反，PPO 和 PDMAEMA 在二嵌段共聚物中更倾向于表现出其均聚物的行为。然后，它们显示出固有的 LCST 特性，因为 PDMAEMA 在高温下变得不溶，而 PPO 在室温以下变得疏水。（5）二嵌段共聚物的两步胶束化。线性共聚物加热时，PPO 先脱水，然后自组装成球形胶束。在 PPO 坍塌和 PEO-b-PPO 自组装之间的一个小温度窗口中，揭示了单分子胶束的中间优势。对于 PPO-b-PDMAEMA，在初始弱络合之后，PPO 分离占主导地位，导致具有 PPO 核的胶束。在 55°C 以上（皮层效应），大量水被困在坍塌的 PDMAEMA 域内，防止沉淀的 PPO-b-PDMAEMA 中 PPO-PDMAEMA 络合。此外，与芘和 4HP 感知到的一样，坍塌的 PDMAEMA 极性较强。总的来说，先进的高分子结构可以导致前所未有的分子内自组装行为，其中内部络合作用阻止了分子间的聚集。
