Impact of Photoactive Monomer Location in Photoresponsive Block Copolymer/Ionic Liquid Solutions
Impact of Photoactive Monomer Location in Photoresponsive Block Copolymer/Ionic Liquid Solutions
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DOI：
10.1021/acs.macromol.2c02113
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发表时间：
2023-01
期刊：
影响因子：
5.5
通讯作者：
Claire L. Seitzinger;T. Lodge
中科院分区：
文献类型：
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作者：
Claire L. Seitzinger;T. Lodge
通过将光敏部分并入嵌段聚合物中，可以用光控制相行为。以前的研究着眼于将偶氮苯（一种常见的光响应分子）作为侧基沿着聚合物的主链，甚至作为溶剂的一部分而不是作为共聚单体。在这里，我们研究的效果的定位悬挂偶氮苯基团沿沿着聚合物主链上的低临界无序-有序转变的聚（甲基丙烯酸甲酯）-嵌段-聚（甲基丙烯酸苄酯）（PMMA-b-PBnMA，或MB）在离子液体1，3-二甲基咪唑双（三氟甲基磺酰基）酰亚胺。使用小角度X-射线散射和紫外线（UV）照射的小振幅振荡剪切流变学，偶氮苯的位置统计沿着甲基丙烯酸苄酯主链（MBsA）相比，定位它作为一个中间块之间的PMMA和PBnMA（MAB）或作为一个端块后的PBnMA（MBA）。研究了离子溶剂中聚合物的两种浓度，35和50重量%。在35重量%下，MBsA在60 °C下微相分离，MBA在100 °C下微相分离，然后MAB在120 °C下微相分离，在50重量%下重复该趋势。MBsA是唯一的聚合物，以35重量%的晶格上，形成六方密堆积的球体。MBsA和MBA在50重量%下均形成六方填充的圆柱体。MBsA在感兴趣的温度范围内一致地有序排列到晶格上，而MBA仅在50重量%时这样做，并且MAB在两种浓度下都保持无序。MBsA也是三个样品中唯一一个成功地在有序和无序之间进行可逆转变的样品。因此，调节偶氮苯单元在热响应性和光响应性聚合物溶液内的位置显著地改变了溶液的整体行为以及用光和温度控制该行为的能力。
By incorporating a photoactive moiety into a block polymer, the phase behavior can be controlled with light. Previous studies have looked at situating azobenzene, a common photoresponsive molecule, along the backbone of the polymer as a pendant group, and even as part of the solvent rather than as a comonomer. Here, we study the effect of the positioning of pendant azobenzene groups along the polymer backbone on the lower critical disorder–order transition of poly(methyl methacrylate)-block-poly(benzyl methacrylate) (PMMA-b-PBnMA, or MB) in the ionic liquid 1,3-dimethyl imidazolium bis(trifluoromethylsulfonyl)imide. Using small-angle X-ray scattering and ultraviolet (UV)-irradiated small-amplitude oscillatory shear rheology, the placement of azobenzene statistically along the benzyl methacrylate backbone (MBsA) is compared to locating it as a midblock between the PMMA and the PBnMA (MAB) or as an end block after the PBnMA (MBA). Two concentrations of polymer in the ionic solvent were studied, 35 and 50 wt %. At 35 wt %, MBsA microphase-separated at 60 °C, MBA at 100 °C, and followed by MAB at 120 °C, a trend that was repeated at 50 wt %. MBsA was the only polymer to order onto a lattice at 35 wt %, forming hexagonally close-packed spheres. Both MBsA and MBA formed hexagonally packed cylinders at 50 wt %. MBsA consistently ordered onto a lattice over the temperature range of interest, while MBA only did so at 50 wt %, and MAB remained disordered at both concentrations. MBsA was also the only sample of the three to successfully transition reversibly between order and disorder with light. Therefore, adjusting the location of the azobenzene units within the thermo- and photoresponsive polymer solution significantly changes the overall behavior of the solutions and the ability to control that behavior with light and temperature.