Cunningham V J, Armes S P, Musa O M
Department of Chemistry , University of Sheffield , Brook Hill , Sheffield , South Yorkshire S3 7HF , UK . Email:
Ashland Specialty Ingredients , 1005 US 202/206 , Bridgewater , NJ 08807 , USA.
Polym Chem. 2016 Mar 14;7(10):1882-1891. doi: 10.1039/c6py00138f. Epub 2016 Feb 18.
A near-monodisperse poly(stearyl methacrylate) macromolecular chain transfer agent (PSMA macro-CTA) was prepared reversible addition-fragmentation chain transfer (RAFT) solution polymerisation in toluene. This PSMA macro-CTA was then utilised as a stabiliser block for the RAFT dispersion polymerisation of a highly polar monomer, -2-(methacryloyloxy)ethyl pyrrolidone (NMEP), in -dodecane at 90 °C. H NMR studies confirmed that the rate of NMEP polymerisation was significantly faster than that of a non-polar monomer (benzyl methacrylate, BzMA) under the same conditions. For example, when targeting a PSMA-PNMEP diblock copolymer, more than 99% NMEP conversion was achieved within 30 min, whereas only 19% BzMA conversion was obtained on the same time scale for the corresponding PSMA-PBzMA synthesis. The resulting PSMA-PNMEP diblock copolymer chains underwent polymerisation-induced self-assembly (PISA) during growth of the insoluble PNMEP block to form either spherical micelles, highly anisotropic worms or polydisperse vesicles, depending on the target DP of the PNMEP chains. Systematic variation of this latter parameter, along with the solids content, allowed the construction of a phase diagram which enabled pure morphologies to be reproducibly targeted. Syntheses conducted at 10% w/w solids led to the formation of kinetically-trapped spheres. A monotonic increase in particle diameter with PNMEP DP was observed for such PISA syntheses, with particle diameters of up to 462 nm being obtained for PSMA-PNMEP. Increasing the copolymer concentration to 15% w/w solids led to worm-like micelles, while vesicles were obtained at 27.5% w/w solids. High (≥95%) NMEP conversions were achieved in all cases and 3 : 1 chloroform/methanol GPC analysis indicated relatively high blocking efficiencies. However, relatively broad molecular weight distributions (/ > 1.50) were observed when targeting PNMEP DPs greater than 150. This indicates light branching caused by the presence of a low level of dimethacrylate impurity. Finally, PSMA-PNMEP spheres were evaluated as Pickering emulsifiers. Unexpectedly, it was found that either water-in-oil or oil-in-water Pickering emulsions could be obtained depending on the shear rate employed for homogenisation. Further investigation suggested that high shear rates lead to inversion of the initial hydrophobic PSMA-PNMEP spheres to form hydrophilic PNMEP-PSMA spheres.
通过在甲苯中进行可逆加成-断裂链转移（RAFT）溶液聚合反应，制备了一种近单分散的聚（甲基丙烯酸硬脂酯）大分子链转移剂（PSMA宏观链转移剂）。然后，将该PSMA宏观链转移剂用作稳定剂嵌段，用于在90℃下于正十二烷中对高极性单体2-（甲基丙烯酰氧基）乙基吡咯烷酮（NMEP）进行RAFT分散聚合反应。1H NMR研究证实，在相同条件下，NMEP的聚合速率明显快于非极性单体（甲基丙烯酸苄酯，BzMA）。例如，当目标产物为PSMA-PNMEP二嵌段共聚物时，在30分钟内NMEP转化率超过99%，而在相同时间范围内，相应的PSMA-PBzMA合成中BzMA转化率仅为19%。在不溶性PNMEP嵌段生长过程中，所得的PSMA-PNMEP二嵌段共聚物链发生聚合诱导自组装（PISA），根据PNMEP链的目标聚合度形成球形胶束、高度各向异性的蠕虫状胶束或多分散囊泡。通过系统改变后一个参数以及固体含量，可以构建一个相图，从而能够可重复地靶向获得纯形态。在10% w/w固体含量下进行的合成导致形成动力学捕获的球体。对于此类PISA合成，观察到粒径随PNMEP聚合度单调增加，PSMA-PNMEP的粒径可达462 nm。将共聚物浓度提高到15% w/w固体含量会导致形成蠕虫状胶束，而在27.5% w/w固体含量下可获得囊泡。在所有情况下，NMEP转化率均达到较高水平（≥95%），并且3:1氯仿/甲醇GPC分析表明封端效率相对较高。然而，当目标PNMEP聚合度大于150时，观察到相对较宽的分子量分布（/ > 1.50）。这表明存在低水平的二甲基丙烯酸酯杂质导致了轻度支化。最后，对PSMA-PNMEP球体作为Pickering乳化剂进行了评估。出乎意料的是，发现根据用于均质化的剪切速率，可以获得油包水或水包油Pickering乳液。进一步研究表明，高剪切速率会导致初始疏水的PSMA-PNMEP球体转变为亲水的PNMEP-PSMA球体。
