Hunter Saul J, Penfold Nicholas J W, Jones Elizabeth R, Zinn Thomas, Mykhaylyk Oleksandr O, Armes Steven P
Dainton Building, Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, Yorkshire S3 7HF, U.K.
DSM Biomedical, Urmonderbaan 22, 6167RD Geleen, The Netherlands.
Macromolecules. 2022 Apr 26;55(8):3051-3062. doi: 10.1021/acs.macromol.2c00379. Epub 2022 Apr 17.
We recently reported that the reversible addition-fragmentation chain transfer (RAFT) aqueous emulsion polymerization of hydroxybutyl methacrylate (HBMA) using a relatively short non-ionic poly(glycerol monomethacrylate) (PGMA) precursor enables convenient preparation of diblock copolymer nano-objects with spherical, worm-like, or vesicular morphologies. We postulated that the relatively high aqueous solubility of HBMA (∼25 g dm at 50 °C) was likely to be a key parameter for overcoming the problem of kinetically trapped spheres that is observed for many RAFT aqueous emulsion polymerization formulations. In this study, we revisit the RAFT aqueous emulsion polymerization of HBMA using a poly(ethylene glycol) (PEG) precursor as a steric stabilizer block. Remarkably, the resulting PEG-PHBMA diblock copolymer nanoparticles exhibit thermoreversible morphological transitions in aqueous solution. More specifically, transmission electron microscopy and small-angle X-ray scattering studies confirmed that spheres are formed at 25 °C, worms at 58 °C, and vesicles at 65 °C. This is the first time that such behavior has been reported for nano-objects prepared by RAFT aqueous emulsion polymerization. Moreover, variable temperature dynamic light scattering and oscillatory rheology studies confirmed that these transitions are highly reversible at 0.1 and 10% w/w, respectively. Variable temperature H NMR studies indicated that (i) the PEG stabilizer block undergoes dehydration on heating and (ii) the apparent degree of hydration of the hydrophobic PHBMA block increases on heating from 25 to 65 °C. This suggests that the change in copolymer morphology is best explained in terms of a uniform plasticization mechanism.
我们最近报道，使用相对较短的非离子型聚甲基丙烯酸甘油单酯（PGMA）前体对甲基丙烯酸羟丁酯（HBMA）进行可逆加成-断裂链转移（RAFT）水乳液聚合，能够方便地制备出具有球形、蠕虫状或囊泡状形态的二嵌段共聚物纳米粒子。我们推测，HBMA相对较高的水溶性（50℃时约为25 g dm）可能是克服许多RAFT水乳液聚合配方中出现的动力学捕获球体问题的关键参数。在本研究中，我们重新研究了以聚乙二醇（PEG）前体作为空间稳定剂嵌段的HBMA的RAFT水乳液聚合。值得注意的是，所得的PEG-PHBMA二嵌段共聚物纳米粒子在水溶液中表现出热可逆的形态转变。更具体地说，透射电子显微镜和小角X射线散射研究证实，在25℃时形成球体，在58℃时形成蠕虫状，在65℃时形成囊泡。这是首次报道通过RAFT水乳液聚合制备的纳米粒子有这种行为。此外，变温动态光散射和振荡流变学研究证实，这些转变在0.1%和10% w/w时分别具有高度可逆性。变温1H NMR研究表明：（i）PEG稳定剂嵌段在加热时发生脱水；（ii）疏水性PHBMA嵌段的表观水合度在从25℃加热到65℃时增加。这表明，共聚物形态的变化最好用均匀增塑机制来解释。
