RAFT aqueous dispersion polymerization of 4-hydroxybutyl acrylate: effect of end-group ionization on the formation and colloidal stability of sterically-stabilized diblock copolymer nanoparticles
RAFT aqueous dispersion polymerization of 4-hydroxybutyl acrylate: effect of end-group ionization on the formation and colloidal stability of sterically-stabilized diblock copolymer nanoparticles
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DOI：
10.1039/d1py01562a
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发表时间：
2022-01-06
影响因子：
4.6
通讯作者：
Armes, Steven P.
中科院分区：
文献类型：
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作者：
Beattie, Deborah L.;Deane, Oliver J.;Armes, Steven P.
采用高效的一锅RAFT水分散聚合法制备了一系列聚丙烯酸羟乙酯(X)-聚(4-羟基丙烯酸丁酯)(Y)(PHEA(X)-PHBA(Y))两嵌段共聚物纳米粒子。通过动态光散射(DLS)和水溶液电泳法对所得的空间稳定纳米颗粒的pH依赖性胶体稳定性进行了评价。HOOC-PHEA(73)-PHBA(217)纳米粒子在pH 5.1以下表现出可逆的絮凝作用，而Mo-PHEA(76)-PHBA(160)纳米粒子在pH 5以上发生絮凝。此外，HOOC-PHEA(73)-PHBA(217)纳米粒子对盐敏感，由于电荷屏蔽，在20-60 mM KCl存在下发生了初始絮凝。因此，这种纳米粒子需要末端基团电离，以通过静电稳定来提供胶体稳定性。然而，降低PHBA/PHEA摩尔比和/或增加PHEA(X)稳定剂DP会导致更有效的空间稳定，从而增强胶体稳定性。在pH值为7的条件下制备了一系列HOOC-PHEA(73)-PHBA(104-421)纳米粒子，通过目测、DLS和剪切诱导偏振光成像对其进行了表征。这些表征技术之间的差异表明，蠕虫和囊泡在稀释方面不稳定。用戊二醛(GA)对纳米粒子进行共价稳定化后，进行了透射电子显微镜研究。更具体地说，以GA为交联剂的HOOC-PHEA(73)-PHBA(243)和HOOC-PHEA(73)-PHBA(421)纳米对象的电子显微镜研究表明，当交联度为0.1%w/w时，两种情况下都存在球体；当交联度为10-20%w/w时，分别存在蠕虫或囊泡。最后，通过变温振荡流变学研究了HOOC-PHEA(73)-PHBA(265)纳米对象：在2℃到50℃之间观察到了可逆球/虫和虫/囊的转变。
A series of all-acrylic poly(2-hydroxyethyl acrylate)(x)-poly(4-hydroxybutyl acrylate)(y) (PHEA(x)-PHBA(y)) diblock copolymer nanoparticles were prepared via an efficient one-pot RAFT aqueous dispersion polymerization protocol using either a carboxylic acid-functionalized RAFT agent (HOOC-PHEA(x)-PHBA(y)) or a morpholine-functionalized RAFT agent (Mo-PHEA(x)-PHBA(y)). The pH-dependent colloidal stability of the resulting sterically-stabilized nanoparticles was assessed by dynamic light scattering (DLS) and aqueous electrophoresis. The HOOC-PHEA(73)-PHBA(217) nanoparticles exhibited reversible flocculation below pH 5.1, whereas the Mo-PHEA(76)-PHBA(160) nanoparticles flocculated above pH 5. Moreover, the HOOC-PHEA(73)-PHBA(217) nanoparticles proved to be sensitive to added salt, with incipient flocculation occurring in the presence of 20-60 mM KCl owing to charge screening. Thus, such nanoparticles require end-group ionization to confer colloidal stability via electrosteric stabilization. However, reducing the PHBA/PHEA molar ratio and/or increasing the PHEA(x) stabilizer DP, leads to more efficient steric stabilization and hence enhanced colloidal stability. A series of HOOC-PHEA(73)-PHBA(104-421) nano-objects prepared at pH 7 were characterized by visual inspection, DLS studies and shear-induced polarized light imaging. Discrepancies between these characterization techniques indicated that the worms and vesicles were unstable with respect to dilution. TEM studies were conducted after covalent stabilization of the nano-objects using glutaraldehyde (GA). More specifically, TEM studies of GA-crosslinked HOOC-PHEA(73)-PHBA(243) and HOOC-PHEA(73)-PHBA(421) nano-objects indicated the presence of spheres in both cases when crosslinked at 0.1% w/w and either worms or vesicles respectively when crosslinked at 10-20% w/w. Finally, HOOC-PHEA(73)-PHBA(265) nano-objects were examined by variable temperature oscillatory rheology: thermoreversible sphere/worm and worm/vesicle transitions were observed between 2 and 50 degrees C.