Preparation and Cross-Linking of All-Acrylamide Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in Aqueous Solution.
Preparation and Cross-Linking of All-Acrylamide Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in Aqueous Solution.
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DOI：
10.1021/acs.macromol.6b02643
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发表时间：
2017-02-28
期刊：
影响因子：
5.5
通讯作者：
Armes SP
中科院分区：
文献类型：
--
作者：
Byard SJ;Williams M;McKenzie BE;Blanazs A;Armes SP
采用可逆加成-断裂链转移（RAFT）水分散聚合法，在70 °C和20%w/w固含量条件下，以双丙酮丙烯酰胺（DAAM）为扩链剂，通过聚合诱导自组装（比萨）制备了一系列聚二甲基丙烯酰胺（PDMAC-PDAAM）二嵌段共聚物纳米粒子。TEM研究表明，平均聚合度（DP）为68或更高的PDMAC macro-CTA导致形成平均直径为40至150 nm的明确定义的球形纳米颗粒。相比之下，当使用相对短的宏观CTA（DP = 40-58）时，形成高度各向异性的蠕虫或多分散囊泡。构建相图以使纯共聚物形态的精确目标成为可能。动态光散射（DLS）和水性电泳研究表明，在大多数情况下，这些PDMAC-PDAAM纳米物体令人惊讶地抵抗溶液pH或温度的变化。然而，在20 °C下将溶液pH从pH 2-3调节至pH 9左右时，PDMAC 40-PDAAM 99蠕虫确实经历部分解离以形成相对短的蠕虫和球体的混合物。此外，在将该蠕虫分散体加热至50 °C时，通过DLS和TEM观察到共聚物形态从蠕虫到短蠕虫和囊泡的混合物的变化。在环境温度下使用己二酸二酰肼（ADH）进行PDMAC-PDAAM球、蠕虫或囊泡的浓缩水性分散体的聚合后交联，所述己二酸二酰肼与疏水酮官能化的PDAAM链反应。通过FT-IR光谱监测腙基团的形成，并提供共价稳定的纳米物体，其在暴露于甲醇时保持完整，甲醇是两个块的良好溶剂。流变学研究表明，交联蠕虫形成了更强的凝胶相比，线性前体蠕虫。
Various carboxylic acid-functionalized poly(N,N-dimethylacrylamide) (PDMAC) macromolecular chain transfer agents (macro-CTAs) were chain-extended with diacetone acrylamide (DAAM) by reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization at 70 °C and 20% w/w solids to produce a series of PDMAC–PDAAM diblock copolymer nano-objects via polymerization-induced self-assembly (PISA). TEM studies indicate that a PDMAC macro-CTA with a mean degree of polymerization (DP) of 68 or higher results in the formation of well-defined spherical nanoparticles with mean diameters ranging from 40 to 150 nm. In contrast, either highly anisotropic worms or polydisperse vesicles are formed when relatively short macro-CTAs (DP = 40–58) are used. A phase diagram was constructed to enable accurate targeting of pure copolymer morphologies. Dynamic light scattering (DLS) and aqueous electrophoresis studies indicated that in most cases these PDMAC–PDAAM nano-objects are surprisingly resistant to changes in either solution pH or temperature. However, PDMAC40–PDAAM99 worms do undergo partial dissociation to form a mixture of relatively short worms and spheres on adjusting the solution pH from pH 2–3 to around pH 9 at 20 °C. Moreover, a change in copolymer morphology from worms to a mixture of short worms and vesicles was observed by DLS and TEM on heating this worm dispersion to 50 °C. Postpolymerization cross-linking of concentrated aqueous dispersions of PDMAC–PDAAM spheres, worms, or vesicles was performed at ambient temperature using adipic acid dihydrazide (ADH), which reacts with the hydrophobic ketone-functionalized PDAAM chains. The formation of hydrazone groups was monitored by FT-IR spectroscopy and afforded covalently stabilized nano-objects that remained intact on exposure to methanol, which is a good solvent for both blocks. Rheological studies indicated that the cross-linked worms formed a stronger gel compared to linear precursor worms.