Phenyl acrylate is a versatile monomer for the synthesis of acrylic diblock copolymer nano-objects via polymerization-induced self-assembly
Phenyl acrylate is a versatile monomer for the synthesis of acrylic diblock copolymer nano-objects via polymerization-induced self-assembly
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DOI：
10.1039/c7py01161j
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发表时间：
2017-09-07
影响因子：
4.6
通讯作者：
Armes, S. P.
中科院分区：
文献类型：
--
作者：
Canning, S. L.;Cunningham, V. J.;Armes, S. P.
在过去的十年左右，聚合诱导自组装（PISA）已被广泛认为是一种多用途的技术，用于合理合成以浓缩分散体形式存在的双嵌段共聚物纳米物体。然而，文献中丙烯酸基PISA配方的例子相对较少，部分原因是这种共聚物通常具有相对较低的玻璃化转变温度（T-g），这妨碍了通过透射电子显微镜进行形态表征。为了解决这个问题，我们选择了丙烯酸苯酯（PhA）作为模型单体，使用可逆加成-碎片链转移（RAFT）聚合在三种PISA配方中生成了憎溶剂嵌段。因此，以聚二甲基丙烯酰胺为基础的链转移剂（CTA）通过RAFT水乳液聚合，通过PhA进行链扩展，得到一系列定义明确的立体稳定球，其平均直径可以通过改变目标聚合度（DP）在38 nm到188 nm之间轻松调节。相比之下，使用聚丙烯酸CTA的PhA的RAFT醇分散聚合导致共聚物的形态从球体到蠕虫到片层，最后是囊泡，因为指向结构的PhA块的目标DP增加。同样，PhA在正庚烷中的RAFT分散聚合也会根据PPhA块的目标DP产生球体、蠕虫或囊泡。1H NMR研究表明，在所有情况下，PhA转化率都达到了> 98%，而GPC分析表明，阻断效率很高。然而，观察到相对较宽的分子量分布（M-w/M-n = 1.37至2.48），这表明在此类PISA合成中广泛的链转移到聚合物中，特别是在RAFT水性乳液聚合配方的情况下。然而，PPhA的相对较高的T-g（50℃）使得使用传统的TEM表征各种共聚物的形态成为可能。
Over the last decade or so, polymerization-induced self-assembly (PISA) has become widely recognized as a versatile technique for the rational synthesis of diblock copolymer nano-objects in the form of concentrated dispersions. However, there are relatively few examples of acrylic-based PISA formulations in the literature, partly because such copolymers typically possess relatively low glass transition temperatures (T-g) that preclude morphological characterization by transmission electron microscopy. To address this problem, we have selected phenyl acrylate (PhA) as a model monomer to generate the solvophobic block in three PISA formulations using reversible addition-fragmentation chain transfer (RAFT) polymerization. Thus, a poly(dimethyl acrylamide)-based chain transfer agent (CTA) is chain-extended using PhA via RAFT aqueous emulsion polymerization to produce a series of well-defined sterically-stabilized spheres whose mean diameter can be readily adjusted from 38 nm to 188 nm by varying the target degree of polymerization (DP). In contrast, RAFT alcoholic dispersion polymerization of PhA using a poly(acrylic acid) CTA leads to an evolution of copolymer morphology from spheres to worms to lamellae and finally vesicles as the target DP of the structure-directing PPhA block is increased. Similarly, RAFT dispersion polymerization of PhA in n-heptane also produces spheres, worms or vesicles depending on the target DP of the PPhA block. 1H NMR studies indicate that > 98% PhA conversion is achieved in all cases, while GPC analysis indicates high blocking efficiencies. However, relatively broad molecular weight distributions are observed (M-w/M-n = 1.37 to 2.48), which suggests extensive chain transfer to polymer in such PISA syntheses, particularly in the case of the RAFT aqueous emulsion polymerization formulation. Nevertheless, the relatively high T-g of PPhA (50 degrees C) enables characterization of the various copolymer morphologies using conventional TEM.