Facile Synthesis of Methacrylic ABC Triblock Copolymer Vesicles by RAFT Aqueous Dispersion Polymerization
Facile Synthesis of Methacrylic ABC Triblock Copolymer Vesicles by RAFT Aqueous Dispersion Polymerization
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DOI：
10.1021/ma300816m
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发表时间：
2012-06-26
期刊：
影响因子：
5.5
通讯作者：
Armes, S. P.
中科院分区：
文献类型：
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作者：
Chambon, P.;Blanazs, A.;Armes, S. P.
聚（单甲基丙烯酸甘油酯-嵌段-2-甲基丙烯酸羟丙酯）[PGMA-PHPMA]二嵌段共聚物囊泡通过RAFT水分散体聚合在70 ℃下制备，然后用作与第三共聚单体进行扩链实验的前体。对于用水溶性HPMA进行的自封闭实验，获得了良好的活性特征，如通过相对低的最终多分散性（M-w/M-n < 1.30）所判断的。这表明RAFT链端保真度很高，至少在几个小时的时间尺度上是如此。使用与水不混溶的单体如甲基丙烯酸甲酯（MMA）或甲基丙烯酸苄酯（BzMA）也导致在“接种”乳液聚合条件下的有效扩链。在70 ° C下在几小时内获得高转化率，但所得ABC三嵌段共聚物链的多分散性略高。TEM研究表明，在囊泡膜内引入第二个疏水性嵌段会产生显著的形态变化。在BzMA的情况下，得到一个独特的framboidal形态，这是由于PHPMA和PBzMA疏水块之间的微相分离。此外，随着PBzMA嵌段的聚合度越高，观察到的球形特征的尺寸单调增加。当使用MMA作为第三共聚单体时，也观察到类似但不太明显的形态变化，这表明在这种情况下发生稍微较弱的微相分离。如果使用双官能单体如乙二醇二甲基丙烯酸酯（EGDMA）作为第三共聚单体，则获得高度交联的囊泡，其可以承受表面活性剂的挑战，与前体线性二嵌段共聚物囊泡不同。在这种情况下，值得注意的是，如果EGDMA最后加入，而不是在HPMA聚合期间加入，则获得好得多的结果。这些水性制剂的稳健、可再现的性质预计将在不断增长的嵌段共聚物囊泡领域带来新的机会，因为它们允许在相对高的固体含量下以多克的量获得新的颗粒形态。
Poly(glycerol monomethacrylate-block-2-hydroxypropyl methacrylate) [PGMA-PHPMA] diblock copolymer vesicles are prepared by RAFT aqueous dispersion polymerization at 70 degrees C and then used as precursors for chain extension experiments with a third comonomer. For self-blocking experiments conducted with water-soluble HPMA, good living character is obtained, as judged by the relatively low final polydispersity (M-w/M-n < 1.30). This suggests that the RAFT chain-end fidelity is high, at least over time scales of a few hours. Using water-immiscible monomers such as methyl methacrylate (MMA) or benzyl methacrylate (BzMA) also leads to efficient chain extension under "seeded" emulsion polymerization conditions. High conversions are obtained within a few hours at 70 degrees C, but polydispersities are somewhat higher for the resulting ABC triblock copolymer chains. TEM studies indicate that introduction of a second hydrophobic block within the vesicle membrane produces remarkable changes in morphology. A distinctive framboidal morphology is obtained in the case of BzMA, which is attributed to microphase separation between the PHPMA and PBzMA hydrophobic blocks. Moreover, there is a monotonic increase in the size of the observed globular features as higher degrees of polymerization for the PBzMA block are targeted. Similar but less distinctive morphological changes are also observed when using MMA as the third comonomer, which suggests that somewhat weaker microphase separation occurs in this case. If a bifunctional monomer such as ethylene glycol dimethacrylate (EGDMA) is used as the third comonomer, highly crosslinked vesicles are obtained that can withstand a surfactant challenge, unlike the precursor linear diblock copolymer vesicles. In this case it is noteworthy that much better results are obtained if the EGDMA is added last, rather than during the HPMA polymerization. The robust, reproducible nature of these aqueous formulations is expected to lead to new opportunities in the growing field of block copolymer vesicles, since they allow access to new particle morphologies in multigram quantities at relatively high solids.