RAFT Synthesis of Sterically Stabilized Methacrylic Nanolatexes and Vesicles by Aqueous Dispersion Polymerization
RAFT Synthesis of Sterically Stabilized Methacrylic Nanolatexes and Vesicles by Aqueous Dispersion Polymerization
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DOI：
10.1002/anie.201001461
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Armes, Steven P.
中科院分区：
文献类型：
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作者：
Li, Yuting;Armes, Steven P.
乳液聚合广泛用于水性涂料。[1]已知减小胶乳粒度可促进聚结并因此增强成膜。然而，较小胶乳的合成通常需要额外的表面活性剂，这可能会损害水性涂料的质量（例如，由于过量表面活性剂的迁移，附着力差和膜质量降低）。[2]原则上，反应性表面活性剂在乳液聚合中提供了优于常规表面活性剂的潜在决定性优势，因为它们与胶乳不可逆地结合，因此在成膜过程中不会迁移;这允许生产无缺陷的涂层，同时降低水分敏感性。[3]在过去的二十年中，可控/活性自由基聚合技术已经成为聚合物合成中的有力工具。[4-8]有许多基于这些方法的胶乳合成的例子。[9]例如，Charleux，[10-15] El-Aasser，[16] Okubo，[17]和Georges [18]使用氮氧介导的活性自由基聚合来介导丙烯酸正丁酯和苯乙烯的细乳液聚合。Matyjaszewski [19-22]和Okubo [23-25]已经优化了ATRP用于（甲基）丙烯酸和苯乙烯单体的（微）乳液聚合。可逆加成-断裂链转移（RAFT）聚合已被Hawkett、[26-29] Charleux、[30-33] El-Aasser、[34] Cunningham、[35]和Zhu在乳液和细乳液聚合的背景下广泛开发。[36]还有许多RAFT合成在非水分散聚合条件下进行。[37-39]然而，据我们所知，只有三个实例应用受控/活性自由基聚合技术通过水分散聚合进行胶乳合成。[40]在每种情况下，相对昂贵的专用单体用于胶乳核，即N-异丙基丙烯酰胺[40 a]或N，N ′-二乙基丙烯酰胺。[40b这种研究的相对缺乏可能是令人惊讶的，因为水分散聚合在概念上比水乳液聚合简单得多，因为在前一种情况下初始反应溶液是均匀的。据推测，实验数据的缺乏仅仅反映了这样一个事实，即有相对较少的乙烯基单体，是适合胶乳合成的水分散体polymerization.Recently，我们报道了使用传统的（非生命）自由基化学的商品甲基丙烯酸单体，甲基丙烯酸2-羟丙酯（HPMA）的水分散体聚合。[41]所得的PHPMA胶乳由聚（N-乙烯基吡咯烷酮）稳定，并且平均粒径可以从约100至1000 nm直径变化，在大多数情况下实现对粒径分布的良好控制。在这里，我们探索的RAFT合成的空间稳定的PHPMA纳米胶乳的直径为20至100 nm的无表面活性剂的水分散聚合使用聚（甘油单甲基丙烯酸酯）为基础的链转移剂（CTA）作为反应性空间稳定剂。因此，对于该原型制剂，所得纳米胶乳的胶乳核和空间稳定剂链都高度羟基化。此外，改变目标PHPMA链的长度允许相当精确地控制空间稳定的纳米胶乳颗粒的最终尺寸（参见方案1，表1和支持信息）。
Emulsion polymerization is widely used for waterborne coatings.[1] Reducing the latex particle size is known to promote coalescence and hence enhance film formation. However, the synthesis of smaller latexes usually requires additional surfactant, which can compromise the quality of waterborne coatings (eg poor adhesion and reduced film quality due to migration of excess surfactant).[2] In principle, reactive surfactants offer a potentially decisive advantage over conventional surfactants in emulsion polymerization because they bind irreversibly to the latex and hence cannot migrate during film formation; this allows defect-free coatings to be produced with reduced moisture sensitivity.[3] Over the last two decades, controlled/living radical polymerization techniques have become powerful tools in polymer synthesis.[4–8] There are many examples of latex syntheses based on these approaches.[9] For example, nitroxide-mediated living radical polymerization has been used by Charleux,[10–15] El-Aasser,[16] Okubo,[17] and Georges [18] to mediate the miniemulsion polymerization of n-butyl acrylate and styrene. ATRP has been optimized by Matyjaszewski [19–22] and Okubo [23–25] for the (mini) emulsion polymerization of (meth) acrylic and styrene monomers. Reversible addition–fragmentation chain transfer (RAFT) polymerization has been extensively exploited in the context of both emulsion and miniemulsion polymerization by Hawkett,[26–29] Charleux,[30–33] El-Aasser,[34] Cunningham,[35] and Zhu.[36] There are also a number of RAFT syntheses conducted under nonaqueous dispersion polymerization conditions.[37–39] However, as far as we are aware, there are only three examples of the application of controlled/living radical polymerization techniques for latex syntheses by aqueous dispersion polymerization.[40] In each case, a relatively expensive speciality monomer was utilized for the latex core, namely N-isopropylacrylamide [40a] or N, N’-diethylacrylamide.[40b, c] This relative lack of research is perhaps surprising, because aqueous dispersion polymerization is conceptually much simpler than aqueous emulsion polymerization since the initial reaction solution is homogeneous in the former case. Presumably, the paucity of experimental data merely reflects the fact that there are relatively few vinyl monomers that are suitable for latex syntheses by aqueous dispersion polymerization.Recently, we reported the use of conventional (nonliving) free radical chemistry for the aqueous dispersion polymerization of a commodity methacrylic monomer, 2-hydroxypropyl methacrylate (HPMA).[41] The resulting PHPMA latexes were stabilized by poly (N-vinylpyrrolidone) and the mean particle diameter could be varied from approximately 100 to 1000 nm diameter, with good control over the particle size distribution being achieved in most cases. Herein we explore the RAFT synthesis of sterically stabilized PHPMA nanolatexes of 20 to 100 nm diameter by surfactant-free aqueous dispersion polymerization using a poly (glycerol monomethacrylate)-based chain transfer agent (CTA) as the reactive steric stabilizer. Thus both the latex cores and the steric stabilizer chains of the resulting nanolatexes are highly hydroxylated for this prototype formulation. Moreover, varying the length of the targeted PHPMA chains allows the final size of the sterically stabilized nanolatex particles to be controlled quite precisely (see Scheme 1, Table 1, and the Supporting Information).