Université de Lyon, Université de Lyon 1, CNRS, UMR 5007, Laboratoire d'Automatique et de Génie des Procédés (LAGEP), 69616 Villeurbanne, France.
Université de Lyon, Université de Lyon 1, CPE Lyon, CNRS, UMR 5265, Laboratoire de Chimie, Catalyse, Polymères et Procédés (C2P2), LCPP Group, 69616 Villeurbanne, France.
Langmuir. 2016 Jun 21;32(24):6046-57. doi: 10.1021/acs.langmuir.6b01080. Epub 2016 Jun 9.
Clay-armored polymer particles were prepared by emulsion polymerization in the presence of Laponite platelets that adsorb at the surface of latex particles and act as stabilizers during the course of the polymerization. While Laponite RDS clay platelets are most often used, the choice of the type of clay still remains an open issue that is addressed in the present article. Four different grades of Laponite were investigated as stabilizers in the emulsion polymerization of styrene. First, the adsorption isotherms of the clays, on preformed polystyrene particles, were determined by ICP-AES analysis of the residual clay in the aqueous phase. Adsorption of clay depended on the type of clay at low concentrations corresponding to adsorption as a monolayer. Adsorption of clay particles as multilayers was observed for all the grades above a certain concentration under the considered ionic strength (mainly due to the initiator ionic species). The stabilization efficiency of these clays was investigated during the polymerization reaction (free of any other stabilizer). The clays did not have the same effect on stabilization, which was related to differences in their compositions and in their adsorption isotherms. The different grades led to different polymer particles sizes and therefore to different polymerization reaction rates. Laponite RDS and S482 gave similar results, ensuring the best stabilization efficiency and the fastest reaction rate; the number of particles increased as the clay concentration increased. Stabilization with Laponite XLS gave the same particles size and number as the latter two clays at low clay concentrations, but it reached an upper limit in the number of nucleated polymer particles at higher concentrations indicating a decrease of stabilization efficiency at high concentrations. Laponite JS did not ensure a sufficient stability of the polymer particles, as the polymerization results were comparable to a stabilizer-free polymerization system.
粘土-聚合物颗粒是通过乳液聚合制备的，其中存在吸附在乳胶颗粒表面并在聚合过程中充当稳定剂的 Laponite 薄片。虽然最常使用 Laponite RDS 粘土薄片，但粘土类型的选择仍然是一个悬而未决的问题，本文对此进行了探讨。研究了四种不同等级的 Laponite 作为苯乙烯乳液聚合中的稳定剂。首先，通过 ICP-AES 分析水相中的残留粘土来确定粘土在预形成的聚苯乙烯颗粒上的吸附等温线。在考虑的离子强度下（主要由于引发剂离子种类），粘土的吸附取决于粘土的类型，在低浓度下对应于单层吸附。对于所有等级的粘土，在一定浓度以上观察到粘土颗粒的多层吸附。在聚合反应中（没有任何其他稳定剂）研究了这些粘土的稳定效率。粘土对稳定的影响不同，这与它们的组成和吸附等温线的差异有关。不同的等级导致不同的聚合物颗粒尺寸，从而导致不同的聚合反应速率。Laponite RDS 和 S482 给出了相似的结果，确保了最佳的稳定效率和最快的反应速率；随着粘土浓度的增加，颗粒数量增加。在低粘土浓度下，Laponite XLS 的稳定作用与后两种粘土相同，可得到相同的颗粒尺寸和数量，但在较高浓度下，成核聚合物颗粒的数量达到上限，表明高浓度下稳定效率下降。Laponite JS 不能确保聚合物颗粒具有足够的稳定性，因为聚合结果与无稳定剂的聚合体系相当。
