Linear-, Cyclic-, and Multiblock Amphiphilic Polyelectrolytes as Surfactants in Emulsion Polymerization: Role of Topological Structure

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• 作者：Lianwei Li ; Jinxian Yang ; Jianfeng Zhou
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：April 9, 2013
• 年：2013
• 卷：46
• 期：7
• 页码：2808-2817
• 全文大小：540K
• 年卷期：v.46,no.7(April 9, 2013)
• ISSN：1520-5835

文摘

Combining atom transfer radical polymerization (ATRP) and 鈥渃lick鈥?chemistry, a set of well-defined amphiphilic block copolymers poly(n-butyl acrylate)-b-poly(acrylic acid) (PnBA₂₀-PAA₈₅) with a similar chemical component, but different topological structures, i.e., linear-, cyclic-, and multiblock structures, were successfully prepared, characterized (size exclusion chromatography (SEC), FT-IR and ¹H NMR), and used as surfactants in emulsion polymerization. Our further transmission electron microscopy (TEM) and laser light scattering (LLS) characterization of the resultant latex particles demonstrates all the surfactants with different topologies can effectively stabilize the latex particles but no significant difference among the solids contents was observed. Moreover, we have, for the first time, experimentally established the quantitative relation between the final number of latex particles (N_p) and the concentration of polymeric surfactant with different topologies (C), i.e., N_p = kC^伪, and the order of our measured exponent 伪 is as follows: 伪_multi(1.10) > 伪_linear(0.81) 鈮?伪_cyclic(0.73), indicating cyclic surfactant molecules behave more like small-molecule surfactants attributed to its strongest unimers extraction and diffusion ability; in contrast, multiblock surfactant molecules can act as seeds to directly nucleate to create latex particles. In addition, N_p,multi > N_p,linear 鈮?N_p,cyclic at higher concentration, and N_p,linear > N_p,cyclic 鈮?N_p,multi at lower concentration was observed. Similar results (伪_multi(1.02) > 伪_linear(0.65) 鈮?伪_cyclic(0.58)) were also observed when polystyrene-b-poly(acrylic acid) (PS₉鈥揚AA₆₀) copolymers were used as surfactants. Further aqueous SEC characterization shows the broad size distribution of our micellar solution has no effect on obtaining narrowly distributed latex particles. Finally, interfacial tension measurement of the micellar solution indicates, compared to multiblock structure, the rate of adsorption at a hydrophobic interface is much faster for linear and cyclic-block structures, agreeing with our observed order of exponent 伪.