Department of Materials Science and the Key Laboratory of Molecular Engineering of Polymers of MOE, Advanced Materials Laboratory, Fudan University, Shanghai 200433, PR China.
Langmuir. 2010 Dec 7;26(23):17836-9. doi: 10.1021/la103833x. Epub 2010 Oct 29.
Styrene-acrylic acid copolymer was synthesized via solution polymerization and then sulfonated by concentrated sulfuric acid. This sulfonated copolymer displays an obvious pH-responsive color change in aqueous solutions (1 g/L) from yellow (pH <6) to khaki (pH 6 to 7)/red (pH 7 to 8) to purple (pH >8). This response is as quick as for small-molecule pH indicators such as methyl orange and phenolphthalein within 1 s and can be reversible. The lowest critical concentration of this pH-responsive copolymer solution is around 0.1 g/L, which is about 50-500 times the necessary amount used for conventional small-molecule pH indicators. An intramolecular cyclization mechanism between a neighboring carboxyl group and a benzene ring to form a sulfonated aromatic ketone is proposed to explain this pH-responsive color change behavior. The molar ratio of 1:1 for styrene to acrylic acid is the most favorable for forming neighboring benzene and carboxyl group pairs in the copolymer chains and subsequently yields sulfonated aromatic ketone chromophores at full capacity.
苯乙烯-丙烯酸共聚物通过溶液聚合合成，然后用浓硫酸磺化。这种磺化共聚物在水溶液（1 g/L）中显示出明显的 pH 响应颜色变化，从黄色（pH <6）变为黄褐色（pH 6 到 7）/红色（pH 7 到 8）到紫色（pH >8）。这种响应速度与甲基橙和酚酞等小分子 pH 指示剂一样快，在 1 秒内即可完成，并且可以是可逆的。这种 pH 响应共聚物溶液的最低临界浓度约为 0.1 g/L，大约是传统小分子 pH 指示剂所需量的 50-500 倍。提出了一种相邻羧基基团和苯环之间的分子内环化机制，以形成磺化芳酮，来解释这种 pH 响应颜色变化行为。苯乙烯与丙烯酸的摩尔比为 1:1 时，最有利于在共聚物链中形成相邻的苯环和羧基基团对，随后以全容量生成磺化芳酮生色团。
