Pinprayoon Orawan, Groves Robert, Saunders Brian R
Polymer Science and Engineering Group, Materials Science Centre, School of Materials, The University of Manchester, Grosvenor Street, Manchester, UK.
J Colloid Interface Sci. 2008 May 15;321(2):315-22. doi: 10.1016/j.jcis.2008.02.037. Epub 2008 Feb 29.
This study investigates the effects of added Ca(2+) on the properties of poly(Bd/MAA) dispersions (1,3-butadiene and methacrylic acid) and considers the effect of particle composition on the pK(a). Four latex dispersions are considered in detail. These include poly(Bd/6MAA) and poly(Bd/20MAA) which contain, 6 and 20 wt% MAA, respectively, based on the total monomer mass used for dispersion preparation. Two model systems are also used for comparison. These are poly(Bd) and poly(EA/33MAA/BDDA) (EA and BDDA are ethyl acrylate and butanediol diacrylate). The latter is a well-studied model pH-responsive microgel. The apparent pK(a) of the poly(Bd/MAA) dispersions was determined from potentiometric titrations and found to increase with Bd content. The pH-dependence of the particle size was studied using photon correlation spectroscopy. Electrophoretic mobility measurements were also used. The hydrodynamic diameters and mobilities exhibited major changes as the pH approached the pK(a) for the particles. The critical coagulation concentrations were also measured. The results indicate that Ca(2+) caused pronounced dispersion instability at low pH. Moreover, Ca(2+) prevents swelling of the poly(Bd/MAA) particles at high pH. It was found that efficient ionic binding of all of the RCOO(-) groups within the poly(Bd/20MAA) particles occurred when the mole ratio of RCOO(-) to Ca(2+) was less than or equal to 2.0. Consideration of all the data leads to the suggestion that poly(Bd/MAA) particles have a core-shell structure. It is suggested that the particle core contains mostly poly(Bd) and that the shell is comprised of lightly crosslinked poly(Bd-co-MAA) copolymer.
本研究考察了添加Ca(2+)对聚（丁二烯/甲基丙烯酸）[1,3 - 丁二烯和甲基丙烯酸]分散体性能的影响，并考虑了颗粒组成对pK(a)的影响。详细研究了四种胶乳分散体。其中包括聚（丁二烯/6甲基丙烯酸）和聚（丁二烯/20甲基丙烯酸），基于用于分散体制备的总单体质量，它们分别含有6 wt%和20 wt%的甲基丙烯酸。还使用了两个模型体系进行比较。它们是聚（丁二烯）和聚（丙烯酸乙酯/33甲基丙烯酸/丁二醇二丙烯酸酯）（丙烯酸乙酯和丁二醇二丙烯酸酯）。后者是一个经过充分研究的pH响应型微凝胶模型。通过电位滴定法测定了聚（丁二烯/甲基丙烯酸）分散体的表观pK(a)，发现其随丁二烯含量增加而升高。使用光子相关光谱法研究了粒径的pH依赖性。还进行了电泳迁移率测量。当pH接近颗粒的pK(a)时，流体动力学直径和迁移率出现了显著变化。还测量了临界聚沉浓度。结果表明，Ca(2+)在低pH下导致明显的分散体不稳定性。此外，Ca(2+)在高pH下阻止聚（丁二烯/甲基丙烯酸）颗粒的溶胀。研究发现，当RCOO(-)与Ca(2+)的摩尔比小于或等于2.0时，聚（丁二烯/20甲基丙烯酸）颗粒内所有RCOO(-)基团会发生有效的离子结合。综合所有数据表明，聚（丁二烯/甲基丙烯酸）颗粒具有核壳结构。推测颗粒核心主要由聚（丁二烯）组成，而壳层由轻度交联的聚（丁二烯 - 共 - 甲基丙烯酸）共聚物构成。
