丙烯酸2-乙基己酯/丙烯酸辐射乳液聚合——乳胶中羧基的分布

2-ETHYL HEXYL ACRYLATE/ACRYLIC ACID RADIATION EMULSION POLYMERIZATION——CARBOXYL DISTRIBUTION IN LATEX

本文用辐射法引发丙烯酸2-乙基己酯/丙烯酸(EHA/AA)乳液共聚合,用酸碱反滴定法研究了剂量率、剂量、乳化剂浓度、固含量、共聚物分子量、丙烯酸浓度、丙烯酸加料方式及丙烯酸预先中和程度等反应条件对乳胶中羧酸可滴定百分比的影响。并对聚合机理作了初步探讨。

Back potentiometric titration with addition of salt NaCl was used to determine the acid titratable percent in EHA/AA radiation emulsion copolymerized latex. It was found that the carboxylic monomer concentration, its neutralized percent, its adding model, the emulsifier concentration, the molecular weight of copolymer have significant effects on the acid titratable percent in polymer latex; while total adsorbed dose and dose rate have no obvious effects. In all cases investigated the acid titratable percent is above 75%, this means that most of the carboxyl groups accumulate in the latex shell of copolymer.Because the solubility of EHA in water is very low, the micelle nucleation takes advantage in emulsion polymerization with EHA as main monomer. When AA concentration in water is high, the homophase nucleation becomes important. After the nucleation period, AA distributes in water and polymer-monomer particles by certain proportion. The AA in particles copolymerizes with EHA and distributes homogeneously in polymer latex at last. While AA in water has two reaction routes: the first, diffusion into the particles, it results in that most of AA accumulates in the latex shell and the concentration of carboxyl group has a gradient along the latex radius; the second, polymerization in water, the resulted polymer is soluble in water or is adsorbed at the latex surface. For unneutralized AA, the first mechanism dominates, while for partly preneutralized AA, the second mechanism takes advantage and will compete with the first mechanism for AA in water.