室温自交联丙烯酸酯乳液的制备与表征

PREPARATION AND CHARACTERIZATION OF AMBIENT SELF-CROSSLINKING ACRYLIC POLYMER LATEXES

使用3种含不饱和双键硅氧烷,乙烯基三(β-甲氧基乙氧基)硅烷(A172)、乙烯基三乙氧基硅烷(VTES)和γ-甲基丙烯酰氧丙基三甲氧基硅烷(A174)为功能单体,采用半连续乳液聚合法制备了室温自交联丙烯酸酯乳液,探讨了硅氧烷功能单体在不同pH条件下水解情况以及其种类和用量对乳液及乳胶膜性能的影响.结果表明,pH在7～9之间时硅氧烷功能单体水解最慢;A172在pH为8.4时5h内就水解完全;增加VTES和A174的用量均能提高乳胶膜的交联度、力学性能和耐水性.控制聚合过程的pH值以抑制硅氧烷功能单体的水解并调节乳液成膜时的pH值以加速硅氧烷功能单体的水解从而增强胶膜的交联程度,发现酸性或碱性条件下得到乳胶膜比中性条件下胶膜的力学和耐水性能均有不同程度的提高,并且在酸性条件下胶膜的性能提高最多.对比使用A174和VTES制备的胶膜,发现这种方法对含有A174胶膜的效果不明显,而含VTES胶膜的性能提高最为显著.

Ambient temperature self-crosslinking acrylic latexes were prepared through semicontinuous emulsion polymerization using 3 different polymerizable alkoxysilanes, i. e. vinyltri （ β-methoxy ethoxy） silane （ A172）, vinyltriethoxysilane （VTES） and 7-methacryloxypropyltrimethoxysilane （A174）. The hydrolysis of these siloxanes under different pH was characterized, and dependence of the latex and polymer properties on these siloxanes and their incorporated amounts in the polymers was studied. Results revealed that the lowest hydrolysis was observed around neutral pH between 7 and 9. A172 was more quickly hydrolyzed at all tested pH, and its hydrolysis was fully accomplished within 5 h at pH 8.4. Polymer crosslinking, mechanical performance and water resistance of the final polymers were significantly enhanced with incorporation of VTES and A174. The hydrolysis can be controlled through pH adjustments during emulsion polymerization and film formation so that to reduce the hydrolysis during emulsion polymerization and to enhance it when film being formed, which entrained higher crosslinking in the final polymer films. It was found that acidic pH was more preferable compared to alkali pH although in both cases films performances were improved when compared with films cast without pH adjustment under neutral pH. This pH adjustment effect was more pronounced in latexes prepared with VTES than in those done with A174.