基于 MALDI-OF质谱探究水性聚氨酯分散体的扩链反应

为更加明确水性聚氨酯分散体的扩链反应机理,采用可水解的聚酯合成水性聚氨酯分散体,可控水解聚酯结构保留氨基甲酸酯结构和脲结构获得一系列水解片段,一些水解片段隐含了扩链反应的信息,采用 MALDI-TOF质谱分析水解片段的结构和组成,可以追溯扩链反应进程和分析扩链反应机理。研究发现预聚体端基结构不同,其反应产物存在较大差异,与亲水结构相连的预聚物的端异氰酸酯基（—NCO）大部分被水和二胺封端,而与疏水结构相连的—NCO端基大部分与水和二胺发生扩链反应。基于研究结果,提出了一种全新的扩链反应机理：扩链反应不仅发生在颗粒表面,也发生在颗粒内部。否定了扩链反应仅发生在颗粒表面的普遍看法。

MALDI-TOF-Based Composition Analysis of the Chain Extension Reaction in Aqueous Polyurethane Dispersions

To clarify the chain extension reaction mechanism of waterborne polyurethane dispersions a selective of hydrolysable polyester was used to synthesize the aq.polyurethane dispersions,where the polyester structure was hydrolyzed but urethane and urea structure were remained,forming a series of hydrolyzed chain segments,some of which could provide the information of chain extension reaction.MALDI-TOF analysis was used to understand the structure and composition of the hydrolyzed segments,which could be used to trace the process of the chain extension reaction and analyze its mechanism.It was found that the segments formed by chain extension reaction were distinguished from other segments due to the different structure of prepolymers.The NCO end groups of the prepolymer attached to a hydrophilic structure were basically terminated by water and diamine,while the NCO end groups attached to a hydrophobic structure were mostly chain extended by water or diamine.Based on the research results,a new mechanism of chain extension reaction was proposed:The chain extension reaction occurs not only on the particle surface but also inside the particle.It negates the commonly accepted hypothesis that the chain extension reaction only occurs on the surface of particles.