首页 | 本学科首页   官方微博 | 高级检索  
     


Star oligomers with different reactivity in low VOC polyurethane coatings: Part II
Authors:J Huybrechts  K Dusek
Affiliation:(1) Du Pont de Nemours, Spinoystraat 6, 2800 Mechelen, Belgium;(2) Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Hevirovskeho nam.2, 16206 Prague 6, Czech Republic
Abstract:Conclusions  In this paper the effects of the reactivity of hydroxyl functional oligomers with a polyisocyanate crosslinking agent have been demonstrated by comparing the potlife/hardness of a 3.5 VOC two-component polyurethane clear coat based on a low TG, high reactive against a high TG, low reactive oligomer. The reaction rate of two polymers forming a crosslinked network becomes diffusion controlled when, during the reaction, the increasing TG comes close to the reaction temperature.4 If this reaction takes place in the presence of a solvent which evaporates during film formation and crosslinking, the speed of evaporation will affect both the reaction rate and the film TG. The results of this study have shown that the reactivity determines the potlife whilst the TG controls the hardness. The reactivity of blends of such oligomers against pure oligomers is different as can be calculated using the theory of branching processes and as shown from practical measurements. Blends of oligomers or a pure oligomer with up to 75% of the properties of the high TG, low reactive oligomer do show a hardness close to the properties of the low TG, high reactive oligomer which further proves that the chemical reactivity controls the overall drying performance. A fast chemical reactivity shortens the potlife with a risk of solvent entrapment near to and at the gel point which results in low hardness.
Keywords:
本文献已被 SpringerLink 等数据库收录!
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号