Crystallinity evolution of soft segments during the synthesis of polyester‐based waterborne polyurethane

Abstract

Polyester‐based waterborne polyurethane (WPU) dispersions having poly(ethylene glycol) adipate diol, isophorone diisocyanate, and hexamethylene diisocyanate as the main raw materials were synthesized by an acetone process. In each step of the synthesis process, the intermediate products were collected, and the crystallization morphologies and relative crystallinity (X) of the soft segments (SSs) in their films were investigated by means of polarizing optical microscopy, differential scanning calorimetry, and X‐ray diffraction. The fracture surfaces and thermostability of the intermediate films were also investigated by scanning electron microscopy (SEM) and TGA, respectively. The results show that the crystalline dimensions of the SSs decreased substantially during the synthesis process of WPU. X of the SSs decreased after the prepolymerization reaction and increased after the hydrophilic chain‐extending reaction, then decreased after emulsification, and finally increased after the secondary chain‐extending reaction. Moreover, The SEM photos indicate that with decreasing crystalline dimensions, the fracture mechanisms of the intermediate films varied gradually from brittle failure to ductile fracture. The thermostability of the intermediates obtained in each step of the synthesis process was in accordance with the variation tendency of the X of the SSs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40270.

Improvement of Mechanical and Thermal Properties of Cationic Waterborne Polyurethane by Using an Amino-Rich Multifunctional Macromolecular Crosslinking Agent

“…Polyurethanes (PUs) are a multipurpose industrial material synthesized by a polyaddition reaction of isocyanate, polyol, and a chain extender, which has been widely used in various industries, like elastomers, coatings, sports, adhesives, etc. , With the increasingly stringent environmental protection policies, waterborne polyurethane (WPU) material has attracted much more attention due to its pollution-free, safe, reliable, and excellent mechanical properties. , However, the molecular weight and crosslinking density of WPUs are generally much lower than those of traditional two-component solvent-based polyurethanes. In addition, the WPU chain has hydrophilic groups and a linear structure, which result in low mechanical properties, poor thermal stability, and poor water resistance in practical applications. ,− To further improve the properties of WPU, many strategies have been developed to modify PU, among which crosslinking modification is one of principal techniques.…”

The Relationship between Solid Content and Particle Size Ratio of Waterborne Polyurethane

“…Li [15] synthesized a waterborne polyurethane with a solid content of 50% using a mixed diisocyanate of HDI (hexamethylene diisocyanate):IPDI (isophorone diisocyanate) with a mass ratio of 30:70. Cao [16] prepared aqueous polyurethane emulsions with a solid content of more than 50% and a viscosity of less than 200 mPa•s using different macromolecular diols as raw materials. However, this cannot be widely used as the application performance is limited by synthetic formulation in many cases [17].…”