Effect of dicarboxylic acids on the performance properties of polyurethane dispersions

Abstract

A series of low molecular weight linear polyester polyols were synthesized by using various diacids, neopentyl glycol, as a diol, and a trimethylol propane, as a branching monomer. Polyurethane dispersions were prepared primarily from isophorone diisocyanate, polyester polyol, and dimethylol propionic acid, as potential ionic center for water dispersibility, and were subsequently chain extended with ethylene diamine. The effect of polyester polyols based on variable diacids, on the physico-chemical and thermal properties of polyurethane dispersions were evaluated by hardness, flexibility, impact resistance, solvent resistance, thermogravimetric analysis, and differential scanning calorimetry. Particle size was evaluated by particle size analyzer. It was observed that the number of alkylene groups present in the polyester polyol soft segment in addition to its molecular weight had a pronounced effect on the particle size, physico-chemical, and thermal properties. With a proper selection of the soft segment, it is possible to fine-tune properties of aqueous polyurethane dispersion coatings with respect to the final application.

Relationship between reagents molar ratio and dispersion stability and film properties of waterborne polyurethanes

“…The pH of the resulting dispersions was measured obtaining an average value of 8.12 ± 0.28. This value is in the range of values found in the literature [3,14], which indicate that carboxylic groups have been successfully neutralized.…”

“…The flexibility of chains adjacent to ionic groups influences in the mobility of ionic groups and therefore, in nanoparticles formation. Thus, at lower IPDI/(PCL + DMPA) molar ratio, that is, at higher polyol content, greater is the flexibility of polyurethane chains resulting in a better dispersion in the aqueous phase under agitation and obtaining smaller particles [3,17,19]. Moreover, the content of carboxylic groups decreases as IPDI/(PCL + DMPA) molar ratio increases.…”

“…2b shows WBPU dispersions which have remained visually stable for over 6 months without showing sedimentation even thought when low DMPA contents (2.5 wt%) are used. The interactions between acid groups and water increases dispersion stability owing to the formation of electrical double layer resulting in particles repulsion and leading to the stabilization mechanism of the dispersion [3,15,16,19]. Therefore, the carboxylic group content of the synthesized WBPUs is enough to maintain electrostatic repulsive forces between particles.…”

“…WBPUs present the advantage of being synthesized by a solvent-free method which implies low organic compound levels and non-toxicity comparing with conventional solventborne polyurethanes besides presenting lower prices [1]. WBPUs are a type of block copolymers which offer the possibility to hierarchically assemble at the nanoscale and develop different morphologies and macroscopic properties [2,3]. They are formed by two blocks; the soft segment (SS) is formed by a macrodiol, whereas the hard segment (HS) generally consists on a diisocyanate and a low molecular weight diol used as chain extender.…”

Synthesis, Properties, and Applications of Ion‐Containing Polyurethane Segmented Copolymers

“…As a result, the synthesis of segmented polyurethanes with charge specifically in the SS requires novel oligomers. Despite the synthetic challenges, several ion‐containing SSs exist as a result of the efforts of many research groups . Ammonium, sulfonate, and carboxylate‐containing SSs were prepared, providing similar ionic variety as charged HS monomers.…”