The Role of Hard Segments of Aqueous Polyurethane-urea Dispersion in Determining the Colloidal Characteristics and Physical Properties

Abstract

A series of aqueous polyurethane-urea dispersions (PUDs) were synthesized to investigate the role of hard segments in determining the colloidal properties in water and the physical properties in PUD films. The chemical structures were modified in terms of, the fraction of the hard segment, the intra-chain distance between hard segments, the amount of ionic COOH group and the type of counterion. The particle size in water decreased with the increase in stabilization of micelles, which was determined by the homogeneity of the distribution of ionic units, flexibility of main chains and hydrophilicity of the neutralized counterions. The physical properties of PUDs were characterized by microphase separation of hard and soft domains. However, the microphase separation structure was not strict at the molecular chain level, that is, the hard domains containing some soft segments and the soft domains containing hard segments existed. The presence of the soft segment in the hard domain lowered the glass transition temperature of the hard domain, consequently affecting the mechanical strength etc., depending on the chain length of soft segment, the content of ionic units, and also on the bulkiness of the counterions. These results will be useful for designing molecular structures of PUDs to obtain the best performance for various applications.