Preparation and characterization of cationic waterborne polyurethanes containing a star-branched polydimethylsiloxane

Cationic waterborne polyurethanes (CWPUs) bring in hydrophilic component to molecular chain, which inevitably deteriorates its water-resistant ability. Here, we synthesized a series of branched chain cationic waterborne polyurethanes (i.e., CWPUs-Si) that had been modified using a novel star-branched polydimethylsiloxane (SB-PDMS) to improve their water-resistant performance. The effects of SB-PDMS content on the properties of the CWPUs-Si polymers (e.g., crystallinity, emulsion stability, mechanical performance, surface element enrichment, surface topography, water resistance), together with the performance of coatings prepared by cathodic electrodeposition, were determined. The results showed that the introduction of SB-PDMS increased phase separation and surface roughness induced by hydrogen bonding while the surface energy decreased, both of which improved water resistance. The polymers showed improved rigidity due to increased content of the hard segments and enhanced physical crosslinking. Except for an increase in pencil hardness, SB-PDMS had no effect on the films prepared by cathodic electrodeposition. The results from this study may provide a strategy to improve the water-resistant properties of CWPUs.