Synthesis and characterization of poly(propylene carbonate) glycol-based waterborne polyurethane with a high solid content

Waterborne polyurethanes (WPUs) with high solid contents were synthesized by using poly(propylene carbonate) glycol (PPC) as the soft segment, methylene-bis(4-cyclohexylisocyanate) (HMDI) and 1,4-butanediol (BDO) as the hard segments, 2,2-bis(hydroxymethyl)butyric acid (DMBA) and 2-[(2-aminoethyl) amino]-ethanesulfonic acid monosodium salt (AAS) as the donors of hydrophilic groups. For comparison, polypropylene glycol (PPG) and polytetramethylene ether glycol (PTMG) were also used as soft segments in the synthesis of WPUs (PPG-WPU and PTMG-WPU, respectively). The particle size and distribution of the emulsions were measured and analyzed by submicron particle size Zeta-potential analyzer and transmission electron microscopy (TEM). The storage stability, contact angle and viscosity of the emulsions were also tested. The structure, mechanical properties, acid and alkali resistance, water absorption and thermogravimetric analyses (TGA) of WPU films were also characterized. The results showed that the WPU emulsions exhibited narrow particle distributions, small particle dimensions, good appearance and excellent storage stability. The emulsion viscosity increased slowly at low solid contents and then showed an abrupt change when the solid content exceeded 52%. PPC-WPU films showed superior overall properties in terms of tensile properties, rubber hardness and T-peel strength relative to the PPG-WPU films or PTMG-WPU films. The water absorption rate of the PPC-WPU film was slightly lower than that of the PPG-WPU film but higher than that of the PTMG-WPU film. The hydrogen atom on the α-C atom and the special structure of bonds in the poly(propylene carbonate) glycol molecular chain resulted in excellent acid and alkali resistance but poor thermal stability at high temperature. Moreover, the crystallinity of the PPC-WPU film was lower than that of the PTMG-WPU film due to the irregular structure of poly(propylene carbonate) glycol.