Preparation and properties of waterborne polyurethanes for water-vapor-permeable coating materials

Waterborne polyurethanes were prepared by polyaddition reaction using isophorone diisocyanate, dimethylol propionic acid, various polyols with a fixed molecular weight (M-n = about 2000), ethylene diamine as a chain extender, and triethylamine as a neutralization agent. Three types of polyols such as (1) solo glycols [polypropylene glycol (PPG) (M-n 2000), poly(tetramethylene oxide) glycol (PTMG) (M-n = 2000), poly(tetramethylene adipate glycol) (PTAd) (M-n = 2000), or polycaprolactone glycol (PCL) (M-n = 2000)], (2) the polyol blends (PPG/PCL, PTMG/PCL, PPG/PTAd, PTMG/PTAd), and (3) a triblock glycol (TBG) (M-n = 1990) were used in this study. The triblock glycol (TBG) [(CL)(4.5)-PTMG (M-n = 1000)-(CL)(4.5) (M-n =1990] was synthesized from PTMG and E-caprolactone (CL) in this study. The triblock glycol was found to have two main melting peaks at about 13 and 40degreesC. This study was examined on the effect of the types of polyols on the particle size, viscosity, dynamic thermal properties, and water vapor permeability. The particle size of the aqueous polyurethaneurea dispersion increased in the order of polyol-blends-based samples (183-350 nm) > TBG-based sample (167 nm) > solo-polyol-based sample (58-96 nm). By dynamic thermal mechanical analysis, the ester-type polyol- (PTAd and PCL) based samples were found to have higher storage modulus and T-g than those of ether-type polyol- (PPG and PTMG) based samples. The water vapor permeability (WVP) increased in the order of TGB-based sample > PCL/PTMG-based sample > PTAd/PTMG-based sample > PCL/PPG-based sample > PTAd/PPG-based sample > PTMG-based sample > PPG-based sample > PCL-based sample > PTAd-based sample. WVP was found to increase in the order of TBG-based sample > polyol-blend based samples > solo-polyol-based samples. It was also found that the samples containing ether-type glycols (PTMG, PPG) had higher permeability than samples having ester-type glycols (PCL, PTAd). PTMG-based samples were found to have higher permeability than PPG-based samples if other compositions were constant. (C) 2003 Wiley Periodicals, Inc.