A new type of polyester polyol, with alkyl side groups, viz. poly(2,4-diethyl-1,5-pentamethylene adipate) glycol (PDPAd) was synthesized and used to improve the hydrolytic stability of waterborne polyurethanes (PU). The results compared favorably with poly(tetramethylene adipate) glycol (PTAd)-based PU and blends of the two types of PU in terms of particle size, thermal, XRD, mechanical, dynamic mechanical, and swell behavior of the dispersion cast films in addition to hydrolytic stability and adhesion properties. Blends of PTAd-based PU and PDPAd-based PU gave significantly improved green (immediate) adhesion and hydrolytic stability due to the synergistic effects of crystallinity (heat of crystallization, high density) and amorphous regions (tack, high thermal stability). (C) 2005 Wiley Periodicals, Inc.