A series of supramolecular soft materials with hydrogen bonded transient networks was prepared by blending carboxy-terminated telechelic poly(ethyl acrylate) (PEA-(COOH)(2)) and polyethyleneimine (PEI). Effects of PEA-(COOH)(2) molecular weight (M-PEA) and the blend ratio on the viscoelastic properties were investigated by rheological and small angle X-ray scattering measurements. Rubbery plateau appeared by adding PEI due to network formation with ionic hydrogen bonded crosslinks between amines on PEI and carboxylic acids on PEA-(COOH)(2). The highest temperature of a storage modulus-loss modulus crossover as well as the highest flow activation energy was attained at a certain mole ratio of amines to carboxylic acids, irrelevant to M-PEA, indicating optimized supramolecular networks were achieved by stoichiometric balance of two functional groups. Since telechelic PEA-(COOH)(2) serves as a network strand, the plateau modulus was inversely proportional to M-PEA, which was consistent with the correlation length between crosslinks estimated by X-ray scattering measurements. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 755-764