Preparation and properties of waterborne poly(urethane urea)s for adhesives: The effects of the 2,2-bis(hydroxylmethyl)propionic acid content on the properties

A series of waterborne poly(urethane urea)s (WBPUs) containing various concentrations (8.3-15.5 mol%) of 2,2-bis(hydroxylmethyl)propionic acid (DMPA) were prepared from isophorone diisocyanate, poly(tetramethylene adipate) glycol, DMPA, ethylenediamine, and triethylamine. The length of the hard segment with the DMPA content was varied from 18.7 to 22.6 wt% at a fixed soft-segment length (2000 g/mol). The effect of the DMPA content on the colloidal properties of WBPU dispersions, the hydrogen-bonding index, water swelling, dynamic mechanical thermal properties, and mechanical properties of WBPU films, and the adhesive strengths of substrates such as chloroprene rubber (CR)/CR, CR/polyurethane foam, CR/ethylene vinyl acetate foam, and thermoplastic olefin sheet/polypropylene foam were investigated. Stable aqueous dispersions of WBPU were obtained when the DMPA concentration was greater than 10 mol%. As the DMPA content increased, the particle size of the WBPU dispersion decreased, but the viscosity of the WBPU dispersion increased. The hydrogen-bonding fraction, water swelling, dynamic storage modulus and relaxation temperature, and tensile strength of the films increased with increasing DMPA content. According to an adhesion test, the substrates adhering to WBPU with greater than 10 mol% DMPA tore at about 8.0 kgf/cm(2) instead of breaking the adhered region. These results suggested that the WBPUs prepared in this study could have potential for adhesive use. (C) 2004 Wiley Periodicals, Inc.