Functional properties of films based on novel waterborne polyurethane dispersions prepared without a chain-extension step

Abstract

A series of novel waterborne polyurethane (PU) dispersions was prepared from a polycarbonate-based macrodiol, 1,6-diisocyanatohexane, 2,2-bis(hydroxymethyl) propionic acid (DMPA) and triethylamine. Different macrodiol-to-DMPA (diol) ratios and different excesses of isocyanate were used, and the typically used chain-extension step was omitted. Systematic measurements of the particle size revealed that PU particles have diameters lower than 100 nm at diol ratios of 1:1 and 1:2, while a diol ratio of 2:1 leads to nanoparticles with diameters closer to 100 nm or higher. The lowest size-dispersity (DLS) index was found for PU dispersions with a diol ratio of 1:1 for all excesses of NCO. The high negative values of ζ-potential (from −40 to −65 mV) of these materials indicate their long-term stability. The tensile properties of flat films made from the PU dispersions depend significantly on the sample composition and vary from 2.7 to 33.8 MPa (Young’s modulus), 0.2 to 28.0 MPa (tensile strength), 112 to 1193% (elongation-at-break) and 0.5 to 93.2 mJ mm−3 (toughness). The films were found to be thermally stable to a minimum of 200 °C. Dispersions prepared with a 30 and 50 mol% excess of NCO and diol ratios of 1:1 and 1:2 are the most promising materials for practical use as coatings or films. These materials can be used alone or together with water-dispersible additives as the matrix for diverse nanocomposite 2D systems.