Reactively dispersed olefins in polyurethanes: A new class of polymer/polymer composite

Maleic anhydride grafted polyethylenes (MAH-g-PE) can be reacted with polyols to create fine phase dispersions in polyurethanes. Desirable blends can only be realized when the anhydrides are in the dehydrated state prior to reaction. The reaction of anhydride with hydroxyls can occur with the polyol prior to addition of isocyanate and chain extender to make the polyurethane, or with an already formed polyurethane heated up above its reversion temperature when hydroxyl functionality becomes available. Phase dispersion kinetics are a function of MAH-g-PE molecular weight and percentage grafted maleic anhydride along the chain, but also on viscosity matching of the forming polyurethane and the MAH-g-PE during the blending operation which maximizes shear stress between the phases. The final result is not strongly dependent on the preparation path. Thermoplastic polyurethane elastomers (TPUs) based on polypropylene oxide and polyethylenoxide/polypropylene oxide triblock copolymer soft segments are compared to industry standard TPUs prepared from polytetramethylene ether glycol (PTMEG) and polycaprolactone (PCL) soft segments. The control TPUs prepared from polypropylene oxide and the polyether triblock are inferior to those of PTMEG and PCL. However; when the polypropylene oxide and the triblock soft segments are prepared with 20% substitution of MAH-g-PE, the creep, thermal and solvent resistance of these elastomers exceeds those of the industry standards, and the tensile properties are comparable. Additionally, TPUs from PTMEG and PCL with added MAH-g-PE can also have their properties improved. The property improvements are a function of improved hard segment phase separation from the soft segment, and the creation of polyester crosslinks between the MAH-g-PE and the polyurethane.

SEM of PE-g-MAH polyol copolymer polyol particles. Full scale of image is ca. 200 μm260