Study on the morphology and thermomechanical properties of poly(urethane-siloxane) networks based on hyperbranched polyester

Two series of polyurethane films based on hyperbranched polyester of the second pseudo-generation (Boltorn (R)), 4,4'-methylenediphenyl diisocyanate and two different siloxane prepolymers, alpha,omega-dihydroxy-(ethylene oxide-poly(dimethylsiloxane)-ethylene oxide) (EO-PDMS-EO) and alpha,omega-dihydroxypropyl-poly(dimethylsiloxane) (HP-PDMS), were prepared by two-step polymerization in solution. The influence of the type and content of soft segment on the morphology, thermomechanical and surface properties of the synthesized polyurethanes was studied by atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), dynamic mechanical thermal analysis (DMTA) and water absorption measurements. It was found that these techniques confirmed existence of microphase separated morphology. Synthesized polyurethanes exhibited two glass transition temperatures and one second relaxation process. The results showed that polyurethanes based on HP-PDMS had higher surface roughness, better microphase separation and waterproof performances. Samples synthesized with lower PDMS content had less hydrophobic surface, but higher crosslinking density and better thermomechanical properties.