Studies of the Thermal and Mechanical Properties of Poly(urethane-siloxane)s Cross-Linked by Hyperbranched Polyesters

Polyurethane networks based on Boltorn hyperbranched polyesters (HBPs) of different pseudogenerations as cross-linkers, alpha,omega-dihydroxy(ethylene oxide-poly(dimethylsiloxane)-ethylene oxide) (EO-PDMS-EO) and 4,4'-methylenediphenyl diisocyanate were synthesized using a two-step polymerization reaction in solution. The influence of the pseudogeneration number of Boltorn HBPs on the thermomechanical and thermal properties and morphologies of polyurethane networks was investigated using FTIR, DMTA, TGA, hardness measurements, SEM, and SAXS. Synthesized polyurethanes showed higher cross-linking density and hardness and lower thermal stability with increasing pseudogeneration number of HBP. Samples with lower EO-PDMS-EO content exhibited slightly better thermal stability and higher hardness. All utilized characterization methods yielded consistent results and confirmed the existence of microphase separated morphology with the appearance of certain microphase mixing between segments as the pseudogeneration number of HBP increased. The obtained results revealed that the synthesized polyurethanes have good thermal and thermomechanical properties, which can be tailored by changing the pseudogeneration number of the HBP or the EO-PDMS-EO content