Thermal properties of poly(urethane-ester-siloxane)s based on hyperbranched polyester

Novel polyurethanes (PUs) were synthesized using hydroxy-terminated hyperbranched polyester (BH-20) and 4,4'-methylenediphenyl diisocyanate (MDI) as hard segments and hydroxy-terminated ethylene oxide-poly(dimethylsiloxane)-ethylene oxide triblock copolymer (PDMS-EO) as soft segment, with soft segment content ranging from 30 to 60 wt %. The PUs were synthesized by two-step solution polymerization method. The influence of the soft segment content on the structure, swelling behavior and thermal properties of PUs was investigated. According to the results obtained by swelling measurements, the increase of the hard segment content resulted in the increase of the crosslinking density of synthesized samples. DSC results showed that the glass transition temperatures increase from 36 to 65A degrees C with increasing hard segment content. It was demonstrated using thermogravimetric analysis (TGA) that thermal stability of investigated PUs increases with increase of the soft PDMS-EO content. This was concluded from the temperatures corresponding to the 10 wt % loss, which represents the beginning of thermal degradation of samples.