Phase transition and domain morphology of siloxane‐containing hard‐segmented polyurethane copolymers

The phase transitions and the morphology of hard‐segment domains of those siloxane‐containing hard‐segmented polyurethane copolymers are studied by differential scanning calorimetry (DSC). The NH‐SiPU2 copolymer, which comprises a siloxane–urea hard segment and a polytetramethylene ether glycol soft segment (PTMG2000), exhibits a high degree of phase‐separation and a highly amorphous structure. Therefore, NH‐SiPU2 copolymer proceeds with a melt‐quenching process and with various annealing conditions, to examine the morphologies and the endothermic behaviors of the siloxane‐containing hard‐segment domains. DSC thermograms of further annealed NH‐SiPU2 indicate that the first endotherm (T₁) at around 75°C is related to the short‐range ordering of amorphous siloxane hard‐segment domains (Region I), and the second endotherm (T₂) at around 160°C is related to the long‐range ordering of amorphous siloxane hard‐segment domains (Region II). The DSC thermograms at annealing temperatures below and above T₁ demonstrate that both the temperature and the enthalpy of T₁ linearly increase with the logarithmic annealing time (log t_a). This result shows that the endothermic behavior of T₁ is typical of enthalpy relaxation, which is caused by the physical aging of the amorphous siloxane hard segment. Additionally, the siloxane hard segments in Region I are movable, and can merge with the more stable Region II under suitable annealing conditions. Transmission electron microscopy shows that Regions I and II are around 200 and 800 nm wide, and that the Region I can be combined with the stable Region II, under suitable annealing conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4242–4252, 2006