Phase structure in segmented polyurethanes having fatty acid-based soft segments

Structural studies on two segmented polyurethanes prepared from modified oleic acid soft segments and butane diol/diphenylmethane diisocyanate hard segments, were performed. Polyurethanes were thermoplastic elastomers with 50% and 70% soft segment concentration (SSC) for TPU-50 and TPU-70, respectively. DMA revealed the co-continuous morphology in TPU-50 and dispersed hard domains in the soft matrix in TPU-70. AFM showed micron size globules in TPU-70 ascribed to hard segment-rich superstructures. Alternating small soft and hard domains were present in TPU-50, with ∼15 nm lateral dimensions and local modulus deviations from 40 to 50 MPa, consistent with co-continuous morphology. The dispersed hard domains in the soft matrix of TPU-70, and co-continuous phases in TPU-50 morphology was confirmed. USAXS showed the domain spacing of TPU-50 was about 13.3 nm. TPU-70 demonstrated domain spacing of about 11.3 nm. USAXS revealed that the interface between phase-separated domains exhibited surface-fractal-like behavior.