Rigid phase domain sizes determination for poly(urethane–urea)s by solid-state NMR spectroscopy. Correlation with mechanical properties

• Polyurethane was obtained by prepolymer method and their tensile properties were investigated.
• The molecular dynamics and domain size of segments were elucidated by using solid-state NMR techniques.
• The dependence of the rigid phase domain size on composition were captured.
• The increase of the rigid domain size leads to molecular motions restriction in polymer matrix.

The solid-state NMR techniques have been applied to study molecular dynamics and domain sizes in polyurethanes based on oligomeric 4,4′-diisicyanate diphenylmethane and polyols with different length. Measurements of proton spin–lattice times in both laboratory frame (T1) and rotating frame (T1ρ) were done for the soft and the rigid segments of all polyurethanes. To determine the size of heterogeneities and characterize the morphology of the polyurethanes the 1H NMR spin-diffusion experiment was performed. The morphology of the dispersed phase was considered cylindrical for all samples. The size of the rigid phase domains was found to be in the range between 4.4 and 8 nm depending on the length of the hard segments. The tensile properties of polyurethane were found to be correlated with molecular mobility in polymer matrix and domain size of rigid phase.

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