STRUCTURE OF THE HARD SEGMENTS IN POLYURETHANE ELASTOMERS

A new model is proposed for the chain conformation and packing of MDI-butandiol hard segments in polyurethane elastomers. The model is based on the structure of methanol-capped MDI (MeMMe), which we have recently determined by single-crystal X-ray methods. Planar zig-zag -CH2CH2-sections connect successive MeMMe units, which have the same conformation as in the monomer structure. Successive monomer units along the chain are related by a centre of symmetry at the central CH2CH2 bond. The chains are linked together in stacks through CO...HN hydrogen bonds which involve half of the urethane groups. The remaining urethanes are similarly hydrogen-bonded to adjacent stacks, and thus the structure is stabilized by hydrogen-bonding in both directions perpendicular to the chain axis. A triclinic unit cell is proposed for the structure with approximate dimensions a = 5.2 A ̊, b = 4.8 A ̊, c = 35.0 A ̊, α = 115°, β = 121° and γ = 85°. The space group is P1 and the cell contains two repeat units of a single chain. © 1979.