DIBENZYLIC STRUCTURES ON MACROMOLECULAR CHAIN .9. THE INTERACTION OF URETHANE-ISOCYANATE GROUPS IN POLYURETHANE FORMATION

The interaction of isocyanate-urethane and isocyanate-amide groups in urethane group formation is studied. Bibenzil-2,2'-di-yl diisocyanate (2,2' BBDI) presents specific behaviour due to the steric specificity of its structure. Rotation of the two aromatic nuclei around ethylenic bridges favours strong intramolecular anchimeric assistance in the se cond step of the 2,2' BBDI with n-butanol (BuOH) reaction. This assist ance also enhances secondary reactions leading to unexpected cyclic al lophanate structure. Mechanisms for these reactions are proposed in co ncordance with kinetic measurements. Copyright (C) 1996 Elsevier Scien ce Ltd