Polymers from multifunctional isocyanates, 3. Synthesis and polyaddition reactions of (liquid‐crystalline) fully aromatic diisocyanatoesters

The regioselective reaction of aliphatic ω‐isocyanatoacyl chlorides with silyl‐protected hydroxy‐nucleophiles was extended to aromatic isocyanatoacyl chlorides. Starting with 3‐ or 4‐isocyanatobenzoyl chloride and 3‐ or 4‐trimethylsiloxyphenyl isocyanate, the four isomeric isocyanatobenzoic acid isocyanatophenyl esters were synthesized in high yields. From terephthaloyl chloride and two moles of a siloxyphenyl isocyanate or from 1,4‐bis(trimethylsiloxybenzene) and two moles of an isocyanatobenzoyl chloride, diesterdiisocyanates were obtained containing 3 benzene rings. The para‐substituted diisocyanates show liquid‐crystalline behaviour. Polyaddition reaction with various diols led to poly(esterurethane)s with a regular sequence of urethane and ester groups. The poly(urethane)s from the para‐substituted diisocyanates have very high melting points (225–350°C). Liquid crystallinity could not be proven unambiguously due to the instability of the urethane linkage at these temperatures.