Polymers of carbonic acid, 5. Nematic polyurethanes derived from 4,4′‐dihydroxybiphenyl and 4,4′‐bipiperidine, ethylene‐4,4′‐bipiperidine or trimethylene‐4,4′‐bipiperidine

Abstract 4,4′‐Bipiperidine (3a), 1,2‐bis(4‐piperidinyl)ethane (3b) and 1,3‐bis(4‐piperidinyl)propane (3c) were condensed with the dichloroformates of p‐phenylene, 2‐methyl‐1,4‐phenylene or 2,5‐biphenylylene. Furthermore, two copolyurethanes were prepared either by mixing 3a and 3c or by mixing the dichloroformates for p‐phenylene and 2,5‐biphenylylene. Inherent viscosities between of 0,6 and 1,7 dl/g were found for the polyurethanes of 3c, but only values below 0,86 dl/g for those of 3a and 3b. The polyurethanes derived from hydroquinone or methylhydroquinone are semicrystalline polymers with a short‐term thermostability up to 310°C. The polyurethanes deriving from phenylhydroquinone are amorphous with a thermostability up to 360°C. The homo‐and copolyurethanes containing 4,4′‐biphenylylene units form a smectic layer structure in the solid state and a nematic melt above the melting point.