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

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.