Modifications in the mesogenic unit of poly(oxytetramethyleneoxycarbonyl‐3‐chloro‐1,4‐phenyleneoxyterephthaloyloxy‐2‐chloro‐1,4‐phenylenecarbonyl)

The effect of asymmetrical chlorine substitution in the mesogenic unit of poly(oxytetramethyleneoxycarbonyl‐3‐chloro‐1,4‐phenyleneoxyterephthaloyloxy‐2‐chloro‐1,4‐phenylenecarbonyl) ( 1 ) has been studied by means of differential scanning calorimetry, optical microscopy and X‐ray diffraction. The polymer presents three‐dimensional ordering, in spite of the substitution, and shows a transition to a nematic mesophase at 274°C and to the isotropic melt at 319°C. As for the unsubstituted polymer poly(oxytetramethyleneoxycarbonyl‐1,4‐phenyleneoxyterephthaloyloxy‐1,4‐phenylenecarbonyl), two different crystalline forms have been observed and some information about their structure has been obtained by Fourier‐Transform Raman spectroscopy and 13 C solid‐state nuclear magnetic resonance. First results indicate that the most important structural differences between both polymorphs occur in the mesogenic unit.