Selectively deuterated liquid crystalline cyanoazobenzene side-chain polyesters. 2. Preparation and characterization of polyesters

Two sets of specifically deuterated cyanoazobenzene side-chain polyadipates and polytetrade-canedioates have been prepared by transesterification in the melt. Combinations of three different, selectively deuterium labeled 2-[6-[4-[(4-cyanophenyl)azo]phenoxy]hexyl]-1,3-propanediols or the non-deuterated analog and diphenyl adipate or tetradecanedioate in perdeuterated or non-deuterated versions were employed. The polyesters have weight average molecular masses in the range 21 000-183 000 as determined by SEC. The phase behaviour of the polyesters have been investigated in detail by differential scanning calorimetry. Whereas the polytetradecanedioates show a complex thermal behaviour with a number of different phases, the polyadipates are less complex and both nematic and smectic A phases have been identified by polarizing optical microscopy. Solution 1H, 13C and 2H NMR spectroscopy have been utilized for both polyester structural assessment and determination of deuterium distribution and content. FTIR spectroscopy has revealed suitable and characteristic vibrations which unequivocally represents the absorption behaviour of individual polyester segments or molecular structures in the different selectively deuterated polyesters.