FORMATION OF HEXAGONAL COLUMNAR MESOPHASES BY LINEAR AND BRANCHED OLIGOAMIDES AND POLYAMIDES

The formation of columnar mesophases by N-acylated azacrown derivative s may be seen as a consequence of their discoid molecular geometry. Vi ewing these materials as cyclic oligomers, they are dust one example o f the various molecular architectures that may be realized based on th e N-acylated ethylenamine fragment. By using linear oligoamides, the h exagonal columnar packing is preserved, the monotropic nature of the m esophase reflecting the higher flexibility of the systems. The corresp onding polymers are accessible by polymer analogous acylation of linea r poly(ethylenimine), in which a high conversion of the amino groups a nd a low polydispersity of the final polymers can be achieved. The res ulting polyamides form enantiotropic mesophases with a hexagonal colum nar structure proven by polarizing microscopy, DSC investigations, and X-ray studies. A helically folded structure of the polymer main chain is proposed whereby this structural motif is probably induced by the packing of the alkyl side chains. Based on side group variations, it w as found that the 3,4-bis(alkyloxy)benzoyl side group particularly mat ches the conformative requirements of the polymer main chain for the f ormation of a columnar structure. Furthermore, a hexagonal columnar me sophase was observed for a non-symmetrically substituted cinnamoyl sid e group. Whereas in the case of linear polymers the mesophase is stabi lized at higher molecular weights,in the case of branched polyamides t he enhanced degree of branching disturbs the chain packing. In the sam e sense, the introduction of chiral groups both in the polymer main ch ain and in the side-chain region disturbs the packing into an ordered columnar structure. A monotropic mesophase was found for a regularly b ranched oligoamide with a presumably discoid molecular structure.