Orientational elastic deformations of main-chain LC aromatic polyesters and low molecular weight nematics in a magnetic field

Orientational elastic deformations in a magnetic field were investigated in the nematic phase of polyphenylterephthaloyl-bis-(4-oxybiphenyl-4'-carbony l), polylterephthaloyl-bis-(4-oxybiphenyl-3'-carbonyl), and their low molec ular weight analogues. Temperature dependences of birefringence Delta n wer e obtained and used to evaluate the degree of orientational order S. The sp lay and bend elasticiy constants, K-1 and K-3, were determined.. The elonga tion of the rigid mesogenic core in polymer molecules leads to an increase in the K-3/K-1 ratio, just as in the case of low molecular weight nematics. No effect of molecular weight on the values of Delta n and K-i was detecte d.