Main chain liquid crystalline polyethers based on conformational isomerism

The synthesis of 1-(4-hydroxyphenyl)-2-(2-chloro-4-hdyroxyphenyl)ethane (ClBPE) a flexible mesogen and polyethers and copolyethers based on ClBPE and α,ω-dibromoalkanes containing from 4 to 20 methylene units are described. With some exceptions, most of the homopolymers display monotropic or virtual mesophases. The virtual isotropic-nematic (Tin) and nematic-nematic transitions (Tn1n2) and corresponding thermodynamice parameters were determined from the copolymerization experiment. The synthesis of 1-(4-hydroxyphenyl)-2-(2-fluoro-4-hydroxyphenyl)ethane (FBPE), 1-(4-hydroxyphenyl)-2-(2-bromo-4-hydroxyphenyl)ethane (BrBPE) and 1-(4-hydroxyphenyl)-2-(2-trifluoromethyl-4-hydroxyphenyl)ethane (CF3BPE) have been described. The homopolymers based on these mesogens (RBPE, where R = F, Cl, Br and CF3) and 1,5-dibromopentane (RBPE-5) and 1,8-dibromooctane (RBPE-8) and the corresponding copolymers based on various ratios of 1,5-dibromopentane and 1,8-dibromooctane (RBPE-5/8(A/B)) are synthesized. The isotropic-nematic transition temperatures and the thermodynamic parameters of RBPE-5 and RBPE-8 were compared with corresponding polyethers based on 1-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl)ethane (MBPE) from the literature. The copolymers based on 1-(4-hydroxyphenyl)-2-(2-R-4 -hydroxyphenyl)ethane (RBPE) where R = F, Cl and CH3 and flexible spacers containing odd number of methylene units (5, 7 and 9) were synthesized for the characterization of low temperature nematic (n2) phase. The synthesis and characterization of copolyethers based on FBPE and various ratios of 1,8-dibromooctane and 1,12-dibromododecane (FBPE-8/12(X/Y)), and of copolymers based on 50/50 molar ratio of 1,8-dibromooctane and 1,12-dibromododecane with various ratios of 1,2-bis(4-hydroxyphenyl)ethane (BPE) and FBPE (BPE/FBPE(A/B)-8/12(50/50)) are presented. The synthesis of 4,4′-bis (2-(4-hydroxyphenyl)ethyl) benzene (PEB), of the polyethers based on PEB and α,ω-dibromalkanes (PEB-X, where X represents the number of methylene units in the flexible spacer and is equal to 5, 7, 8, 9, 10 and 12), of the polyether based on BPE and 1,9-dibromononane (BPE-9) and of copolyethers based on 1,9-dibromononane with various ratios of BPE to PEB (BPE/PEB(A/B)-9, where A/B is the molar ratio of BPE to PEB) are presented. (Abstract shortened with permission of author.