Mercedes Perez Mendez - Cholesteric Liquid-Crystal Copolyester, Poly[oxycarbonyl-        1,4-phenylene- oxy - 1,4 terephthaloyl- oxy- 1,4-phenylene- carbonyloxy (1,2-dodecane)] [C34H36O8]n, Synthesized from Racemic Materials: Kinetics, Structure and Op...

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      Journal of Engineering Research and Applications, ISSN:   2248-9622, Vol. 5, Issue 7, (Part - 2) July 2015, pp.48-62,   Mercedes Pérez Méndez and J. Sanguino, 



        The cholesteric liquid-crystal   poly[oxycarbonyl-1,4-phenylene-oxy-1,4   terephthaloyl-oxy-1,4-phenylene- carbonyloxy(1,2-dodecane)]   [C34H36O8]n, named   PTOBDME, synthesized by polycondensation reaction from equimolar   quantities of TOBC and the racemic mixture of glycol (R-S-1,2   dodecanediol), exhibits unexpected optical activity and chiral   morphology. The structure of racemic-PTOBDME, under different   polymerization kinetics conditions, is analyzed by conventional   NMR techniques and compared with those of polymer enantiomers   R-PTOBDME and S-PTOBDME obtained starting R(+)1,2 and   S(-)1,2-dodecanediol respectively. Molecular models based on the   NMR signals intensities are proposed. The optical activity of   racemic- PTOBDME is evaluated by measuring the ORD values during   kinetics study, and compared to the chiral polymers. Each   enantiomeric polymer seems to present the same stereoregular   head-tail, isotactic structure than the racemic, which we explain   by the higher reactivity of the primary hydroxyl than the   secondary one in the glycol through polycondensation. For each   enantiomer, two independent sets of signals were observed by NMR,   explained as two diastereomeric helical conformers: gg and gt,   related with two possible staggered conformations, along the   copolymer backbone. Chirality in racemic-PTOBDME is proposed to   be due to the kinetic resolution of a preferable helical   diastereomer, such as Sgt, with respect to the possible four   forms, while the R/S ratio of asymmetric carbon atoms remained   50:50. Chiral amplification is observed in R-PTOBDME and   S-PTOBDME due to a helical screw sense excess. Optimum yield was   obtained for racemic PTOBDME, after 120 minutes polycondensated   and decanted in toluene for 24 hours. Two weeks later a second   fraction precipitated from the toluene mother liquor with 67.6%   chiral excess. After eight months and two weeks a third fraction   precipitated with 85.2% chiral excess.

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