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Abstract
4′-(11-Vinyloxyundecanyloxy)-4-biphenylyl (2R,3S)-2-fluro-3-methylpentanoate (15) (2R 94%ee) and 4′-(11-vinyloxyundecanyloxy)-4-biphenylyl (2S,3S)-2-fluoro-3-methylpentanoate (16) (2S 90%ee) diastereomers and their corresponding homopolymers with well-defined molecular weight and narrow molecular weight distribution were synthesized and characterized. The phase behavior of 15 and poly(15) is quite different from those of 16 and poly(16), respectively. 15 displays enantiotropic S A and S X (unidentified smectic) phases and a crystalline phase, while 16 displays only a monotropic S A phase and a crystalline phase. Both poly(15) and poly(16) display enantiotropic S A and S X2 (unidentified smectic) phases. An additional unidentified smectic phase (S X1) was observed for both low molecular weight polymers, i.e., at DP < 5 for poly(15) and at DP < 9 for poly(16). However, the transition temperatures of poly(15) are 15–20°C higher than those of poly(16) when their phase behaviors are compared using polymers with the same molecular weight. Neither monomers nor polymers displayed an S c* phase. Phase diagrams were investigated in detail in binary mixtures of 15 with 16 and poly(15) with poly(16) as a function of the composition of the two diastereomeric structural units. In all investigated systems the diastereomeric structural units derived from the two monomers are isomorphic within all their mesophases and over the entire range of compositions. Heterochiral molecular recognition was detected only in the S X1 phase of the polymer mixtures via a large positive deviation from the ideal values of the S X1-S X2 transition temperatures. On the contrary, the S A-I transition temperatures of all mixtures showed a good agreement with the theoretical values calculated from the Schröder-van Laar equation, suggesting that the two diastereomeric structures form an ideal solution in the S A phase and, therefore, there is no heterochiral recognition between the 2R and 2S stereogenic centers in this phase. The S X1-S X2 transition temperatures showed negative deviations from the ideal values, indicating the nonideal solution behavior of the two diastereomeric structural units in the S X2 phase.