SYNTHESIS AND THERMAL-PROPERTIES OF FERROELECTRIC SIDE-CHAIN LIQUID-CRYSTALLINE POLYSILOXANES BASED ON NAPHTHYL BIPHENYLCARBOXYLATE MESOGENIC GROUPS AND OLIGOOXYETHYLENE SPACERS

In this work, three series of ferroelectric side-chain polysiloxanes c ontaining oligooxyethylene spacers and (S)-2-methyl-1-butyl (2S)-2-[6- (4-hydroxybiphenyl-4'-carbonyloxy)-2'- naphthyl]propionates, (R)-1-met hylheptyl (2S)-2-[6-(4-hydroxybiphenyl-4'-carbonyloxy)-2'- naphthyl]pr opionates, and (2S,3S)-2-chloro-3-methylpentyl [6-(4-hydroxybiphenyl-4 '-carbonyloxy)-2'-naphthyl] propionates mesogenic groups were synthesi zed. The mesomorphic behaviors of three series of ferroelectric side-c hain liquid-crystalline polysiloxanes were also studied using differen tial scanning calorimetry, optical polarizing microscopy, and high-res olution X-ray diffraction measurements. Some of these side-chain polys iloxanes containing four phenyl rings of ester cores (i.e., -Ph-Ph-COO -naphthyl-) and chiral heptyl tail present a smectic A (S-A), and a ch iral smectic C (Sc) phase (around 100 degrees C). Another two series containing four phenyl rings of ester cores and chiral butyl and penty l chain tail reveal a cholesteric (N), an S-A phase and an Sc* phase. The polymer PS12NC derivative with one unit of oxyethylene spacer (n = 1) of PSn2NC series reveals a N phase, a twist grain boundary A (TG B(A)) phase, and a Sc phase. X-ray investigations reveal that the pac king of mesogenic groups for PS02NA, PS02NB, PS02NC with the shortest spacers (n = 0) exhibit a bilayer (two-layer) packing structures. More over, polymer PS32NA, PS32NB, PS32NC with the longest spacer chain (n = 3) reveal a monolayer packing structure. However, these two types of packing structure appear simultaneously in PS12BNA (n = 1), PS12NC (n = 1), PS12NB (n = 1), and PS22NB (n = 2), depending on the chiral tai l length. Results obtained in this study again demonstrate that the te ndency toward chiral smectic C mesomorphism increases as the rigidity of phenyl ester mesogens increases via the flexible oligooxyethylene s pacers system. Furthermore, the thermal stability of the chiral smecti c C mesophase is determined by the flexibility of the chiral tail.