Laterally attached side-chain liquid crystalline polynorbornenes designed to exhibit a chiral smectic C phase

In order to better assign the thermotropic properties of laterally attached side-chain liquid crystalline polymers (SCLCPs), a series of model compounds, {lcub}2,5-bis[(3'-fluoro-4'- n-alkoxyphenyl)ethynyl]phenyl{rcub}-alkanes, with spacer lengths m = 2 to 10, and 12 with n-alkoxy substituent lengths of n = 8 and n = 10 were synthesized and compared with previous results of m = 0, 1, and 11.1,2 The thermotropic behavior of the models were analyzed by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). For all model compounds, only a nematic phase was observed. The isotropization temperature decreased rapidly for the spacer length m = 0 to 3 and then converged toward a constant value for longer spacer lengths. Interestingly, the n = 8 model compounds were more stable, had a larger isotropization temperature, than the n = 10 model compounds for m < 8, but the n = 10 model compounds have a higher isotropization temperature than the n = 8 model compounds for m ≥ 8.; Ring-opening metathesis polymerization (ROMP) of achiral 5-[[[[2 ',5'-bis[2-(3'-fluoro-4 '-decyloxyphenyl)ethynyl]phenyl]alkyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-enes were completed for a series of spacer lengths m = 3 to 10, and 12 and gave polymers with a degree of polymerization (DP,) of 40 to 167 and polydispersity (pdi) of 1.17 to 1.38. The thermotropic behavior was studied by DSC and POM. For all achiral polymers, only a nematic phase was observed. As with the model compounds, the isotropization temperature rapidly destabilizes for m = 1 to 3 and converges to a constant value for longer spacer lengths. Furthermore, there was excellent correlation between the value of the isotropization temperature of the models and the achiral polymers.; Since the polymer with the short spacer length m = 1 was the only one with a smectic C phase, chiral poly{lcub}5-{lcub}1-[[[2' ',5''-bis[2-(3 '-fluoro-4'-decyloxyphenyl)ethynyl]phenyl]ethyl]oxy]carbonyl{rcub}bicyclo[2.2.1]hept-2-ene and poly{lcub}5-{lcub}1-[[[2'',5' '-bis[2-(3'-fluoro-4 '-decyloxyphenyl)ethynyl]phenyl]ethyl]oxy]carbonyl{rcub}bicyclo[2.2.1]hept-2-ene-co-5-{lcub}[[2 ',5'-bis[2-(3'-fluoro-4 '-decyloxyphenyl)ethynyl]benzyl]oxy]carbonyl{rcub}bicyclo[2.2.1]hept-2-ene were synthesized by ROMP and gave polymers in high yield. The homopolymer had a DPn = 21 and a pdi of 1.13. The copolymer had a DPn = 95.4 and a pdi of 1.36. The thermotropic behavior was studied by DSC and POM. The homopolymer showed no liquid crystallinity, just a glass transition at 38.7°C. The copolymer was able to reestablish the liquid crystallinity, however only nematic textures were present.