Decrease in the isotropization temperature and enthalpy of main-chain polymer smectic liquid crystals as a result of the inclusion of chain ends

Main-chain liquid crystal (LC) PB-10-xn polyesters with number average degrees of polymerization (xn) ranging from 12 to 50 were prepared. The PB-10 polyesters formed smectic I (SmI) LCs that consisted of 40-nm-thick lamellae stacked along the polymer chain direction. Although the LC lamella thickness (dLC) was largely independent of xn, the isotropization temperature (Ti) of the SmI LCs decreased by 12 °C with decreasing xn. Such a decrease in Ti can be explained by the inclusion of polymer chain ends in the LC lamellae, which resulted in the low isotropization enthalpy and curved LC lamellae, as observed in PB-10-12.