Synthesis and liquid crystal behavior of new side chain aliphatic polycarbonates based on cholesterol

Abstract

In this study, we synthesized a series of new liquid crystal aliphatic block polycarbonates copolymers mPEG43-b-P(MCC-Cn)51 (n=1–4) via the ring-opening polymerization, hydrogenation reduction and coupling reaction, which contained side functionalized cholesteryl groups and were different in the number of the flexible methylene groups. The chemical structures of the chiral compounds and copolymers obtained in this study were characterized by FT-IR and 1H NMR spectra, and the average molecular weights of the copolymers were investigated by average molecular weights gel permeation chromatographic (GPC). The polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used to characterize the liquid crystal behavior. The relationship of the structure and phase behavior of the chiral compounds and copolymers influenced by spacer lengths was discussed. As a result, the chiral compounds with two methylene only showed a smectic A (SmA) phase, while those with more methylene showed a SmA phase and cholesteric phase. As the number of the flexible methylene groups increased, the corresponding melting temperature, the transition temperatures of LC phases and the isotropic temperature of chiral compounds all showed a decreasing trend, and mesophase temperature range narrowed. The polycarbonate copolymer with two methylene did not show mesomorphism, while the copolymers with longer spacer length seemed beneficial for the formation of mesophases at room temperature and revealed a smectic A phase with an interdigitated molecular arrangement on heating and cooling cycles. The results showed a decreased tendency toward the glass temperature, and an increased tendency toward isotropic temperature for the LC copolymers with an increase of the spacer length.