A series of polyesters, which are comprised of aromatic main chain backbones and flexible aliphatic side chains with 4-cyanobiphenyl end groups, has been synthesized based on a polycondensation of 2,2‘-bis(trifluoromethyl)-4,4‘-biphenyldiyldicarbonyl chloride with 2,2‘-bis{ω-[(4-(4-cyanophenyl)phenoxy]-n-alkoxy)carbonyl]}-4,4‘-biphenyldiol (PEFBP). For a PEFBP polyester containing eleven methylene units in the side chains, PEFBP(n = 11), multiple phase transitions can be found via differential scanning calorimetry during cooling and heating at varying rates. Different phase structures are identified by wide-angle X-ray diffraction and electron diffraction experiments, while morphologies of these ordered states are observed by polarized light and transmission electron microscopy. During cooling, a high temperature nematic (N) phase is formed at 193 °C independent of the cooling rate due to the combined orientational order of the cyanobiphenyl groups in the side chains and the aromatic polyester backbones. At a temperature of 90 °C, a new ordered low-temperature phase with an orthorhombic lattice (KO) starts to form at a cooling rate equal to or slower than 10 °C/min. However, the formation temperature of this phase is too close to the glass transition temperature (60 °C) to proceed to completion. Only at very slow heating rates (e.g., 1 °C/min), can the KO phase further develop. This phase melts at around 120 °C during heating and returns to the N phase. A new crystalline phase with a triclinic lattice at high temperatures (KT1) appears at 130 °C. It then transfers to a second triclinic crystalline phase (KT2). This KT2 phase melts at around 180 °C and, again, returns to the N phase. At 193 °C, isotropization occurs. This complicated phase behavior can be explained by the monotropic origin of the KO and KT1 phases with respect to the KT2 phase, which are metastable in the whole temperature region.

Liquid crystalline polyethers have been synthesized from 1-(4-hydroxy-4‘-biphenylyl)-2-(4-hydroxyphenyl)propane and α,ω-dibromoalkanes with even-numbers of methylene units [TPP(n = even)s]. Multiple phase transitions are found during cooling and heating via differential scanning calorimetry (DSC), and they show little undercooling dependence. Ordered structure identifications are based on experimental observations of wide angle X-ray powder and fiber diffraction experiments at different temperatures. Polarized light and transmission electron microscopy observations on mesophase morphology combined with DSC results on thermodynamic transition properties also provide additional evidence for these phase assignments. Moreover, the contributions of the mesogenic groups and the methylene units to each ordering process are obtained based on the changes of transition enthalpy and entropy. In TPP(n ≤ 8)s the highest temperature transition is from the isotropic melt to a nematic phase. This nematic phase is only stable in a narrow temperature range. For instance, it is 12 °C for TPP(n = 4) and 6 °C for TPP(n = 8). When the number of methylene units n ≥ 10, the isotropic melt directly enters a smectic F phase. The second transition in TPP(n ≤ 8)s is from the nematic to the smectic F phase. As a result, the smectic F phase exists for all TPP(n = even)s. Decreasing the temperature further leads to another transition in TPP(n = even)s to form a smectic crystal G phase which is followed by a transition to a smectic crystal H phase. This smectic crystal H phase remains for TPP(n ≤ 8)s down to their glass transition temperatures, while in TPP(n ≥ 10)s further ordering processes occur and crystal phases are observed. A phase diagram of TPP(n = even)s is constructed.

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Two polyimides having the same backbone chemical structure and different pendant side groups at the 2-and 29-positions of the diamine, the six methylene units capped with 4-cyanobiphenyl end groups and trifluoromethyl, were synthesized (6FDA-6CBO and 6FDA-PFMB). Surface-enhanced Raman scattering and surface optical second harmonic generation measurements show that after rubbing the major change in 6FDA-PFMB surface appears in the orientation of the dianhydride, which was originally planar, but becomes tilted with respect to the surface plane. In the case of 6FDA-6CBO, rubbing also causes the originally planar 4-cyanobiphenyls to tilt away from the surface and assume an azimuthally anisotropic distribution.

A series of polyesters consisting of aromatic main-chain backbones and flexible aliphatic side chains with 4-cyanobiphenyl end groups has been synthesized on the basis of the polycondensation of 2,2‘-bis(trifluoromethyl)-4,4‘-biphenyldicarbonyl chloride with 2,2‘-bis{ω-[4-(4-cyanophenyl)phenyoxy]-n-alkoxycarbonyl]}-4,4‘-biphenyldiol (PEFBP). As recently reported, for a PEFBP polyester containing eleven methylene units in the side chains, PEFBP(n=11), four different structures have been identified in addition to the isotropic melt. They are as follows:  an orthorhombic crystalline phase (KO), two triclinic crystalline phases (KT1 and KT2) in the high-temperature region, and a nematic phase (N). To further understand the phase transformation mechanisms involved, in this publication, overall phase transformation kinetics have been carried out using isothermal differential scanning calorimety (DSC) experiments. Special attention has been given to the temperature regions where three phases (KO, KT1, and KT2) exist. It is found that each phase possesses its own transformation rates. Three overall transformation rate regions are observed that are separated at temperatures of 95 and 113 °C, which serve as rate boundaries between these different phases. For the linear growth rates measured by polarized light microscopy (PLM), the growth rate of the KO phase is difficult to be detected due to its fast transformation rates. The linear growth rates of the KT1 and KT2 phases can, however, be measured. Although these rate regions generally correspond to the overall transformation rates obtained from DSC, a rate minimum can be observed at 130 °C in the linear growth rate data of the KT2 phase above 113 °C. This minimum is formed due to the introduction of a new linear growth rate branch above 130 °C. The morphological studies under PLM, transmission electron microscopy, and the melting temperature changes using DSC indicate that these two growth rate branches in the KT2 phase correspond to two kinds of morphological developments:  folded chain spherulites and extended chain single crystals. Furthermore, the linear growth rates are affected more by this morphological change compared to the overall transformation rates.