A series of liquid crystalline polyethers has been synthesized from 1-(4-hydroxy-4‘-biphenylyl)-2-(4-hydroxyphenyl)propane and α,ω-dibromoalkanes [TPP(n)]. From the differential scanning calorimetry experiments, the TPP(n=odd)s show multiple phase transitions during cooling and heating. For each TPP(n=odd) the supercooling dependence of these transitions is found to be small. A phase diagram of the transition temperatures and the enthalpy and entropy changes of the transitions with respect to the number of methylene units (n) for TPP(n=odd)s have been obtained. Analyses have been conducted regarding the contributions of both the mesogenic groups and the methylene units to the differently ordered structures. Identification of the ordered structures in each phase has been carried out by combining wide angle X-ray powder and fiber diffraction experiments at different temperatures with polarized light and transmission electron microscopy experiments on the liquid crystal morphology and defects. It is found that for TPP(n≤13)s the highest temperature transition is from the isotropic melt to a nematic phase. However, for TPP(n≥15)s, the isotropic melt directly converts to a smectic F phase having a monoclinic unit cell (a pseudohexagonal packing tilted toward a side). The WAXD fiber patterns for this phase show that the chain orientation is parallel to the fiber direction. For TPP(n≤13)s formation of a smectic F phase with a monoclinic unit cell from the nematic phase can also be determined and the WAXD fiber pattern shows that the chain orientation is at an angle ranging between 0 and 20° with respect to the fiber direction. With an increase in the number of methylene units, this angle gradually decreases until n = 15, where this angle becomes zero. Further cooling leads to a smectic crystal G phase for all TPP(n=odd)s, and the different chain orientations with respect to the fiber direction in the WAXD fiber patterns still exist. TPP(n≤9)s remain in the smectic crystal G phase down to their glass transition temperatures, while TPP(n≥11)s form a smectic crystal H phase (a tilted herringbone, orthorhombic packing tilted toward the b-axis side, and a > b) in a low temperature range.

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.

Based on our differential scanning calorimetry observations, a polyether 1 synthesized from 4'-[2-(4-hydroxyphenyl)propyl]-4-biphenylol and 1,9-dibromononane shows multiple transition behavior during cooling and heating. Furthermore, these transition temperatures do not exhibit significant supercooling dependence. Detailed analyses of the wide-angle Xray diffraction powder and fiber patterns at different temperatures have indicated that highly ordered smectic F and G phases exist in this polyether and are differentiated from traditional crystalline phases.

Highly faceted, regular, lathlike lamellar single crystals of syndiotactic polypropylene (s-PP) fractions have been investigated through transmission electron microscopy (TEM), atomic force microscopy (AFM), and electron diffraction (ED). Single crystals of s-PP over 1 μm in size can be grown from the melt in thin films. ED results obtained from the s-PP single crystals indicate a unit cell III with a = 1.450 nm, b = 1.120 nm, and c = 0.740 nm as proposed by Lovinger and Lotz. At high crystallization temperatures, relatively low molecular weight s-PP fractions can grow lamellar single crystals with microsectors. The polyethylene decoration method has been used to identify the chain folding direction, and no preferred orientation has been observed on the nonsectorized lamellar crystals. Sectorized lamellar single crystals show two different regions. In the sectors along the long axis (the b-axis), the chain folding is found to be parallel to the 010 direction. In the sectors along the short axis (the a-axis), little preferred orientation can be found. The deformation method of nonsectorized, high molecular weight s-PP single crystals on a plastic film has also been utilized to determine the chain folding direction. Microfibrillar structures can be observed in the cracks of the single crystals along both the a- and b-axes after deformation. This indicates that the folding direction in these nonsectorized, high molecular weight s-PP single crystals may be either along the (110) planes or a combination of the (100) and (010) microfolding and microsectoring. Zigzag-shaped edges on the deformed single crystals along the a-axis are also observed, and the sliding planes can be identified as the (110) planes.

Two-arm poly(ethylene oxide) (PEO) fractions with different molecular weights (MWs) have been prepared. For each fraction, both arms have equal lengths of MW = 2300 or 5500. The MWs and molecular weight distributions of two-arm PEOs after fractionation are determined from vapor pressure osmometry, gel permeation chromatography, and light scattering. Compared to linear PEO fractions with similar molecular lengths, the two-arm PEOs can be viewed as linear chains with a well-defined defect at the center of the molecule. Self-diffusion coefficients of the two-arm PEOs are measured and compared with linear PEOs having molecular lengths equivalent to both a single arm and a whole molecule. The crystallization behavior of the PEOs is monitored via wide angle X-ray diffraction, small angle X-ray scattering, and differential scanning calorimetry. Over a wide undercooling range, the two-arm PEO molecules do not appear to recognize the defects at the center of the chains during the initial stage of crystallization. During this stage of crystallization, they form nonintegral folding chain crystals having a fold length longer than the arm length. The defects are recognized only after the initial crystallization and gradually migrate to the lamellar surface through an apparent thinning process. The crystallization kinetics of the two-arm PEOs are significantly slower than those of the linear PEO molecules having a length equivalent to a single arm as well as a combined length of two arms. The melting behavior of the two-arm PEOs is, however, similar to that of linear PEOs which have a length of a single arm. The single lamellar crystal morphology of the two-arm PEOs observed via polarized light microscopy shows the faceting−rounding−refaceting effect with decreasing undercooling. Nevertheless, refaceted single crystals at very low undercoolings have a rectangular shape rather than the hexagonal one generally observed in the linear PEOs. This difference in the single crystal morphology may be caused by a change in the folding directions due to the large defects on the lamellar surfaces.