Polarizing microscopy liquid crystalline polymers

Ferrocene-containing liquid crystalline polymers 30 have been reported from the solution polymerization of l,T-bis(chlorocarbonyl)ferrocene, terephthaloyl chloride, and methylhydroquinone in refluxing dichloromethane [38], as indicated in Scheme 10-11. With one exception, these ferrocene containing copolyesters were reported to have birefringent melts. The presence of liquid crystallinity was verified by differential scanning calorimetry (DSC), polarized light microscopy, and X-ray diffraction studies. 

As briefly mentioned earlier, thermal studies have been used in conjunction with characterization by polarized light microscopy to determine the miscibility of polymeric and small molecule liquid crystals and low molecular weight mesogens, of the same or different types of liquid crystallinity, can also be used as plasticizers or diluents for polymers, as demonstrated in a study involving side chain liquid crystalline polymers... 

Liquid crystalline polymers containing ferrocene in their side chains have been reported.235-240 Deschenaux used free-radical synthesis to prepare thermotropic liquid crystalline polymethacrylates containing ferrocene (Scheme 2.46).235 Polarized light microscopy showed that monomer 171 and its corresponding polymer 172 exhibited enantiotropic smectic A and C phases. 

A complete characterization of liquid crystalline polymers should include at least two aspects the characterization of the molecular structure and that of the condensed state structure. Since the first characterization is nothing more than what is practiced for non-liquid-crystalline polymers, we will restrict the discussion to only a short introduction of methods mostly used in the characterization of the presence and the main types of polymeric liquid crystal phases. The methods include the mostly used polarizing optical microscopy (POM, Section 4.1), differential scanning calorimetry (DSC, Section 4.2) and X-ray diffraction (Section 4.3). The less frequently used methods such as miscibility studies, infrared spectroscopy and NMR spectroscopy will also be discussed briefly (Section 4.4). 

It has been shown that CNTs seed the formation of oriented domains in a liquid crystalline polymer [82]. Using polarized light microscopy it was observed that the molecular alignment in large domains was homogeneous and controlled by the direction of the nanombes nucleus. CNT films have been generated by deposition... 

Polarized microscopy has been one of the most important methods for structural assessment of liquid-crystalline polymers. It goes back to Demus and Richter (1978) who presented a great number of photomicrographs of small-molecule liquid crystals. Liquid-crystalline polymers are presented in detail in Chapter 6. Figure 11.16 shows a series of photomicrographs of different liquid-crystalline and crystalline monomers and polymers. The schlieren... 

Thermotropic liquid crystalline PPV derivatives 43 were prepared by the coupling of dihalodialkoxybenzene and divinylbenzene in the presence of a palladium catalyst, as outlined in Scheme 47 [133]. Polarized light microscopy, as a function of temperature, showed evidence of a nematically ordered structure in the material. X-ray diffraction analysis of the pristine polymers showed them to be semi-crystalline in nature, although the crystallinity of the polymer changed dramatically upon heating above 100 °C. 

Except for the structure containing 100% of ferrocene unit, which decomposed before melting, all the organometallic copolymers exhibited birefringent melts. Nematic textures were identified by means of polarized optical microscopy and, in one case, by X-ray diffraction studies. For comparison purposes, a polymer without ferrocene unit was prepared, but showed no mesomorphism. The authors deduced that the ferrocene framework was contributing to the liquid crystallinity of the ferrocene-containing polymers. 

Characterization. The liquid crystalline properties of the side-chain monomers (III) and polymers (I) have been studied by Differential Scanning Calorimetry (DSC), Polarized Optical Microscopy (POM) and X-ray diffraction. The thermal transition data and phase types for all monomers (III) and polymers (I) are summarized in Table HI. A representative DSC scan for the monomer (El) and polymer (p with a four-carbon tail (n=4) and six-carbon flexible spacer (m=6) are shown in Figures 1 and 2 respectively. The first peak at -24°C shown in Figure 1 is the crystal to smectic... 

A dispersion of spherulitic liquid crystalline particles in brine exists between 0.8 gm/dl NaCl (Figure 2(a), first sample on the left) and 1.2 gm/dl. As the salinity is increased to about 1.4 gm/dl NaCl, the amount of liquid crystals as well as the birefringence increase, and the texture observed using PLS is intermediate between those of the spherulite (S) and lamellar (L) structures. The aqueous solution is a homogeneous lamellar phase between 1.6 and 1.8 gm/dl NaCl. The surfactant molecules form bilayers with their polar heads toward the brine. Figure 3(a) shows the lamellar structure as observed by polarized microscopy at 1.6 gm/dl salt and without any polymer. The bands represent "oily streaks" in a planar background. 

A Nicolet Magna 550 Fourier Transform Infrared Spectrometer (FTIR) and a Bruker MW 250 MHz proton NMR were used to verify the chemical structure of all monomers and polymers. Optical activity of the compounds was measured at 25 on a Perkin-Elmer Polarimeter in chloroform. A Waters Gel Permeation Chromatograph with 440 UV absorption detector and R401 differential refructometer was used to determine the molecular weights of the polymers tetrahydrofuran was used as the mobile phase at 1.0 mL/min, and the Waters polystyrene gel columns were calibrated with monodisperse polystyrene standards. Polarizing optical microscopy was used to identify liquid crystalline phases using a Leitz optical microscope with a CCD camera attachment... 

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