Thermal polarizing microscopy

Characterization of Monomers and Polymers. Phase transitions of monomers were determined by means of Differential Scanning Caloimetry (DSC) using the Perkin Elmer Dl C IB and thermal polarizing microscopy. 

In summary, polarizing microscopy provides a vast amount of information about the composition and three-dimensional structure of a variety of samples. The technique can reveal information about thermal history and the stresses and strains to which a specimen was subjected during formation. Polarizing microscopy is a relatively inexpensive and well accessible investigative and quality control tool. 

Melting points of polyesters and polyamides were taken from the Brandrup, J., Immergut, E. H., Polymer Handbook, Wiley, New York, 1967. The data do not represent true thermodynamic melting points but have been determined for polymers of unknown degree of crystallinity by methods such as differential thermal analysis, polarization microscopy, capillary tube, and others. Five conclusions can be drawn from the data. 

The technique of depolarized light intensity (DLI) microscopy was introduced by Magill (80) in 1960. Basic elements of the apparatus were a light source, polarizers, a sample holder, an analyzer, and a suitable recording system. Barrall and Johnson (74) and Miller (75, 76) have described applications of this technique to polymeric samples. Miller (75) prefers to call this technique thermal polarization analysis (TPA). 

The thermal reaction of cobalt polymers 4.28 with isocyanates at 120 °C leads to 2-pyridone-containing polymers such as 4.30 [70]. Well-characterized, yellow polyesters 4.31 containing skeletal (cyclobutadiene)cobalt moieties in the main chain have been prepared by interfacial polycondensation approaches [73]. The use of solubilizing alkoxy substituents R afforded materials with Mn = 5,400-16,300 (PDI = 1.3-1.8). Analogous materials to 4.31 with a 1,3-disposition of the main-chain substituents on the cyclobutadiene ligands have also been studied [73, 74]. Thermotropic liquid crystallinity was detected by polarizing microscopy, with, in some cases, mesophases stable over the temperature range from about 110 to >250°C. 

Sample synthesis was carried out as previously des-cribed, using either solution or interfacial polycondensation. Characterization was as in reference 3 DSC and polarizing microscopy were carried out using controlled sample thermal history as described in references 4,5. 

The N + I biphase finds its origin in polydispersity in chain length coupled with polydispersity in chain flexibility and is observed within a temperature range delineated by and T. Polarizing microscopy observation of the biphase in Pi (n = 10, M = 18 700) is illustrated in Figures 6.5a-c for three different conditions of thermal history [42]. It is apparent that textures and biphase width both depend on sample thermal treatment. 

Thermal polarized light microscopy of liquid crystal systems still primarily involves the identification of phase types. Recently, however, a number of novel phases with complex structures have been discovered and detailed examinations of the configurations of their defects are required in order to provide a basis for future phase classification. Thermal microscopy is also used extensively in examination of the alignment processes of liquid crystals, and, in a related context, electric-field studies on meso-phases are carried out in aligned cells. Electric-field studies are now used as adjuncts to phase classification, e.g., antiferroelectric phases are sometimes identified in the microscope with the aid of electric-field studies. 

For the effeets of storage time, the tricaprin/tristearin blend 50 50 (w/w) was melted at 80°C for 20 min, and then cooled to 5°C by direct inunersion in a water bath for 10 min, and the sample was inserted inside the NMR spectrometer heated to 40°C. The sample was kept at this temperature for 14 days. For polarized microscopy, the thermal diagram applied to the sample was the same, but the tricaprin/tristearin blend 75 25 (w/w) was used for a matter of clarity. 

The basic methods for the determination of phase transition temperatures (7 ) are DSC (differential scanning calorimetry), DTA (differential thermal analysis), and polarization microscopy. Every method has its advantages and restrictions. DSC allows one to determine the enthalpies of phase transitions (A// ). Microscopy allows one both to determine the phase transition temperatures and to identify the t)fpe of mesophase. DTA gives reliable results for melting temperatures of LCs that show solid-state polymorphism, and of LC mixtures. The differences in that can be found in publications by different authors arise from different measurement techniques and the presence of impurities. We have selected the data with the higher 7 values in such cases. 

Percec and coworkers [184] utilized a similar strategy for the conversion of perfluorinated alkylene functionalized 3,4,5-trihydroxy benzoic acid-type dendrons into methyl methacrylate functionalized dendritic macromonomers. Characterization of the resulting linear-dendritic architectural copolymers involved DSC, x-ray diffraction, and thermal optical polarized microscopy. It was concluded that the self-assembly of the pendant dendritic mesogens forced the linear backbone into a tilted, helical ribbon-type structure. The self-assembly behavior was largely controlled by the multiplicity, composition, and molecular weights of the pendant dendritic mesogens. 

The imidization process, either thermally or chemically induced, may be followed by a variety of means. It has been traditionally studied on poly(amic acid)s, as well as with molecular models, by IR and NMR spectroscopy [47,48]. But many other analytical methods have been used, for instance TGA [41,49,50], DSC [42,51], polarizing microscopy [41], gas chromatography [52,53], microdielectrometry [54], or torsional braid analysis [55]. From the numerous contributions on this topic some conclusions can be drawn. Among other features, we remark that a rate reduction of the imidation and the rate constant occurs as the conversion increases, so that it can not be considered as a classical first order reaction. This phenomenon has been explained by considering entropic factors [56]. Since the kinetic data could not be unequivocally assimilated to a determined reaction order, they were interpreted as if the imidization reaetion could be divided into rapid and slow first order cyclization steps. The retardation in... 

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