Polymers microscopy, polarized light

Polarization microscopy Polarized light Areas of spherulites Dedicated polymer structures only T-dependence... 

Polarized light microscopy is the study of the microstructures of objects using their interactions with polarized light [1,2,23-27,31-33]. The method is widely applicable to polymers [34] and to liquid crystals [34-37]. The polarizing micro-... 

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. 

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. 

The characterization of liquid crystals by polarized light microscopy is the most straightforward method available and, whenever possible, it should be carried out in the initial stages of an investigation on new polymers. Thermal analyses alone can be misleading. In this procedure, a thin layer of the melt is kept at constant temperature on a hot-sta and obsawed between crossed polars. The appearance or texture of the melt is dependent on the structure of the mesophase, and, therefore, it is often possible to directly identify the type of mesophase present by this method. A good review of the microscopy of liquid crj b ajqjears in the books by Hartshome and by Demus and Richter... 

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... 

Footnote (f) shows that solid-state polymerized BDft/f>5 BG/35 BD gave similar results, but an additional endotherm was present in the region where the polymer was sufficiently molten to flow. When this polymer was prepared in the melt, however, these softening and melting endotherms were not present because of a broad exotherm in this area [footnote (e) ]. We have been unable to demonstrate by polarizing light microscopy or by x-ray diffraction studies that these copolyesters actually are smectic. (We had the same problems discussed earlier for the BDA/EG/HD copolyesters.)... 

In this paper it has been shown that the polyethers based on the non-rigid rodlike mesogen bis(4-hydroxyphenoxy)-p-xylene and dibromoalkanes exhibit smectic meso-morphism. Furthermore, the molecular mass of the polyethers follows a pronounced odd-even dependence due to differences in solubility of the different polymers during the polymerization. DSC and polarized light microscopy also revealed an odd-even dependence of the temperatures and enthalpy and entropy changes associated with... 

Because the crystallization of polymers from their melts is related to their mi-crostructural properties, such as chain conformations and entanglements [83], the polarized light microscopy results suggests a molecular-level difference between the coalesced and as-received PETs even in their melts. 

Polarized light microscopy has long been used in chemical and mlneraloglcal studies, and was raised to a high level of applicability by Walter McCrone and associates, culminating in the extensive Particle Atlas(6), which included Innumerable glasses, organics and 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. 

Prior to the use of more sophisticated methods, light microscopy should be the first experimental method to observe blend morphology in the micro meter range. The method is particularly useful when the light microscope is equipped with a hot stage. The phase behavior is usually best observed in the phase contrast transmission mode. When crystalline polymers are involved, valuable information is obtained using polarized light [Tanaka and Nishi, 1985 Keith and Padden, 1964]. 

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