Low molar mass material

Separation of heat-sensitive materials. High molar mass material is often heat sensitive and will decompose if distilled at high temperature. Low molar mass material can also be heat sensitive, particularly when its nature is highly reactive. Such material will normally be distilled under vacuum to reduce the boiling temperature. Crystallization and liquid-liquid extraction can be used as alternatives to the separation of high molar mass heat-sensitive materials. 

In summary, distillation is not well suited for separating either low molar mass materials or high molar mass heat-sensitive materials. However, distillation might still be the best method for these cases, since the basic advantages of distillation (potential for high throughput, any feed concentration and high purity) still prevail. 

The most common alternative to distillation for the separation of low molar mass materials is absorption. In absorption, a gas mixture is contacted with a liquid solvent that preferentially dissolves one or more components of the gas. Absorption processes often require an extraneous material to be introduced into the process to act as liquid solvent. If it is possible to use one of the materials already in the process, this should be done in preference to introducing an extraneous material. Liquid flowrate, temperature and pressure are important variables to be set. 

The most common alternative to distillation for the separation of low molar mass materials is absorption. Liquid flowrate, temperature and pressure are important variables to be set, but no attempt should be made to carry out any optimization in the early stages of a design. 

Delaunay-Bertoncini, N., van der Wielen, F. W. M., De Voogt, P., Erlandsson, B., and Schoenmakers, P. J. (2004), Analysis of low-molar-mass materials in commercial rubber samples by Soxhlet and headspace extractions followed by GC-MS analysis, /. Pharm. Biomed. Anal, 35,1059-1073. 

At low temperatures, partial co-crystallisation was indicated by transmission electron microscopy and differential scanning calorimetry [156, 157]. Both electron microscopy of stained sections and optical microscopy showed that the segregated low molar mass material was present as small domains between the stacks of dominant lamellae within the spherulites/ax-ialites [115, 157, 158],... 

Organic Light-Emitting Diodes Using Low-Molar-Mass Materials (LMMMs)... 

The configuration and construction of monolayer and multilayer OLEDs have undergone substantial changes and modifications since these first reports of organic electroluminescence from low-molar-mass materials. Several types of OLEDs using small organic and organometallic molecules are described schematically below. 

Figure 5.1 Schematic representation of a monolayer OLED using low-molar-mass materials incorporating an electroluminescent material between a transparent anode and a cathode.

Organic Light-Emitting Diodes Using Low-Molar-Mass Materials (LMMMs) 161 Table 5.5 Transition temperatures CC) for the columnar liquid crystals (17-21)... 

Fine tuning of material properties therefore can be achieved by using mixtures of mesogens attached to the periphery of the scaffold. In addition, the disordering induced can substantially lower melting points and widen temperature ranges of desirable liquid crystal phases. Furthermore, such materials are miscible with low-molar-mass materials, and can be used to modify their physical properties. 

Fig. 11 A,B. Scheme of mobilities in smectic layer structures of A a low molar mass material having alkyl substituents B a LC-main chain polymer...

For example, McCormick and coworkers [173] have dispersed pyrene in block copolymers of AMPS and 3-(acrylamido)-3-methylbutanoate (AMBA). The pH response of the system was investigated by using the sensitivity of the fluorescence spectrum of the probe to the polarity of the medium. Figure 2.12a shows an example of the spectra at two pH extremes the decrease in the intensity of band 1 from pH 9.0 to 1.0 is indicative of pyrene, which resides in a more hydrophobic environment and is consistent with the formation of micelles under acidic conditions. Figure 2.12b shows a plot of the resultant /1 to /3 ratio across the pH range. A dramatic decrease in the ratio is observed between pH 5.0 and 6.0. This supports NMR data, which indicates that dehydration of the PAMBA block occurs at pH 5.5, which serves to create near monodisperse micelles, which can solubilize low molar mass material. 

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