Hot stage

Melting temperatures of as-polymerized powders are high, ie, 198—205°C as measured by differential thermal analysis (dta) or hot-stage microscopy (76). Two peaks are usually observed in dta curves a small lower temperature peak and the main melting peak. The small peak seems to be related to polymer crystallized by precipitation rather than during polymerization. 

The melting point of adipyl hydrazide reported in the literature is 171° however, values as high as 179° have been observed. The checkers observed values of 174-177° and 179-181° for products of two runs, when the crystals were placed on a hot stage alter the temperature had reached 160°. 

Differential scanning calorimetry Differential thermal analysis Hot stage microscope... 

The DTA or hot-stage microscope can be used under ignition conditions to obtain an ignition temperature. The nature of the decomposition can also be observed at a range of temperatures. Observations such as decomposition with evolution of gases prior to ignition are regarded as potentially hazardous. 

McCrone of ARF, consists of following the behavior of crysts of the compd on a hot stage microscope at temps close to the mp. The most stable samples of MEDINA were found to be those recrystd from et chloride/iso-Pr ale the least were prepd by vacuum evapn (Ref 11, p 30)... 

Melting Point, Determination. Most methods for the detn of mp are microprocedures, and may be conveniently classified on the basis of the type of app used for the detn (1) the capillary tube method. (2) the heating bar method, and (3) the microscope heating stage (micro hot stage) method. 

For more precise work, micro hot stage methods under a microscope are used. For all compds, except those which are isotropic or become so on heating, the mp can best be observed by means of a polarizing microscope, since the temp at which color disappears arid the space lattice is ruptured is the true mp. Among numerous models of micro-hot stages, the Kofler micro-hot stage has attained widespread use and is commercially available (Refs 3 4)... 

More recently the thermal decompn of single large ciysts of AP has been studied on a hot-stage microscope. It was found that the low temp decompn started on a cryst face as a dark spot which rapidly expanded into a hole which then spread thruout the cryst. The ciysts were not consumed, but a residue of finely powd AP was always left (Ref 45)... 

If the phases present can be unambiguously identified, microscopy can be used to determine the geometry of interface initiation and advance, and to provide information about particle sizes of components of mixed reactants in a powder. Problems of interpretation arise where materials are poorly crystallized and where crystallites are small, opaque, porous or form solid solutions. With the hot-stage microscope, the progress of reactions can be followed in some instances and the occurrence of sintering and/or melting detected. 

Characterization439 Inherent viscosity before and after solid-sate polymerization is 0.46 and 3.20 dL/g, respectively (0.5 g/dL in pentafluorophenol at 25°C). DSC Tg = 135°C, Tm = 317°C. A copolyester of similar composition440 exhibited a liquid crystalline behavior with crystal-nematic and nematic-isotropic transition temperatures at 307 and 410°C, respectively (measured by DSC and hot-stage polarizing microscopy). The high-resolution solid-state 13C NMR study of a copolyester with a composition corresponding to z2/zi = 1-35 has been reported.441... 

The melting point was taken on a Reichert hot stage microscope. This instrument is available from William J. Hacker and Company, Inc., P.O. Box 646, West Caldwell, New Jersey 07006. 

One further approach, which has not properly been explored, is based upon the axiom of Harbottle s (29) that if an isotopic difference is found, there must have been little reaction subsequent to the initial hot stage. That is, these subsequent reactions are expected to be normal chemical reactions with essentially no isotopic preference, such that any such reaction would tend to wash out possible isotope effects. This problem is worth pursuing further, since some isotopic effects have been observed where subsequent exchange is to be expected. 

In the case of optical observation of FCCs, film samples were put in a hot stage (Linkam, LK-600). Temperature was calibrated using standard materials. In and Sn Nitrogen gas was used at the rate of 50 ml/min. The number of isolated crystals near the center of the sample was counted. 

Since it was known that theophylline monohydrate can be thermally dehydrated to form either the stable Form I or the metastable Form I, the effect of different drying methods on the phase composition was studied [89], Using either a multichamber microscale fluid bed dryer or the hot stage of a variable-temperature XRPD diffractometer, Form I was produced when the drying was conducted at 40-50°C. Drying at 60°C in the VT-XRPD unit yielded only Form I, while mixtures of products were produced in the microscale fluid bed dryer even at temperatures as high as 90 °C. 

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