Condensation improved analysis

We report here the results of our recent studies of poly(alkyl/arylphosphazenes) with particular emphasis on the following areas (1) the overall scope of, and recent improvements in, the condensation polymerization method (2) the characterization of a representative series of these polymers by dilute solution techniques (viscosity, membrane osmometry, light scattering, and size exclusion chromatography), thermal analysis (TGA and DSC), NMR spectroscopy, and X-ray diffraction (3) the preparation and preliminary thermolysis reactions of new, functionalized phosphoranimine monomers and (4) the mechanism of the polymerization reaction. 

Since the labeling technique was introduced, a large number of further publications on the paper chromatography of phosphates have appeared (159), but these papers will not be considered separately here. They serve to confirm what was already partly known, and they describe improvements in technique, thereby reducing the risk of hydrolysis of the condensed phosphates in the acid medium used in chromatography. They also show how the accuracy of quantitative analysis could be increased (226). 

The matrix isolation procedure relies on the condensation of H20 and C02 on a liquid-nitrogen-cooled cold finger to form a stable matrix for radicals and other atmospheric species (Figure 9). Typically about 20 L of air are required to achieve the desired sensitivity for ambient measurements. A matrix of deuterated water (D20) narrowed the EPR line widths and improved the signal-to-noise ratio, and thus this matrix has been used for measurements since October 1982. Recent improvements in the use of this matrix isolation-EPR technique have been in the analysis of the spectra. 

A portion (30.5 g) of the residue collected above was subjected to fractional distillation under reduced pressure (0.1-0.15 mm/Hg). The temperature was slowly raised to 125°C and the materials collected were kept separate. The temperature was then raised between 140°-160°C where the major fraction was collected (14 g). GC analysis showed >96% THC. Further purification on a silica gel column gives THC with at least 98% purity. An improvement of this process includes the use of high pressure liquid chromatography (HPLC). The preparation of dronabinol and related compounds have employed acid-catalyzed electrophilic condensation of a 5-alkylresorcinol such as 5-n-pentylresorcinol (commonly known as olivetol) and a menthadienol, followed by cyclization yield of desired product is about 17-22% (Petrzilka et al., Helv. Chim. Acta, 52, 1102 (1969)). 

We turn now to the question of validity of the Kelvin equation. Although the thermodynamic basis of the Kelvin equation is well established (Defay and Prigogine 1966), its reliability for pore size analysis is questionable. In this context, there are three related questions (1) What is the exact relation between the meniscus curvature and the pore size and shape (2) Is the Kelvin equation applicable in the range of narrow mesopores (say >vp < 5 nm) (3) Does the surface tension vary with pore width The answers to these questions are still elusive, but recent theoretical work has improved our understanding of mesopore filling and the nature of the condensate. 

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