Chronomer

The required acid sensitivity can be achieved by preparing polymers with ortho ester linkages in their backbone. The first poly-(ortho ester) has been described in a series of patents by Choi and Heller (3-6), assigned to the ALZA corporation. These proprietary materials were first designated with the trade name Chronomer and later Alzamer. They are prepared by a transesterification as follows ... 

A reference frame that, while resisting unambiguous definition, serves to measure the progress/motion of chemical/physical processes. The SI unit for time is the second (symbohzed as s). See Time Chronomals... 

A chronomal is a dimensionless parameter [symbohzed by I or /(a)] that is proportional to time. Chronomals are especially useful in deahng with diffusion, chemical reactions, and other related processes. One can chose to express the properties of such systems as t equal to Kb Ib, where Kb contains all the physical constants and has overall units of time, whereas Ib is a chronomal expressed in terms of the extent of reaction C In many respects, the chronomal can be regarded as dimensionless time. 

Symbol for extent or advancement (or extent of reaction) of a chemical reaction. is the symbol for rate of conversion in which = d SI unit is mol s See Extent of Reaction Time Chronomals... 

TIME CHRONOMALS TIME-CORRELATED SINGLE PHOTON COUNTING... 

Fig. 1.2.4 Chronomal plots for particle growth as a function of reaction time. (From Ref. 25. Courtesy of M. Mecklenborg, The American Ceramic Society Inc., Westerville, Ohio.)...

Monodisperse spherical oxide particles were prepared by the hydrolysis of metal alkoxide in homogeneous alcohol in an emulsion state. The formation mechanism from homogeneous alcohol and emulsion state was discussed by chronomal analysis and in situ observation using laser photo scattering. Two types of continuous systems for the industrial production of monodispersed oxide powders were also offered. 

Monodisperse oxide particles were only formed at the narrow concentration range in alcohol solution. Monodisperse particles, which have submi-crometer order with narrow size distribution, were amorphous and hydrated. The spherical morphology was retained after the crystallization. The rate-determining step of particle growth was polynuclear layer growth of first order from Nielsen s chronomal analysis. 

The reaction finished within 1 h at 26°C.. They used seed crystals of CdS to promote the uniformity of the final product, and analyzed the growth kinetics using Nielsen s chronomal. The isoelectric point in terms of pH was determined to be 3.7 by electrokinetic measurement. They also prepared zinc sulfide (ZnS polycrystalline spheres), whose isoelectric point in pH was 3.0 (2), lead sulfide (PbS monocrystalline cubic galena) (3), cadmium zinc sulfide (CdS/ZnS amorphous and crystalline spheres) (3), and cadmium lead sulfide (CdS/PbS crystalline polyhedra) (3), in a similar manner. 

After the choice of the constants has been made, e.g., by regression analysis, it is absolutely necessary either to draw a large-scale diagram of the relation between the real times and those shown by the clock or better to prepare a table containing the real times and those calculated by means of the chronomal. By this procedure any systematic deviations can at once be detected. If the constants have been found by regression analysis and systematic deviations still exist, this means that the mechanism of the clock is incorrect, i.e., that the functions /< have been incorrectly chosen. 

This equation assumes that all the nuclei are the same size, R. The equation gives an expression for the increase in particle size with time for various growth rate mechanisms. This expression is similar to that used by Nielsen [2] in his chronomal analysis. The only difference is that chronomal analysis uses the fiaction precipitated, cAf), as a variable instead of the mean particle size, R(f). The fraction precipitated is defined as... 

Cornehsson G. Broadly pertinent chronobiology methods quantify phosphate dynamics (chronome) in blood and urine. Clin Chem 1992 38 329-33. 

Halberg F, Cornelissen G, Wilson D et al (2009) Chronobiology and chronomics detecting and applying the cycles of nature. Biologist (London) 56 209-214... 

Although the Alza poly(ortho ester) system has never been structurally identified other than by its tradename Chronomer, and later Alzamer, several publications provide a general description of the use of the polymer for the release of naltrexone (46) and contraceptive steroids (47. 48, 49). 

A Cancer Survivor s Almanac Charting Your Journey, edited by Barbara Hoffman, with an introduction by Fitzhugh MuUin. 1996. Minneapolis, MN National Coalition for Cancer Survivorship, Chronomed Pub. 

This poly (ortho ester) was originally denoted by the Alza Corporation as Chronomer and is currently known as Alzamer. Its use has been described in a number of publications. Unfortunately, these do not identify the material beyond the code names of Cl 11 and ClOlct. However, it can be inferred that ClOlct refers to a polymer prepared from diethoxytetrahydrofuran and cis/ fr /K-cyclohexanedimethanol and Cl 11 refers to a polymer prepared from diethoxytetrahydrofuran and 1,6-hexanediol. 

The work of Schoeman et al. [22] demonstrated this conclusion more convincingly by use of a chronomal analysis of the conversion with respect to time, a technique suggested previously by Nielsen [62]. In such an analysis, the linear growth rate of the population of crystals is hypothesized to depend on certain driving forces, and the time dependence of the crystal size function is then derived for the circumstance when new crystal nucleation does not occur, as was observed in these experiments. For example, if diffusional transport from the bulk fluid phase to the surface of uniformly sized spherical particles is assumed to be rate limiting, then the change of the particle radius is given by the solution of ... 

Fig. 8. Results of the chronomal analysis for silicalite crystal growth limitation by diffusion or first, second, or third order surface reaction. The limiting step is suggested by the linear relation over time, i.e., the first order surface reaction step. Reprinted by permission of the publisher from Analysis of the crystal growth mechanism of TPA-silicalite-l by BJ Schoeman, J Sterte, and J-E Otterstedt, Zeolites, 14,568, copyright 1994 by Elsevier Science Inc.

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