Controlled depolymerization

An enzyme, acid, or oxidative "breaker" is added to effect a controlled depolymerization and thus a programmed loss of fluid viscosity. This depolymerization is timed to occur when the sandladen fluid is opposite the productive formation. The sand then drops out of suspension and is packed against the formation. The sand creates a high permeability fluid pathway from the formation... 

During anaphase, when the sister chromatids split at the centromere, this balance is lost [Fig. 5-37(/>)J. The dynein motors in the kinetochores drive the sister chromatids to the poles. The speed at which this happens may be regulated by the controlled depolymerization of the kinetochore microtubules. The poles can now move apart and the overlap between polar microtubules shortens. It would be completely lost but for rapid polymerization at the plus ends of these filaments. 

Supercritical water can be used to controllably depolymerize the rubber compounds. Tires decompose into high-molecular-weight olefins (MW 1000-10000), or oils (max. 90%). Roy [9] discussed vacuum pyrolysis at 2nd ISFR. 

Various dermatan sulfate derived di-, tetra-, hexa-, octa-, deca- and dodeca-saccharide mixtures have been prepared and purified (on a semi-preparative scale) by controlled depolymerization of dermatan sulfate using chondroitin ABC lyase, The pathways of InsPe hydrolysis by phytase from wheat bran of Triticum aestivum have recently been established. ... 

Controlled depolymerization (as in pyrolysis) renders selectively pure monomers. In the case of PMMA (acrylics) it is successfully commercialized, and the yield is quite high. The pure monomer may replace virgin raw material. PET is also prone to depolymerization (via hydrolysis) as are other polycondensation resins, such as polyamides (Nylon) and even polyurethanes. 

Low molecular weight branched alkanes and monocyclic alkanes in petroleum can be explained by the thermally-controlled depolymerization (named catagenesis) of the sedimentary kerogen. Hence, we will expect the thermodynamically stable isomers to dominate. Analyses of single alkanes and cycloalkanes by MS were discussed in Section III.A.2, but the complex mixtures have to be examined by GC/MS utilizing the computerized treatment of the data . 

Supercritical water and carbon dioxide have been used for controlled depolymerization of natural rubber and automotive tires at 380 and 276 bar. It is shown that the extent of... 

Each of the process steps is free of organic solvent water is used in the fermentation while molten lactide and polymer serve as the reaction media in monomer and pofymer production. The essential novelty of the process lies in the ability to go from lactic acid to a low molecular weight potylactic acid, followed by controlled depolymerization to produce the cyclic... 

The technology to produce PLA economically on a commercial scale has been intensively developed in the last two decades. For the conversion of lactic acid to high-molecular PLA Cargill-Dow uses a solvent free process and a novel distillation process to produce a range of polymers [305]. In this process lactic acid is converted in to a low molecular weight poly (lactic acid) that is then converted in the cyclic dimer, lactide, by controlled depolymerization. 

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