Depolymerization Deposits

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

A breaker an enzyme (at T<140°F), strong oxidizing agent, or an acid, is used to depolymerize polysaccharides and break crosslinks such that viscosity declines at a controlled rate so that the proppant may be deposited in the fracture. Too rapid proppant dropout would cause a premature "sand-out" which prevents future extension of the fracture. Peroxydisulfates are the most frequently used breakers. Less reactive organic peroxides may be preferred for high temperature formations (85). 

If polymerization is carried out under conditions of high nucleation, polymer chains are deposited rapidly and indiscriminately and the active sites necessary for growth are occluded. If growth is carried out near the equilibrium concentration, depolymerization becomes important and again the active sites become occluded. 

In a sense, it is unfortunate that discussions of the chemical degradation of VI improvers combine thermal and oxidative effects since the two processes are quite different. A simple thermal process is one which can take place in the absence of oxygen and would include processes such as the random thermal scission of a polymer backbone, which may be followed by depolymerization. Another possibility for PMAs or SPEs is pyrolysis of the ester side chains to form olefin and acid. The acid, in turn, can react with an adjacent ester to form a cyclic anhydride with elimination of alcohol. Adjacent acid groups can eliminate water to make an anhydride [74], There is no evidence that depolymerization and ester pyrolysis are issues in the engine oil itself, but they may be a factor if the VI improver is trapped in deposits. 

N-acetyl-P-D-glucosaminidase, which catalyze the total depolymerization to monomers. The monomeric aminosugars become available to the fibroblasts, which proliferate under the action of lL-1, for incorporation into chondroitin 4- and 6-sulfate, hyaluronan, and keratan sulfate, thus guiding the ordered deposition of collagen, which is also influenced by chito-oligomers. 

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