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Polymerization
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Polymerization is a necessary process. Only through this forming of larger molecules could the human brain exist. In actuality, nothing at all could exist without polymerization, for without a brain to experience life and define its processes, there would be no reason to exist.
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R[I]ng Opening Metathesis Polymerization (ROMP), a term coined by CalTech chemist Robert Grubbs, is a variant of the olefin metathesis reaction. The reaction uses strained cyclic olefins to produce stereoregular and monodisperse polymers and co-polymers.
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Polymerization reactions are controlled by a number of closely related factors, such as the mechanism, thermodynamics and kinetics of the process. In a polymerization, these parameters vary as monomer is depleted and polymer formed, resulting in process conditions strongly dependent on time.
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Polymerization contraction stress of dental composites is often associated with marginal and interfacial failures of bonded restorations. The magnitude of stress depends on composite composition (filler content and matrix composition) and its ability to flow before gelation, which is related to the cavity configuration and curing characteristics of the composite. This article reviews variations among studies regarding contraction-stress-testing methods and contraction stress values of current composites, and discusses the validity of contraction stress studies in relation to results from microleakage tests. The effects of lower curing rates and alternative curing routines on contraction stress values are ... discussed, as well as the use of low-elastic-modulus liners. Moreover, studies with experimental dimethacrylate-based composites and recent developments in low-shrinkage monomers are described.
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Polymerization is used in the petroleum industry to indicate the production of gasoline components, hence the term "polymer" gasoline. Furthermore, it is not essential that only one type of monomer be involved. If unlike olefin molecules are combined, the process is referred to as "copolymerization." Polymerization in the true sense of the word is normally prevented, and all attempts are made to terminate the reaction at the dimer or trimer (three monomers joined together) stage. However, in the petrochemical section of a refinery, polymerization, which results in the production of, for instance, polyethylene, is allowed to proceed until materials of the required high molecular weight have been produced.
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Additional components such as PMMA-powder and a regulator allow for a controlled polymerization by temperatures between -8 and -20°C, which guarantee a dispersion of the heat generated during polymerization. The polymerization time is between 18 and 24 hours using a volume between 3 and 15 ml for the above temperature range. After necessary pre-treatment of the tissue, all current staining methods can be applied to the MMA sections after removal of the polymer. These include classical staining as well as immuno- and enzyme-histochemistry. In-situ hybridization (ISH) techniques can ... be performed.
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