Reversibility polymerization reactions

Butadiene and steam (0.5 mole steam/mole butadiene) are fed to a tubular-flow reactor which operates at 1180°F and a constant pressure of 1 atm. The reactor is noncatalytic. Considering only the reversible polymerization reaction to the dimer, determine a) the length of 4-in.-ID reactor required to obtain a conversion of 40% of the butadiene with a total feed rate of 20 lb moles/hr and-(b) the space velocity, measured as (liters feed gas)/(hr)(liters reactor volume) (at 1180°F and 1 atm), required to obtain a conversion of 40%. 

Figure 1.23 In reversible polymerization reactions, the reaction rate might increase with temperature in the usual way (A). Eventually, the depolymerization reaction (B) becomes more important and the propagation rate decreases with increasing temperature (C). The temperature at which the propagation rate becomes zero is called the ceiling temperature T. ...

S. J. Visco et al. proposed a new rechargeable battery system at room temperature by using reversible polymerization reaction of organic sulfur compound in place of inorganic sulfur. As for 2,5-dimercapto 1,3,4-thiadiazole (DMcT) chemical... 

This is an exothermic, reversible, homogeneous reaction taking place in a single liquid phase. The liquid butadiene feed contains 0.5 percent normal butane as an impurity. The sulfur dioxide is essentially pure. The mole ratio of sulfur dioxide to butadiene must be kept above 1 to prevent unwanted polymerization reactions. A value of 1.2 is assumed. The temperature in the process must be kept above 65°C to prevent crystallization of the butadiene sulfone but below lOO C to prevent its decomposition. The product must contain less than 0.5 wt% butadiene and less thM 0.3 wt% sulfur dioxide. 

In addition to solubilization, entrapment of polymers inside reversed micelles can be achieved by performing in situ suitable polymerization reactions. This methodology has some specific peculiarities, such as easy control of the polymerization degree and synthesis of a distinct variety of polymeric structures. The size and shape of polymers could be modulated by the appropriate selection of the reversed micellar system and of synthesis conditions [31,191]. This kind of control of polymerization could model and/or mimic some aspects of that occurring in biological systems. 

The core of reversed micelles can be transformed to a highly viscous domain (nanogel) by entrapping appropriate species, such as viscous solvents and hydrophilic macromolecules, or by performing in situ appropriate polymerization reactions or intramolecular cross-linking of water-soluble polymer chains [232-234]. 

The highlighted section reacts with water in a reverse condensation reaction to give the monomer that polymerizes with glycerol. 

Container molecules are of great interest because their encapsulated guests often exhibit novel and unusual properties, which are not observed in the free or solvated state (8,9). They are used today as probes of isolated molecules and of the intrinsic characteristics of the liquid state, and are capable of enantiose-lective recognition (10), reversible polymerization (11), isolation of reactive species (12-14), and promoting reactions within their interiors (15-18). For a valuable introduction to this area the reader is directed to some excellent review articles (15,19-21). 

For the polymerization, either in the melt or solid phase, the reaction is driven to the polymer by removing ethylene glycol. The polymerization reaction is typically catalyzed by solutions consisting of antimony trioxide or germanium oxide. Both polycondensation catalysts also catalyze the reverse reaction, which is driven by an excess of ethylene glycol at melt conditions, generally above 255 °C. The polymerization reaction follows second-order kinetics with an activation energy of 22 000 cal/mol [6],... 

MICROSCOPIC DIFFUSION CONTROL MACROSCOPIC DIFFUSION CONTROL MICROSCOPIC REVERSIBILITY CHEMICAL REACTION DETAILED BALANCING, RRINCIRLE OF CHEMICAL KINETICS MICROTUBULE ASSEMBLY KINETICS BIOCHEMICAL SELF-ASSEMBLY ACTIN ASSEMBLY KINETICS HEMOGLOBINS POLYMERIZATION... 

ATRP has become the most widely applied CRP technique due to its simple mechanism and commercially available reagents. This technique was first reported in 1995, independently by Sawamoto and Matyjaszewski [28, 29]. The polymerization mechanism is based on the reversible redox reaction between alkyl halides and transition metal complexes. Scheme 1 illustrates the mechanism of normal ATRP. 

Many, if not most, step polymerizations involve equilibrium reactions, and it becomes important to analyze how the equilibrium affects the extent of conversion and, more importantly, the polymer molecular weight. A polymerization in which the monomer(s) and polymer are in equilibrium is referred to as an equilibrium polymerization or reversible polymerization. A first consideration is whether an equilibrium polymerization will yield high-molecular-weight polymer if carried out in a closed system. By a closed system is meant one where none of the products of the forward reaction are removed. Nothing is done to push or drive the equilibrium point for the reaction system toward the polymer side. Under these conditions the concentrations of products (polymer and usually a small molecule such as water) build up until the rate of the reverse reaction becomes equal to the polymerization rate. The reverse reaction is referred to generally as a depolymerization reaction other terms such as hydrolysis or glycolysis may be used as applicable in specific systems. The polymer molecular weight is determined by the extent to which the forward reaction has proceeded when equilibrium is established. 

Consider the reversible condensation polymerization reaction of a hydroxyacid A to form a polyester polymer,... 

Reversible redox reactions can initiate radical chemistry without a follow-up reduction or oxidation reaction. In successful reactions of this type, the redox step that produces the radical is thermodynamically disfavored. For example, Cu(I) complexes react reversibly with alkyl hahdes to give Cu(II) hahde complexes and an alkyl radical. The alkyl radical can react in, for example, an addition reaction, and the product radical will react with the Cu(II) hahde to give a new alkyl halide. This type of reaction sequence, which has been apphed in living radical polymerizations, is in the general family of nonchain radical reactions discussed earlier. ... 

Consider a long, thin mold being fed at constant temperatme with two bifunctional monomers, AA and BB. The feed has a molecular weight of Mq, and the polymerization reaction, which is assumed to be reversible, proceeds by the reaction of A and B functional groups in an idealized step polymerization reaction (cf. Section 3.3.1.1) ... 

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