Mechanism and kinetics of step-growth polymerization

Mechanism and Kinetics of Step-Growth Polymerization and, the molecular weight distribution is ... 

Kinetic considerations are of paramount importance in understanding the mechanism of step-growth polymerization. As stated in Chapter 1, chain-growth polymerizations take place in discrete steps. Each step is a reaction between two functional groups for instance, in a polyesterification reaction it is a reaction between -COOH and -OH. The increase in molecular weight is slow. The first step is a condensation between two monomers to form a dimer ... 

Abstract Polymers are macromolecules derived by the combination of one or more chemical units (monomers) that repeat themselves along the molecule. The lUPAC Gold Book defines a polymer as A molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. Several ways of classification can be adopted depending on their source (natural and synthetic), their structure (linear, branched and crosslinked), the polymerization mechanism (step-growth and chain polymers) and molecular forces (Elastomers, fibres, thermoplastic and thermosetting polymers). In this chapter, the molecular mechanisms and kinetic of polymer formation reactions were explored and particular attention was devoted to the main polymerization techniques. Finally, an overview of the most employed synthetic materials in biomedical field is performed. 

If the mechanism of termination is disproportionation then the degree of polymerization is the same as the kinetic chain length. The initial reaction between the radical and the first monomer molecule is fast and so only subsequent additions need be considered. The molecule M, has been formed by (/ - 1) addition reactions. The probability that one of these reactions has taken place is a and so using the analogy of step-growth polymerization the probability that (/ - 1) successive addition reactions have taken place is The probability that the last reaction is... 

To a different extent, the theory of step-growth polymerization was also applied to interpret the kinetics and the mechanism of OA of NPs, in which NPs with common... 

Step-growth polymerizations have widely been developed in industrial applications whereas knowledge of their mechanisms and of their kinetics has remained far below that of chain polymerization reactions. 

Chain-growth polymerizations are so called because their mechanisms comprise chains of kinetic events. For successful polymerization, the sequence of reactions must first be initiated by some agent, and monomers must be added consecutively to a growing macromolecule. This chain of events may then be terminated by a reaction that is inherent in the system or by the action of impurities. In any case, we can usefully distinguish between at least three different reaction types in a kinetic polymerization chain. These are initiation, propagation, and termination reactions. (Recall that theie is only one reaction involved in step-growth polymerizations where the monomers add to the end of a macromolecule without the intervention of an active center.)... 

There are some fundamental differences in the engineering of step-growth and chain-growth polymerizations because of basic distinctions in the mechanisms of these reactions. A propagation reaction (Section 6.3.2) in a kinetic chain sequence must be fast or the series of monomer additions will not be long enough to produce... 

The way in which a plasma polymer is formed has been explained by the rapid step growth polymerization mechanism, which is depicted in Figure 5.3. The essential elementary reactions are stepwise recombination of reactive species (free radicals) and stepwise addition of or intrusion via hydrogen abstraction by impinging free radicals. It is important to recognize that these elementary reactions are essentially oligomerization reactions, which do not form polymers by themselves on each cycle. In order to form a polymeric deposition, a certain number of steps (cycle) must be repeated in gas phase and more importantly at the surface. The number of steps is collectively termed the kinetic pathlength. 

M. F. Dmmm and J. R. LeBlanc, in Kinetics and Mechanisms of Polymerization Step Growth Polymerizations (Ed. D. H. Solomon), Marcel Dekker, New York, 1972. 

New York Solomon DH (1969) Kinetics and mechanisms of polymerization series, vol 2 — Ring opening and vol 3 — step growth. Marcel Dekker, New York). For a steady-state chain polymerization reaction, Rp is defined by the following equation... 

Phase-transfer catalysis (PTC) has been recently applied to the preparation of polyethers by polycondensation 1 1. This method offers several advantages over solution conducted nucleophilic displacement step-growth polymerizations. These include the substitution of inexpensive solvents for anhydrous aprotic solvents such as DMSO, DMAC etc. .., lower reaction temperatures and shorter reaction times. We wish to report our results concerning the preparation of polyethers from bisphenol A (BPA) and 1,4-dichloro-2-butene (DCB) under PTC conditions. The kinetics and the mechanism of this new type of polycondensation are described. 

Jones DC, White TR (1972) Step-growth polymerizations. In Salomon DH (ed) Kinetics and mechanisms of polymerizations. Marcel Dekker, New York, vol. 3, p. 41... 

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