Step-Growth Polymerization

Step-Growth Polymerization. Step-growth polymerization is characterized by the fact that chains always maintain their terminal reactivity and continue to react together to form longer chains as the reaction proceeds, i.e., x — mer + y — mer (x + y)-mer. Because there are reactions that follow this mechanism but do not produce a molecule of condensation, the terms step-growth and polycondensation are not exactly synonymous. 

A Comparison of Step-Growth and Chain-Growth Polymerizations Step-Growth Chain-Growth... 

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. 

Three broad types of polymerization processes are generally recognized chain-addition polymerization, step-growth polymerization, and coordination polymerization. 

Furan, Furfural, Hydroxymethylfurfural, Furan polymers. Chain polymerizations. Step-growth polymerizations, Furan polyesters, Furan polyamides, Furan polyurethanes, Furan-containing conjugated oligomers, Diels-Alder reaction, Dendrimers, Reversible crosslinking... 

Polymerizations in which chain growth occurs in a stepwise manner are called step owth or condensation polymerizations. Step-growth polymers are formed by reaction between difunctional molecules, with each new bond created in a separate step. During polymerization, monomers react to form dimers, dimers react with monomers to form trimers, dimers react with dimers to form tetramers, and so on. 

Nevertheless, conductive polymers have also been synthesized using other techniques, such as chain polymerization, step-growth polymerization, chanical vapor deposition, solid-state polymerization, soluble-precursor polymer preparation, and concentrated anulsion polymerization, to name just a few. Most of these techniques, however, are time consuming and involve the use of costly chemicals. 

Chain-growth polymerization Step-growth polymerization ... 

Several polymer types and classes are known to exhibit photoconductivity. Consequently no preferred method of synthesis exists. The known photoconductive polymers are prepared by almost all common methods like free-radical, cationic, anionic, coordination, and ring-opening polymerization, step-growth polymerization, and polymeranalo-gous reactions. The only common requirement for all photoconductive materials is that they have to be of extreme purity. It is well known [40-42] that even traces of impurities act as traps and have drastic influence on both quantum yield and carrier mobility. 

There are several approaches to the synthesis of heterochain PCSs, which can be divided into three large groups chain ring opening and vinyl polymerizations, step-growth reactions (polymerization and polycondensation), and polymer-analogous transformations. 

Synthetic polymers used to form fibers are often classified on the basis of their mechanism of polymerization--step growth (condensation) or chain growth (addition) polymerization. Step growth polymerization involves multifunctional monomers which undergo successive condensation with a second monomer or with itself to form a dimer, which in turn condenses with another dimer to form a tetramer, etc., usually with loss of a small molecule such as water. Chain growth involves the instantaneous growth of a long molecular chain from unsaturated monomer units, followed by initiation of a second chain, etc. The two methods are outl ined below schematically ... 

Photochemical polycondensations I Photoinduced addition polymerizations (step-growth polymerizations) I (active center polymerizations)... 

Synthetic polymers can be derived either from the chemical modification of existing ones or through polymerization of simple molecules (called monomers). Such conversions of monomers into polymers can be obtained either through the basic condensation/addition reactions of organic chemistry or via chain reactions whose requirements and kinetic treatment are quite different. It leads to two categories of polymerization step-growth polymerization and chain polymerization, which will be presented in this chapter and Chapter 8, respectively. 

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