What is step reaction polymerization

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Step reactions - introduction

Polymerization reactions with step growth - hereinafter referred to as step reactions - differ significantly from the polymerization reactions with chain growth, as they play a role in free-radical and ionic polymerization.

Step reactions
In step reactions, molecules react with one another that have at least two functional groups. A distinction is made between reactions of monomers same Type (AB type) with two different functional groups and reactions of two different Monomer types (AA // BB type) each having the same Function.
Tab. 1
Examples
Monomer type Formula representationType
α-amino acid 2 x R-CHNH2-COOHFROM
Dicarboxylic acid and diamineHOOC-R-COOH + H2N-R'-NH2AA // BB

In step reactions, two monomers react with each other in the first step, forming dimers which - like the monomers - have the ability to react further. Activation is required for each individual linking step. Two growing chains can also react with one another without breaking off, as is the case with the radical chain reaction. The probability that two molecules will react is independent of their degree of polymerization. Chains of different lengths are also linked to one another. As the conversion progresses, molecules with ever higher molar masses are formed.