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Inpolymer chemistry,condensation polymers are any kind ofpolymers whose process ofpolymerization involves acondensation reaction (i.e. a small molecule, such aswater ormethanol, is produced as a byproduct). Naturalproteins as well as some common plastics such asnylon andPETE are formed in this way. Condensation polymers are formed by polycondensation, when the polymer is formed by condensation reactions between species of alldegrees of polymerization, or by condensativechain polymerization, when the polymer is formed by sequential addition of monomers to anactive site in achain reaction. The main alternative forms of polymerization are chain polymerization andpolyaddition, both of which giveaddition polymers.
Polycondensation:a polymerization in which the growth of polymer chains proceeds by condensation reactions between molecules of all degrees of polymerization.Notes:
- The growth steps are expressed by:
- Px + Py → Px+y + L (x,y = 1, 2, …)
- wherePx andPy denote chains of degrees of polymerizationx andy, respectively, and L a low-molar-mass by-product.
- The earlier term 'polycondensation' was synonymous with 'condensation polymerization'. The current definitions of polycondensation and condensative chain polymerization were both embraced by the earlier term 'polycondensation'.[1]
Condensation polymerization is a form ofstep-growth polymerization. Linear polymers are produced frombifunctional monomers, i.e. compounds with two reactiveend-groups. Common condensation polymers includepolyesters,polyamides such asnylon,polyacetals, andproteins.[2][3]
One important class of condensation polymers arepolyamides.[4] They arise from the reaction ofcarboxylic acid and an amine. Examples includenylons andproteins. When prepared from amino-carboxylic acids, e.g. amino acids, the stoichiometry of the polymerization includes co-formation of water:
When prepared fromdiamines anddicarboxylic acids, e.g. the production ofnylon 66, the polymerization produces two molecules of water per repeat unit:
Another important class of condensation polymers arepolyesters.[5] They arise from the reaction of acarboxylic acid and an alcohol. An example ispolyethyleneterephthalate, the common plastic PET (recycling #1 in the USA):
-3-hydroxybutyrat.svg)
Condensation polymers tend to be more biodegradable thanaddition polymers. The peptide or ester bonds between monomers can be hydrolysed, especially in the presence of catalysts or bacterialenzymes.[6]
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