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, …)
where Px and Py denote chains of degrees of polymerization x and y, 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]
One important class of condensation polymers are polyamides.[4] They arise from the reaction of carboxylic acid and an amine. Examples include nylons and proteins. When prepared from amino-carboxylic acids, e.g. amino acids, the stoichiometry of the polymerization includes co-formation of water:
n H2N-X-CO2H → [HN-X-C(O)]n + (n-1) H2O
When prepared from diamines and dicarboxylic acids, e.g. the production of nylon 66, the polymerization produces two molecules of water per repeat unit:
n H2N-X-NH2 + n HO2C-Y-CO2H → [HN-X-NHC(O)-Y-C(O)]n + (2n-1) H2O
Another important class of condensation polymers are polyesters.[5] They arise from the reaction of a carboxylic acid and an alcohol. An example is polyethyleneterephthalate, the common plastic PET (recycling #1 in the USA):
n HO-X-OH + n HO2C-Y-CO2H → [O-X-O2C-Y-C(O)]n + (2n-1) H2O
Condensation polymers tend to be more biodegradable than addition polymers. The peptide or ester bonds between monomers can be hydrolysed, especially in the presence of catalysts or bacterial enzymes.[6]
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