Condensation polymer

Polyethylene terephthalate(PET) is a common condensation polymer.

Inpolymer chemistry,condensation polymersare any kind ofpolymerswhose process ofpolymerizationinvolves acondensation reaction(i.e. a small molecule, such aswaterormethanol,is produced as a byproduct). Naturalproteinsas well as some common plastics such asnylonandPETEare 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 sitein achain reaction.The main alternative forms of polymerization are chain polymerization andpolyaddition,both of which giveaddition polymers.

IUPACdefinition

Polycondensation A polymerization in which the growth of polymer chains proceeds by condensation reactions between molecules of all degrees of polymerization. Notes: 1. The growth steps are expressed by: P_x+P_y→P_x+y+L {x}∈{1,2,…∞};{y}∈{1,2,…∞}

where P_xand P_ydenote chains of degrees of polymerization x and y, respectively, and L a low-molar-mass by-product. 2. 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'.

Condensation polymerization is a form ofstep-growth polymerization.Linear polymers are produced frombifunctionalmonomers, i.e. compounds with two reactiveend-groups.Common condensation polymers includepolyesters,polyamidessuch asnylon,polyacetals,andproteins.

Polyamides

One important class of condensation polymers arepolyamides.They arise from the reaction ofcarboxylic acidand an amine. Examples includenylonsandproteins.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 fromdiaminesanddicarboxylic acids,e.g. the production ofnylon 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

General chemical structure of one type of condensation polymer

Polyesters

Another important class of condensation polymers arepolyesters.They arise from the reaction of acarboxylic acidand an alcohol. An example ispolyethyleneterephthalate,the common plastic PETE (recycling #1 in the USA):

n HO-X-OH + n HO₂C-Y-CO₂H → [O-X-O₂C-Y-C(O)]_n+ (2n-1) H₂O

Structure ofpoly-(R)-3-hydroxybutyrate (P3HB),a naturally-occurring polymer.

Safety and environmental considerations

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.

See also

• Biopolymer
• Epoxy resins
• Polyamide
• Polyester

External links

• Polymers (and condensation polymers) - Virtual Text of Organic Chemistry, William Reusch