Polycondensation is the process of synthesizing polymers from polyfunctional (most often bifunctional) compounds, usually accompanied by the release of low molecular weight by-products ( water , alcohols , etc.) during the interaction of functional groups.
The molecular weight of the polymer formed during the polycondensation depends on the ratio of the starting components, the reaction conditions.
Content
Linear and three-dimensional polycondensation
The polycondensation reaction can involve either one monomer with two different functional groups: for example, the synthesis of poly-Ξ΅-caproamide ( nylon- 6, nylon ) from Ξ΅-aminocaproic acid , or two monomers carrying different functional groups, for example, the synthesis of nylon 66 by polycondensation of adipic acid and hexamethylenediamine ; in this case, polymers of linear structure are formed (linear polycondensation, see Fig. 1). If the monomer (or monomers) carry more than two functional groups, cross-linked polymers of a three-dimensional network structure are formed (three-dimensional polycondensation). In order to obtain such polymers, crosslinking polyfunctional components are often added to the monomer mixture.
The reactions of the synthesis of polymers from cyclic monomers by the cycle opening mechanism stand apart - addition, for example, the synthesis of nylon -6 from caprolactam (cyclic amide of Ξ΅-aminocaproic acid); despite the fact that the release of a low molecular weight fragment does not occur, such reactions are more often referred to as polycondensation.
The main industrial groups of polymers synthesized by polycondensation
- Linear polymers
- Polyamides
- Polyurethanes
- Polycarbonates
- Polyesters
- Polysiloxanes
- Cross-linked polymers
- Alkyd resins
- Melamine Aldehyde Resins
- Urea-aldehyde resins
- Phenol-Aldehyde Resins
Polycondensation in the chemistry of natural compounds
Almost all biopolymers ( proteins , DNA and RNA , cellulose , chitin , etc.) are synthesized in living organisms by polycondensation with the participation of the corresponding enzyme complexes.
In some ways, the exception is the biosynthesis of poly isoprenes (including rubber ), which occurs by enzymatic addition of isoprenyl pyrophosphate with allyl rearrangement and cleavage of the pyrophosphate anion . In this case, the monomer carries one functional group, and the mechanism of attachment with allyl rearrangement is close to the mechanism of anionic polymerization in the synthesis of butadiene rubber according to Lebedev . Nevertheless, due to the cleavage of the low molecular weight pyrophosphate fragment, the biosynthesis of polyisoprenes is a polycondensation reaction.
See also
- Polymerization
- Polymers