Formation and Hydrolysis of Condensation Polymers
Condensation polymers
Condensation polymers are created when monomers with two reactive functional groups join together, releasing a small molecule such as water or hydrogen chloride (HCl).
This contrasts with addition polymerization, where no by-product is formed.
How Does Condensation Polymerization Work?
- In a condensation reaction, two monomers react to form a covalent bond, creating a polymer chain.
- Each monomer must have at least two functional groups to allow for chain growth.
- The small molecule released during this reaction is a by-product of the bond-forming process.
Think of condensation polymerization like building a chain of paperclips: each clip represents a monomer, and the small piece of metal you snip off when linking them is the by-product.
Polyamides
- Polyamides are formed through the reaction between a dicarboxylic acid and a diamine.
- The functional groups involved are the carboxyl group (-COOH) and the amino group (-NH2), which form an amide linkage (-CONH-).
Nylon-6,6 is made by reacting hexanedioic acid with hexane-1,6-diamine. $$\mathrm{HOOC{-}(CH_2)_4{-}COOH} + \mathrm{H_2N{-}(CH_2)_6{-}NH_2}$$ $$\rightarrow \mathrm{[-CO{-}(CH_2)_4{-}CO{-}NH{-}(CH_2)_6{-}NH-]_n} + (n-1)\,\mathrm{H_2O}$$
Polyesters
- Polyesters are formed through the reaction between a dicarboxylic acid and a diol.
- The functional groups involved are the carboxyl group (-COOH) and the hydroxyl group (-OH), which form an ester linkage (-COO-).
PET is made by reacting terephthalic acid with ethane-1,2-diol. $$\text{HOOC-C}_6\text{H}_4\text{-COOH} + \text{HO-(CH}_2\text{)_2-OH}$$ $$\rightarrow \text{[-CO-C}_6\text{H}_4\text{-CO-O-(CH}_2\text{)_2-O-]}_n + (n-1) \text{H}_2\text{O}$$
TipCondensation polymers often alternate between two types of monomers, creating a repeating ABAB pattern in the polymer chain.
