Question

Why is the polymerization of diamines with dicarboxylic acids spontaneous, despite the fact the process dramatically increases the order of the system as the bonds form?

Answer 1

Dicarboxylic acid represent an important class of water - soluble organic compounds founds in atmosphere . In this work we are studying properties of dicarboxylic acid homodimer complexes (HO 2 (CH 2) n CO 2- [ HO 2 (CH 2) n CO 2 H ], n = 0-12), as potentially important intermediates in aerosol formation process . Our approach is based  on experimental data from negative ion photoelectron spectra of the dimer complexes combined with updated measurements of the corresponding monomer species .  

These results are analyzed with quantum - mechanical calculations , which provide further information about equillibrium structure , thermochemical parameters associated with the complex formation , and evaporation rates . Calculation indicate that these dimer complexes are characterized by the presence of the strong intermolecular hydrogen bonds with high binding energies and are thermodynamically favorable to form with low evaporation rates . these results imply that dicarboxylic acids not only can contribute to the heterogeneous complexes formation involving sulfuric acid and dicarboxylic acids , but also can promote the formation of homogeneous complexes by involving dicarboxylic acids themselves.

Answer 2

The polymerization of diamines with dicarboxylic acids to form polyamides (also known as nylon) is spontaneous due to the thermodynamic driving force associated with the formation of strong covalent bonds and the release of water molecules as a byproduct.

Although the polymerization process increases the order of the system as new bonds are formed between the monomers, it is still spontaneous for the following reasons:

1. Exothermic Reaction: The formation of polyamides involves the condensation reaction between diamines and dicarboxylic acids, resulting in the release of water molecules (H2O) as a byproduct. This condensation reaction is exothermic, meaning it releases energy to the surroundings. The release of energy in the form of heat helps drive the reaction forward, making it spontaneous.

2. Stability of Covalent Bonds: The formation of polyamides involves the formation of strong covalent bonds between the amine and carboxylic acid functional groups. Covalent bonds are very stable and have lower energy than the individual monomers. The system tends to move towards lower energy states, making the polymerization process thermodynamically favorable and spontaneous.

3. Entropy Change: Although the polymerization process increases the order of the system by forming long-chain polymers, it also leads to an increase in the entropy (randomness) of the system due to the release of water molecules. The entropy increase associated with the release of water molecules helps to drive the reaction forward and make it spontaneous.

4. Removal of Reaction Byproduct: The spontaneous nature of the reaction is also facilitated by the removal of the reaction byproduct (water) from the system. As the water is formed, it is removed from the reaction site, preventing its accumulation and further driving the reaction forward.