Comparison Between Addition and Condensation Polymerization
Differences
| Feature | Addition Polymerization | Condensation Polymerization |
|---|---|---|
| Monomer Requirement | Monomers must contain at least one double or triple bond (unsaturated compounds like alkenes). | Monomers must contain two or more functional groups (e.g., -OH, -COOH, -NH₂). |
| Byproducts | No byproducts are formed; the polymer is the sole product. | Small molecules such as water ($H_2O$), ammonia ($NH_3$), or HCl are eliminated. |
| Molecular Weight | The molecular mass of the polymer is an integral multiple of the monomer's mass. | The molecular mass of the polymer is less than the sum of the monomers' masses due to byproduct loss. |
| Reaction Mechanism | Follows a chain-growth mechanism (initiation, propagation, and termination). | Follows a step-growth mechanism; any two species can react at any time. |
| Growth Kinetics | Monoblock addition occurs rapidly at the active center; monomer concentration decreases steadily. | Polymer chains grow slowly throughout the matrix; monomers disappear early in the reaction. |
| Examples | Polyethylene, PVC, Polystyrene, Teflon. | Nylon 6,6, Terylene (Dacron), Bakelite. |
Analysis
1. Addition Polymerization
This process typically involves a free radical, ionic, or coordination mechanism. The reaction begins when an initiator creates an active center on a monomer, which then adds subsequent monomers in a rapid chain reaction. Because no atoms are lost during the process, the empirical formula of the polymer is identical to that of the monomer.
Formation of Polyethylene
In this mechanism, the $\pi$-bond of the ethylene monomer is broken under specific temperature and pressure conditions (often involving a catalyst or initiator). The carbon atoms then form new $\sigma$-bonds to link into a long saturated chain. No atoms are lost during this transition.
$$n(CH_2=CH_2) \xrightarrow{\text{Polymerization}} -[CH_2-CH_2]_n-$$
2. Condensation Polymerization
This process involves a series of condensation reactions between bi-functional or poly-functional monomers. Unlike addition polymerization, the reaction is relatively slow and requires the removal of small molecules to drive the equilibrium toward polymer formation. The resulting polymers often contain heteroatoms (like Nitrogen or Oxygen) within the main backbone.
Synthesis of Nylon 6,6
This process involves the reaction between Adipic Acid and Hexamethylenediamine. Each monomer is bifunctional, allowing the reaction to proceed at both ends. As the amide linkage ($–CONH–$) forms, a molecule of water is eliminated for every bond created.
$$n(HOOC(CH_2)_4COOH) + n(H_2N(CH_2)_6NH_2) \rightarrow -[CO(CH_2)_4CONH(CH_2)_6NH]_n- + 2nH_2O$$
Comparative Summary
| Feature | Addition (Polyethylene) | Condensation (Nylon 6,6) |
|---|---|---|
| Active Species | Free radicals, cations, or anions | Reactive functional groups (Carboxyl & Amine) |
| Chain Growth | Rapid addition at the chain end | Step-wise growth across all molecules |
| Atom Economy | 100% (High efficiency) | Lower (due to byproduct mass loss) |
Test Your Knowledge
Test your knowledge on the fundamental differences between Addition and Condensation polymerization.
Explanation:
Unsaturated bonds (like in ethylene) are necessary to open up and form new single bonds in a chain-growth mechanism.
Explanation:
The reaction between a carboxylic acid group and an amine group results in an amide bond formation with the elimination of water.
Explanation:
Addition polymerization proceeds through active centers (radicals or ions) that add monomers rapidly to the end of a growing chain.
Explanation:
In condensation polymerization, the elimination of a byproduct (like water or HCl) means the mass of the resulting repeating unit is less than the sum of the masses of the reacting monomers.
Explanation:
PVC is formed by the chain-growth addition of vinyl chloride monomers ($CH_2=CHCl$). The others (Nylon, Bakelite, Terylene) are all products of condensation or step-growth reactions.