Methods of Polymerisation — Revision Notes

⚡ 30-Second Revision

Polymerisation: — Monomers $\rightarrow$ Polymer
Addition Polymerisation (Chain-Growth):

- Monomers: Unsaturated (C=C, C$\equiv$C) - No by-product eliminated. - Polymer empirical formula = Monomer empirical formula. - Mechanisms: Free Radical, Cationic, Anionic. - Examples: Polyethylene, PVC, Teflon, Polystyrene.

Free Radical Mechanism: — Initiation (radical formation) $\rightarrow$ Propagation (chain growth) $\rightarrow$ Termination (radical deactivation).
Condensation Polymerisation (Step-Growth):

- Monomers: Bifunctional/Polyfunctional (e.g., -OH, -COOH, -NH$_2$) - Small by-product eliminated (e.g., $H_2O$, $HCl$). - Polymer empirical formula $\neq$ Monomer empirical formula. - Examples: Nylon 6,6, Dacron (Polyester), Bakelite.

Ring-Opening Polymerisation: — For cyclic monomers (e.g., Caprolactam $\rightarrow$ Nylon 6). No by-product.

2-Minute Revision

Polymerisation is the process of forming large molecules (polymers) from small repeating units (monomers). The two main methods are Addition and Condensation. Addition polymerisation involves monomers with double or triple bonds adding directly to each other without losing any atoms.

The polymer's repeating unit has the same empirical formula as the monomer. It's often called chain-growth and can proceed via free radical, cationic, or anionic mechanisms. Key examples include polyethylene from ethene, PVC from vinyl chloride, and Teflon from tetrafluoroethene.

Condensation polymerisation, also known as step-growth, involves monomers with two or more functional groups reacting to form a polymer while eliminating small molecules like water or alcohol. Here, the polymer's repeating unit has a different empirical formula than the monomer(s).

Examples include Nylon 6,6 from hexamethylenediamine and adipic acid, and polyesters like Dacron from ethylene glycol and terephthalic acid. A special case is Ring-opening polymerisation for cyclic monomers like caprolactam to form Nylon 6, where no by-product is lost.

5-Minute Revision

To master 'Methods of Polymerisation' for NEET, focus on the fundamental distinctions and key examples. Addition Polymerisation is a chain-growth process where unsaturated monomers (like alkenes or vinyl compounds) link together without losing any atoms.

The polymer's repeating unit will have the exact same empirical formula as the monomer. The most common mechanism is Free Radical Polymerisation, which involves three stages: Initiation (an initiator forms free radicals that attack the monomer), Propagation (the growing radical chain adds more monomers), and Termination (two radicals combine or disproportionate to end chain growth).

Examples include polyethylene, polypropylene, PVC, and Teflon. Condensation Polymerisation, on the other hand, is a step-growth process. It involves monomers with at least two reactive functional groups (e.

g., -OH, -COOH, -NH$_2$) reacting to form a polymer, with the simultaneous elimination of small molecules such as water, alcohol, or HCl. Consequently, the empirical formula of the polymer's repeating unit differs from the monomer(s).

Classic examples are Nylon 6,6 (from hexamethylenediamine and adipic acid, eliminating water) and polyesters like Dacron (from ethylene glycol and terephthalic acid, also eliminating water). A distinct method is Ring-Opening Polymerisation, where cyclic monomers (like caprolactam) open their rings to form linear polymers (like Nylon 6) without losing small molecules.

For NEET, be able to identify the polymerisation type from monomer/polymer structures, recall common polymer examples and their monomers, and understand the basic steps of free radical polymerisation.

Pay close attention to the presence or absence of by-products.

Prelims Revision Notes

Methods of Polymerisation: NEET Revision Notes

1. Polymerisation Definition:

* Process of joining small molecules (monomers) into large macromolecules (polymers).

2. Addition Polymerisation (Chain-Growth Polymerisation):

* Monomers: Unsaturated compounds (alkenes, alkynes, vinyl monomers) with C=C or C$\equiv$C bonds. * Mechanism: Monomers add to each other without the loss of any atoms. * By-products: None.

* Empirical Formula: Polymer repeating unit has the same empirical formula as the monomer. * Growth: Rapid chain growth from an active center. * Types of Initiation: * Free Radical Polymerisation: Most common.

Initiators (peroxides, azo compounds) form free radicals. Steps: Initiation (radical formation), Propagation (chain extension), Termination (radical deactivation by coupling or disproportionation). * Cationic Polymerisation: For monomers with electron-donating groups (e.

g., isobutylene). Initiated by Lewis acids ($BF_3$, $AlCl_3$). * Anionic Polymerisation: For monomers with electron-withdrawing groups (e.g., acrylonitrile, methyl methacrylate). Initiated by strong nucleophiles (e.

g., n-butyllithium).

3. Condensation Polymerisation (Step-Growth Polymerisation):

* Monomers: Bifunctional or polyfunctional compounds with reactive functional groups (e.g., -OH, -COOH, -NH$_2$). Can be two different types of monomers. * Mechanism: Monomers react with the elimination of small molecules.

* By-products: Small molecules like $H_2O$, $HCl$, $CH_3OH$ are eliminated. * Empirical Formula: Polymer repeating unit has a different empirical formula than the monomer(s). * Growth: Stepwise growth, gradual increase in molecular weight.

* Examples: * Polyamides: Nylon 6,6 (from hexamethylenediamine and adipic acid). * Polyesters: Dacron/Terylene (from ethylene glycol and terephthalic acid). * Phenol-Formaldehyde resins (Bakelite): From phenol and formaldehyde.

* Urea-Formaldehyde resins: From urea and formaldehyde.

4. Ring-Opening Polymerisation:

* Monomers: Cyclic compounds (e.g., lactams, lactones). * Mechanism: Ring opens to form a linear polymer. * By-products: None. * Example: Nylon 6 (from caprolactam).

Key Points for NEET:

Be able to distinguish addition from condensation based on monomer structure and by-product formation.
Memorize common polymer examples and their corresponding monomers and polymerisation methods.
Understand the basic steps of free radical polymerisation.
Identify the repeating unit of a polymer.

Vyyuha Quick Recall

To remember the two main types of polymerisation and their key features:

All Always Add And No By-products (Addition Polymerisation: Always adds, No By-products)

Condensation Cuts Constantly, Creating Water (Condensation Polymerisation: Cuts small molecules, often Water)