What is the primary difference between addition and condensation polymerization?

The fundamental distinction lies in whether small molecules are eliminated during the polymerization process. In addition polymerization, monomers add to each other without the loss of any atoms, meaning the empirical formula of the monomer and the repeating unit of the polymer are identical. This typically occurs with unsaturated monomers (containing double or triple bonds). In contrast, condensation polymerization involves the reaction of monomers with the elimination of small molecules such as water, alcohol, or ammonia. Consequently, the repeating unit of a condensation polymer has a different empirical formula than its constituent monomers.

Why do polymers have a range of molecular weights instead of a single fixed value?

Polymers are formed by the linking of many monomer units, and in any given polymerization reaction, the chains do not all grow to precisely the same length. The termination step in polymerization can occur at different stages for different growing chains, leading to a distribution of chain lengths. Therefore, a polymer sample is a mixture of macromolecules with varying degrees of polymerization and thus varying molecular weights. This is why we refer to average molecular weights, such as number average ($ar{M}_n$) and weight average ($ar{M}_w$), rather than a single absolute molecular weight.

What makes some polymers thermoplastic and others thermosetting?

The key difference lies in their molecular structure and the nature of intermolecular forces. Thermoplastics are typically linear or slightly branched polymers with relatively weak intermolecular forces. These forces can be overcome by heating, allowing the polymer chains to slide past each other, making the material soft and moldable. Upon cooling, it hardens. This process is reversible. Thermosetting plastics, on the other hand, have extensive cross-linking between polymer chains, forming a rigid, three-dimensional network structure. Once heated and molded, these covalent cross-links are formed, making the material permanently hard and infusible. Reheating them causes degradation rather than softening.

What is the significance of vulcanization of rubber?

Natural rubber, a polyisoprene, is soft, sticky, and has low tensile strength, especially at high temperatures. Vulcanization is a process where natural rubber is heated with sulfur (and sometimes other additives). Sulfur forms cross-links between the polymer chains, significantly improving the rubber's properties. It becomes harder, stronger, more elastic, less sticky, and more resistant to abrasion and temperature changes. This enhanced durability and elasticity make vulcanized rubber suitable for applications like tires, where natural rubber alone would be inadequate.

Can all synthetic polymers be recycled or are they all harmful to the environment?

Not all synthetic polymers can be recycled, and their environmental impact varies. Thermoplastics, due to their ability to be melted and reshaped, are generally recyclable (e.g., PET, HDPE). However, thermosetting plastics cannot be recycled in the same way because their cross-linked structure prevents remelting. While many synthetic polymers are non-biodegradable and contribute to plastic pollution, research is ongoing to develop new biodegradable synthetic polymers (like PHBV) that can be broken down by microorganisms. The environmental impact also depends on proper waste management and consumer behavior.

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Polymers

Chemistry

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Version 1Updated 22 Mar 2026

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Polymers are high molecular mass substances formed by the repetitive linking of a large number of simple molecules, known as monomers, through covalent bonds. This process of forming polymers from monomers is termed polymerization. These macromolecules, often referred to as giant molecules, possess unique physical and chemical properties that are distinct from their constituent monomers. The term …

Quick Summary

Polymers are large molecules (macromolecules) formed by linking many small repeating units called monomers through a process called polymerization. They are broadly classified by their source (natural, synthetic, semi-synthetic), structure (linear, branched, cross-linked), and mode of formation (addition or condensation).

Addition polymerization involves direct joining of monomers, often unsaturated, without losing any atoms, exemplified by polythene from ethene. Condensation polymerization involves the elimination of small molecules like water during monomer linkage, such as in the formation of Nylon-6,6.

Polymers also differ in their intermolecular forces, leading to categories like elastomers (stretchy, weak forces), fibers (strong, high tensile strength), thermoplastics (soften on heating, reversible), and thermosetting plastics (harden irreversibly on heating, cross-linked).

Key examples include natural rubber, PVC, nylon, and Bakelite. Understanding monomer-polymer relationships and classification is crucial for NEET.

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Key Concepts

Addition Polymerization vs. Condensation Polymerization

These are the two primary modes of polymer formation. **Addition polymerization** involves the direct joining…

Homopolymers vs. Copolymers

This classification is based on the number and type of monomer units involved in the polymerization. A…

Number Average Molecular Weight (

\bar{M}_n

) and Weight Average Molecular Weight (

\bar{M}_w

)

Since polymer samples consist of chains of varying lengths, a single molecular weight value is insufficient.…

Monomer: — Building block of a polymer.

Polymerization: — Process of forming polymer from monomers.

Addition Polymerization: — Monomers add without loss of atoms (e.g., ethene

\rightarrow

polythene).

Condensation Polymerization: — Monomers react with elimination of small molecules (e.g., Nylon-6,6

\rightarrow

H_2O

eliminated).

Natural Polymers: — Starch, Cellulose, Proteins, Natural Rubber (Isoprene).

Synthetic Polymers: — Polythene, PVC, Nylon, Teflon, Bakelite.

Thermoplastics: — Soften on heating, reversible (Polythene, PVC).

Thermosetting Plastics: — Harden irreversibly on heating, cross-linked (Bakelite, Melamine).

Elastomers: — Rubber-like elasticity (Natural Rubber, Buna-S).

Fibers: — High tensile strength (Nylon-6,6, Terylene).

Biodegradable Polymers: — PHBV, Nylon-2-Nylon-6.

Please Memorize All Classifications, Types, Examples, Functions, and Biodegradability for NEET Polymers.

Polymerization (Addition, Condensation)

Monomers (Key examples)

All Classifications (Source, Structure, Forces)

Copolymers (Buna-S, Buna-N)

Thermoplastics (PVC, Polythene) & Thermosets (Bakelite)

Elastomers (Rubber) & Fibers (Nylon)

Biodegradable (PHBV, Nylon-2-Nylon-6)

Natural Rubber (Isoprene) & Neoprene (Chloroprene)

Properties & Uses

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