What is a Polymer?

A polymer (from Greek poly meaning "many" and meros meaning "parts") is a large, chain-like macromolecule composed of thousands of repeating, smaller chemical units.

• Monomer: The single, basic building-block molecule that links together to form the polymer.

• Degree of Polymerization (DP): The total number of repeating monomer units in a single polymer chain. A higher DP generally results in a stronger fiber because longer chains can entangle and bond more effectively.

What is Polymerization?

Polymerization is the chemical reaction that binds these individual monomers together to form the long polymer chain. In textile science, the two primary methods of creating these chains are Addition Polymerization and Condensation Polymerization.

1. Addition (Chain-Growth) Polymerization

In addition polymerization, monomers join together end-to-end to form a polymer chain without the loss of any atoms or molecules. The total mass of the resulting polymer is exactly equal to the total mass of the monomers used.

• The Mechanism: This process typically requires monomers that contain carbon-carbon double bonds (unsaturated). An initiator (like a free radical) breaks the double bond, making the monomer highly reactive. It then quickly links to the next monomer, creating a rapid chain reaction.

• By-products: None. The polymer has the exact same empirical chemical formula as the monomer.

• Reaction Speed: Very fast chain reaction.

• Textile Examples:

  • Polypropylene: Made from propylene monomers.

  • Polyethylene: Made from ethylene monomers.

  • Acrylic (Polyacrylonitrile): Made from acrylonitrile monomers.

2. Condensation (Step-Growth) Polymerization

In condensation polymerization, monomers join together through a chemical reaction that simultaneously eliminates a small, secondary molecule as a by-product (most commonly water, but sometimes hydrogen chloride or methanol).

• The Mechanism: This process requires monomers that have two or more reactive functional groups (like hydroxyl, carboxyl, or amine groups) at their ends. The reaction happens in a step-wise manner (dimers form, then trimers, then eventually long chains) rather than a rapid chain reaction.

• By-products: Yes (e.g., $H_2O$, $HCl$). Because these molecules are lost, the resulting polymer has a slightly different chemical composition than the original monomers.

• Reaction Speed: Slower, step-by-step growth.

• Textile Examples:

  • Polyester (PET): Formed by the condensation of an alcohol (ethylene glycol) and an acid (terephthalic acid), releasing water.

  • Nylon (Polyamide): Formed by the reaction of diamines and dicarboxylic acids, releasing water.

  • Natural Fibers: Both cellulose (cotton, linen) and proteins (wool, silk) are natural condensation polymers formed by plants and animals, respectively, with water being the eliminated by-product during their natural synthesis.

Summary Comparison Table

Feature	Addition Polymerization	Condensation Polymerization
Monomer Requirement	Must have double bonds (unsaturated).	Must have two or more reactive functional groups.
By-products Formed?	No by-products.	Yes (typically water, HCl, or methanol).
Growth Mechanism	Rapid chain reaction (Chain-growth).	Slower, step-by-step reaction (Step-growth).
Polymer Composition	Identical empirical formula to the monomer.	Different empirical formula than the monomers.
Common Textile Fibers	Acrylic, Polypropylene, Polyethylene	Polyester, Nylon, Cotton (Cellulose), Wool (Protein)