---
title: "Define polymer in brief"
subject: "Civil Engineering Materials"
chapter: 10
key: "semester_3/civil_engineering_materials:define-polymer"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/define-polymer
site: BCT Engineering
---

# Define polymer in brief

Civil Engineering Materials · Chapter 10: Asphalt, Bitumen, Tar and Miscellaneous Materials

- Asked in: 2059 Poush (old course), 2 marks; 2057 Chaitra (old course), 2 marks (asked 2 times)
- Video: [Polymers: Crash Course Chemistry #45](https://www.youtube.com/watch?v=rHxxLYzJ8Sw) — CrashCourse
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/define-polymer
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-10

## Question

What is a polymer?

## Short answer

A polymer is a large molecule formed by joining many small monomers via chemical bonds. Polymerization (addition or condensation) creates macromolecules with high molecular mass; they can be natural (rubber) or synthetic (plastics), and linear, branched or cross-linked.

## Answer

A **polymer** is a large molecule (macromolecule) formed by joining many small repeating units called **monomers** by chemical bonds. Its relative molecular mass is usually very high, in thousands to millions. Examples: polyethylene from ethylene, PVC from vinyl chloride, and natural polymers like rubber, cellulose and protein.

- **Polymerization** is the chemical process of joining monomers into the polymer, by addition (e.g. ethylene to polyethylene) or condensation (e.g. phenol and formaldehyde to Bakelite, with water released).
- Polymers can be **natural** (rubber, wood, cellulose) or **synthetic** (plastics, synthetic fibres, resins).
- Based on structure they may be **linear, branched or cross-linked**, which decides whether they are thermoplastic or thermosetting.

```text
 n [CH2=CH2]  --heat,pressure,catalyst-->  [-CH2-CH2-]n
   ethylene                                  polyethylene
```

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A polymer is formed by joining what?
   A. Atoms of metal
   B. Many small repeating monomers
   C. Two large crystals
   D. Salts
   Answer: B. A macromolecule of many monomers joined by chemical bonds. (Key point: Definition)

2. Bakelite from phenol and formaldehyde is formed by what?
   A. Addition polymerization
   B. Condensation with water released
   C. Distillation
   D. Oxidation
   Answer: B. Condensation polymerization releases water; ethylene to polyethylene is addition. (Key point: Polymerization types)

3. What decides if a polymer is thermoplastic or thermosetting?
   A. Colour
   B. Linear, branched or cross-linked structure
   C. Cost
   D. Density only
   Answer: B. Structure decides its thermal behaviour. (Key point: Structure)