---
title: "Polyurethane preparation and uses"
subject: "Engineering Chemistry"
chapter: 4
key: "semester_2/engineering_chemistry:polyurethane-preparation-uses"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/polyurethane-preparation-uses
site: BCT Engineering
---

# Polyurethane preparation and uses

Engineering Chemistry · Chapter 4: Engineering Polymers

- Asked in: 2071 Bhadra, 2 marks
- Video: [Polyurethane:Synthesis and Uses](https://www.youtube.com/watch?v=hmC2iEP3Ii0) — Bharat Raut
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/polyurethane-preparation-uses
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-4

## Question

Mention preparation and uses of polyurethane.

## Short answer

Polyurethane is prepared by step-growth addition polymerization of a diisocyanate (e.g., TDI) with a diol, forming urethane links. Uses: flexible foams (mattresses, cushions), rigid foams (insulation), coatings, adhesives, elastic fibres (spandex), and medical devices.

## Answer

#### Preparation
Polyurethane is formed by **step-growth addition polymerisation** of a diisocyanate with a diol (polyol). For example, toluene-2,4-diisocyanate (TDI) or methylene diphenyl diisocyanate (MDI) reacts with ethylene glycol or a polyether polyol:

```text
n OCN–R–NCO + n HO–R'–OH → [–CO–NH–R–NH–CO–O–R'–O–]ₙ
 (diisocyanate)   (diol)         polyurethane
```
The urethane link (–NH–CO–O–) joins the units. No small molecule is lost. Water added in the mixture reacts with –NCO to give CO₂, which blows the polymer into a foam. With a higher functionality polyol a cross-linked polymer is obtained.

#### Uses
- Flexible foams for mattresses, cushions and car seats.
- Rigid foams for thermal insulation of refrigerators and buildings.
- Paints, varnishes and coatings, adhesives and sealants.
- Elastic fibres (spandex/Lycra), shoe soles, rollers, wheels and synthetic leather.
- Medical uses such as catheters and artificial heart parts.

## Check yourself

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

1. Polyurethane is formed from which reactants?
   A. Diisocyanate and diol
   B. Diamine and diacid
   C. Phenol and HCHO
   D. Styrene
   Answer: A. Diisocyanate + polyol forms the urethane link. (Key point: Preparation)

2. What small molecule is lost in forming the urethane link?
   A. Water
   B. HCl
   C. None
   D. CO2
   Answer: C. It is addition polymerisation; no small molecule is lost. (Key point: No by-product)

3. Rigid polyurethane foams are used for what?
   A. Thermal insulation of refrigerators and buildings
   B. Mattresses
   C. Non-stick pans
   D. Sutures
   Answer: A. Flexible foams are for cushions; rigid foams insulate. (Key point: Rigid foam use)

4. What gives a cross-linked polyurethane?
   A. A polyol of higher functionality
   B. Adding water only
   C. Cooling
   D. Adding NaOH
   Answer: A. A polyol with more than two OH groups gives cross-links. (Key point: Cross-linking)

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