Polymer Engineering Lecture 1: Introduction to Polymers

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Questions and Answers

What is the characteristic of linear polymers?

They have a branched chain structure

They have a straight long chain with side chains

They have a network structure

Their molecules are closely packed and have high density, tensile strength (correct)

What is an example of a crosslinked or network polymer?

PVC

Polyethene

Bakelite (correct)

Polypropylene

What is the characteristic of branched chain polymers?

They have a network structure

They have a straight long chain with different side chains (correct)

They have a straight long chain with no side chains

Their molecules are closely packed and have high density, tensile strength

What is an example of a branched chain polymer?

Polypropylene Signup and view all the answers

What is the term for the number of junction points per unit volume in crosslinked polymers?

Degree of crosslinking Signup and view all the answers

What is the characteristic of addition polymers?

They are formed by the repeated addition of monomers Signup and view all the answers

What is an example of an addition polymer?

Polyethene Signup and view all the answers

What is the term for addition polymers formed from a single monomeric species?

Homopolymers Signup and view all the answers

What type of reaction is involved in the formation of condensation polymers?

Condensation reaction Signup and view all the answers

What is an example of a condensation polymer?

Nylon 6, 6 Signup and view all the answers

What type of intermolecular forces are responsible for the mechanical properties of polymers?

Van-der waals forces and hydrogen bonding Signup and view all the answers

What is the characteristic of elastomers?

Weak intermolecular forces Signup and view all the answers

What type of polymers have strong intermolecular forces like hydrogen bonding?

Fibres Signup and view all the answers

What is the characteristic of thermoplastic polymers?

Can be softened on heating and hardened on cooling Signup and view all the answers

What is the characteristic of thermosetting polymers?

Hard and infusible on heating Signup and view all the answers

What is an example of a thermoplastic polymer?

Polythene Signup and view all the answers

What does the Greek word 'poly' mean in the term 'polymer'?

Many Signup and view all the answers

What is the minimum functionality required for a substance to be a monomer?

Two Signup and view all the answers

What is the chemical reaction in which two or more molecules combine to form a molecule of high molecular weight?

Polymerization Signup and view all the answers

What is the term for the number of monomer or repeating units in the polymer chain?

Degree of Polymerization Signup and view all the answers

What is the formula to calculate the average molecular weight of a polymer?

DP X Weight of repeating unit Signup and view all the answers

Which of the following is an example of a natural polymer?

Proteins Signup and view all the answers

What is the term for the polymers obtained by simple chemical treatment of natural polymers?

Semi-synthetic polymers Signup and view all the answers

Which of the following is an example of a synthetic polymer?

Nylon Signup and view all the answers

What is the characteristic of a homopolymer?

A single type of repeat unit Signup and view all the answers

What is the characteristic of crystalline polymers?

Both crystalline and amorphous regions Signup and view all the answers

What is the characteristic of rubbers?

Long-range elasticity Signup and view all the answers

What is the characteristic of fibres?

Tensile strength ranges between 20000-150000 psi Signup and view all the answers

What is the characteristic of plastics?

Tensile strength ranges between 4000-13000 psi Signup and view all the answers

What is the characteristic of cross-linked or heavily branched molecules?

Cannot be reused or recycled Signup and view all the answers

What is the term for a polymer containing two different monomers?

Copolymer Signup and view all the answers

What type of bonding may exist in polymeric materials?

Various types of bonding Signup and view all the answers

Study Notes

Introduction to Polymers

Polymer is a large molecule comprising repeating structural units joined by covalent bonds.
The word "polymer" comes from the Greek words "poly" meaning many and "mer" meaning unit or parts.
Monomer is a small molecule or repeating unit in the structure of a polymer, which has a functionality of at least two.

Polymerization

Polymerization is a chemical reaction in which two or more molecules of one or more substances combine to form a molecule of high molecular weight.
Degree of polymerization (DP) is the number of monomer or repeating units in a polymer chain.

Classification of Polymers

Based on Source

Natural polymers: found in nature, examples include proteins, cellulose, starch, resins, and rubber.
Semi-synthetic polymers: obtained by simple chemical treatment of natural polymers, examples include starch and silicones.
Synthetic polymers: obtained by polymerization of simple chemical molecules in a laboratory, examples include nylon, polyethene, polystyrene, synthetic rubber, PVC, and Teflon.

Based on Structure

Linear polymers: monomers are linked to form a long straight chain with no side chains, examples include polyethene, PVC, and nylons.
Branched chain polymers: have a straight long chain with different side chains, examples include polypropylene, amylopectin, and glycogen.
Crosslinked or network polymers: two linear chains are joined together by covalent bonds, examples include Bakelite, melamine, formaldehyde resins, and vulcanized rubber.

Based on Mode of Polymerization

Addition polymers: formed by the repeated addition of monomer molecules possessing double or triple bonds, examples include polythene and polypropene.
Condensation polymers: formed by the combination of two monomers by removal of small molecules, examples include nylon 6, 6.

Based on Molecular Forces

Elastomers: rubber-like solids with elastic properties, examples include buna-S, buna-N, and neoprene.
Fibers: thread-forming solids with high tensile strength, examples include polyamides (nylon 6, 6) and polyesters (terylene).
Thermoplastic polymers: can be softened on heating and hardened on cooling, examples include polythene, polypropene, and PVC.
Thermosetting polymers: hard and infusible on heating, examples include bakelite, urea-formaldehyde resins, and melamine.

Based on Type of Monomers

Homopolymers: contain a single type of repeat unit, examples include polystyrene.
Copolymers: made up of two different monomers, examples include butadiene-styrene rubber.

Based on Morphology

Crystalline polymers: have crystalline and amorphous regions, characterized by their melting temperature (Tm).

Based on End Use

Rubbers: dimensionally unstable, characterized by low molecular cohesion and poor mechanical properties.
Plastics: stronger than rubbers, exhibit tensile strength between 4000-13000 psi.
Fibers: strongest of the three, exhibit tensile strength between 20000-150000 psi.

Bonding in Polymers

Various types of bonding may exist in polymeric materials, including covalent bonds, van-der waals forces, and hydrogen bonding.

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Description

Learn about the basics of polymers, including the definition of polymers, monomers, and their structures, in this introductory lecture on polymer engineering.