Structures and Properties of Polymers: A Comprehensive Guide, Lecture notes of Statics

An in-depth exploration of the structures and properties of polymers, both naturally occurring and synthetic. It covers topics such as hydrocarbon molecules, polymer molecules, molecular weight, molecular shape, molecular configurations, thermoplastic and thermosetting polymers, copolymers, and polymer crystallinity. The document also includes examples and computations to illustrate key concepts.

Typology: Lecture notes

2020/2021

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Structures of Polymers
Naturally occurring polymers
wood, rubber, cotton, wool, leather, silk
proteins, enzymes, starches, cellulose
Modern scientific research tools have made possible the determination of the
molecular structures of this group of materials and the development of
numerous polymers that are synthesized from small organic molecules.
Synthetic polymers
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Structures of Polymers

Naturally occurring polymers

wood, rubber, cotton, wool, leather, silk

proteins, enzymes, starches, cellulose

Modern scientific research tools have made possible the determination of the

molecular structures of this group of materials and the development of

numerous polymers that are synthesized from small organic molecules.

Synthetic polymers

Structures of Polymers

What is a Polymer?

Poly mer

many repeat unit

Hydrocarbon Molecules

Unsaturated hydrocarbons

Molecules that have double and triple bonds

Possible for another atom or group of atoms to became attached to the

original molecule

Double bond found in ethylene, C 2 H 4

Triple bond found in acetylene, C 2 H 2

Hydrocarbon Molecules

Isomerism

Two compounds with same chemical formula can have different atomic

arrangments

Ex.: butane and isobutane

Some of the physical properties of hydrocarbon will depend on the isomeric

state.

T bbutane = − 0. 5 ◦C, T bisobutane = − 12. 3 ◦C

Polymer Molecules

Macromolecules

Atoms bound together by covalent interatomic bonds within each molecule

For carbon-chain polymers

Backbone of carbon atom string

Side bonding with atoms or radicals

Possible both chain and side double bonds

Repeat units

Monomer is the small molecule from which a polymer is synthesized

Chemistry of Polymer Molecules

Ethylene (C 2 H 4 ), a gas at ambient temperature and pressure

Polymerization

Reaction between an initiator or catalyst species (R·) and

the ethylene monomer

Sequential addition of monomer units to this actively growing chain molecule

Chemistry of Polymer Molecules

Polytetrafluoroethylene (PTFE, trade name Teflon)

Polyvinylchloride (PVC)

Some polymers with generalized form

Chemistry of Polymer Molecules

Common polymeric materials

Chemistry of Polymer Molecules

Homopolymer

When all of the repeating units along a chain are of the same type.

Copolymer

When chains are composed of two or more different repeat unit.

Functionality

Number of bonds that a given monomer can form

Bifunctional and trifuntional

Molecular Weight

Not all chains in a polymer are of the same length.

– i.e., there is a distribution of molecular weights.

Average molecular weight

Number-average molecular weight

Mn =

xi Mi

Weight-average molecular weight

Mw =

wi Mi

Molecular Weight

Example 4.1 Computations of average molecular weights and degree of

polymerization (PVC)

Data from Figure 4.3a

⇒ xi and Mi

Molecular Weight

Example 5.1 Continued

Number-average molecular weight

Degree of polymerization

DP =

Mn

m

21152 g/mol

(2 × 12 .01 + 3 × 1 .01 + 35.45) g/mol

Molecular Weight

Many polymer properties are affected by the length of the polymer chains.

The melting or softening temperature increases with increasing molecular

weight.

At room temperature

Liquids for polymers with very short chains (the order of 100 g/mol)

Waxy solids (such as paraffin wax) and soft resins for approximately 1000 g/mol

Solid (or high) polymer ranging between 10000 and several million g/mol

The same polymer material can have quite different properties if it is produced

with a different molecular weight.

Molecular Shape

Single chain bonds are capable of rotating and bending in three dimensions.

Straight chain Twisted chain