Muddiest Points

Muddiest Points:• “I don’t get the difference between a monomer, a

mer, and a polymer?”• “How do I calculate degree of polymerization?”• “How does degree of polymerization affect polymer

properties?”• “I don’t get polymer microstructures and how they

affect properties?”• “I don’t get the different techniques for processing

polymers.”

Polymers I: Introduction to Polymers

What is a Polymer?

Poly merMany Units

repeatunit

repeatunit

repeatunit

What is a Polymer?Definition:

PE Milk Container PVC Pipe PP Rope

•C-C rotations along the chain give the polymer molecule a loosely-coiled, string-like shape

Polymer Chain Geometry

CarbonHydrogen

What are Important Polymer Concepts & Terminology?Monomers, Mers, Polymers, and Degree of PolymerizationDegree of Polymerization:

Concept and Definition

• Monomer - small, unreacted single molecule for polymer.

Ethylene Monomer:

• Mer – single repeat unit of a polymer

Polyethylene Mer:2 C-C chain bonds / mer

• Polymer – entire polymer chain

Polyethylene Molecule: n mers / chain molecule

n = degree of polymerization (DP) = n mers / chain molecule n= DP =

n = DP =

• n is typically 100 10,000 but may go higher than 100,000

number of mer units polymer molecule

molecular weight of polymer molecule molecular weight of mer

Hydrogen

Carbon

Ethylene Monomers

Candle (Paraffin)

Container (HDPE)

n (DP) 10 10,000

MW Chain (g/mol)

(28 g/mol )(10) =280 g/mol

(28 g/mol)(10000) = 280,000 g/mol

Tm (°C)

MW of Molecule = n * MW Mer

2.Why does the Tm increase with more C atoms in chain?

1. What are the similarities and differences of candles and plastic milk containers?

How Degree of Polymerization Affects Properties: Melting Point

n= Degree of Polymerization (DP) Molecular Weight= MW

Tem

pera

ture

(°C)

Number of carbons= 2n = 2* DP

What are the Four Different Types of Polymer Structure and Morphology?

• Polymer – a long chain molecule of 1-D covalently bonded repeat units or a network of 3-D covalently bonded repeat units

• Length of molecule varies from 1,000s to 100,000s of atoms long.

• Four main classes of polymer solids we will consider are:

–Thermoplastic AMORPHOUS polymers are 1-D covalently-bonded chains. They are randomly-oriented and form a glassy solid. When heated, they melt; when cooled, they solidify; and they can be remelted (melt recyclable).

- Thermoplastic SEMICRYSTALLINE polymers also have 1-D covalently-bonded chains. They form layers of thin, chain-folded crystalline lamellae separated by amorphous regions and are connected with tie molecules. When heated, they melt. When cooled, they solidify and can be remelted (melt recyclable).

– Heat Set ELASTOMERS are 3-D LIGHTLY to MODERATELY crosslinked networks of long chain molecules that are covalently crosslinked during a curing chemical reaction. After the cure, the 3-D network maintains its structural integrity when heated (not melt recyclable).

–Heat Set THERMOSETS are 3-D HIGHLY crosslinked networks of covalently-bonded molecules. The thermoset reaction forms a rigid amorphous solid with very good thermal resistance (not melt recyclable).

PS Glass

PE Trash Bag

Rubber Shoe Sole

Bakelite Billiard Balls

How can Polymers be Classified?

What is the Effect of Structure & Morphology on Mechanical Properties?

Polymer E (MPa)

TS (MPa) %EL

Natural Rubber 2.5 20 600-

1000%

HDPE 830 28 300-600%

Polystyrene 3100 40 1.2-2.5%

Bakelite 6900 55 0.1%

A

B

CPS Glass PE Trash Bag

Rubber Shoe SoleD

Bakelite Billiard Balls

Morphology and Thermal & Mechanical Properties

Lightly X-linkedElastomer

Heavily X-linkedThermoset

Semicrystalline Polymer

Amorphous Polymer

Thermoplastic Polymers Heat Set Polymers

Tg = 100CT25 < TgGlassy

Tg = -103CTg < T25

Elastic

Tg = -90C; Tm = 130CTg < T25 < Tm

Flexible

Tg = 163CT25 < Tg

Rigid

Tg = Glass Transition Temperature, below which a polymer is rigid and brittle

PS Glass PE Trash Bag Rubber Shoe Sole Bakelite Billiard Balls

1010

What is the Effect of Structure on Processing of Plastics?

• Thermoplastics – Amorphous & Semicrystalline• Processing can be continuous – only cooling required• Heat to melt, shape & cool below Tg or Tm• Can be reversibly melted and solidfied, i.e. recyclable• Ex: PE, PP, PS.

• Heat Sets – Thermosets and Elastomers– Processing not continuous – one part at a time– Heating & crosslink reaction require time in fixed shape mold– Permanent 3-D crosslinked network – not recyclable– Shape is permanent – does not change with heat; will only degrade

– Elastomer + crosslink agent (S, O) mixed, shaped, reacted– Ex. polybutadiene, polyisoprene– Thermoset prepolymer pressed into a shape & reacted – Ex: Bakelite, urethane, epoxy

For additional information on polymer processing terminology go to: GOOGLE “matsciasu” and get Quizlet.com vocabulary e-flash cards for 6.2 Polymers II – Processing

PS Glass

PE Trash Bag

Rubber Shoe Sole

Bakelite Billiard Balls

Processing for Thermoplastic and Crosslinked Polymers

PS Glass PE Trash Bag

Rubber Shoe Sole

Bakelite Billiard Balls

ThermoplasticAmorphous

ThermoplasticSemicrystalline

Heat SetElastomers

Heat SetThermosets

Processing: Film Blowing

Processing: Injection Molding

Processing: Transfer Molding

Processing: Compression Molding

Effect of Molecular Weight and Bonding on Properties

Metals Ceramics Polymers

0.2

8

0.6

1

Wood( grain)

AFRE( fibers)

CFRE*GFRE*

Glass fibers only

Carbon fibers only

A ramid fibers only

Epoxy only

0.4

0.8

2

46

10

20

406080

100

200

600800

10001200

400

C FRE( fibers)

G FRE( fibers)*

G FRE(|| fibers)*

A FRE(|| fibers)*

C FRE(|| fibers)*

Why is elastic modulus of polymers two orders of magnitude less than metals or ceramics?

How do Polymer Properties Compare to Metals and Ceramics?

Property Polymer Metal Ceramic

E (GPa) 0.2-4 40-400 10-1200

Tensile Strength (Mpa)

26-60(Fibers~700)

200-3400 70-140

Ductility (% elongation)

2-500 1-8 1<

Tm (°C) 100-250 200-2800 500-4000

Coefficient of Thermal

Expansion(m/m-K)

15 x10-6 -100 x10-6

5x10-6 -12x10-6

1x10-6 -5x10-6

E (G

Pa)

Wrap-Up

• “What is a polymer?”

• “I don’t get the difference between a mer and a monomer.”

• “How do I calculate degree of polymerization?”

• “How does degree of polymerization affect polymer properties?”

• “I don’t get polymer microstructures and how they affect properties.”

• “I don’t get the different techniques for processing polymers.”

Polymers I: Introduction to Polymers