A brief introduction to polymers

July 24, 2014

What is a polymer• A polymer is large [big] molecule made

up of repeating units of a smaller molecules called as Monomers.• Polymer : derived from Greek [ ‘poly’

means many and “meros” means parts.

• Examples : Polyethylene [PE], Polystyrene [PS]

Carbon Chains are the Backbone of Polymers

• Carbon has four valence electrons and will make four bonds.

• Carbon can bond with itself and form long chains

• Other elements used in polymers – Hydrogen– Oxygen– Nitrogen– Chlorine– Fluorine– Silicon

The word, polymer, implies that polymers are constructed from pieces (monomers) that can be easily connected into long chains (polymer). When you look at the above shapes, your mind should see that they could easily fit together.

Suppose our repeat unit is an “X.” Then, a linearpolymer based on “X” would look like the following:

… --X--X--X--X--X--X--X--X--X--X--X--X--…

where each “X” represents a “mer.”

• Naturally occurring polymers have been usedfor thousands of years– wood, rubber, cotton, wool, leather, silk,..

Etc

• Artificial polymers are, indeed, relatively recent and mostly date from after WW-II

– in many cases, the artificial material is both better and cheaper than the natural

alternative

Crude oil is a mixture of assorted polymers that can be separated by fractional distillation

Properties of Polymers• vs other materials

– Lower density

– Lower mp

– High molecular weight

– Opaque to transparent

– Rigid to flexible

– Bouncy? Inelastic?

– Absorb water? Repel water?

• ADVANTAGES– Color range– Insulator– Light weight– Corrosion resistant– Easy to process

• DISADVANTAGES– Difficult to repair– Odors??– Unstable at high temps– Can be costly– Subject to deterioration by

solvents– Can be toxic

Polymer Powders Samples

• Water lock – hydrophilic (having affinity for water)– absorbs 800x its mass in distilled water.

– add Salt

• Water molecules are attracted to the negative charges by hydrogen bonding.

• Recall this is the attraction between H and O due to polar bonds

ABOUT SODIUM POLYACRYLATE

Polymer Powders Samples

• Instant Snow– A cross linked hydrophilic powder

Polyacrylate, But Different• Instant Snow is the same

material, but the structure is different so the water molecules become absorbed inside the polyacrylate so it expands and feels dry

• Grow beasts and shapes are similar in that they absorb water and expand

Polymer Powders Samples

• HDPE powder – hydrophobic (afraid of water)

Polymer Powders Samples

• Water Gel Crystals and Spheres– hydrophilic with semi-permeable cover– ghost crystals– index of refraction

• Grow beasts

Polymer Powders

• Water lock – Hydrophilic

• Instant Snow – Hydroscopic crosslink

• HDPE Powder – Hydrophobic

• Gel Crystals – Hydroscopic with semi-permeable cover

distilled water tap water

0.45% saltwater

0.9% saltwater

no water

Ways to Classify Polymers

• Natural vs. Synthetic

• How They Join (Type of Polymerization)– Addition– Condensation

• How They Respond to Heat– Thermoplastics– Thermosets

Natural and Synthetic Polymers

Natural Synthetic (man-made)

• Skin ▪ Plastic bags• Cotton ▪ Polyester fiber• Starch ▪ Glue• Latex (natural rubber) ▪ synthetic Rubber• Silk ▪ Polyurethane Foams• Vitamin C ▪ Vitamin C • Cellulose ▪ Polyethylene

NOTE: Our resource for the raw materials to make synthetic polymers is oil (petroleum).

Polymers Natural vs Synthetic

• Natural – Rubber (latex)– Cotton–Wool

• Synthetic – Plastics – All around us • Clothes, containers, packaging, etc…

Industrially Important Polymers

Polyethylene (PE)

POLYMER MER APPLICATIONS

Polypropylene (PP)

electrical wire insulation, flexible tubing, squeeze

bottles

carpet fibers, ropes, pipes liquid containers (cups,

buckets, tanks)

Industrially Important Polymers

Polystyrene (PS)

POLYMER MER APPLICATIONS

Polyvinyl Chloride (PVC)

packaging foams, egg cartons, lighting panels,

electrical appliance components

bottles, hoses, pipes, valves, electrical wire

insulation, toys, raincoats

Polyethylene

LDPE (sandwich wrap)• Low density polyethylene (trees with branches)

HDPE (milk jug)• High density polyethylene (trees without

branches)

Polymer Structures

• Linear Polymers

• Branched Polymers

• Cross-Linked Polymers

• Networked Polymers

Various Polymer Structures

Linear Structure

• Molecules are free to move. Slide back & forth against each other easily, so they are thermoplastic: can be reshaped or reformed with heat.

Branched Structure

• Side chains prevent easy movement. More heat required to soften, but still mostly thermoplastic.

Side chain

Cross-linked Structure

• Adjacent molecules have formed bonds, so individual molecules can’t slide past each other. They retain their shape when heated, so are thermoset: cannot be reformed with heat (not recyclable).

Holding chains together

• covalent bonds – stronger – ex. rubber

• intermolecular forces – weaker – ex. slime

• entanglement – ex. HDPE – – (analogy: 50 pieces of yarn – each 6

feet long – jumble and wad them up – throw them down in a pile on the ground – try to pull out one piece – what happens???)

Polymer Networks Include amorphous and crystalline regions:

Classifying Polymers: Response to Heat

• Thermoplastic–Reforms/reshapes with heat–All recyclables–Milk jug

• Thermoset–Sets with chemical reaction

• Elastomer – Is elastic

Polymers • Timeline of Plastics • 1868     Cellulose Nitrate • 1900     Viscose Rayon • 1909     Phenol-Formaldehyde • 1927     Cellulose Acetate • 1933     Polyethylene • 1936     Acrylic or Polymethyl Methacrylate • 1938     Polystyrene • 1939     Nylon • 1941     Polyethylene Terephthalate • 1942     Low Density Polyethylene • 1942     Unsaturated Polyester • 1957     Polypropylene • 1964     Polyimide • 1970     Thermoplastic Polyester • 1978     Linear Low Density Polyethylene • 1985     Liquid Crystal Polymers