Lecture 2 Polymerization Rxns• Review functional groups

• Free-radical polymerization

• Condensation

• Types of polymers

Functional Group Summary

Alcohol Ether Thiol

Carboxyl

Aldehyde Ketone

Phosphate

Polymerization Reactions

There are four main types of polymerization reactions1. Free Radical Polymerizations.2. Condensation Polymerizations.3. Cationic Polymerizations.4. Anionic Polymerizations.

We will only talk about the first two

Free Radical Polymerization

Most free radical polymerizations involve 3-steps1. Initiation – to get things started2. Propagation – to grow the polymer3. Termination – to end the reaction

A good example is the synthesis of polyethylene (polyethene)• HDPE and LDPE are used in beverage containers, toys,

tubing, etc.

• Initiation – Formation of a free radical – often by heating a peroxide.(this is slightly different than described by textbook)

• Termination – the process ends when two radicals collide and react.

• Propagation – the free radical reacts with an ethylene, which gives a free radical to react with another ethylene, which gives…

Other Polyalkenes react similarly

Ethylene (C2H4) contains a C=C double bond.How many double bonds are in a molecule of polyethylene that is composed of 100 ethylene units?

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20%20%20%20%20% 1. 0

2. 983. 994. 1005. 199

Condensation Reactions• Reactions that generate water as a product (in general)• Three main types

– alcohol + alcohol ether + water

– carboxylic acid + amine amide + water

– carboxylic acid + alcohol ester + water

Functional Group Summary

Alcohol Ether Thiol

Carboxyl Ester Amide

Aldehyde KetonePhosphate

Condensation Polymers• Polymer versions of these reactions generate

– Polyethers– Polyamides– Polyesters

• For instance, nylon 66 is a polyamide

Which of the following is a polyamide?

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25%25%25%25% 1. Nylon 86

2. Kevlar3. Protein4. Silk

Polymer Properties• Intermolecular Interactions are critical• Individual molecules are weak• Joining molecules together restricts motion – stronger

• Molecules connected by Van der Waals forces (polyethylene), H-bonds (silk, nylon), covalent bonds (rubber).

• The creation of covalent bonds between polymers is called cross-linking

• First big application was rubber – 1839 Charles Goodyear

Degree of cross-linking controls properties

(Of course, properties of the monomers is more important.)

Effect of cross-linking on rubber

Types of Polymers

• Polymers can be divided into three categories based on their form and resistance to stretching:– Plastics (polyethylene, nylon, polyvinylchloride)– Fibers (nylon, dacron, kevlar)– Elastomers (rubber)

Plastics

• Plastic is a type of polymer that hardens on cooling or evaporation of the solvent.– Thermoplastics – plastics that melt or deform when

heated• High Density Polyethylene (HDPE) – very rigid and

strong, used to make bottle caps, toys, cabinets for electronic devices

• Low Density Polyethylene (LDPE) – soft, semi-rigid, used to make plastic bags, squeeze bottles

– Thermosetting – plastics that retain their structural integrity when heated

• Formica

Fibers

• Synthetic fibers are thin threads of polymer made by forcing a fluid thermoplastic material through a set of tiny pores

• Polar functional groups produce strong dipolar forces that add significant strength to the material.

Kevlar

Elastomers• A flexible polymer that can be distorted.• Most contain alkenes (double bonds)

– Combination of single and double bonds prevents tight packing of chains

• The polymer chains are held together by cross-links.• Cross-links – links formed across chains in addition to the

bonds along the chains.• The number of cross-links will determine the degree of

flexibility and the strength of the polymer.

Today• Chemistry seminar 4:00

Monday• Finish CAPA

– Tutors available Sun 6-8 and Wed 8-10 SC3031• Finish reading Chapt 13• Write up extra credit report