Lecture 4 Chapter 13 - Polymers• Functional Groups

• Condensation Rxns

• Free Radical Rxns

Chemistry – the whole year on one page• Last semester

– Basic atomic theory– Stoichiometry, balancing reactions– Thermodynamics (intro)– Light, spectroscopy– Electrons, orbitals, quantum numbers– Bonding, molecular shapes and orbitals– Intermolecular interactions, phases

• This semester– Solutions, colligative properties– Polymers– Thermodynamics (revisited), enthalpy and entropy– Kinetics, reaction mechanisms– Equilibria– Acids, bases, and buffers– Redox reactions and electrochemistry– Nuclear chemistry– Coordination chemistry

Polymers

• Medium to huge molecules– Made by repeating many (poly) small units (mers)

• Enable the huge variety of life & modern materials– Difficult to overestimate $$ importance of polymers– Essentially all biological reactions and structures are

polymers

Making Polymers

• We will deal entirely with organic polymers (C-based)• Key to making polymers is controlling chemical reactions• Functional groups are key sites of reactivity

– Basically anything that is not a C-C single bond– Sites of typical reactions– Used to classify organic compounds– Serve as a basis for naming compounds

Alcohols• Alcohols are organic compounds whose functional group

is the hydroxyl group (or -OH) bonded to a tetrahedral carbon (i.e., four single bonds).

C OC

The hydroxyl functional group

H HH H

H HThe chemical formula is usually written C2H5OH

Thiols• A thiol is just like an alcohol except the O has been

replaced by S

C SC

The thiolfunctional group

H HH H

H H

• Classified depending on the number of carbon atoms bonded to the -C-OH

CH3- C - OH

H

HPrimary (1°)

CH3 - C - OH

H

CH3

Secondary (2°)CH3 - C - OH

CH3

CH3

Tertiary (3°)

Classification of Alcohols

This classification scheme is generally used for all functional groups.

Amines

• The functional group of an amine is an amino group - a nitrogen atom bonded to one, two or three carbon atoms

H - N - R

H

: H - N - R

R : R - N - R

R

:

H - N - H

H

:

Ammonia – not an amine

1°, 2°, and 3° amines

Note that R generally means any organic thing. It could be as simple as CH3, or something really big and complicated.

Aldehydes and Ketones

• Aldehydes and ketones contain a carbonyl group, C=O• In an aldehyde, the carbonyl group is terminal - bonded to

a hydrogen, a -CHO group• In a ketone, the carbonyl group is internal - bonded

between two carbon atoms

H - C - C - C - H H - C - C - C - H

H H O

H H

H HO

H H

propanaldehyde

(an aldehyde)

acetone

(a ketone)

Carboxylic acid

• Organic acids contain a carboxyl group… -COOH• It’s a combination of a carbonyl (C=O) and a

hydroxyl (-OH) group• carbonyl + hydroxyl = carboxyl

• The carboxyl group always terminates a chain of carbon atoms

- C -

O=

-OH - C - OH

O=

CH3 - CH2 - C - OH

O= propanoic acid

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, squeeze bottles, 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?

0%5%5%2%88% 1. 0

2. 983. 994. 1005. 199

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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?

24%5%52%19% 1. Nylon 86

2. Kevlar3. Protein4. Silk

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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 are at least as important.)

Effect of cross-linking on rubber

Today• Finish up CAPA #2 (due tomorrow)

Friday• Finish reading Chapt 13• Go to seminar