Importance of Functional Groups in the Synthesis of Polymers Indicators C-3.5 and C-3.7 South Carolina Science Standards Chemistry Section.

Importance of Functional Groups in the Synthesis of Polymers

Indicators C-3.5 and C-3.7South Carolina Science Standards

Chemistry Section

Cl CC Cl

O

O

NN H

HH

H

..

..

sebacoyl dichloride(decanedioyl dichloride)This is the same thing as

1,10-dichloro-1,10-decan-1,10-dialfor which you wrote a structural formula in the prelab quiz

1,6-hexandiamineThis is the same thing as

hexane-1,6-diaminefor which you wrote a structural

formula in the prelab quiz

The reaction illustrated here has been simplified and is just one of many methods for synthesizing nylon. The actual reaction has many more steps.

amine group

Pay close attention to how the reaction takes place between the functional groups. In this case the reaction occurs between an amine group and a carbonyl group.

carbonyl group

An alkyl halide group (a chloro- group) is also attached to the same carbon that is part of the carbonyl group.

alkyl halide group(chloro- group)

Nylon SynthesisExample of a step reaction

Cl CC Cl

O

O

NN H

HH

H

..

..

sebacoyl dichloride(decanedioyl dichloride)

This is the same thing as the 1,10-dichloro-1,10-didecanal for which you wrote a structural formula in the

prelab quiz

hydrocarbon parent chain

Notice also that the reaction is NOT taking place between the hydrocarbon groups in the parent chains or between the hydrocarbon groups and functional groups.

hydrocarbon parent chain

1,6-hexandiamineThis is the same thing as

Hexane-1,6-diaminefor which you wrote a structural

formula in the prelab quiz

The reaction IS taking place between functional groups.

CC Cl

O

O

sebacoyl dichloride(decanedioyl dichloride)

This is the same thing as the 1,10-dichloro-1,10-didecanal for which you wrote a structural formula in the

prelab quiz

NN

HH

H

..

..: H

Cl :..

: ..

1,6-hexandiamineThis is the same thing as

Hexane-1,6-diaminefor which you wrote a structural

formula in the prelab quiz

NN

HH

H

..

..:

CC Cl

O

O

sebacoyl dichloride(decanedioyl dichloride)

This is the same thing as the 1,10-dichloro-1,10-didecanal for which you wrote a structural formula in the

prelab quiz

H+

Cl :..

: ..+

1,6-hexandiamineThis is the same thing as

Hexane-1,6-diaminefor which you wrote a structural

formula in the prelab quiz

NN

HH

H

..

..:

CC Cl

O

O

sebacoyl dichloride(decanedioyl dichloride)

H+

Cl :..

: ..

covalent bond

This kind of polymerization reaction in which molecular growth occurs due to the interaction of functional groups is called step growth polymerization.

HCl must be removed from the reaction container to prevent decomposition (a reverse reaction).

The byproduct of THIS reaction is hydrochloric acid (HCl). Other step reactions produce different byproducts.

Note: You will learn more about reversible reactions in the equilibrium unit later in the semester.

Another term for this class of reaction is condensation polymerization. The term condensation refers to the production of the small byproduct; HCl.

1,6-hexandiamine

CC

O

OCl :..

: ..Cl :..

: ..

NN

H

HH

H ..

..:

:

NN

H

H

H ..

..:

:

CC

O

O

Cl :..

: ..

H+ + Cl

CC

O

OCl :..

: ..Cl :..

: ..

NN

H

HH

H ..

..:

:

Polymerization is not just one reaction between two molecules.

The reaction continues to covalently bond molecules together into really long chains.

Notice—again—how the reactions are all taking place at the functional groups and NOT at the hydrocarbon groups.

NN

CC

O

O

H

H

**n

The repeating unit in the polymer is usually indicated in this manner.

A polymer such as this one which was synthesized from 2 different monomers is called a copolymer.

This polymer is called nylon.

There are different forms of nylon. This particular form is called nylon 6, 8 due to the number of carbon atoms in the 2 copolymer parts of the repeat unit.

6 carbon chain

8 carbon chain

repeat unit

NC

CN

NC

CN

O

O

O

O

H

H H

H

NC

CN

NC

CN

O

O

O

O

H

H H

H

NC

CN

NC

CN

O

O

O

O

H

H H

H

NC

CN

NC

CN

O

O

O

O

H

H H

H

NC

CN

NC

CN

O

O

O

O

H

H H

H

NC

CN

NC

CN

O

O

O

O

H

H H

H

NC

CN

NC

CN

O

O

O

O

H

H H

H

NC

CN

NC

CN

O

O

O

O

H

H H

H

NC

CN

NC

CN

O

O

O

O

H

H H

H

NC

CN

NC

CN

O

O

O

O

H

H H

H

The long chains have a weak (side-to-side) attractions to each other. Because there are so many of them, however, the combination of these bonds is quite strong.

The weak(side-to-side) attraction is called hydrogen bonding.

The hydrogen bonds are NOT the same as covalent bonds. These hydrogen bonds are illustrated here as 3 dashed lines.

Note: This is the same kind of attraction that holds the 2 sides of DNA together.

PET SynthesisExample of a step growth polymerization

COCH3

O

C O CH3

O

ethylene glycol

dimethyl isophthalate

ester functional groups

hydroxyl or alcohol functional groups

Guess where the reaction will take place?

CH2 CH2 O HH O

PET SynthesisExample of a step growth polymerization

CH2 CH2 O HH O

COCH3

O

C O CH3

O

ethylene glycol

dimethyl isophthalate

esterification

A catalyst of some kind is needed to make this reaction occur.

OCH3 H

COCH3

O

C O CH3

O

COCH2

O

C O CH3

O

CH2OH

CH2 CH2 O HH O

methanol byproduct

ester group

Remember that this kind of polymerization reaction with more than one monomer and a byproduct is called a step growth reaction or condensation reaction.

Methanol must be removed from the reaction container to prevent decomposition (a reverse reaction).

The byproduct of THIS reaction is methanol (CH3OH).

COCH2

O

C O CH2

O

CH2O CH2C O C

O

C

OO

C

O

OCH2

repeat unit

OCH3 H

methanol byproduct:A methanol molecule is formed every time an

ester linkage is formed.

x

COCH2

O

C

O

CH2O* *n

polyethylene terephthalate

PET

ester group

This kind of polymer is called a polyester because the copolymers—dimethyl isophthalate and ethylene glycol—form an ester linkage. Through the structure, the ester is the highest priority functional group and it repeats itself over and over.

repeat unit

Polyethelene SynthesisExample of chain growth polymerization

ethylene(ethene)

CH2 CH2 CH2 CH2

A catalyst of some kind is needed to make this reaction occur.

Pay close attention to how the reaction takes place between the functional groups. In this case the reaction occurs between alkenyl groups (i.e. between double bonds).

CH2 CH2 CH2CH2CH2 CH2 CH2 CH2

CH2 CH2 CH2 CH2CH2 CH2

CH2CH2CH2CH2CH2CH2CH2 CH2 CH2 CH2

This kind of polymerization reaction which has just one type of monomer is called a chain reaction. An older term for this class of reaction is a addition reaction.

Polymer Synthesis

The BIG IDEA!• From this activity…

– You are NOT expected to understand all the intricacies of polymer synthesis.

– You ARE expected to understand from this activity that FUNCTIONAL GROUPS are the locations where reactions take place in organic chemical reactions.

The End