PowerPoint Lecture Presentation
by
J. David Robertson
University of Missouri
Organic Chemistry II :
Synthetic and Natural
Organic Polymer
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A polymer is a high molar mass molecular
compound made up of many repeating chemical
units.
Naturally occurring
polymers
•Proteins
•Nucleic acids
•Cellulose
•Rubber
Synthetic polymers
•Nylon
•Dacron
•Lucite
25.1
POLYMERS
Substances that consists of very large molecules called
macromolecules that are made up of many repeating
subunits called monomers.
Differences between monomers can affect properties of
polymer such as solubility, flexibility or strength.
Natural polymers
Synthetic polymers
Protein, cellulose,
natural rubber.
Polyethylene, poly (vinyl
chloride) polystyrene, etc…..
Homopolymer
Copolymer
The simple repeating unit of a polymer is the monomer.
Homopolymer is a polymer made up of only one type
of monomer.
( CF2
CF2 )n
Teflon
( CH2
CH2 )n
Polyethylene
( CH2
CH )n
Cl
PVC
25.2
Copolymer is a polymer made up of two or more
monomers.
( CH
CH2
CH2
CH
CH
CH2 )n
Styrene-butadiene rubber
25.2
Stereoisomers of Polymers:
R groups on same
side of chain:
Isotactic
R groups alternate
from side to side:
Syndiotactic
R groups disposed
at random:
Atactic
Comparisons of stereoisomer
Atactic
Syndiotactic
Isotactic
Soft and rubbery,
amorphous and
relatively weak.
Low density and
low tensile
strength but high
degree of
flexibility.
Have better
impact strength
than isotactic.
Has the highest
melting point,
greatest
crstallinity,
superior
mechanical
properties.
* Isotactic polymer can be synthesize selectively using
Ziegler-Natta catalysts.
The catalysts are based on titanium tetrachloride, TiCl4
and triethylaluminum, Al(C2H5)3.
• The tacticity of a polymer affects the
packing between molecules (crystallinity)
and thus affects its physical properties such
as the melting temperature, mechanical
strength and elasticity.
Structure regularity:
Isotactic > Syndiotactic > Atactic
25.2
POLIMERIZATION
The reactions by which monomers are joined
together.
Synthetic polymers are created by means of
a) addition polymerization;
b)condensation polymerization.
ADDITION POLYMERIZATION
Addition polymerization involves the
breaking of double or triple bonds, which
are used to link monomers in to chains.
The free radical mechanism explains how
the polymerization is initiated.
Free radicals are very reactive, short-lived atom
or molecule which have one or more unpaired
electrons.
ADDITION POLYMERIZATION
The free radical mechanism can be divided into
three stages:
a) Initiation
b) Propagation
c) Termination
ADDITION POLYMERIZATION
Initiation:
The creation of free radicals is necessary for
propagation.
May involve the formation of free radicals from stable
species or may involve reactions of free radicals with
stable molecules to form more free radicals.
ADDITION POLYMERIZATION
Propagation:
The rapid reaction of free radicals and monomers, and
the subsequent repetition to create the repeating chain.
ADDITION POLYMERIZATION
Termination:
Two radicals react in a way that prevents further
propagation, that is by coupling where two radicals
react to form a single molecule.
ADDITION POLYMERIZATION (additional info)
Symmetrical monomers such as ethylene and tetrafluoroethylene can
join together in only one way. Mono-substituted monomers, on the
other hand, may join together in organized ways, described in the
following diagram.
Most mono-substituted monomers, including propylene, vinyl chloride,
styrene, acrylonitrile and acrylic esters, prefer to join in a head-to-tail
fashion, with some randomness occurring from time to time. This is
because ‘head to tail’ polymer is more stable due to less steric
hindrance (less crowding of the substitution group).
CONDENSATION POLYMERIZATION
Also known as dehydration reaction in which two
monomers react with the concurrent loss of water.
Examples: polyester (Dacron); polyamide (Nylon
66, Kevlar); polyurethane (Spandex).
Usage of Some Plastics
Type of plastic
Usage
PET,
polyethyleneterephthalate
Soft drink bottles, photographic films, etc…
PVC, polyvinylchloride
‘Synthetic leather’ upholstery, water pipes,
bottles for cooking oils, garden hoses,
laboratory tubing, etc…
PS, polystyrene
Styrofoam, hot-drink cups, fast food
containers, etc…
PP, polypropylene
Drinking straws, bottle caps, bread and
cheese wrap, etc…
HDPE, high density
polyethylene
Containers for food, liquid detergents,
shampoo, etc…
LDPE, low density
polyethylene
Films for food wrapping, plastic bags, flexible
containers such as squeeze bottles for
condensed milk, etc…
HDPE vs LDPE
Linear PE vs Branched PE
High density
Low density
Linear PE (HDPE) is much stronger than
branched PE (LDPE), but LDPE is cheaper and
easier to make.
Low density Polyethylene (LDPE)
Produced by
ethylene gas.
free
radical
polymerization
of
Polymer chain with branching.
Low crystallinity, more flexible, melting point ~115oC.
Uses: film and sheet-packaging, trash bag,
household wraps, toys, squeeze bottle, etc…
A molecule of
LDPE.
High density Polyethylene (LDPE)
Synthesized from ethylene using metal as the catalyst.
Linear polymer molecule with no branches.
High crystallinity, stiffer, harder and more opaque
than LDPE.
Melting point 133oC-138oC.
Uses: containers and lid, food bottles, motor oil
bottles, etc…
A molecule of
HDPE.
Sample Questions:
1.
2.
Which pair of polymer both occurs naturally?
A. Starch and nylon.
B. Starch and cellulose.
C. Protein and nylon.
D. Protein and plastic.
E. Cellulose and nylon.
The segment below represents the polymer named
A. Polybutylene.
B. Polyvinyl chloride.
C. Polypropylene.
D. Polystyrene.
E. Polyethylene.
Sample Questions:
3. A manufacturer plans to construct plastic reagent
bottles, some of which will be used for 20%
solutions of hydrochloric acid and sodium
hydroxide. Among the following materials, which
would be least suitable for this purpose?
A. High density polyethylene.
B. Polypropylene.
C. Nylon 66.
D. Polystyrene.
E. Polyethylene oxide.
Sample Questions:
4. Which one of the following molecules COULD NOT
serve as a monomer for an addition polymer?
A.
D.
B.
E.
C.
Sample Questions:
5.
A polymerization reaction that produces small
molecules (such as water) as well as the polymer is
classified as a/an _________ polymer.
A
addition
B.
natural
C.
condensation
D.
elimination
E.
co-polymer
6.
What are Natta-Ziegler catalysts? What is their role
in polymer synthesis?
Sample Questions:
7.(a) Write all the equations involve in the three
steps of polymerization of ethylene,
CH2 = CH2 to form polyethylene.
(b)
What do you think is attached at the end of the
polymer chain when all of the ethylene monomer
molecules have been polymerized?
Sample Questions:
8.
Ethan-1,2-diol and hexan-1,6-dioic acid can produce
a long chain compound of repeating units whereas
ethanol and hexanoic acid are incapable of forming
a long chain compound.
(a)
What name is given to a long chain compound
formed by repeating units of small molecules?
(b)
What name is given to small molecules capable
of forming such long chain compound?
(c)
What type of reaction occurs in the linking of units
of ethanol and hexanoic acid?
(d)
What type of polymerization occurs in the linking of
ethan-1,2-diol and hexan-1,6-dioic acid?
Sample Questions:
9. Draw the polymer that is form by the reaction between:
HO2C-CH2-CH2-CH2-CH2-CO2H and
H2N-CH2-CH2-CH2-CH2-CH2-CH2-NH2
What type of polymerization reaction is this?
10. High density polyethylene (HDPE) and low density
polyethylene (LDPE) are both made from the same
monomer, ethylene. However, HDPE is tough and rigid,
whereas LDPE is soft and flexible. What difference in
structure accounts for the difference in the properties of
HDPE and LDPE?
Sample Questions:
11.
The structure of the monomer styrene is shown below:
Draw the structure of a portion of a chain of
polystyrene that contains two (2) repeating units.
12.
Below are some monomers used in making
polyamides and polyesters. Which two monomers
can be combined to make a polyamide?
Sample Questions:
13.
Match the following terms with the correct definition:
Ziegler-Natta catalyst , Isoprene , Homopolymer
Syndiotactic polymers
Definition
(i)
One of the major components that
constitute natural rubber and are used
to make synthetic rubbers.
(ii)
A polymer structure in which the monomer
units attached to the polymer backbone
alternate in a-b-a-b fashion on one side
of the backbone.
Answer
Sample Questions:
Ziegler-Natta catalyst , Isoprene , Homopolymer
Syndiotactic polymers
Definition
(iii) This polymer is formed from a single
monomer; an example is polyethylene,
which is formed from the polymerization
of ethylene.
(iv) These
compounds
on
titanium
tetrachloride and the organometallic
compound triethylaluminium, they are
used in the production of unbranched,
stereoregular polyalkene polymers.
Answer
Sample Questions:
14.
The addition polymer polyvinyl chloride (PVC) has the
structure:
(i)
Draw the structure of the monomer from which
PVC is made.
(ii)
How many monomer units are in a PVC polymer
that has a molar mass of 1.33  105 g/mol?
Sample Questions:
15.
The structures below represent two different samples
of polyethylene, each with the same number of
monomer units.
Structure I
Structure II
(i) Based on the concept of density, which is the
structure of high-density polyethylene (HDPE) and
which is low-density polyethylene (LDPE)?
(ii) List three (3) differences between LDPE and HDPE.