Transcript Section_11-3

Section 11.3—Polymers
How do polymer properties vary for various applications?
Polymers & Monomers
Polymer – Very large molecules built
from chains or networks of smaller
molecules (usually 1,000 to 50,000
smaller molecules).
Monomer – The smaller molecules
making up the polymer.
Polymer Structures
Polymers can be made of:
Repeating patterns of monomers
One monomer over and over again
Random combinations of polymers
Structure of polymer determines the
properties of the polymer
Functional groups can affect properties
Sequence and type of monomers can affect
properties
Thermoplastic & Thermoset
Thermoplastic polymer – can be
heated and molded into another shape
and then cooled. This can be done
over and over again.
Thermoset polymer – Cannot be
heated and re-molded.
Why can’t thermoset plastics be re-molded?
When thermoset polymers are shaped for
the first time, cross-linkages are formed.
Cross-linkages are connections between
various polymer strands that hold the polymers
in place next to each other
Heating does not break these crosslinkages
So even when heated you can’t break these
chains apart and reshape them.
Addition & Condensation reactions
Addition Polymerization – each
monomer is added onto the end with
the use of an initiatior.
Condensation Polymerization – Two
monomers combine and release a small
molecule, usually water.
Initiators & Radicals
Initiator – Something that gets a
reaction started. Often is a radical.
Radical – Molecule with one free
electron that is very reactive as it tries
to get a full valence shell.
Carbon
atom
with one
free
electron
Addition polymerization
A monomer Is
exposed to an
initiator (Z)
and forms a
highly reactive
structure
Another
monomer
collides
with the
reactive
structure
And the two
monomers
join
This is repeated
over and over
again to form a
long chain
Addition Polymerization
When the initiator reacts with a monomer,
the monomer becomes very reactive and
reacts with another monomer and the
chain grows
Only need small amount of initiator
Occur rapidly
Builds a chain until all the monomers are
used or the reaction is quenched (stopped
by the addition of another compound)
Addition Polymerization, continued
 Are usually exothermic
 Produce large polymers
 Can produce unwanted, uncontrolled results
Side-branching can occur, resulting in different polymers
produced in the same “batch”
 Rubber is a polymer of isoprene.
But when allowed to react uncontrolled, rubber is not the
product.
A regulator (enzyme, catalyst, etc.) is needed to insure
the monomers combine in the correct order
Condensation polymerization
Two monomers with functional groups react
And release a small molecule
And then this process repeats
Condensation Polymerization
A small molecule is released when two
molecules condense (combine)
Often a water molecule is released
The released molecule must be removed
to drive the reaction to the right
Le Chatelier’s Principle
Do not need initiator
Produce smaller, more controlled
polymers
Polymer Properties
 Strength of intermolecular forces between
polymer chains depends on functional groups
and side-branching of polymers
 More intermolecular forces between polymer
chains =
Higher melting & boiling points
More rigid polymers
 More side-branching =
Chains less able to pack closely and form IMF’s
Lower melting & boiling points
Less rigid polymers
Polymer Properties
 Cross-linkages are chemical bonds (as opposed
to the physical attractions of intermolecular
forces)
Once formed, a chemical reaction must occur to break
them (remember thermoset plastics!)
Cross-linkages can change a liquid polymer into a solid
or gel-like polymer
 The properties of the polymer determine the
recycling needs of the polymer
Triangles on the bottom of plastics with numbers in them
indicate how the plastic is to be recycled
Polymers in Biology
Polymers are found everywhere in nature:
Proteins
DNA
RNA
The monomers that form these polymers
are called amino acids
There are 20 different amino acids, that in
different combinations make up the different
polymers in our body.
What did you learn about
polymers?
Polymers
Are made of
Bond type
Monomers
Which are
Can be
Organic
compounds
Properties vary
with
Which contains
chains of
Carbon
atoms
Structure
Functional
Group