Transcript Chemistry You Need to Know

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.
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.