Transcript Polymers

Polymers
Larry Scheffler
Version 1.0
Definitions
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Polymer: a long chain molecule made
up of many small identical units.
Monomer: the smallest repeating unit of
a polymer (propene in polypropylene).
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IUPAC Definition
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A polymer is a substance composed of
molecules characterized by the multiple
repetition of one or more species of
atoms or groups of atoms (constitutional
repeating units) linked to each other in
amounts sufficient to provide a set of
properties that do not vary markedly with
the addition of one or a few of the
constitutional repeating units.”
Common Polymers
• Polymers are common in nature. Wood,
rubber, cotton, silk, proteins, enzymes,
and cellulose are all examples of polymers
• A wide variety of synthetic polymers have
been produced, largely from petroleum
based raw materials. These include
polyurethane, teflon, polyethylene,
polystyrene, and nylon.
Common Polymers
Polymer Recycling Codes
Common household polymers
Polymers
• The number code indicates the polymer type
Polymers
• Types of synthetic and natural polymers.
Addition Polymers
• Addition polymerization: a reaction in which
unsaturated monomers combine with each other to form
a polymer
• Example: Tetrafluoroethene can be polymerized to form
polytetrafluoroethene, commonly known as Teflon
Addition Polymers
• Some common addition polymers
• Many plastics are
addition polymers
made from
hydrocarbon
sources.
• The hydrocarbon
must be
unsaturated in order
to polymerize
Addition Polymers
• Polyvinyl chloride
• Polyvinyl chloride or
PVC is wide used
for pipes and other
structural materials
• Vinyl chloride is
also known as
chloroethene
Condensation Polymers
• Condensation polymers form from
condensation reactions.
• In a condensation polymer a smaller
molecule such as water is eliminated
• In order to form a condensation polymer
the monomer must have two functional
groups
Example of a Condensation
Polymer
• Nylon 6-6 is a condensation polymer
• It is also a copolymer since it is made from
two different monomers
Example of a Condensation
Polymer 2
• Dacron is also a condensation polymer
Ethylene Glycol (1,2ethanediol)
para Terephthalic acid
Dacron is an example of a polyester
• It is also a copolymer since it is made from two
different monomers
Co-polymers
• Co polymers are made from than one
monomer
• Many natural polymers are copolymers.
For example, proteins are condensation
polymers formed by joining as many as 20
different amino acids
Polymer Structure
• Molecular Mass:
– Polymers are high molecular mass structures
– Extremely large molecular weights are to be found in
polymers with very long chains.
• Molecular Shape:
– Polymer chain molecules are usually straight chains
– These chains may bend, coil and kink, leading to
extensive intertwining and entanglement of neighboring
chain molecules.
– These random coils and molecular entanglements are
responsible for many of the important characteristics of
polymers.
The Polymer Structure
Determines its Characteristics
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The physical properties of a polymer, such as its strength
and flexibility depend on:
Chain length - In general, the longer the chains the
stronger the polymer;
Side groups - Polar side groups give stronger attraction
between polymer chains, making the polymer stronger;
Branching - Straight, unbranched chains can pack
together more closely than highly branched chains.
These polymers are more crystalline and therefore
stronger;
Cross-linking - If polymer chains are linked together
extensively by covalent bonds, the polymer is harder and
more difficult to melt.
Structure: Linear Polymers
–Linear Polymers have monomer
units that are joined together end to
end in single flexible chain.
–Linear polymers have extensive van
der Waals attractions between the
chains.
–Examples: polyethylene, polyvinyl
chloride, polystyrene, and nylon
Structure: Branched Polymers
– Branched Polymers have side or branch
chains are connected to the main ones.
– The branches, considered to be the part
of the main-chain molecules, result from
side reactions that occur during the
synthesis of the polymer.
– The packing efficiency is reduced with
the formation of side branches, which
results in a lowering of the polymer
density
Structure: Cross-Linked Polymers
– Adjacent linear chains are joined one to
another at various positions by covalent
bonds.
– The process of cross linking is achieved either
during synthesis or by a nonreversible
chemical reaction that is usually carried out at
an elevated temperature.
– This cross linking is accomplished by additive
atoms or molecules that are covalently bonded
to the chains.
– Many of the rubber elastic materials are cross
linked. In case of rubbers, it is called
vulcanization
Structure: Network Polymers
– Network Polymers have trifunctional
monomer units,
– Having three active covalent bonds allow
these polymers to form three-dimensional
networks instead of the linear chain
framework
– Network polymers have distinctive
mechanical and thermal properties.
– Examples include epoxies and other
adhesives.
Polymer Properties
Cross-Linked Polymer
Stretch
Relax
The cross-links hold the chains together.
When released, the polymer will return to it's
original form.
Linear Polymer
Stretch
The chains can be stretched, which causes
them to flow past each other. When released,
the polymer will not return to its original form.
Polymer Microstructure
Polyolefins with side chains have stereocenters on every
other carbon
CH3
n
CH3 CH3 CH3 CH3 CH3 CH3 CH3
With so many stereocenters, the stereochemistry can be complex.
There are three main stereochemical classifications for polymers.
Atactic: random orientation
Isotactic: All stereocenters have same orientation
Syndiotactic: Alternating stereochemistry
Microstructure and Properties
• Tacticity affects the physical properties
– Atactic polymers will generally be amorphous, soft,
flexible materials
– Isotactic and syndiotactic polymers will be more
crystalline, thus harder and less flexible.
• Polypropylene (PP) is a good example
– Atactic polypropylene is a low melting, gooey material
– Isoatactic polypropylene is is high melting (176º),
crystalline, tough material that is industrially useful
– Syndiotactic polypropylene is has similar properties,
but is very clear. It is harder to synthesize