Assignment 3 Polymeric Materials VU21218
Assignment 3 Polymeric Materials VU21218
Assignment 3 Polymeric Materials VU21218
Polymers are very useful materials because their structures can be altered
and tailored to produce materials. A polymer is composed of many simple
molecules that are repeating structural units called monomers. Covalent
bonds hold the atoms in the polymer molecules together and secondary
bonds then hold groups of polymer chains together to form the polymeric
material. Copolymers are polymers composed of two or more different
types of monomers. Carbon is the most common element in polymers.
The chemical bonds in polymers are also different than those found in
metals and ceramics. A molecule is a group of atoms held together by
covalent bonds. Examples of polymers are polyvinyl chloride (PVC). Typical
structures are
Double and triple bonds can exist between C atoms (sharing of two or
three electron pairs). These bonds are called unsaturated bonds.
Unsaturated molecules are more reactive.
Ethylene, C2H4
Supersaturated polymeric molecules are not possible under normal,
unmodified circumstances. In order to supersaturate a polymeric
molecule, temperature can be raised, which allows more solvent to be
dissolved into the polymeric molecules.
Alternatively, high
Addition polymerisation;
Condensation polymerisation.
will increase at a constant rate. The heat amount of heat required to raise
the temperature of one gram of the polymer one degree Celsius is called
the heat capacity.
Now the temperature will continue to increase until the polymer reaches
its melting point. When this happens, the temperature will hold steady for
awhile, even though you're adding heat to the polymer. It will hold steady
until the polymer has completely melted. Then the temperature of the
polymer will begin to increase once again. The temperature rising stops
because melting requires energy. All the energy you add to a crystalline
polymer at its melting point goes into melting, and none of it goes into
raising the temperature. This heat is called the latent heat of melting.
So, two things happen when a crystalline polymer melts: It absorbs a
certain amount of heat, the latent heat of melting, and it undergoes a
change in its heat capacity. Any change brought about by heat, whether it
is melting or freezing, or boiling or condensation, which has a change in
heat capacity, and a latent heat involved, is called a first order transition.
The graph shows how the sample heats up at one rate below the Tg and
then heats up at a higher rate above the Tg. The lower slope below the Tg
is due to the lower heat capacity for the amorphous polymer. Above the
Tg, the rubbery, flexible polymer has a higher heat capacity.
The polymer does undergo an increase in its heat capacity when it
undergoes the glass transition. Because the glass transition involves
change in heat capacity, but it doesn't involve a latent heat, this transition
is called a second order transition.
Answer to the question no 6
Polymers are very large molecules that are made up of thousands - even
millions - of atoms that are bonded together in a repeating pattern. The
structure of a polymer is easily visualized by imagining a chain. The chain
has many links that are connected together. In the same way the atoms
within the polymer are bonded to each other to form links in the polymer
chain. The molecular links in the polymer chain are called repeat units
that are formed from one or more molecules called monomers.
Polymer Properties: The disordered tangling of the polymer chains
create what is known as an amorphous structure. Amorphous polymers
are typically transparent and much easier to melt to make materials like
kitchen cling film.
Properties of Polymers: 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
Applications of Polymers:
market.
Polymers also demanding in sports playground equipment, various
balls, golf clubs, swimming pools, and protective helmets are often
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