Rana zia ur rehman
Graduate Reseracher at KASIT (Korea Advanced of science & Technology)
My Email ID: email@example.com
Published on: Mar 4, 2016
Transcripts - Polymer 2
TOPIC TO BE PRESENTED
WHAT ARE POLYMERS
The word polymer is derived from the Greek words
poly- meaning "many"; and meros meaning "part".
The term was coined in 1833 by Jöns Jacob
A polymer is a large molecule (macromolecule)
composed of repeating structural units. These
subunits are typically connected by covalent
Starting in 1811, Henri Braconnot did pioneering
work in derivative cellulose compounds, perhaps
the earliest important work in polymer science.
A chemical reaction in which simple molecules
(monomers) are added to each other to form
long-chain molecules (polymers) without by-
The monomers that are involved in condensation
polymerization are not the same as those in
. In living cells, they may be synthesized by
enzyme-mediated processes, such as the
formation of DNA catalyzed by DNA polymerase.
Many commercially important polymers are
synthesized by chemical modification of
naturally occurring polymers.
The tensile strength of a material quantifies how much stress
the material will endure before suffering permanent
This is very important in applications that rely
upon a polymer's physical strength or durability. For example,
a rubber band with a higher tensile strength will hold a greater
weight before snapping. In general, tensile strength increases
with polymer chain length and crosslinking of polymer chains
The toughness is a measure of the energy a sample
can absorb before it breaks.
Young's Modulus quantifies the elasticity of the
polymer. It is defined, for small strains, as the ratio
of rate of change of stress to strain. Like tensile
strength, this is highly relevant in polymer
applications involving the physical properties of
polymers, such as rubber bands.
The physical state and morphology of a polymer have a strong
influence on its mechanical properties. A simple measure of the
differences produced in mechanical behaviour is the elongation
that occurs when a plastic is loaded (stressed) in tension.
The term melting point, when applied to polymers, suggests
not a solid-liquid phase transition but a transition from a
crystalline or semi-crystalline phase to a solid amorphous
THERMOSET POLYMERS BECOME HARD AND EVENTUALLY
BURN ON HEATING THEY ARE NOT RECYCLEABLE
THERMOPLASTIC POLYMERS ARE SOFTEN AND MELTED ON
THERE ARE TWO TYPES OF POLYMERS
POLYMERS THAT CONTAINS SINGLE TYPE OF
REPEATED UNIT ARE CALLED HOMOPOLYMERS
POLYMERS WHICH ARE MADE OF DIFFERENT
TYPES OF MONOMERS ARE CALLED
IT IS THE AVERAGE NO OF MERS IN A POLYMER.GREATER
THE DEGREE GREATER WILL BE THE MOLECULAR WEIGHT
Polymers are not crystalline in nature but to
some extant crystallinity can be induced in it by
The physical properties of a polymer are strongly dependent on the
size or length of the polymer chain. For example, as chain length is
increased, melting and boiling temperatures increase quickly .Impact
resistance also tends to increase with chain length.
Polymer degradation is a change in the properties—
tensile strength, color, shape, molecular weight, etc due
to environmental factors, such as heat, light, chemicals
etc. It is often due to the scission of polymer chain
Rubber is the most important of all elastomers.
Natural rubber is a polymer whose repeating unit is
isoprene. This material, obtained from the bark of the
rubber tree, has been used by humans for many
The two main types of plastics are thermoplastics and thermosets.
Thermoplastics soften on heating and harden on cooling while
thermosets, on heating, flow and cross-link to form rigid material
which does not soften on future heating. Thermoplastics account
for the majority of commercial usage e.g polyethylene
Natural fibers such as cotton, wool, and silk have been
used by humans for many centuries. In 1885, artificial silk
was patented and launched the modern fiber industry.
Man-made fibers include materials such as nylon,
polyester, rayon, and acrylic.