Transcript CHE 351 POLYMER TECHNOLOGY * Polymer (Poly many) & …

CHE 411
POLYMER TECHNOLOGY
Prof. AbdulAziz A. M. Wazzan
CHAPTER ONE
Polymer Chemistry
INTRODUCTION

Polymer (Poly  many) & (meros  part)

Polymer is a long molecule consisting of many small units
(monomers) joined end to end (together).
Example:
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Polyethylene 1 [ CH2 - CH2 ]n 2
where:
n  number of ethylene monomers which join together to
form a molecules. Usually of order 10 4 up to 106
1 , 2  The end group at very small concentration,
they have no effect on the mechanical properties of the
polymer but it give a chemical stability. (Initiate a
degradation process) (Unzips).
 There
are two molecular factors that affect
the mechanical properties of a polymer.
 1. The length of the molecules which is  to
n which is  to molecular size or relative
molar mass
 2. The shape of the molecules. (Branches),
branching affected by the polymerization
conditions. Branching can affect the
toughness, creep resistance and the modulus.
CLASSIFICATION OF POLYMERS
Polymer
Thermoplastics
Crystalline
Thermosets
Elastomers
Amorphous
(non crystalline)
This classification based on the molecular
structure of the polymers.
STRUCTURE

*
Polymer macromolecules have a linear structure which
represented with a chain with two ends.
linear
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*
or nonlinear structure such as branched and Network
Branching point
branched
*
Junction point
network
Branched polymer have side chains or branches of significant
length which are bonded to the main chain at branch point.

Example
 Heating ethylene gas at  200 oC and high pressure of 
2000 atmosphere in the presence of suitable
polymerization initiation will result in LDPE used for
film & packaging.
New site for branching
[ C-C-C-C=C-C-C]
Low pressure process give linear PE or HDPE
Used for pipe, bottles.
There is also LLDPE made with copolymerization
of ethylene with suitable butane co-monomens
using ziegler - Natta type catalysis.
CROSS LINKED POLYMERS
A
three dimensional structures in which
each chain is connected to all others by a
sequence of junction points. They are
characterize by their crosslink density or
degree of crosslinking.
THERMOPLASTICS: (Plastics)

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Linear or branched which can be melt upon the application of heat.
They can be moulded in different shape using different techniques. Such
as injection moulding and extrusion.
Crystallization is not easily obtained upon cooling to the solid state
because it required a considerable ordering of the highly coiled and
entangled macromolecules.
These which crystallize do not form perfectly crystalline materials but
(sime-crystalline) with both crystalline and amorphous regions.
Crystalline can be characterized by Tm (melting temperature). where as
Tg (Glass Transition Temperature) characterize the amorphous required
for both (amorphous polymer and sime crystalline)
Tg is the temperature at which the material transform from the glassy
state (hard) to the rubbery state (soft). (On set of chain motion) below Tg
chain are not moving and frozen.
Both Tg and Tm increases with increasing the chain stiffness and force of
intermolecular attraction
ELASTOMERS

* Crosslinked rubbery polymers which can be
stretched easily to high extensions (3 to 10 times
there original length) and rapidly recover to the
original dimension when the applied stress is
released.
THERMOSETS
* Normally rigid materials and net-work
polymer where chain motion is restricted by a
high degree of crosslinking .
 example (eggs).

HOMOPOLYMERS
Definition of a homopolymer is a polymer derived
from one species of monomer (one type of Repeat
Unit R.U.)
 ---- A-A-A-A-A-A--- or [ A ]n
 where:
 n is the number of R.U. linked together to form
the macromolecule.
 See table 1.1
slight difference in chemical
structure can lead to very significant difference in
properties.

COPOLYMERS

Definition is a polymer derived from more than
one species of monomer (two or more type of
repeat unit R.U.).
CATEGORIES OF COPOLYMERS
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1. Statistical copolymer are copolymers which the sequential distribution of
the R.U. obeys known statical laws.
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2. Random copolymer it is one typed statistical copolymer in which the
distribution of R.U is truly random.
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----A-A-B-B-B-A-A-B-B-B-A-A-A----
----B-A-A-A- B-B-A-A-B-A-A-A-----
3. Alternating copolymer have only two different types of R.U. and these are
arranged alternately along the polymer chain.
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
-----A-B-A-B-A-B-----
The above three have a properties which are intermediate to those of the
desirable properties. Of the homopolymer in one single materials.
4.
Block copolymers a linear copolymers in which the R.U. exist
only in long sequences. Or blocks of the same type.

Di block -----A-A-A-A-A-B-B-B-B-B-B-B-B----

Tri block ----A-A-A-A-B-B-B-B-B-A-A-AA------
5.
Graft copolymers are branched polymers in which the
branches have a different Chemical structure to that of the main
chain.
B-B-B-B-B----------A-A-A-A-A-A- A-A-A-A-A-A----B-B-B-B-B-B-B-----Block & Graft properties characteristic of each of the constituent
homopolymers.
Example
Rubber toughened particles
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