Lecture # 9
Polymer structure
Characteristic ,Applications and processing of
polymers
Learning objectives:
1- Describe a typical polymer molecule in terms of its structure
and how the molecule may be generated from repeat unit.
2- Cite the differences in behavior for thermoplastic and
thermosetting polymers.
3- Describe the mechanical properties of polymers.
4-State the applications and processing of polymers.
What are Polymers?
• Greek word Poly = many; Mer = unit 
Polymer = many units
• The term polymer denotes a molecule made
up by the repetition of smaller molecules, the
monomer.
• The repeating structure is mostly based on a
carbon backbone.
2
2
Polymers
Polymer = Poly + mer
Polymerization
Mers
Polymer
3
Other Examples:
H
H
Poly(ethylene) (PE)
H
H
F
F
F
F
Poly(tetrafluoroethylene)
(PTFE Teflon)
Cl
CH3
Poly(vinyl chloride)
Poly(propylene)
(PVC)
(PP)
4
Chain Microstructure
5
5
Polymer structure chain:
THERMOPLASTIC AND THERMOSETTING POLYMERS
Thermoplastics:
Thermoplastics soften when heated (and eventually liquefy)
and harden when cooled—processes that are totally reversible
and may be repeated.
THERMOSETTING POLYMERS
Thermosetting polymers are network polymers.They become
permanently hard during their formation, and do not soften
upon heating.
POLYMER CRYSTALLINITY
The crystalline state may exist in polymeric materials. However,
since it involves molecules instead of just atoms or ions, as with
metals and ceramics, the atomic arrangements will be more
complex for polymers.
We think of polymer crystallinity as the packing of molecular
chains to produce an ordered atomic array. Crystal structures may
be specified in terms of unit cells, which are often quite complex.
DEFECTS IN POLYMERS
Mechanical Behavior of Polymers
STRESS–STRAIN BEHAVIOR
Three typically different types of stress–strain behavior are found for
polymeric materials, as represented in Figure 15.1. Curve A illustrates
the stress–strain character for a brittle polymer, inasmuch as it fractures
while deforming elastically.
The behavior for a plastic material, curve B, is similar to that for many
metallic materials; the initial deformation is elastic, which is followed by
yielding and a region of plastic deformation. Finally, the deformation
displayed by curve C is totally elastic; this rubber-like elasticity (large
recoverable strains produced at low stress levels) is displayed by a class
of polymers termed the elastomers
Polymer Synthesis and Processing
Polymerization
Polymer Additives
•The final sections of this lecture treated synthesis and fabrication techniques for
polymeric materials. Synthesis of large molecular weight polymers is attained by
polymerization, of which there are two types: addition and condensation. The properties
of polymers may be further modified by using additives; these include fillers,
plasticizers, stabilizers, colorants, and flame retardants.
Forming Techniques for Plastics
•Fabrication of plastic polymers is usually accomplished by shaping the
material in molten form at an elevated temperature, using at least one of
several different molding techniques—compression, transfer, injection, and
blow. Extrusion and casting are also possible.
Fabrication of Fibers and Films
•Some fibers are spun from a viscous melt, after
which they are plastically elongated during a
drawing operation, which improves the mechanical
strength. Films are formed by extrusion and
blowing..