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Dr. P. Lucas
U of A
MSE 110
Polymers properties
SUMMARY FROM LAST CLASS
•T
h
e
numberaverage molecular weight
is expressed as:
Where x
i
is the fraction of chain within the size range i. And M
i
is the mean
molecular weight of the chain range i.
•
The probability of entanglement increases with chain length hence the viscosity and
consequently the Tg increases with polymer chain length.
•
Crosslinking of the polymer chain limits sliding or “reptation” and improve the
mechanical properties of the polymer.
•A
n
elastomer
stretches under applied stress but can regain its shape.
•
Thermoplastic
polymers can be reversibly melted.
•
Thermosetting
polymers undergo extensive covalent crosslinking when heated and
become permanently rigid.
•
The Elastic Modulus E of a linear chain polymer change from solid to rubbery to
liquid when heated.
•
Simple polymer chains can fold and align to form crystalline platelets.
•
Crystalline polymers are a mixture of up to 70% crystallite embedded in a
amorphous matrix.
•
Elastic deformation
corresponds to a reversible deformation
•
Plastic deformation
corresponds to an irreversible deformation
•
Cold drawing of crystalline polymers align the chains in the direction of the stress
and therefore improve the tensile strength by a factor up to ×5.
∑
=
i
i
n
M
x
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View Full Document Dr. P. Lucas
U of A
MSE 110
Network polymers
•
Resin + hardener are mixed to initiate
polymerization and form a highly cross
linked 3D network polymer.
POLYMERS
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This note was uploaded on 11/19/2009 for the course MSE 110 taught by Professor Lucas during the Spring '08 term at University of Arizona Tucson.
 Spring '08
 Lucas

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