Page 82 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Polymer Structure (Morphology) 45

TABLE 2.6
General Property Performance–Structure Relationships
Addition of
Increased Increased Addition of Backbone
Increased Cross- Increased mol. wt. Polar Back Stiffening
Crystallinity linking mol. wt. Distribution Bone Units Groups
Abrasion + + + − + −
resistance
Brittleness − M + + + +
Chemical + V + − − +
resistance
Hardness + + + + + +
+ + + − + +
T g
Solubility − − − 0 − −
Tensile strength + M + − + +
Toughness − − + − + −
Yield + + + + + +
+, increase in property; 0, little or no effect; −, decrease in property; M, property passes through a maximum; V, variable
results dependent on particular sample and temperature.

R

R S S
R R
S
S
S
R S S S R
R
R

R
R

FIGURE 2.19 Chemical cross-linking of polyethylene chains through formation of disulfi de linkages.

Chemical cross-linking is given many names depending on the particular area of application.
For instance, for hair, the name “setting” is often associated with the breakage and subsequent ref-
ormation of thiol cross-links. For tires, the terms vulcanization and curing are associated with the
formation of sulfur-associated chemical cross-links (Figure 2.19).

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