Chemistry Reference
In-Depth Information
(a)
Viscous
liquid
Rubbery
Mobile
liquid
T
g
Rigid glassy solid
Molecular weight
(b)
Rubbery
liquid
Viscous
liquid
Mobile
liquid
Rubbery
T
m
Tough, leathery solid
T
g
Rigid
semicrystalline
solid
Crystalline
solid
Molecular weight
FIGURE 4.3
Approximate relations between temperature, molecular weight, and physical state for (a)
an amorphous polymer and (b) a semicrystalline polymer.
size and perfection of crystallites. Chain ends ordinarily have different steric
requirements from interchain units, and the ends will either produce lattice imper-
fections in crystallites or will not be incorporated into these regions at all. In
either case,
T
m
is reduced when the polymer contains significant proportions of
lower molecular weight species and hence of chain ends.
4.3
Crystallization of Polymers
Order is Heaven's first law.
—Alexander Pope, Essay on Man
Sections of polymer chains must be capable of packing together in ordered peri-
odic arrays for crystallization to occur. This requires that the macromolecules be
