Chemistry Reference
In-Depth Information
10
8
6
Increasing plasticizer level
4
Temperature
FIGURE 4.11
Modulus versus temperature for a plasticized amorphous polymer.
4.4.2
Effect of Polymer Structure on T
g
Observed
T
g
's vary from
123
C for poly(dimethyl siloxane) (1-43) to 273
Cfor
polyhydantoin (4-2) polymers used as wire enamels and to even higher temperatures
for other polymers in which the main chain consists largely of aromatic structures.
This range of behavior can be rationalized, and the effects of polymer structure on
T
g
can be predicted qualitatively. Since the glass-to-rubber transition reflects the onset
of movements of sizable segments of the polymer backbone, it is reasonable to
expect that
T
g
will be affected by the flexibility of the macromolecules and by the
intensities of intermolecular forces.
Table 4.2
lists
T
g
and
T
m
values for a number of
polymers. The relations between intra- and interchain features of the macromolecular
structure and
T
g
are summarized in the following paragraphs.
2
(CH
3
)
2
O
C
C
O
N
N
C
x
O
4-2
