Chemistry Reference
In-Depth Information
Table 3.2.
TR ANSITION TEMPER ATURES FOR SOME SYMMETRIC
POLYSILOX ANE ELASTOMERS HAVING REPEAT UNITS [Si((C
2
)
m
CH
3
)
2
-O-]
Polymer
m
10
-3
M (g/mol)
T
m
(
o
C)
T
i
(
o
C)
Poly(dimethylsiloxane)
a
0
High
-43
None
Poly(diethylsiloxane)
b
1
765
—
53
“
“
425
—
52
“
“
172
—
46
“
“
100
—
34
“
“
58
—
23
“
“
~25
—
None
Poly(di-
n
-propyl-siloxane)
c
2
87
—
207
“
“
68
—
177
“
“
51
—
172
“
“
43
—
145
“
“
~10
—
None
Poly(di-
n
-butyl-siloxane)
c
3
128
—
299
“
3
28
—
216
Poly(di-
n
-pentyl-siloxane)
c
4
High
—
330
Poly(di-
n
-hexyl-siloxane)
c
5
“
—
330
Poly(di-
n
-heptyl-siloxane)
d
6
“
375
e
None
Poly(di-
n
-octyl-siloxane)
d
7
“
28
e
None
Poly(di-
n
-nonyl-siloxane)
d
8
“
31
e
None
Poly(di-
n
-decyl-siloxane)
d
9
“
47
e
None
a
See note 345.
b
See note 154.
c
See note 346.
d
See note 167.
e
Crystallization of the side chains, rather than the backbones.
Since stretching a PDES aligns the chains in the direction of the liquid-
crystalline structures, the values of
T
i
should also increase with elonga-
tion,
99
as has been found experimentally.
150
As expected, the values of
T
i
level off at higher elongations.
There are a number of other acyclic polysiloxanes. For example, symmetric
polysiloxanes having
m
= 2-9 have been investigated, with some properties
listed in several handbook articles.
162
These specific polymers and some recent
relevant studies on them are (i) poly(di-
n
-propyl- siloxane),
163-165
(iii) poly(di-
n
-
butyl-siloxane),
163, 166
(iii) poly(di-
n
-pentyl-siloxane,
152, 163
(vii) poly(di-
n
-hexyl-
siloxane),
152,
163
(vii) poly(di-
n
-heptyl-siloxane),
167
(v i) poly(di-
n
-octyl-siloxane),
167
(vii) ii) poly(di-
n
-nonyl-siloxane),
167
and (viii) poly(di-
n
-decyl-siloxane).
152, 167, 99
The isotropization temperatures show an interesting increase with in-
creasing
m,
the number of methylene groups in the side chains.
168
The melt-
ing points of the same polymers also increase with
m
, but with a smaller
