Chemistry Reference
In-Depth Information
Random
AABBBABBAABAAABBABAAA
Diblock
AAAAAABBBBB
Triblock
AAAAAABBBBBAAAAA
AAAAABBBBBCCCCC
Figure 8.1:
Types of copolymers.
those in which one or more of the blocks is a polysiloxane.
6,
38,
39
If the
blocks are relatively long, separation into a two-phase system invaria-
bly occurs. Frequently, one block will be in a continuous phase and the
other will be dispersed in domains having an average size the order of a
few hundred angstroms. Such materials can have unique mechanical
properties not available from homopolymer species. Sometimes similar
properties can be obtained by the simple blending of two or more
polymers.
40
Examples of blocks used with polydimethylsiloxane (PDMS) include
imides,
41-48
epoxies,
49
butadienes,
50-54
ε-caprolactones,
55
amides having tri-
chlorogermyl pendant groups,
56
urethanes,
57-60
ureas,
61-65
poly(ethylene
glycols),
66
polystyrene,
67-74
vinyl acetates,
75,
76
acrylates or methacry-
lates,
77-84
2-vinylpyridine,
85
and even other polysiloxanes.
86-88
Some results
have also been reported for polyesters,
89,
90
polyethers,
91
hydroxyethers of
bisphenol A,
92
bisphenol A arylene ether sulfones,
93
vinylpyridinebenzoxa-
zines,
94
methyloxazolines,
95
terpyridines,
96
polysulfones,
97,
98
γ-benzyl-L-
glutamate,
99
and carboranes.
100
Two other examples are foamed
polypropylene
101
and melamine resins.
102
Even ABA,
103,
104
ABC triblock co-
polymers,
105
and ABCBA pentablock copolymers involving PDMS have been
reported.
106
In a number of cases, the block used with the PDMS is sufficiently
polar to give an amphiphilic block copolymer. Such materials form inter-
esting structures in polar or nonpolar solvents. In the first case, the polar
chains act like a corona around the nonpolar core, and in the latter, the
nonpolar chains are a corona around the polar core. Examples include
blocks of poly(ethylene oxide),
107-112
acrylamides,
113-115
sugars,
116
glucono-
lactone,
117
hydrolysable siloxanes,
118
and maleic anhydride—vinyl ethyl
ethers.
119
