Biomedical Engineering Reference
In-Depth Information
(a)
12000
25°C
29°C
35°C
38°C
40°C
42°C
65°C
95°C
125°C
155°C
8000
4000
185°C
215°C
0
0.1
0.2
0.3
0.4
0.5
q
(1/nm)
0.6
0.7
0.8
0.9
(b)
0.1
Temperature
0.08
T = 21°C
T = 8°C
T = 2°C
T = -5°C
T = -11°C
0.06
0.04
0.02
0
0.6
0
0.2
0.4
q
(1/nm)
0.8
1
2.16
(a) Evolution of the microphase separation of the hydrophilic PEO
segments and the hydrophobic PTMO segments. (Source: Reprinted
with permission from Ref. 49. Copyright 2003. John and Wiley, Inc.)
(b) Evolution of the phases in hydrated poly(DTE-
co
-PEG carbonate)
s with temperature. (Source: Reprinted with permission from Ref. 52.
Copyright 2010. Elsevier B.V.)
2.6.3 Phase behaviors in copolymers
In copolymers, segments of different polymers are covalently bonded so as
to combine the useful properties of the constituent polymers without the
undesirable effects of large-scale phase separation that invariably happen
in a blend. Nevertheless, at length scales ~100 Å, the copolymers with di-,
tri- and multi-blocks as well as graft copolymers show interesting phase
behavior.
48
These behaviors have been studied extensively in many copo-
lymers, especially in polyurethane segmented block copolymers.
49-51
These
polymers consist of low
T
g
'soft' blocks that are covalently linked to 'hard'
blocks to yield high- performance materials. The factors that determine the
