Biomedical Engineering Reference
In-Depth Information
Table 2
Analysis of the products [
hb-
P
32
(
m
)] obtained from the polycyclotrimerizations
of aliphatic diynes
32
(
m
) with different lengths (
m
) of methylene spacers
a
Solubility
b
Tr i pl e b ond
c
Back biting
d
M
w
e
M
n
e
No.
Spacer
M
w
/
1
-(CH
2
)
2
-
Soluble
Not observed
Strong
∼
3000
2.3
2
-(CH
2
)
3
-
Soluble
Not observed
Very strong
∼
900
1.5
3
-(CH
2
)
4
-
Soluble
Observed
Medium
∼
60 000
4.9
4
-(CH
2
)
5
-
Soluble
Not observed
Medium
∼
40 000
5.0
5
-(CH
2
)
6
-
Soluble
Observed
Very weak
∼
600 000
23.0
6
-(CH
2
)
8
-
Insoluble
7
-(CH
2
)
9
-
Soluble
Observed
Weak
∼
200 000
7.9
8
-(CH
2
)
10
-
Insoluble
a
The polymerization reactions were carried out in toluene at room temperature under
nitrogen by using TaCl
5
- Ph
4
Sn as catalyst
b
Tested at room temperature in common organic solvents including toluene, benzene,
chloroform, DCM, and THF
c
Signal in the
1
HNMRspectrumof
hb
-PAP
d
Signal intensity in the
1
HNMRspectrumof
hb
-PAP
e
Estimated by SEC in THF on the basis of a linear polystyrene calibration
izations are difficult to control, forming polymers with very high
M
w
sand
extremely broad PDIs (Table 2, nos. 5 and 7) or even totally insoluble gels
(Table 2, nos. 6 and 8).
A unique odd-even effect of the monomers in the diyne polycyclotrimer-
ization was observed. In the aliphatic diynes with an odd number of methy-
lene spacers, their triple bonds locate in the same side, which facilitates the
back-biting reaction (Scheme 21). In contrast, in the diynes with an even
number of methylene units, their triple bonds locate in the opposite sides:
these unfavorable positions frustrate the back-biting reaction. Consequently,
hb
-P
32
(4) possessed triple bond residues in its final structure, whereas its
congener
hb
-P
32
(5) did not.
Scheme 21
Odd-even effect in the back-biting reaction
