Chemistry Reference
In-Depth Information
(i-Pr)
3
Si
Si(i-Pr)
3
O
+
(i-Pr)
3
Si
Si(i-Pr)
3
R
R
R
R
R
R
R
R
R
R
The above condensation reactions were carried out at 180-200
C in aromatic solvents [
250
].
Preparation of dendrimers usually involves numerous synthetic steps. Some attempted to simplify
the process by merely forming hyperbranched polymer. The products have less perfect structures than
dendrimers, but offer the advantage of being synthesized in only one step. A recent publication
describes preparation of hyperbranched poly(
-caprolactone)s [
251
]. Living ring opening
polymerizations were carried out with the aid aluminum benzyl oxide as the initiator. The resultant
polymers were then functionalized with benzylidine-protected 2,2
0
bis(hydroxymethyl)propionic acid.
After a subsequent deprotection,
e
-dihydroxyl functional AB
2
macromonomers
formed. These AB
2
polyesters were then condensed into hyperbranched polymers through a room-
temperature esterification synthesis using dicyclohexylcarbodiimide and 4-(dimethylamino)
pyridinium 4-toluenesulfonate [
251
].
a
-carboxylic-
o
7.18.2 Polyrotaxanes
Preparation of polymeric materials that consist of linear structures threaded through large rings
literature describing such preparations [
252
,
253
]. In many instances, crown ethers are used to have
