Chemistry Reference
In-Depth Information
weight of the product and the monomer to initiator ratio as well as to monomer conversion. The
process is believed to proceed by protonation of the lactone by triflic acid and then followed by a
nucleophilic attack by the initiating alcohol:
H
O
O
H
ROH
CF
3
SO
2
O
+
+
O
RO
OH
It is believed that the controlled cationic ring-opening polymerization proceeds by an “activated
anionic mechanism” as suggested by Penczek [
91
]. According to his suggestion, the acid activates the
cyclic ester and the alcohol subsequently initiates the polymerization.
Kakuchi and coworkers reported controlled/living cationic ring-opening polymerizations of
d
-valerolactone and
e
-caprolactone with the aid of diphenyl phosphate [
89
]. The reaction was
illustrated as follows:
HO
P
O
O
O
O
O
O
R
O
ROH
+
O
H
n
-caprolactone was carried out using 3-
phenyl-1-propanol as the initiator and diphenyl phosphate as the catalyst in toluene at room temperature.
They reported that the reaction proceeded homogeneously to yield poly(
The ring-opening polymerization of
d
-valerolactone and
e
d
e
-
caprolactone) with narrow polydispersity indices. Analyses indicated a presence of residues of the initiator.
-valerolactone) and poly(
5.8.2 Anionic Polymerization of Lactones
In anionic polymerizations the initiations result from attacks by bases upon the carbonyl groups:
O
O
O
R
+
(CH
2
)
5
O
R
5
Common initiators are Li and K alkoxides. In addition to that, it was reported that phosphazene bases
can be used to carry out polymerizations of cyclic esters [
92
]. Also, commercially available materials,
like
tert
-butoxybis(dimethylamino)methane and tris(dimethylamino)methane yield high molecular
weight polylactic acid by ring-opening polymerization with narrow molecular weight distribution:
O
O
O
O
n
O
O
