Chemistry Reference
In-Depth Information
O
OH
O
H
4-5
n
HO
O
O
HO
HO
O
O
O
OH
P
OH
OMe
OMe
O
O
O
O
OH
H
4-5
n
O
or
O
O
O
BnO
BnO
O
BnO
BnO
OBn
OBn
OMe
OMe
Scheme 4 Functionalization of methyl 2,3,4 tri-O-benzyl-
a
-
D
-glucopyranoside and
methyl-
a
-
D
- glucopyranoside via binaphthyl-diyl hydrogen phosphate catalyzed ring-
opening polymerization of
d
-valerolactone and
e
-caprolactone.
26
10-60 min reaction
time at 60
1
C, 1-2% catalyst.
(Ð
M
r
1.2 in mild conditions and
r
1.5 in the bulk at 120 1C) could be
obtained, together with number-average degrees of polymerization
24
up
to 100 corresponding to the monomer/initiator ratio, as a consequence of
a well-controlled polymerization occurring without any side reaction.
Later, the same authors
26
reported the functionalization of
monosaccharides by poly(e-caprolactone) and poly(d-valerolactone) using
e-caprolactone or d-valerolactone as monomer and binaphthyl-diyl
hydrogen phosphate as organocatalyst (rac-BNPH - Scheme 4). The
polymerization was performed in bulk at 60 1C using 1% binaphthyl-diyl
hydrogen phosphate in combination with 0.5% carbohydrate co-initiator.
The polymerizations were found to be quantitative in 60 minutes, and
the resulting polymers were characterized by extremely narrow
distributions (Ð
M
o
1.10) The commercial carbohydrate methyl-a-
D
-
glucopyranoside bearing a primary alcohol and 3 other secondary
alcohols was also employed using the same conditions, giving rise to
functionalized polymers quantitatively after about 1 and 2.5 hours for
d-valerolactone and e-caprolactone, respectively. From the number-
average molecular weight value, as well from NMR data, it can be
estimated that that the initiation eciency is only partial, the secondary
alcohol functions being less reactive than the primary ones, resulting
interestingly in the one step synthesis of polyesters functionalized
monosaccharide moieties bearing hydrophilic hydroxyl groups. Similar
results were obtained using the pure (R)- and (S)-BNPH enantiomers as
catalyst instead of the racemic mixture, highlighting no particular effect
of the chirality on the initiation step.
3 Polyesters functionalized cyclodextrins (CD) via
organocatalyzed ring-opening polymerization
The ability of cyclodextrins to form inclusion complexes with various
molecules can lead to specific effects when conducting the ring-opening
polymerization of cyclic esters in their presence. Native cyclodextrins bear
furthermore hydroxyl groups which are able to initiate the ring-opening
polymerization, thereby inducing again functionalized cyclodextrins.
Search WWH ::
Custom Search