Chemistry Reference
In-Depth Information
OBz
OBz
CH
2
BOP or DTBP
*
R
1
:Ac
Bz
Bn
Me
O
C
OBz
*
n
120 °C, 6h
BzO
O
ρ
=10%
OBz
OBz
BzO
exofructene
Bz-5,6-
CH
2
OBz
O
O
benzyl peroxyd
e
toluene
24h, 80 °C
OBz
OBz
O
H
2
C
CH
+
CH
2
C
CH
2
CH
R=
O
C
OBz
O
BzO
m
CH
2
n
R
R
O
O
OBz
OBz
N
BzO
Bz-5,6-exofructene
CH
2
OBz
OBz
OBz
CH
2
benzyl peroxyd
e
toluene
24h, 80 °C
O
C
OBz
+
CH
2
C
CH
CH
BzO
n
m
O
O
X
O
OBz
O
O
X
OBz
BzO
Bz-5,6-
exofructene
with X = O or NH
CH
2
OBz
Scheme 4 Free-radical copolymerization of an exo-cyclic unsaturated sugar-based
monomers (type II).
28
preparation of unique polymers where one carbon atom of the sugar ring
is included in the chain backbone. The corresponding fructose-based
polymers were characterized in term of comonomer composition, ther-
mal behavior (glass transition, Tg) and optical activity.
More recently, the controlled radical polymerization (CRP) by various
methods including atom transfer radical polymerization (ATRP), revers-
ible addition-fragmentation chain transfer (RAFT) polymerization, and
nitroxide-mediated polymerization (NMP), as well as cyanoxyl-mediated
free radical polymerization have allowed chemists to synthesize well-
defined glycopolymers that, in some cases, have particular end-group
functionalities. A review focuses on the synthesis of original glycopoly-
mers by these techniques and their applications.
29
Between the two approaches presented in the above paragraphs,
namely (i) the generation of an alkenyl function within the carbohydrate
or (ii) its functionalization with a conventional monomer unit, a com-
promise option consists in introducing on hydroxyl functions a poly-
merizable unsaturation with a reduced number of atoms in the form of
vinyl or allyl ether functions.
3 Homopolymerization and copolymerization of vinyl
and allyl ethers
Vinyl- and allyl- ethers do not homopolymerize satisfactorily by free-
radical mechanism,
30
but they are reported to react eciently by a cat-
ionic process.
31
Interestingly, both types of donor monomers do also
copolymerize easily with appropriate comonomers by a free radical
mechanism. The specific conjugation of non-bonding electrons with the
ethylenic p system exhibited by vinyl ether favors the formation of a
stable charge transfer complex (CTC) with electron-acceptor monomers
such as butenedioic derivatives leading to alternating copolymers (dialkyl
Search WWH ::
Custom Search