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hydrophilic monomer
15
or of a hydrophobic norbornene in aqueous emulsion
(catalyst precursor
16a
or
16b
added as methylene chloride solution) or suspen-
sion can be living. For example, at a monomer to catalyst ratio
15/16b
=100, poly-
15
(78% yield) with
M
w
/
M
n
1.07 vs. polystyrene standards was obtained [115]. As
a surfactant for polymerization in emulsion, the cationic dodecyltrimethylammo-
nium bromide (DTAB) was used preferentially. Block copolymers of narrow mo-
lecular weight distribution were also prepared.
With water-soluble carbene complexes
17
and water-soluble monomers
18
, liv-
ing polymerization can be carried out in aqueous solution, without the addition of
surfactants or organic cosolvents [116].
Addition of small amounts of acid (up to 1 equiv. DCl) is advantageous for cata-
lyst performance. Remarkably the metal-alkylidene moiety is not attacked by the
acid, but a monophosphine complex and the phosphonium salt of the ligand are
formed instead. Monitoring of ruthenium-alkylidene species during the polymer-
ization reaction by NMR confirms their high stability towards water.
ROMP of norbornene in aqueous emulsion employing ruthenium(IV) com-
plexes
3
-
C
10
H
16
)Ru(OH
2
)(OAc)]BF
4
as catalyst precursors has been reported by Wache
[118]. High molecular weight polymer with an unusually high
cis
content was ob-
tained at rates of 100 TO h
-1
.
Kiessling et al. have utilized ROMP for the synthesis of neoglycopolymers, i.e. for
synthetic, non-natural polymers bearing carbohydrate moieties [119]. Carbohydrate-
substituted monomers can be employed without protection of the hydroxo-groups,
considerably reducing synthetic effort. As the monomers and also the desired poly-
mers are water-soluble, aqueous ROMP can offer the advantage of a homogeneous
reaction, which is beneficial for molecular weight control and catalyst efficiency.
The ROMP of 7-oxanorbornenes substituted with glucose or mannose moieties
bound via
C
-or
O
-glycosidic linkages afforded neoglycopolymers, such as
19
[120,
121].
The polymerization can be carried out with an aqueous solution of RuCl
3
as a
catalyst precursor. Relative molecular weights of ca. 10
6
by comparison to dextran
3
:
[117] with
bis(allyl)
ligands
such as
the water-soluble
[(
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