the chain end fidelity and molecular weight distribution tend to be difficult to
elucidate [27–29]. Thus, more efforts are necessary to develop a proper catalyst
system that could efficiently catalyse the polymerization of glycomonomers under
different conditions, especially in aqueous media.
1
1.3 Reversible Addition-Fragmentation Chain Transfer
Polymerization
Since the discovery of reversible addition-fragmentation chain transfer (RAFT) in
1998 it has become one of the most popular living polymerization processes because
it is tolerant of a wide variety of functional monomers and reaction conditions and
also is promising in bio-applications [42, 43]. For the synthesis of glycopolymers,
RAFT is probably the most popular LRP route at present (with about twice as many
published papers than ATRP/transition metal-mediated strategies for the synthesis
of glycopolymers) and different strategies have been developed for polymerization of
both protected and unprotected glycomonomers [2, 43]. As an interesting case, direct
RAFT polymerization of unprotected glycomonomers in pure water was reported in
2003, at which time direct aqueous ATRP of glycomonomers was still a challenge
[24, 44]. Now, most RAFT polymerizations of glycomonomers are conducted in
aqueous systems with some ratio of organic solvents (DMF, alcohol, DMSO etc.)
with the aim of solubilizing the RAFT agents and radical sources. Most of these
polymerizations are carried out at 60–80
C, although use of aqueous RAFT at
ambient temperature has already been reported (Table 2) [45].
2 Novel Strategies in the Post-glycosylation
of Pre-formed Polymers
2.1 Copper-Catalyzed Azide–Alkyne Cycloaddition Reaction
Copper-catalyzed azide–alkyne cycloaddition (CuAAC) has been widely used in
the post-glycosylation of pre-formed polymers, for which the protected alkyne monomers can be first polymerized by various LRP strategies followed by removal of
trimethylsilyl (TMS) protection groups using tetrabutylammonium fluoride (TBAF)/
acetic acid for click reaction with azido functional sugars (Fig. 3) [59, 60]. This
approach avoids the use of hazardous azide-functionalized monomers and utilizes the
diversity of well-documented azido functional sugars [59].
1 X means that in the corresponding literatures H 2 O or DMSO were used as the solvent for
polymerization, but the polymerization is not successful or out of control under relevant conditions.
46
Q. Zhang and D.M. Haddleton
elucidate [27–29]. Thus, more efforts are necessary to develop a proper catalyst
system that could efficiently catalyse the polymerization of glycomonomers under
different conditions, especially in aqueous media.
1
1.3 Reversible Addition-Fragmentation Chain Transfer
Polymerization
Since the discovery of reversible addition-fragmentation chain transfer (RAFT) in
1998 it has become one of the most popular living polymerization processes because
it is tolerant of a wide variety of functional monomers and reaction conditions and
also is promising in bio-applications [42, 43]. For the synthesis of glycopolymers,
RAFT is probably the most popular LRP route at present (with about twice as many
published papers than ATRP/transition metal-mediated strategies for the synthesis
of glycopolymers) and different strategies have been developed for polymerization of
both protected and unprotected glycomonomers [2, 43]. As an interesting case, direct
RAFT polymerization of unprotected glycomonomers in pure water was reported in
2003, at which time direct aqueous ATRP of glycomonomers was still a challenge
[24, 44]. Now, most RAFT polymerizations of glycomonomers are conducted in
aqueous systems with some ratio of organic solvents (DMF, alcohol, DMSO etc.)
with the aim of solubilizing the RAFT agents and radical sources. Most of these
polymerizations are carried out at 60–80
C, although use of aqueous RAFT at
ambient temperature has already been reported (Table 2) [45].
2 Novel Strategies in the Post-glycosylation
of Pre-formed Polymers
2.1 Copper-Catalyzed Azide–Alkyne Cycloaddition Reaction
Copper-catalyzed azide–alkyne cycloaddition (CuAAC) has been widely used in
the post-glycosylation of pre-formed polymers, for which the protected alkyne monomers can be first polymerized by various LRP strategies followed by removal of
trimethylsilyl (TMS) protection groups using tetrabutylammonium fluoride (TBAF)/
acetic acid for click reaction with azido functional sugars (Fig. 3) [59, 60]. This
approach avoids the use of hazardous azide-functionalized monomers and utilizes the
diversity of well-documented azido functional sugars [59].
1 X means that in the corresponding literatures H 2 O or DMSO were used as the solvent for
polymerization, but the polymerization is not successful or out of control under relevant conditions.
46
Q. Zhang and D.M. Haddleton