copolymer topology results in a homogeneous, ultrathin polymer film that
introduces the possibility to switch the surface polarity thermally or by contact
with a solvent. The synthetic route described here for junction-point reactive block
copolymers is of a general nature. The resulting materials can be used for tailoring
of the surface wettability of a variety of flat surfaces and curved surfaces such
nanoparticles. An important feature of this approach is that attachment to the
interface is the final step of the approach, permitting the tailoring of the block
copolymer structure in homogeneous solution prior to the final surface attachment,
in pronounced contrast to established “grafting from” routes.
Ultrathin polymer films capable of stimuli-responsive wetting are particularly
interesting because they permit reversible switching in surface properties from
hydrophilic to hydrophobic and thus offer potential applications in the field of selfcleaning [228], “smart” coatings [229, 230] and also for microfluidic devices [231].
Y-shaped polymer brushes consisting of two incompatible polymer chains that are
covalently linked to the surface with an in-chain anchor group have only been the
subject of a few studies. The main advantage of these structures is the homogenous
distribution of both incompatible polymer chains over the surface, due to the
suppression of segregation processes. In the few reported approaches, these
Y-shaped polymer brushes have been obtained by grafting-from [232] (attachment
of a difunctional initiator to the substrate) or grafting-to [233] (grafting via junctionpoint functionalized block copolymers) strategies. Theoretical studies were carried
out by Zhulina and Balazs [234]. Tsukruk and coworkers used carboxy-terminated PS
and poly(tert-butyl acrylate) attached to 3,5-dihydroxybenzoic acid as an AB 2
anchoring moiety [233, 235]. Wang et al. presented a hydrosilylation grafting-to
process to link block copolymers to silicon surfaces via a Si–H junction point [236]
To synthesize junction-point reactive block copolymers we combined carbanionic
and oxyanionic polymerization with new bifunctional termination strategies based on
tailored epoxide building units. As a precondition for the junction-point reactive block
copolymers, a semicontinuous strategy for the rapid preparation of multihydroxyl
functional polystyrenes has been established. It relies on the high stability of the
acetal-protecting groups of the respective protected glycidyl ethers towards strong
bases [237a]. The synthesis is carried out in a continuously operating microstructured
reaction device for living carbanionic polymerization. The reaction is terminated with
specifically tailored glycidyl ethers, followed by deprotection of the introduced end
group moieties. Based on the termination with functional epoxide derivatives, a series
of block copolymers bearing a single in-chain amino functionality was synthesized via
anionic polymerization of styrene and ethylene oxide [237b]. By means of both a
conventional and a continuous setup, living polystyrene was quantitatively
end-functionalized with an oxirane (DBAG, dibenzyl-aminoglycidol; Fig. 59) prior
to the polymerization of the PEO segment. The in-chain amine was conjugated with a
fluorescent dye, evidencing full junction-point functionalization (Fig. 59).
As a consequence of this work, a general strategy for the synthesis of reversibly
stimuli-responsive Y-shaped polymer brushes and their surface attachment has been
developed (Fig. 60) [237c]. The preparation of the respective junction-point reactive
block copolymers relies on a combination of carbanionic and oxyanionic
184
K. Binder et al.
introduces the possibility to switch the surface polarity thermally or by contact
with a solvent. The synthetic route described here for junction-point reactive block
copolymers is of a general nature. The resulting materials can be used for tailoring
of the surface wettability of a variety of flat surfaces and curved surfaces such
nanoparticles. An important feature of this approach is that attachment to the
interface is the final step of the approach, permitting the tailoring of the block
copolymer structure in homogeneous solution prior to the final surface attachment,
in pronounced contrast to established “grafting from” routes.
Ultrathin polymer films capable of stimuli-responsive wetting are particularly
interesting because they permit reversible switching in surface properties from
hydrophilic to hydrophobic and thus offer potential applications in the field of selfcleaning [228], “smart” coatings [229, 230] and also for microfluidic devices [231].
Y-shaped polymer brushes consisting of two incompatible polymer chains that are
covalently linked to the surface with an in-chain anchor group have only been the
subject of a few studies. The main advantage of these structures is the homogenous
distribution of both incompatible polymer chains over the surface, due to the
suppression of segregation processes. In the few reported approaches, these
Y-shaped polymer brushes have been obtained by grafting-from [232] (attachment
of a difunctional initiator to the substrate) or grafting-to [233] (grafting via junctionpoint functionalized block copolymers) strategies. Theoretical studies were carried
out by Zhulina and Balazs [234]. Tsukruk and coworkers used carboxy-terminated PS
and poly(tert-butyl acrylate) attached to 3,5-dihydroxybenzoic acid as an AB 2
anchoring moiety [233, 235]. Wang et al. presented a hydrosilylation grafting-to
process to link block copolymers to silicon surfaces via a Si–H junction point [236]
To synthesize junction-point reactive block copolymers we combined carbanionic
and oxyanionic polymerization with new bifunctional termination strategies based on
tailored epoxide building units. As a precondition for the junction-point reactive block
copolymers, a semicontinuous strategy for the rapid preparation of multihydroxyl
functional polystyrenes has been established. It relies on the high stability of the
acetal-protecting groups of the respective protected glycidyl ethers towards strong
bases [237a]. The synthesis is carried out in a continuously operating microstructured
reaction device for living carbanionic polymerization. The reaction is terminated with
specifically tailored glycidyl ethers, followed by deprotection of the introduced end
group moieties. Based on the termination with functional epoxide derivatives, a series
of block copolymers bearing a single in-chain amino functionality was synthesized via
anionic polymerization of styrene and ethylene oxide [237b]. By means of both a
conventional and a continuous setup, living polystyrene was quantitatively
end-functionalized with an oxirane (DBAG, dibenzyl-aminoglycidol; Fig. 59) prior
to the polymerization of the PEO segment. The in-chain amine was conjugated with a
fluorescent dye, evidencing full junction-point functionalization (Fig. 59).
As a consequence of this work, a general strategy for the synthesis of reversibly
stimuli-responsive Y-shaped polymer brushes and their surface attachment has been
developed (Fig. 60) [237c]. The preparation of the respective junction-point reactive
block copolymers relies on a combination of carbanionic and oxyanionic
184
K. Binder et al.