imidazolium cations, and an outer shell of n-alkyl chains [68]. Here, ring-opening
cationic polymerization of 3-ethyl-3-hydroxymethyloxetane yields polyoxetane
polyols (PEHO) with number-average molar mass of 1,800–2,400 g/mol and degree
of branching of 50%. In a polymer-analogous reaction, the tosylate endgroups
alkylate 1-(n-alkyl)imidazoles to produce nanoPILs with onion-like topology.
Whereas methylimidazolium-functionalized nanoPILs with tosylate counter anions
(PEHO-C1ImTos) are water soluble, both increasing the n-alkyl chain length and
exchanging the tosylate counter ions for 4-dodecylbenzenesulfonate render such
nanoPILs organophilic. As evidenced by the absence of weight loss under nitrogen
atmosphere up to 300
C, such nanoPILs are remarkably thermally stable, thus
meeting the demands of polymer melt processing. Organophilic micelle-like
nanoPILs containing a nonpolar outer n-octadecyl shell (PEHO-C18ImTos) are
highly effective phase-transfer agents and transporters. Hence, they enable the
transfer of water-soluble food colorants such as Brilliant Blue FCF (E133) from
water into chloroform and even into polypropylene melts. Moreover, as illustrated in
Fig. 2, functionalized graphene is transported from the aqueous phase into toluene.
Stable nonaqueous graphene dispersions are obtained. The addition of polystyrene
to nanoPIL-stabilized graphene dispersions affords melt-processable graphene/
polystyrene nanocomposites exhibiting improved electrical conductivity [68]. Both
the n-alkyl-substituted and the corresponding semifluorinated nanoPILs are highly
effective as reactors and dispersing agents, thus enabling the preparation of transition
metal nanoparticle dispersions in organic media [69].
Owing to their good thermal stability, nanoPILs containing polyoxetane cores
and N-butylimidazolium shells (PEHO-C4ImTos) are useful additives and blend
components for melt processing of thermoplastics. For example, PEHO-C4ImTos
was blended with poly(styrene-co-acrylonitrile), SAN, containing 30 wt %
acrylonitrile. After extrusion blending in a twin-screw mini-extruder at 210
C,
the samples were injection molded at the same temperature. For comparison, the
corresponding low molecular weight IL, 1-butyl-3-methylimidazolium tosylate
(BMImTos), was also melt blended together with SAN using the identical
processing conditions. The contents of nanoPIL and the corresponding IL were
varied between 0 and 20 wt%. As is apparent from Fig. 3, the low molecular weight
BMImTos is fully miscible with SAN and severely plasticizes the SAN matrix. In
fact, with increasing BMImTos content, the SAN is rendered soft and flexible, as
evidenced by the drastic decrease in glass transition temperature. This is paralleled
by a drastic decay in strength and stiffness. In sharp contrast, PEHO-C4ImTos does
not affect the SAN glass transition temperature, even at high content.
The close inspection of the SAN/PEHO-C4ImTos blend morphology by means of
TEM revealed that PEHO-C4ImTos phase separated. Hence, uniformly dispersed
nanodroplets are formed within the SAN matrix. The average nanodroplet diameter
varied between 50 and 200 nm. Taking into account the high molecular weight of this
nanoPIL, it is not surprising that no leaching problems were encountered. Upon
matching the compatibility by increasing the n-alkyl chain length to n-octadecyl,
PIL nanodroplets were formed in nonpolar polymers such as polypropylene
(PP) [68]. With increasing PEHO-C18ImTos content, the average nanodroplet size
Nanostructured Polymeric Ionic Liquids
437
cationic polymerization of 3-ethyl-3-hydroxymethyloxetane yields polyoxetane
polyols (PEHO) with number-average molar mass of 1,800–2,400 g/mol and degree
of branching of 50%. In a polymer-analogous reaction, the tosylate endgroups
alkylate 1-(n-alkyl)imidazoles to produce nanoPILs with onion-like topology.
Whereas methylimidazolium-functionalized nanoPILs with tosylate counter anions
(PEHO-C1ImTos) are water soluble, both increasing the n-alkyl chain length and
exchanging the tosylate counter ions for 4-dodecylbenzenesulfonate render such
nanoPILs organophilic. As evidenced by the absence of weight loss under nitrogen
atmosphere up to 300
C, such nanoPILs are remarkably thermally stable, thus
meeting the demands of polymer melt processing. Organophilic micelle-like
nanoPILs containing a nonpolar outer n-octadecyl shell (PEHO-C18ImTos) are
highly effective phase-transfer agents and transporters. Hence, they enable the
transfer of water-soluble food colorants such as Brilliant Blue FCF (E133) from
water into chloroform and even into polypropylene melts. Moreover, as illustrated in
Fig. 2, functionalized graphene is transported from the aqueous phase into toluene.
Stable nonaqueous graphene dispersions are obtained. The addition of polystyrene
to nanoPIL-stabilized graphene dispersions affords melt-processable graphene/
polystyrene nanocomposites exhibiting improved electrical conductivity [68]. Both
the n-alkyl-substituted and the corresponding semifluorinated nanoPILs are highly
effective as reactors and dispersing agents, thus enabling the preparation of transition
metal nanoparticle dispersions in organic media [69].
Owing to their good thermal stability, nanoPILs containing polyoxetane cores
and N-butylimidazolium shells (PEHO-C4ImTos) are useful additives and blend
components for melt processing of thermoplastics. For example, PEHO-C4ImTos
was blended with poly(styrene-co-acrylonitrile), SAN, containing 30 wt %
acrylonitrile. After extrusion blending in a twin-screw mini-extruder at 210
C,
the samples were injection molded at the same temperature. For comparison, the
corresponding low molecular weight IL, 1-butyl-3-methylimidazolium tosylate
(BMImTos), was also melt blended together with SAN using the identical
processing conditions. The contents of nanoPIL and the corresponding IL were
varied between 0 and 20 wt%. As is apparent from Fig. 3, the low molecular weight
BMImTos is fully miscible with SAN and severely plasticizes the SAN matrix. In
fact, with increasing BMImTos content, the SAN is rendered soft and flexible, as
evidenced by the drastic decrease in glass transition temperature. This is paralleled
by a drastic decay in strength and stiffness. In sharp contrast, PEHO-C4ImTos does
not affect the SAN glass transition temperature, even at high content.
The close inspection of the SAN/PEHO-C4ImTos blend morphology by means of
TEM revealed that PEHO-C4ImTos phase separated. Hence, uniformly dispersed
nanodroplets are formed within the SAN matrix. The average nanodroplet diameter
varied between 50 and 200 nm. Taking into account the high molecular weight of this
nanoPIL, it is not surprising that no leaching problems were encountered. Upon
matching the compatibility by increasing the n-alkyl chain length to n-octadecyl,
PIL nanodroplets were formed in nonpolar polymers such as polypropylene
(PP) [68]. With increasing PEHO-C18ImTos content, the average nanodroplet size
Nanostructured Polymeric Ionic Liquids
437