Structured semifluorinated polymer ionic liquids for metal nanoparticle preparation and dispersion in fluorous compartments

Article abstract of DOI:10.1021/ma400551e

Structured semifluorinated polymer ionic liquids (FPILs) contain a flexible hyperbranched polyether core connected with a covalently attached shell of imidazolium cations and perfluorinated alkyl chains at their periphery. In a facile synthesis, alkylatio

Full text of DOI:10.1021/ma400551e

Article
pubs.acs.org/Macromolecules
Structured Semifluorinated Polymer Ionic Liquids for Metal
Nanoparticle Preparation and Dispersion in Fluorous Compartments
Kristina Schadt, Benjamin Kerscher, Ralf Thomann, and Rolf Mulhaupt*
̈
Freiburg Materials Research Center (FMF) and Institute for Macromolecular Chemistry, Albert-Ludwigs-University of Freiburg,
Stefan-Meier-Str. 31, 79104 Freiburg i. Br., Germany
*
S Supporting Information
ABSTRACT: Structured semifluorinated polymer ionic liquids (FPILs) contain
a flexible hyperbranched polyether core connected with a covalently attached
shell of imidazolium cations and perfluorinated alkyl chains at their periphery. In a
facile synthesis, alkylation of tosylated poly(3-ethyl-3-hydroxymethyloxetane)
(
PEHO) converts 1-(n-1H,1H,2H,2H-perfluorooctyl)imidazole into hyper-
branched FPILs. They form fluorous compartments for the preparation and
effective dispersion of Ag and Au nanoparticles. Only in the presence of the
nonfluorinated (PIL) and the semifluorinated polymeric ionic liquids (FPIL), Ag
and Au cations are reduced in N,N-dimethylacetamide (DMAC) to form stable
metal particle dispersions with average nanoparticle sizes varying between 2 and
13 nm. In the absence of the hyperbranched PEHO core, the corresponding low
molecular weight ILs fail to afford stable nanoparticle dispersions. In contrast to the corresponding nonfluorinated PIL, FPIL
enables to produce both spherical and flaky uniformly dispersed nanoparticles as a function of the FPIL content. This is
attributed to the self-assembly of FPIL at nanoparticle interfaces. Designing nanostructured FPILs and FPIL-mediated metal
nanoparticle dispersion is of interest to fluorous multiphase catalysis in fluorous compartmentalized ionic systems without
requiring the use of fluorinated solvents.
anometer-scaled structuring of ionic liquids (ILs) by self-
assembly of amphiphilic ILs, containing long alkyl chains,
amphiphiles, dendritic and hyperbranched PILs offer unique
opportunities regarding easy design of multifunctional
architectures and matching polarity with different media.
Moreover, micelle-like hyperbranched and dendritic PILs can
assemble at surfaces and interfaces to produce ultrathin layers.
While many dendritic PILs require tedious multistep
N
or by blending ILs together with various low and high
molecular weight amphiphiles, respectively, represents a
synthetic tool for preparing nano- and micrometer-sized
compartments for synthesis and dispersion of nanoparticles.
The diversified applications of compartmentalized ILs range
from nanophase-separated reaction and sorption media to
nanoreactors, phase transfer and dispersing agents, catalysts,
and smart materials such as micellar transporters for temper-
ature-switchable shuttling of ingredients between different
13
syntheses, hyperbranched PILs with micelle-like topologies
are readily available. Typical examples of hyperbranched PILs
14
include polyethylenimines and ionenes such as alkylated
15
lutidines. In contrast to hyperbranched PILs, containing IL
moieties in the core and n-alkyl chains in their nonpolar shells,
the incoporation of IL moieties as shell in the periphery of
nonionic hyperbranched polymer cores can considerably lower
both softening temperatures and viscosities. For example,
polyglycidol was esterified with ω-bromoacyl chlorides and
alkylated with tertiary amines to incorporate pyridinium or
1
−9
phases.
Since the assemblies of most low molecular weight
ILs are shear-, pH-, and temperature-sensitive, structured
polymer ionic liquids (PILs) with micelle-like topologies and
stable conformations are designed. The incorporation of
polymer cores and backbones into ionic liquids enables
10
processing typical for polymeric materials. Moreover, PILs
afford significantly improved dispersion of metal nanoparticles.
Apart from entropic and osmotic stabilizing effects typical for
conventional polymer dispersing agents, PILs provide highly
effective electrosteric stabilization owing to the presence of
16
imidazolium groups into the shell. For example, rhodium
nanoparticles were immobilized on hyperbranched polyelec-
17
trolytes and used as catalyst in a hydroformylation. In a recent
advance, polyglycidol tosylates were used to alkylate 1-
methylimidazole to produce hyperbranched polyethers con-
11
ionic groups in the polymer. Hence, PILs are recognized as
effective dispersing agents used for nanoparticle preparation.
For instance, Au-NP dispersions, stabilized by a linear
18
taining an imidazolium shell. In this synthetic strategy,
poly(3-ethyl-3-hydroxymethyloxetane) tosylates were used to
alkylate 1-(n-alkyl) imidazoles in order to produce PILs
−
−
polyvinylimidazolium PIL (poly[C10VIm ][Cl ]), containing
imidazolium moieties as side chains, were produced by
photopolymerization of 1-decyl-3-vinylimidazolium chloride in
Received: March 14, 2013
Revised: May 25, 2013
Published: June 12, 2013
the presence of HAuCl . The resulting Au-NP dispersions were
4
1
0,12
used to prepare electrodes.
In the families of PIL
©
2013 American Chemical Society
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Macromolecules
Article
containing a hyperbranched polyether core, an inner
imidazolium shell with variable counterions, and an outer
alkyl shell with variable n-alkyl chain length. Such onion-like
PILs serve as very robust compartmentalized ionic systems for
preparation, transport, and dispersion of various nanoparticles
chains on nanoparticle size and shape as well as dispersion
stability.
RESULTS AND DISCUSSION
■
Synthesis of Semifluorinated Polymer Ionic Liquid
PEHO-C8F13ImOTs and Polymer Ionic Liquid PEHO-
C8ImOTs. As illustrated in Scheme 1, the nanometer-scale
19
including functionalized graphenes. Little is known on
synthesis and application of semifluorinated hyperbranched
polymer ionic liquids (FPILs), in particular with respect to
creating fluorous compartments for nanoparticle syntheses. As
compared to fluorine-free n-alkyl-substituted ILs, the incorpo-
ration of perfluoroalkyl chains can markedly improve thermal
and oxidative stabilities, reduce surface energy, and enhance
Scheme 1. Synthesis of Hyperbranched Semifluorinated and
the Corresponding Fluorine-Free Polymer Ionic Liquids
with Hyperbranched Polyoxetane Core and Substituted
Imidazolium Tosylate Shell
20
oxygen and carbon dioxide solubility. In principle, it is feasible
that nanoparticles dispersed in such fluorous compartments can
serve as fluorous biphase catalyst systems which do not require
the addition of fluorinated solvents. This concept was first
demonstrated for nanoparticles encapsulated in perfluoroether-
21
functionalized PAMAM dendrimers. During recent years,
significant progress has been made in the synthesis and
application of low molecular weight fluorinated ILs (FILs)
22
substituted with perfluorinated alkyl chains. As compared to
the corresponding fluorine-free n-alkyl-substituted ILs, carbon
dioxide solubility of FILs substantially increased with increasing
2
3,24
chain length of the perfluorinated alkyl substituent.
Similar
to low molecular weight FILs nonionic semifluorinated
dendrimers with a fluorinated shell were reported to transport
2
5
CO molecules. The presence of a perfluoroalkyl shell in the
2
periphery of a dendritic core renders semifluorinated
26
dendrimers soluble in various fluorinated solvents. This is
2
0
paralleled by significantly increased oxygen solubility.
Fluorinated solvents are of interest in the aerobic oxidation
27
of organometallic compounds. In a recent advance, nonionic
dendritic fluoroalcohols containing polyglycidol cores were
claimed to function as very effective catalysts for alkene
2
8
epoxidation with hydrogen peroxide. Owing to their low
surface energy, semifluorinated nonionic hyperbranched
polymers comprising a polyglycidol core and perfluoroalkyl
shell migrate to the surface of poly(methyl methacrylate) and
self-assemble to produce in situ ultrathin nanocoatings at the
structured hyperbranched fluorine-containing PEHO-C8F13-
ImOTs with molecular architectures resembling micelles was
prepared in a facile three-step synthesis, similar to that
previously reported for the preparation of fluorine-free
19
structured PILs. In the first step, 3-ethyl-3-hydroxymethyl-
oxetane was polymerized by cationic ring-opening polymer-
ization to produce hydroxy-functional poly(3-ethyl-3-hydrox-
ymethyloxetane) (PEHO-OH) as flexible and very robust
polyether core, following synthetic procedures reported by
2
9
polymer surface. The self-assembly of nonionic dendronized
semifluorinated Janus dendrimers was reported to produce
3
0
vesicular columns useful as reverse thermal actuators.
Furthermore, the self-assembly of phosphonium FILs was
used to create superhydrophobic coatings. One of the first
dendritic FPILs was prepared by protonation of amine-
terminated dendritic poly(propylene imine) and poly-
amidoamine) with a fluorinated alkane carboxylic acid. As a
function of ionic bond formation and microsegregation of the
dendritic branches and the fluorinated peripheral chains, it was
possible to control the formation of liquid crystalline phases.
Yet, in view of the envisioned application as compartmentalized
fluorous ionic media for nanoparticle synthesis, the covalent
attachment of the perfluorinated alkyl chains via hydrolytically
stable linkers is highly desirable.
Herein we report on a synthetic strategy for the preparation
of nanostructured FPILs, containing a flexible hyperbranched
fluorine-free polyoxetane core, an inner imidazolium shell with
tosylate counterions, and an outer shell consisting of covalently
attached 1H,1H,2H,2H-perfluorooctyl groups. Such hyper-
branched FPILs are employed as fluorous ionic reaction
compartments for the preparation of silver and gold nano-
particles. Fluorine-free and semifluorinated PILs are compared
in order to understand the influence of the perfluoroalkyl
31
33
Pencek and co-workers. According to the NMR spectroscopic
end group analysis of trifluoroacetylated PEHO (PEHO-TFA),
1
the calculated hydroxyl group number was 1.00 ( H NMR) and
the degree of branching 49% investigated by 13C-inverse-gated
(
NMR. The number-average molecular mass (M ) of the
n
resulting PEHO-OH was determined, by size exclusion
chromatography measurements of the PEHO-TFA, to be
1700 g/mol with a polydispersity M /M of 1.9. The thermal
32
w
n
characterization revealed a glass transition temperature of 34
°C (DSC) and a thermal stability up to 290 °C (TGA). In the
second step, PEHO-OH was tosylated by reacting it with tosyl
chloride to produce PEHO-OTs with a degree of substitution
1
of 95%, as determined by H NMR spectroscopy. In the third
step, PEHO-OTs was used to alkylate 1-(n-1H,1H,2H,2H-
perfluorooctyl)imidazole and the corresponding fluorine-free 1-
(n-octyl-)imidazole, respectively, to produce both the fluorine-
containing PEHO-C8F13ImOTs, containing perfluorohexyl
groups in the outer shell, and the corresponding fluorine-free
PEHO-C8ImOTs, both of which contain tosylate as counter-
anion.
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The degrees of PEHO-OTs conversion are 0.87 for the
fluorine-free PIL. The Debye rings correspond to the Ag
reaction with the fluorine-free imidazole and 0.92 for the
semifluorinated imidazole as determined by H NMR spec-
surfaces 111, 200, 220, and 311, and the ratios of these Debye
ring radii are in accord with the literature.
1
34
troscopy. The molecular weight was calculated from PEHO-
OTs and the degree of modification to be 5900 g/mol for the
fluorine-free PEHO-C8ImOTs and 8100 g/mol for the
fluorine-containing PEHO-C8F13ImOTs. While the semi-
fluorinated PEHO-C8F13ImOTs had a glass transition temper-
ature of 62 °C, the glass transition of the corresponding
fluorine-free PEHO-C8ImOTs was significantly lower with 8
Obviously, the presence of perfluoroalkyl groups promotes
the formation of smaller and better dispersed Ag-NPs in the
case of the same concentrations. The Ag content and the Ag/
imidazolium molar ratio (Ag/Im) were varied in order to
examine their influence on the average Ag-NP size. The results
are listed in Table 1.
At low Ag/Im molar ratios up to 0.07 spherical Ag-NPs with
an average diameter varying between 3 and 13 nm, as
determined by TEM image analyses, resulted in the presence
of both the PIL and the FPIL. In the case of the nonfluorinated
PIL, higher Ag/Im molar ratios afforded exclusively spherical
particles. In contrast, in the presence of fluorinated FPIL at an
Ag/Im molar ratio of 0.09 it was possible to produce flaky
particles. The Ag-NP size increased in both cases with
increasing Ag/Im molar ratio. Moreover, the average Ag-NP
size was also affected by both the (F)PIL content and the
precursor concentration. At constant precursor concentration,
increasing (F)PIL concentration decreased the average Ag-NP
size. However, at constant (F)PIL concentration, increasing the
precursor concentration increased the Ag-NP size. However, it
is not possible to make such a direct comparison of the
resulting particle sizes in the presence of the nonfluorinated
PEHO-C8ImOTs and the fluorine-containing PEHO-C8F13-
ImOTs. Interestingly, also the shape of the Ag-NPs is
influenced by the reaction parameters. While the fluorine-free
PEHO-C8ImOTs addition afforded the formation of exclu-
sively spherical particles, the addition of fluorine-containing
PEHO-C8F13ImOTs gave spherical and also flaky Ag-NPs,
especially when using higher Ag/Im molar ratios. There are
several reports in the literature on the formation of flaky
particles, but the origins of this change in morphology are not
°
C owing to the higher molecular weight of the fluorine-
containing FPIL. According to thermogravimetric analysis, the
incorporation of the 1H,1H,2H,2H-perfluorooctyl groups
marginally affect thermal stability, which is still up to 320 °C.
Synthesis of Silver Nanoparticles (Ag-NPs). The Ag-
NPs were synthesized by reduction of AgNO with NaBH in
3
4
N,N-dimethylacetamide (DMAC) under an argon atmosphere
at room temperature in the presence of PIL or FPIL. Since
increasing fluorine content can drastically increase oxygen
solubility, all samples were carefully degassed prior to their use
as compartmentalized systems. Silver nitrate was added to a
DMAC solution of fluorine-containing PEHO-C8F13ImOTs
and the fluorine-free PEHO-C8ImOTs, respectively. After
stirring for 1 h to ensure complete penetration of the salt
into the hyperbranched polymer ionic liquids, the reducing
agent NaBH was added. Thereby the color of the solution
4
changed within a few minutes from brown, respectively orange,
to yellow-brown for PEHO-C8ImOTs (cf. Figure 1b) and red
3
5,36
yet well understood.
to influence the shape of the resulting nanoparticles. The
The reaction conditions were reported
37
38
formation of flaky particles improves the specific surface area
and can improve electrical conductivity. They were used as
39
40
active ingredient of antimicrobial films. Most likely, fluorine-
containing PEHO-C8F13ImOTs assemble at the Ag-NP
surfaces and influence the growth of the Ag-NPs. Since
fluorine-containing PEHO-C8F13ImOTs has a higher glass
transition temperature than the nonfluorinated PEHO-
C8ImOTs, it is likely that fluorine-containing PEHO-
C8F13ImOTs forms different assemblies at the Ag-NP
interface.
Figure 1. Ag mirror in DMAC (a) and Ag nanoparticles in the
presence of nonfluorinated PEHO-C8ImOTs (b) and fluorine-
containing PEHO-C8F13ImOTs (c).
for fluorine-containing PEHO-C8F13ImOTs (cf. Figure 1c). In
the presence of both polymer ionic liquids stable dispersions
were formed. However, as is apparent from Figure 1a, silver
precipitated and formed a silver mirror at the flask surface when
polymer ionic liquids were absent. As verified by transmission
electron microscopy (TEM) images and selected area
diffraction (SAED) analyses displayed in Figure 2, Ag-NPs
were formed in the presence of both fluorine-containing and
Preparation of Gold Nanoparticles (Au-NPs). Gold
nanoparticles (Au-NPs) were prepared in DMAC by chemical
reduction of HAuCl with NaBH at room temperature in
4
4
presence of the fluorine-containing PEHO-C8F13ImOTs or
nonfluorinated PEHO-C8ImOTs. Again the precursor was
dissolved in a solution of fluorine-containing PEHO-C8F13-
ImOTs or PEHO-C8ImOTs in DMAC under argon and stirred
for an hour prior to the addition of the reducing agent NaBH4.
Within a few minutes the color of the solution changed from
brown, respectively orange, to ruby. TEM and SAED attested
the formation of zerovalent Au-NPs. The Debye rings of the
corresponding electron diffraction patterns could be sub-
scripted very close to the reported data of the gold cell
parameters which indicated the formation of zerovalent metal
41
nanoparticles. As illustrated in Figure 3, in DMAC no stable
Au-NP dispersions were formed and precipitation of Au
occurred in the absence of (F)PIL and also in the presence of
Figure 2. TEM images and SAED pattern of Ag-NPs, prepared in the
presence of nonfluorinated PEHO-C8ImOTs (a, Ag-7@PIL) and
fluorine-containing PEHO-C8F13ImOTs (b and c, Ag-4@FPIL).
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Table 1. Synthesis of Ag-NPs in the Presence of Nonfluorinated PEHO-C8ImOTs (PIL) and Fluorine-Containing PEHO-
C8F13ImOTs (FPIL)
a
b
c
d
c(Ag) [mg/mL]
c((F)PIL) [mg/mL]
Ag(0) [wt %]
Ag/Im ratio [mol/mol]
dTEM [nm]
Ag-1@FPIL
Ag-2@FPIL
Ag-3@FPIL
Ag-4@FPIL
Ag-5@PIL
Ag-6@PIL
Ag-7@PIL
Ag-8@PIL
0.2
0.2
0.3
0.4
0.2
0.4
0.4
0.9
10
12
12
16
12
12
14
19
1.3
8.0
1.3
1.6
8.0
2.1
1.8
3.0
0.06
0.05
0.07
0.09
0.03
0.08
0.07
9 ± 2
3 ± 1
13 ± 5
8 ± 3
e
6 ± 5
9 ± 5
8 ± 2
0.11
10 ± 3
a
b
c
c(Ag) stands for the concentration of the silver salt. c((F)PIL) stands for the concentration of the (F)PIL. Ag(0) [wt %] indicates mass Ag(0) to
d
mass Ag(0) and mass (F)PIL. Ag/Im molar ratio indicates moles of Ag per mole of imidazolium groups of PEHO-C8ImOTs/PEHO-
C8F13ImOTs. The TEM micrographs show flaky particles.
e
Figure 3. Au precipitate in DMAC (a) and Au-NPs in the presence of
nonfluorinated PEHO-C8ImOTs (b), fluorine-containing PEHO-
C8F13ImOTs (c), and C8-IL (d).
Figure 4. TEM images of Au-NPs prepared in DMAC in the presence
of nonfluorinated PEHO-C8ImOTs (a, Au-6@PEHO-C8ImOTs) and
fluorine-containing PEHO-C8F13ImOTs (b, Au-2@PEHO-C8F13-
ImOTs).
the similar low molecular weight 1-methyl-3-octylimidazolium
tosylate (C8-IL), which does not contain a PEHO core but has
the same composition as the PIL shell. The influences of the Au
concentration, Au/Im molar ratio, and (F)PIL content on Au-
NP size are listed in Table 2.
The TEM micrographs of Au-NPs in Figure 4 showed the
existence of spherical particles with an average diameter varying
between 4 and 13 nm in the presence of the (F)PIL. The NPs
were distributed homogenously in the presence of fluorine-free
PEHO-C8ImOTs, whereas in the presence of fluorine-
containing PIL PEHO-C8F13ImOTs the resulting Au-NPs
were dispersed within nanometer-scaled compartments. More-
over, the Au-NP sizes are controlled by varying the precursor
concentration. At constant (F)PIL concentration the Au-NP
size decreased with increasing precursor concentration.
Although the direct comparison of nanoparticle formation in
the presence and the absence of flour in the PILs is difficult, it is
obvious that only in the presence of the fluorine-containing PIL
PEHO-C8F13ImOTs the Au-NPs are dispersed in nanometer-
scaled compartments.
CONCLUSIONS
■
The alkylation of N-alkyl- and N-perfluoroalkylethyl-substituted
imidazoles with poly(3-ethyl-3-hydroxymethyloxetane) tosylate
represents a very versatile synthetic route to new families of
semifluorinated and the corresponding fluorine-free nano-
structured polymer ionic liquids with dimensions and molecular
architectures resembling those of micelles. A characteristic
feature is the presence of a flexible hyperbranched polyether
core with covalent attachment of an inner imidazolium cation
shell and of semifluorinated alkyl or n-alkyl chains at their
Table 2. Synthesis of Au-NP in the Presence of C8-IL, PEHO-C8ImOTs (PIL), and Fluorine-Containing PEHO-C8F13ImOTs
(FPIL)
a
b
c
d
c(Au) [mg/mL]
c((F)PIL) [mg/mL]
Au(0) [wt %]
Au/Im ratio [mol/mol]
dTEM [nm]
e
f
Au@C8IL
1.0
0.2
0.4
0.6
1.0
0.4
0.4
1.6
15
3.4
1.1
2.2
3.5
5.7
2.2
1.5
5.5
0.06
0.03
0.07
0.11
0.12
0.04
0.03
0.12
5 ± 3
Au-1@FPIL
Au-2@FPIL
Au-3@FPIL
Au-4@PIL
Au-5@PIL
Au-6@PIL
Au-7@PIL
10
10
10
10
10
15
15
13 ± 4
6 ± 2
4 ± 2
7 ± 2
12 ± 4
9 ± 4
13 ± 5
a
b
c
c(Au) stands for the concentration of the gold salt. c((F)PIL) stands for the concentration of the (F)PIL. Au(0) [wt %] indicates mass Au(0) to
d
mass Au(0) and mass F(PIL). Au/Im molar ratio indicates moles of Au per mole of imidazolium groups of PEHO-C8ImOTs/PEHO-
C8F13ImOTs. c stands for the concentration of the IL 1-methyl-3-octylimidazolium tosylate. Not representative because the most precipitated on
e
f
the bottom of the flask and could not be analyzed with TEM.
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periphery. In contrast to micellar systems, prepared by self-
assembly of low molecular weight amphiphilic ionic liquids,
such nanometer-scaled structured hyperbranched polymer
electrolytes are multifunctional and very robust, even at
elevated temperatures. Their polarity can be tuned to render
them soluble in most organic solvents (see Supporting
Information). Owing to the presence of semifluorinated alkyl
groups at their periphery, such hyperbranched FPILs and their
assemblies represent fluorous compartments which can be used
as fluorous ionic compartments for chemical reactions,
including nanoparticle formation and their dispersion. Only
in the presence of PEHO-C8ImOTs and fluorine-containing
PEHO-C8F13ImOTs the reduction of silver and gold cations
in DMAC effects formation of stable dispersions of the
corresponding nanometer-scaled metal particles. Without
attachment of a polyether core, the similar low molecular
weight alkylated imidazoles are ineffective under the same
reaction conditions. The comparison of fluorine-free and
fluorine-containing PIL with similar topology clearly demon-
strated that both size and shape of the metal particles are
influenced by the fluorine-containing PEHO-C8F13ImOTs
content and process parameters. In addition to spherical
nanoparticles at low fluorine-containing PEHO-C8F13ImOTs
content, it was possible to produce flaky particles at high
fluorine-containing PEHO-C8F13ImOTs concentrations and
even nanoparticle dispersions in nanometer-scaled compart-
ments. Although more research is required to examine these
particle growth mechanisms, the self-assembly of fluorine-
containing PEHO-C8F13ImOTs via interactions of the
perfluorinated chains at the nanoparticle interfaces plays an
important role. In fact, FPIL are too small to serve as host for
nanoparticles, but they readily assemble at nanoparticle
interfaces to produce excellent steric stabilization. This self-
assembly affords fluorous compartments for various catalytically
active metal particles and complexes. High solubility in carbon
dioxide and dissolution of oxygen could be exploited in various
catalytic reactions including catalytic oxidation and carbon
dioxide conversion reactions. On the basis of this versatile
synthetic route, it should be possible to vary the chain length of
the perfluorinated chains as well as the natures of counter-
anions. Such nanostructured FPILs could offer new oppor-
tunities for fluorous nanophase catalysis.
and the raw product was purified by column chromatography. The
product was obtained as a yellowish solid (13.5 g, 50%).
Synthesis of the Semifluorinated and Nonfluorinated
Polymer Ionic Liquids. The synthesis of hyperbranched PEHO
and the functionalization to tosylated PEHO (PEHO-OTs) as well as
the functionalization to trifluoracetylated PEHO (PEHO-TFA) were
15
done according to the literature. Prior to the functionalization to the
FPIL and the PIL, the PEHO-OTs was dried under vacuum at 80 °C.
Synthesis of the Semifluorinated Polymer Ionic Liquid
PEHO-C8F13ImOTs. PEHO-OTs and 1-(n-1H,1H,2H,2H-perfluor-
ooctylimidazole (1.70 equiv with respect to tosylgroups) were mixed
under an argon atmosphere. The mixture was stirred at 120 °C for 10
days. The mixture was dissolved in methanol. The FPIL was isolated
by precipitation in toluene twice. This afforded the product in yields of
7
5%−88%.
Synthesis of the Polymer Ionic Liquid PEHO-C8ImOTs.
PEHO-OTs and 1-octylimidazole (1.70 equiv with respect to tosyl-
groups) were mixed under an argon atmosphere. The mixture was
heated to 120 °C for 7 days. The mixture was dissolved in CHCl . The
3
PIL was isolated by precipitation in toluene twice. This afforded the
product in yields of 74%−83%.
Detailed information on the PEHO derivatives and the PIL and
FPIL is found in the Supporting Information.
Synthesis of 1-Methyl-3-octylimidaziolium Bromide. 1-Octyl
bromide (3.50 mL, 3.90 g, 22.0 mmol, 1.10 equiv) was added dropwise
to a solution of 1-methylimidazole (1.60 mL, 1.60 g. 22.0 mmol) in
toluene (20 mL). The mixture was refluxed for 24 h. After cooling to
room temperature, the solvent was removed under reduced pressure.
The raw product was purified by drying at 100 °C for 2 days in
vacuum. The product was obtained as a colorless viscous liquid (5.00
g, 90%).
Synthesis of the Ionic Liquid 1-Methyl-3-octylimidazolium
4
3
Tosylate (MOImOTs). 1-Methyl-3-octylimidazolium bromide (1.50
g, 5.42 mmol, 1.00 equiv) was dissolved in water (0.5 mL). p-
TsOH·H O (1.03 g, 5.42 mmol, 1.00 equiv) was added slowly. The
2
resulting mixture was stirred at room temperature for 4 h. The solvent
was removed under reduced pressure. After drying at 60 °C in vacuum,
the product was obtained as a viscous yellowish liquid (1.98 g, 99%).
Synthesis of Ag and Au Nanoparticles. The procedures for the
synthesis of Ag and Au nanoparticles which are encapsulated in a
hyperbranched polymer are adopted with slight variations from those
4
4
reported in the literature for dendrimers. The metal nanoparticles
were prepared using AgNO3 or HAuCl4 as metal precursor and
sodium borohydride as reducing agent.
Fluorine-containing PEHO-C8F13ImOTs or nonfluorinated
PEHO-C8ImOTs was dissolved under argon in DMAC, and the
precursor salt for silver nanoparticles, AgNO , was added. After 1 h,
3
NaBH (3 equiv) was added to the mixture of the silver salt and
PEHO-C8F13ImOTs or PEHO-C8ImOTs while stirring. The
reaction mixture turned yellow-brown within a few minutes after
4
METHODS
■
Materials and Methods. Added information to the synthesis
described below as well as most experimental detail for nanoparticle
syntheses and methods for characterization is found in the Supporting
Information.
Synthesis of 1-(n-1H,1H,2H,2H-Perfluorooctyl)imidazole.
The preparation of 1-(n-1H,1H,2H,2H-perfluorooctyl)imidazole was
addition of NaBH . The stirring was continued for an hour to
4
complete the reaction. For TEM observations, solutions containing Ag
nanoparticles were coated on a TEM grid and the solvent was
removed under vacuum.
The reference without polymer ionic liquid was conducted in
42
adopted by a literature procedure. Potassium (1.03 g, 26.4 mmol,
.20 equiv) was melted in dry toluene (40 mL) at 100 °C under argon.
analogy. Within a few minutes after addition of NaBH
was found on the vessel wall.
4
a silver mirror
1
Imidazole (1.79 g, 26.4 mmol, 1.20 equiv) was added, and the solution
was stirred at 100 °C for 2 h. After cooling to 60 °C 1H,1H,2H,2H-
perfluorooctyl iodide (5.40 mL, 10.4 g, 22.0 mmol) was added, and the
mixture was heated for 4.5 days at 110 °C. The solvent was removed
under reduced pressure, and the raw product was purified by column
chromatography. The product was obtained as a yellowish solid (2.16
g, 24%).
The preparation of gold nanoparticles was conducted in analogy to
the silver nanoparticles. An aqueous solution containing 50 wt % was
used as precursor. After the addition of an excess NaBH to the
4
mixture of salt and PEHO-C8F13ImOTs or PEHO-C8ImOTs the
color of the solution turned to ruby within a few minutes. The
solutions containing Au nanoparticles were analyzed as described
before.
Synthesis of 1-Octylimidazole. Imidazole (20.4 g, 30.0 mmol,
.00 equiv) was dissolved in a mixture of methanol (20 mL) and 50%
aqueous KOH solution (35 mL) and heated at 100 °C. 1-Octyl
bromide (26.0 mL, 29.0 g, 15.0 mmol) was added dropwise during a
period of 90 min. The reaction mixture was stirred at 100 °C for
another 90 min. The solvent was removed under reduced pressure,
The reference without polymer ionic liquid was conducted in
analogy. Within a few minutes after addition of NaBH4 gold
precipitated and was found on the bottom of the vessel.
Detailed information can be found in the Supporting Information.
Reduction of HAuCl4 in Presence of the IL MOImOTs.
MOImOTs (124 mg, 0.4 mmol) was dissolved in DMAC (8 mL)
2
4
803
dx.doi.org/10.1021/ma400551e | Macromolecules 2013, 46, 4799−4804

Macromolecules
Article
under argon at room temperature. HAuCl (6.6 μL, 7.6 mg, 23 μmol)
(25) Cooper, A. I.; Londono, J. D.; Wignall, G.; McClain, J. B.;
Samulski, E. T.; Lin, J. S.; Dobrynin, A.; Rubinstein, M.; Burke, A. L.
C.; Frechet, J. M. J.; DeSimone, J. M. Nature 1997, 389 (6649), 368−
371.
4
was added and stirred for an hour. NaBH (2.6 mg, 69 μmol, 3.0
4
equiv) was added, and the solution was stirred for another hour.
Within a few minutes a precipitate of Au(0) was formed.
(
26) Garcia-Bernabe,
́
A.; Kram
̈
er, M.; Olah
̀
, B.; Haag, R. Chem.Eur.
J. 2004, 10 (11), 2822−2830.
ASSOCIATED CONTENT
■
(
(
27) Klement, I.; Knochel, P. Synlett 1996, 1996 (10), 1004−1006.
28) Berkessel, A.; Kramer, J.; Mummy, F.; Neudorfl, J.-M.; Haag, R.
*
S
Supporting Information
̈
̈
Experimental details of the nanoparticle syntheses, details of the
characterization of the polyionic liquids, and further informa-
tion on the solubility of the polyionic liquids. This material is
available free of charge via the Internet at http://pubs.acs.org.
Angew. Chem. 2012, 125 (2), 767−771.
(29) Thomann, Y.; Haag, R.; Brenn, R.; Delto, R.; Weickman, H.;
Thomann, R.; Mulhaupt, R. Macromol. Chem. Phys. 2005, 206 (1),
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1
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Chem. Soc. 2012, 134 (9), 4408−4420.
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1831−1833.
AUTHOR INFORMATION
■
Corresponding Author
E-mail: rolfmuelhaupt@web.de (R.M.).
(
32) Martín-Rapun
Givenchy, E. T.; Guittard, F. Liq. Cryst. 2007, 34 (3), 395−400.
33) Bednarek, M.; Biedron, T.; Helinski, J.; Kaluzynski, K.; Kubisa,
P.; Penczek, S. Macromol. Rapid Commun. 1999, 20 (7), 369−372.
34) http://rruff.geo.arizona.edu/AMS/xtal_data/DIFfiles/11922.
txt.
́
; Marcos, M.; Omenat, A.; Serrano, J. L.; de
*
Notes
(
The authors declare no competing financial interest.
(
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