New acetylacetone-polymer modified nanoparticles as magnetically separable complexing agents

Article abstract of DOI:10.1039/c5ra20137c

In this paper, we present two methods of synthesis of new bifunctional polymeric nanohybrids and their full characterization. These nanohybrids consist of a magnetic nanoparticle core and polymeric shell which possess the ability to complex metal ions and organic compounds. Synthesized materials exhibit superparamagnetic properties and can thus be easily separated from complex mixtures by using an external magnetic field (facile separation, purification and recyclability). Herein, the syntheses of three bifunctional monomers are presented. Each of them was used to prepare the homopolymeric shell and two types of copolymeric shells (using styrene as a comonomer) around the magnetite nanoparticles. A surface initiated RAFT/MADIX polymerization technique was employed to prepare polymeric shells. Afterwards, post-modification of azide functionalized polymeric shells using the Huisgen "click" reaction was performed. Finally, twelve types of nanohybrids were prepared and their physicochemical properties were investigated. Additionally, the ability of nanohybrids to complex lanthanides and spectroscopic properties of obtained materials were studied.

Full text of DOI:10.1039/c5ra20137c

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New acetylacetone-polymer modified
nanoparticles as magnetically separable
Cite this: RSC Adv., 2015, 5, 100281
complexing agents†
a
a
I. Misztalewska, A. Z. Wilczewska, O. Wojtasik,a K. H. Markiewicz,a P. Kuchlewskia
*
and A. M. Majcherb
In this paper, we present two methods of synthesis of new bifunctional polymeric nanohybrids and their full
characterization. These nanohybrids consist of a magnetic nanoparticle core and polymeric shell which
possess the ability to complex metal ions and organic compounds. Synthesized materials exhibit
superparamagnetic properties and can thus be easily separated from complex mixtures by using an
external magnetic field (facile separation, purification and recyclability). Herein, the syntheses of three
bifunctional monomers are presented. Each of them was used to prepare the homopolymeric shell and
two types of copolymeric shells (using styrene as a comonomer) around the magnetite nanoparticles. A
surface initiated RAFT/MADIX polymerization technique was employed to prepare polymeric shells.
Afterwards, post-modification of azide functionalized polymeric shells using the Huisgen “click” reaction
was performed. Finally, twelve types of nanohybrids were prepared and their physicochemical properties
were investigated. Additionally, the ability of nanohybrids to complex lanthanides and spectroscopic
properties of obtained materials were studied.
Received 29th September 2015
Accepted 13th November 2015
DOI: 10.1039/c5ra20137c
www.rsc.org/advances
reactions. This makes them an ideal homogeneous catalysts for
organic synthetic chemistry.10 Furthermore, anticancer and insulin
1. Introduction
mimetic activity of vanadyl acetylacetonate complex were exam-
ined.11 However, due to their bad solubility in water and good
solubility in organic solvents, acetylacetonate metal organic
complexes are difficult to recover from the organic solution by
water wash method. Additionally, these complexes are usually
thermally unstable because of their low decomposition tempera-
tures.12 These problems could be solved by anchoring ligands/
complexes on a solid phase, for example on magnetic nano-
particles surface (MNP). Thin and homogenous polymer shells
with acetylacetonate moiety around MNP can be obtain by surface
initiated RAFT/MADIX polymerization technique.
RAFT/MADIX (Reversible Addition–Fragmentation chain
Transfer/Macromolecular Design via Interchange of Xanthates)
technique is a type of controlled radical polymerization which
utilizes dithiocarbonates (xanthates) to mediate polymerization
by a reversible chain transfer process. It can be realized by
simple introduction of a small amount of dithiocarbonate to
a conventional free-radical system (monomer + initiator). This
polymerization method provides control over growth, dis-
persity, composition and architecture of polymers.13 Therefore,
a variety of polymeric layers with well-designed and well-dened
properties can be obtained. Another advantage of RAFT/MADIX
polymerization is a great tolerance of dithiocarbonates (DTC)
towards most of the functional groups present in monomer.14
In this paper, a “graing from” approach was applied to
introduce DTC on the surface of magnetic nanoparticles (MNP).
b-Diketones represent one of the oldest classes of versatile
chelating ligands forming very stable chelate complexes with
various metal ions.1 Plenty of studies have been done on these
chelating reagents, especially in the eld of solvent extraction of
metal ions.2 In recent decades, complexes of lanthanide (euro-
pium,3 terbium) ions and b-diketones have attracted much atten-
tion because of their spectroscopic properties. They are widely
used as e.g. light-converting optical materials, light-emitting
diodes, luminescent probes, etc.4 One of the best-known
compounds, which belongs to this group, is acetylacetone. Acety-
lacetone, as such, is used as a chelating agent in e.g. nanoparticles
synthesis (BaTiO3),5 sol–gel synthesis method (MgAl2O4 powders),6
Michael polyaddition reaction7 and spray pyrolysis solutions
(preparation of indium, tin oxide lms).8 It is also used as a metal-
complexing agent in formation of a variety of catalysts, e.g. iron,
cobalt or nickel complexes in oxidation reactions.9 Acetylacetonate
metal organic complexes show nucleophilicity, electrophilicity,
ability of oxidation–reduction, and selectivity in some chemical
aUniversity of Bialystok, Insitute of Chemistry, K. Ciolkowskiego 1K, 15-245 Bialystok,
Poland. E-mail: agawilcz@uwb.edu.pl
bJagiellonian University, Faculty of Physics, Astronomy and Applied Computer Science,
Prof. S. Lojasiewicza 11, 30-348 Cracow, Poland
† Electronic supplementary information (ESI) available: Additional experimental
data, IR, UV-Vis, luminescence and NMR spectras, TGA/DTG curves, SEM/EDX
measurements. See DOI: 10.1039/c5ra20137c
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It is worth mentioning that there are only a few papers15
1H NMR (400 MHz, CDCl3, d, ppm): 3.86 (t, 1H, J ¼ 7.5 Hz),
describing use of “graing from” strategy for anchoring DTC to 3.12 (d, 2H, J ¼ 2.7 Hz), 2.70 (dd, 2H, J1 ¼ 2.6 Hz, J2 ¼ 7.5 Hz),
the MNP surface. RAFT/MADIX polymerization reactions were 2.26 (s, 6H), 2.23 (s, 6H), 2.03 (t, 1H, J ¼ 2.7 Hz); 13C NMR (100
conducted to prepare polymeric shells around magnetic cores. MHz, CDCl3, d, ppm): 202.1, 190.8, 106.4, 81.6, 80.2, 70.7, 68.6,
Three different monomers were utilized to obtain homopoly- 66.5, 29.3, 23.0, 17.3; FT-IR (ATR, n) cmꢁ1: 3308, 3024, 1731,
meric, random and block copolymeric shells with chelating 1702, 1604, 1421, 1360, 1152, 646.
properties. Additionally, post-modication reaction
– the
second method for introducing chelating groups on the MNP 2.4. “Click” reaction
surface – was investigated. Anchoring polymers on MNP allows
55 mg (0.29 mmol) of cooper(I) iodide and 30 mL of dried THF
fast separation of nanohybrids, good recovery aer usage and
also enables reapplication of the material. Since acetylacetonate
based ligands are broadly used in different areas of science and
industry, and recovery of its complexes is of great importance,
anchoring of acetylacetone type ligands on magnetically sepa-
rable solid phase seems to be very promising solution. It is
worth of pointing out that up-to-date, there is only one report
describing acetylacetone based polymers (obtained by non-
controlled radical polymerization) and their composites (not
nanohybrids) with MNP.16
were placed in a ask. Then, 507 mg (3.19 mmol) of 4-vinyl-
benzylazide, 400 mg (2.9 mmol) of 3-propargylpenta-2,4-dione,
1 mL (5.8 mmol) of diisopropylethylamine (DIPEA) and 50 mg
(0.29 mmol) of sodium ascorbate were added. The reaction
ꢀ
mixture was stirred at inert atmosphere at 40 C for 24 hours.
Next, the solvent was removed under reduced pressure, reaction
mixture was diluted by ethyl acetate and the catalyst was l-
trated on Celite. Subsequently, the mixture was washed by aq.
10% HCl and dried over anhydrous Na2SO4. The product was
puried by dry ash chromatography (hexane : ethyl acetate,
8 : 2 with 1% triethylamine). The 648 mg (2.18 mmol) of white
solid was obtained, 56% yield.
2. Experimental section
2.1. Materials and methods
1H NMR (400 MHz, CD3OD, d, ppm): 7.68 (s, 1H), 7.28 (m,
2H), 7.22 (m, 2H), 6.71 (dd, 1H, J1 ¼ 11 Hz, J2 ¼ 6.7 Hz), 5.77 (d,
1H, J ¼ 17.2 Hz), 5.50 (s, 2H), 5.24 (d, 1H, J ¼ 11 Hz), 3.15 (s, 2H),
2.17 (s, 6H); 13C NMR (100 MHz, CD3OD, d, ppm): 205.4, 192.7,
148.7, 146.1, 139.3, 137.4, 129.3, 127.7, 124.2, 114.9, 109.0, 67.6,
54.6, 29.9, 24.7, 23.4; FT-IR (ATR, n) cmꢁ1: 3119, 3072, 2995,
2926, 1699, 1629, 1511, 1315, 1046; mp: 74.7–76.0 ꢀC; MS (m/z):
calculated for C17H19N3O2 ꢁ297.36, found 297.15; EA: 69.0% C,
6.2% H, 13.7% N, 11.1% O (calculated 68.7% C, 6.4% H, 14.1%
N, 10.8% O).
All reagents such as acetylacetone, propargyl bromide, sodium
azide, 4-vinylbenzylchloride, styrene, sodium iodide, cooper(I)
iodide, sodium ascorbate were purchased from Aldrich Chem-
ical Company and used as received. Hexane, dichloromethane
and ethyl acetate were purchased from Avantor Performance
Materials Poland and were distilled before use. THF and acetone
were purchased from Avantor Performance Materials Poland
and were dried according to the standard protocols17 before use.
2.2. 4-Vinylbenzylazide
2.5. 3-(4-Vinylbenzyl)penta-2,4-dione
A 5.1 g (78 mmol) of sodium azide and 2.28 g (6.54 mmol) of
CTAB was dissolved in 430 mL of deionized water. Subse-
quently, 9.23 mL (65 mmol) of 4-vinylbenzylchloride were
Into a 25 mL round bottomed ask, 1.06 g (4.3 mmol) of
4-vinylbenzyliodide was placed. Subsequently,
6
mL
(58.1 mmol) of acetylacetone and 1.2 g (8.7 mmol) of dried
potassium carbonate were added. Reaction was stirred for
ꢀ
added. Reaction was stirred for 24 hours at 40 C. Aer extrac-
ꢀ
tion (DCM) the product was puried by dry ash chromatog-
raphy (hexane) and monomer was obtained as yellow oil with
95% yield.
24 hours in 50 C, aer completion of reaction (TLC) excess of
acetylacetone was evaporated and 20 mL of DCM was added.
Potassium carbonate was then drained and solvent was evapo-
rated. Crude product was puried using dry ash chromatog-
raphy (hexane : dichloromethane, 1 : 1). The product was
obtained as yellow oil, 70% yield.
1H NMR (400 MHz, CDCl3, d, ppm): 7.48 (d, 2H), 7.32 (d, 2H),
6.78 (dd, 1H, J1 ¼ 10.9 Hz, J2 ¼ 17.6 Hz), 5.83 (d, 1H, J ¼ 16.7 Hz),
5.34 (d, 1H, J ¼ 10 Hz), 4.35 (s, 2H); 13C NMR (100 MHz, CDCl3,
d, ppm): 137.5, 136.1, 134.7, 128.3, 126.5, 114.3, 54.4; FT-IR
(ATR, n) cmꢁ1: 3088, 2928, 2931, 2094, 1242, 990, 822.
1H NMR (400 MHz, CD3Cl, d, ppm): 7.34 (m, 4H), 7.12 (m,
4H), 6.70 (dd, 2H, J1 ¼ 10.3 Hz, J2 ¼ 17.6 Hz), 5.72 (d, 2H, J ¼
13.3 Hz), 5.22 (d, 2H, J ¼ 10.4 Hz), 4.00 (t, 1H, J ¼ 7.5 Hz), 3.65 (s,
2H), 3.14 (d, 2H, J ¼ 7.5 Hz), 2.13 (s, 6H), 2.08 (s, 6H); 13C NMR
(100 MHz, CD3Cl, d, ppm): 203.2, 191.8, 139.3, 137.6, 135.8,
128.7, 127.5, 126.5, 113.6, 113.4, 108.1, 69.8, 33.9, 32.6, 29.6,
23.3; FT-IR (ATR, n) cmꢁ1: 3085, 3005, 2924, 1727, 1699, 1605,
1510, 1406, 1356, 990, 907.
2.3. 3-Propargylpenta-2,4-dione
1.49 g of dried potassium carbonate (10.8 mmol) was placed in
a ask and then dried acetone was added (100 mL). Simulta-
neously, 1 mL (9 mmol) of propargyl bromide (80% solution in
toluene) and 4.4 mL (45 mmol) of acetylacetone were added.
The reaction was stirred for 24 hours at 60 ꢀC at inert atmo-
sphere. Next, the mixture was ltrated and the solvent was
2.6. General procedure for surface initiated polymerization
removed under reduced pressure. The product was puried by Magnetic nanoparticles with dithiocarbonate groups on their
dry ash chromatography (hexane : dichloromethane 7 : 3). It surface (50 mg) were sonically dispersed in 2 mL of toluene.
was obtained as yellow oil, yield 86%.
Then, the monomer (50 mg) and 2 mg of AIBN were added. The
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reaction mixture was stirred for over 24 h at 80 ꢀC. The initiator Hitachi F7000 Fluorescence Spectrophotometer. Magnetic
was added partially (each part was 2 mg), aer 2, 6 and 16 hours properties of the nanoparticles were studied using a Quantum
of stirring. Next, the nanoparticles were separated by external Design MPMS 5XL SQUID-type magnetometer. Each sample was
magnetic eld and washed at least 3 times by toluene and then placed in a standard gelatine capsule and immobilised with
ꢀ
by methanol. The product was dried at 60 C overnight.
varnish glue for the measurement. All the data were carefully
In the case of random copolymerization monomers were corrected for the diamagnetic contribution of the holder.
mixed in molar ratio 1 : 5 (bifunctional monomer : styrene).
For block copolymerization reaction styrene coated nano-
particles with 11% of polystyrene content were taken as a start-
ing material.
3. Results and discussion
3.1. Synthesis of new bifunctional monomers
Three different vinyl monomers were synthesized (Fig. 1) and
2.7. General procedure for post modication reaction
then used for preparation of polymeric shells on magnetic
nanoparticles.
Magnetic nanoparticles with polymeric shells (25 mg)
were sonically dispersed in 1.5 mL of dried THF. Then
3-propargylpenta-2,4-dione (25 mg), 3.45 mg of cooper(I) iodide,
3.56 mg of sodium ascorbate and 63 mL of dried DIPEA were
added to the magnetic nanoparticles solution. The reaction
mixture was stirred at inert atmosphere at 40 ꢀC for 4 days. Next,
the nanoparticles were separated by placing in an external
magnetic eld and then washed by deionized water and meth-
Two of them contain acetylacetonate moiety (monomer 2
and monomer 3). The presence of azide groups on the third one
(monomer 1) allows further modication aer polymerization
reaction resulting in introducing of b-diketone groups onto the
polymeric shell. Synthesis of monomer 2 was performed in
a three-step synthetic path. Firstly, the 4-vinylbenzylazide
(monomer 1) was synthesized in the substitution reaction of
4-vinylbenzylchloride with sodium azide using standard phase
transfer catalysis protocol (with CTAB as surfactant).18 Next,
acetylacetonate acetylene (2a) derivative was obtained in
substitution reaction of acetylacetone by propargyl bromide
(mole ratio 5 : 1) with potassium carbonate as base and acetone
as solvent.19 In this reaction, excess of acetylacetone was used to
avoid formation of by-product – 3,3-disubstituted acetylacetone.
The last step was “click” type Huisgen reaction which allows
preparation of 1,2,3-triazole bifunctional derivatives (Fig. 1.2).
The product of copper catalyzed Huisgen reaction should be
obtained at the room temperature, unfortunately in our case
stirring at room temperature even for one week was not effec-
tive. According to the structure of starting material (presence of
vinyl bond sensitive for light and temperature) the reaction
mixture was slightly heated and covered against sunlight. Under
such conditions the desired product was obtained with several
percent of yield. Furthermore, it was observed that heating of
the reaction mixture till 40 ꢀC does not cause polymerization of
ꢀ
anol. The product was dried at 60 C overnight.
2.8. General procedure for complexation reaction of
lanthanides
Magnetic nanoparticles with polymeric shell (20 mg) were
sonically dispersed in 2 mL of methanol. Then 2.6 mL of
piperidine was added and mixture was stirred for 15 min.
Aerwards 2.5 mg of lanthanide chloride was added and stirred
at room temperature for 24 hours. Nanoparticles were separated
by using external magnetic eld, and washedꢀby deionized water
and methanol. The product was dried at 60 C overnight.
2.9. Measurements
The formation of magnetic nanoparticles, particle size and
morphology were conrmed by transmission electron micros-
copy (TEM) (Tecnai G2 X-TWIN). Samples for TEM were
prepared on holey carbon cooper grids. Energy-dispersive X-ray
spectroscopy (EDX – detector Ametek Octane Pro) analyses were
collected from the samples imaged by SEM (TFP 2017/12
Inspect S50 FEI). Samples for SEM microscopy were prepared
on aluminium tables and were covered by 4 nm Au layer (Leica
ACE 200 coater) in order to improve imagining. Surface modi-
cations were conrmed by ATR FT-IR (Nicolet 6700). Ther-
mogravimetric analysis (TGA) was performed on a Mettler
Toledo Star TGA/DSC unit. Differential scanning calorimetry
(DSC) was performed on a Mettler Toledo Star DSC system.
Argon was used as a purge gas (200 mL minꢁ1 – DSC, and 20
mL minꢁ1 – TGA). Samples between 2 and 5 mg were placed in
aluminium pans and heated from 50 ꢀC to 950 ꢀC (TGA) or from
25 ꢀC to 480 ꢀC (DSC) with a heating rate of 10 ꢀC minꢁ1. The 1H
NMR and 13C NMR spectra were recorded on a Bruker Avance II
spectrometer (400 MHz and 100 MHz respectively). The melting
points were measured by Mettler Toledo MP 70 Melting Point
System. Elemental analyses were performed on Elementar Vario
Micro Cube, UV-Vis spectra were investigated on Jasco V-670
Spectrophotometer and luminescence analyses were done on Fig. 1 Synthesis of three different vinyl monomers.
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compare the properties of the obtained polymeric shell, another
two monomers known from the literature were synthesized and
polymerized as well. The monomer 3 (rstly synthesized by Dow
Chem. Co.21) was prepared via a new synthetic protocol,
including usage of 4-vinylbenzyliodide (Fig. 1.3). Monomers 2
and 3 were prepared in the scope of investigation of inuence of
linkage between vinyl and acetylacetone functional groups on
chelating properties of the obtained polymers.
3.2. Surface initiated polymerization reactions
Fig. 2 Synthesis of polymeric shells (DTC – dithiocarbonate).
In this research, core–shell superparamagnetic nanoparticles
with iron oxide core and aminosilane shell were used.
Their synthesis, characterization and applications were
described in our previous papers.15a,22 The ethyl dithiocarbonate
(DTC) was used as chain transfer agent and was covalently
bonded to the surface of nanoparticles.15a RAFT/MADIX poly-
merization was employed to create polymeric shells with
chelating properties.
To investigate the relation between polymeric shell structure
and its chelating activity, three types of polymerization were
performed on the surface of MNP: homopolymerization, block
copolymerization and random copolymerization (Fig. 2).
Homopolymerization introduces the largest amount (mass
ratio) of functional groups on the surface of MNP, however, the
steric hindrance can reduce their availability for metal ions. For
this reason, random copolymers were prepared with styrene as
4-vinylbenzylazide and thus the Huisgen reaction was carried
out at this temperature. Aer 24 hours of stirring at 40 C the
ꢀ
product (monomer 2) was obtained with 75% yield. According
to the literature,20 during a cooper-catalysed Huisgen reaction
only one regioisomer should be formed (1,4-substituted 1,2,3-
triazole). In our case, mixture of two 1,4- and 1,5-substituted
regioisomers was obtained (mole ratio 3 : 1 respectively,
conrmed by NMR and HPLC). The mixture of regioisomers was
puried using dry column chromatography. In further research,
only 1,4-substituted regioisomer was considered (produced
with 56% yield). This monomer was polymerized on the surface
of dithiocarbonate-coated magnetic nanoparticles using surface
initiated RAFT/MADIX polymerization technique. In order to
Table 1 Polymeric shells anchored on MNP
Type of monomer
% of mass
Type of polymeric shell
Homopolymer
No. of nanohybrid
R1
R2
decomposition (by TGA)
4
–CH2N3
—
25
5
—
33
6
7
—
34
31
Random copolymer
–H
–CH2N3
8
23.5
9
16.5
54
Block copolymer
10
–H
–CH2N3
11
12
64
17
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Fig. 3 Scheme of post modification reaction.
comonomer. Styrene units in the polymer chain separate large
functional groups of synthesized monomers, improving avail-
ability of chelating moiety. The block copolymers were prepared
in order to test if the distance between functional groups and
magnetic core affects the properties of polymeric shells. In the
instance of the homopolymer, the functional polymeric shell is
very close to the magnetic core whereas in the case of the block
copolymer, two polymeric layers were prepared one aer
another. As a result, MNP with inner polystyrene and external
chelating shells were obtained. Additionally, polymerization of
4-vinylbenzylazide on MNP was performed. In the next step,
azide groups were modied further. The inuence of the method
of shell preparation on its chelating properties was investigated.
All polymerization reactions were handled in the same
conditions i.e. stirring for 24 hours at 80 ꢀC in toluene. Initially,
three different solvents were investigated: methanol, THF and
toluene. The best results i.e. the highest thicknesses of poly-
meric shell (determined by TG analysis) were obtained using
toluene as a solvent. AIBN was used as an initiator and it was
added in three portions, at the beginning of the polymerization,
aer two hours and aer 16 hours of stirring at inert atmo-
sphere. All the results are presented in Table 1. Additionally,
RAFT/MADIX polymerization reaction of monomer 2 in solution
was performed. Tg of the obtained polymer determined by the
Fig. 4 ATR FT-IR spectra of polymer modified MNP.
“click” reaction was raised as the most useful and widely
employed functionalization way within polymer chemistry,23 the
Huisgen “click” reaction protocol was applied to modify azide-
functionalized polymeric shells. In this manner, nanoparticles
were sonically dispersed in dried THF and then 3-
propargylpenta-2,4-dione (2a), copper(I) iodide and sodium
ascorbate were added (Fig. 3).
The mixture was stirred for 4 days at 40 ꢀC. The introduction
of the acetylacetone moiety was investigated by ATR FT-IR
spectroscopy. Each of the polymeric nanohybrids containing
azide groups were modied in this way. As a result, three
different sorts of materials were obtained, i.e. nanoparticles
covered by homopolymeric, random copolymeric and block
copolymeric sells (13, 14 and 15 respectively). The reaction was
stopped when the characteristic peak of –N3 moiety at around
2000 cmꢁ1 disappeared. A large advantage of this process is the
very fast purication of the product aer the reaction (separa-
tion by external magnetic eld took approx. 10 minutes).
Additionally, in this case, chromatography protocol, applied for
purication of monomer 2, was omitted. Nevertheless, this
process has some disadvantages. As it was mentioned before,
the Huisgen reaction gives two regioisomers (1,4- and
1,5-substituted) as products and their formation in the post-
modication reaction cannot be excluded. Moreover, there is
no certainty that 100% of azide groups were modied due to
their steric inaccessibility.
ꢀ
DSC method was 65 C (see ESI†).
It can be noticed that the highest mass increase occurred in
the cases of block copolymerization reactions (MNP 10,
MNP 11). Homopolymerization reactions also gave good results.
The lowest mass increase was observed in copolymerization
reaction with monomer 3 as a starting material (MNP 9). This
result suggests low polymerizability of this monomer. Owing to
the lowest efficiency of random copolymerization reactions,
MNP with homopolymeric and block copolymeric shells were
studied further.
3.3. Post-modication reaction
As it was mentioned above, preparation of monomer 2 was time-
and cost-consuming (56% yield aer separation of mixture of
regioisomers) and took three steps in the synthetic path.
Furthermore, despite the facility of producing monomer 3 it
shows poor polymerizability in the applied conditions. For
these reasons another way of introducing chelating groups on
the MNP surface was applied. Azide-functionalized polymeric
shells (homo- and copolymeric) were obtained (MNP 4, 7 and
Fig.
5 Magnetisation as a function of external magnetic field
measured for MNP with polystyrene shell (MNP@PS) compared with
MNP 10 and 15 (left) and MNP with aminosilane shell compared with
MNP 4 and 13 measured in 400 K. Solid lines represent LA fits to the
10). Since the CuAAC (copper catalyzed azide–alkyne coupling) data.
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3.4.2. Magnetisation. Magnetisation versus eld curves
were measured within a range of temperatures. The bare
nanoparticles exhibited superparamagnetic behaviour at room
temperature, however, for the rest of the samples it was
necessary to increase the temperature up to the experimentally
available maximum of 400
K to approach the super-
paramagnetic region and to obtain closing of the hysteretic
loops that were still visible at 300 K. Law of approach to satu-
ration (LA) was tted to the data in high magnetic elds to
obtain the values of the saturation magnetisation.24
Fig.
6 Magnetisation as a function of external magnetic field
It can be observed (Fig. 5) that introduction of new func-
tional groups to polymeric shell using the post-modication
reaction slightly reduces the value of the saturation magnet-
isation (e.g. from 68.9 to 64.3 and 52.5 emu gꢁ1, for MNP@NH2,
MNP 4 and 13, respectively).
measured for MNP with polystyrene shell compared with MNP 5 and
11, at 400 K. Solid lines represent LA fits to the data.
3.4. Characterization of MNP with polymeric shell
On the other hand, increasing of thickness of polymeric shell
(creation of block copolymeric shell) causes reduction of the
value of MS by over a half (for the MNP coated by PS-block-M2
polymeric shell (11) MS ¼ 27.6 emu gꢁ1 – Fig. 6).
Obtained polymeric nanohybrids were characterized by ATR FT-
IR spectroscopy, TG analyses, DSC, TEM and SEM microscopy.
Magnetic properties were also investigated.
3.4.1. Infrared spectra. The FT-IR spectra off all modied
nanoparticles are presented in Fig. 4. In the IR spectra of MNP
aer polymerization and copolymerization reactions the char-
acteristic peaks at around 560 and 1100 cmꢁ1 can be assigned to
Fe–O and Si–O stretching bonds respectively (Si–O bonds are
presented in the inorganic shell which was created by a sol–gel
method with APTMS as starting material).15,22
It was proven that magnetisation values barely depends on
the type of monomer which creates the polymeric shell (the MS
values oscillate from 45.5 – MNP 5 to 55.5 emu gꢁ1 – MNP 4).
3.4.3. Thermogravimetric analyses. TGA studies were
carried out for magnetic nanoparticles aer polymerization
reactions of three presented monomers (homo, random, and
block polymerization), and aer chemical modication of
polyazides present on MNP.
Additionally, two peaks at around 2900 cmꢁ1 represent
stretching bond of –CH2 groups present in polymeric chain and
the one over 3000 cmꢁ1 represent stretching bonds of –C–H
present in aromatic rings. In the 4-vinylbenzylazide spectra of
modied nanoparticles (Fig. 4a) the characteristic peaks around
2000 cmꢁ1, representing stretching bonds of azide group,
occurred. In the spectra of MNP modied by polymerization
reactions of monomer 2 (Fig. 4b) two characteristic peaks were
observed. First, at around 1700 cmꢁ1 represents stretching of
C]O group present in the acetylacetonate moiety, second at
around 1650 cmꢁ1 corresponds to the stretching bond of the
C–H group in 1,2,3-triazole ring. Aer a chemical modication
of materials 4, 7 and 10 characteristic peak of C]O stretching
bond occurred at around 1680 cmꢁ1, and also, strong narrow
peak at 1569 cmꢁ1 that can be assigned to N]N stretching
bond (present in 1,2,3-triazole ring) appeared.
Fig. 7 shows the TG curves of magnetic nanoparticles
covered by: homopolymers MNP 4, MNP 5, MNP 6 and MNP 13
(Fig. 7a), random copolymers MNP 7, MNP 8, MNP 9 and MNP
14 (Fig. 7b) and block copolymers MNP 10, MNP 11, MNP 12
and MNP 15 (Fig. 7c). TG curve refers to the temperature-
dependent mass change in percent, and DTG curve refers to
the rate of mass change (see ESI†). The TGA curves show weight
loss from 13 to 35% for all nanohybrids with homopolymers,
16.5–36% and 18–66% for nanoparticles covered by random
polymeric and block copolymeric shells, respectively. For the
block copolymerization, polystyrene nanoparticles with 11% of
polystyrene weight content were used. Comparing the shell type
(homopolymeric and copolymeric) and inuence of the mono-
mer type, the best polymerization results were obtained in the
case of monomer 2, whereas the lowest mass increase was ach-
ieved for monomer 3. In the thermograms of all nanohybrids, two
Table 2 Comparison of mass decomposition during TGA analyses for
nanohybrids before and after post modification
% of mass
Type of
polymeric shell
Post
modication
decomposition
(by TGA)
Sample
Homopolymer
No
Yes
No
Yes
No
Yes
MNP 4
MNP 13
MNP 7
MNP 14
MNP 12
MNP 15
25
34
31
36
35
41.5
Random copolymer
Block copolymer
Fig. 7 TGA and DSC curves of synthesized nanohybrids.
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Table 4 Content of samarium ions in different polymeric nanohybrids
Nanohybrids with samarium
complex
Sm3+ [%mass]a
MNP@PM1 (4)
7.93
MNP@PS-block-PM1 (10)
MNP@PM2 (5)
MNP@PS-block-PM2 (11)
MNP@PM3 (6)
21.03
10.24
11.70
7.47
MNP@PS-block-PM3 (12)
MNP@PM1_mod (13)
MNP@PS-block-PM1_mod (15)
10.58
4.51
9.96
Fig. 8 SEM and TEM photographs of MNP 12 with samarium ions.
a
Calculated by SEM/EDX.
broad degradation region between 200 and 500 ꢀC, and between
700 and 850 ꢀC were observed (TGA/DTG curves are presented in
ESI†). Typical region of decomposition of polystyrene is about
400–450 ꢀC.15 The changes in the degradation regions conrm
modication of nanoparticles by azide and acetylacetone groups.
Additionally, in the case of post-modied nanoparticles higher
weight loss was observed in comparison to polyazide covered
nanohybrids. It is caused by the increase of weight during “click”
reaction on polyazide shells (Table 2) (Fig. 7).
In Fig. 7d, DSC curves of nanohybrids: MNP 5, MNP 8, MNP
11 with homopolymeric coating and aer post modication of
azide moiety (MNP 15) were presented. Differences in the shape
of DSC heating curves of nanoparticles conrm changes in the
chemical nature of polymeric shells obtained from different
monomers as well as before and aer “click” reaction.
4-vinylbenzylazide as co-monomer (MNP 10). The latter ones
show the highest amount of complexed ions (excluding erbium
ion). For further tests samarium ions were chosen because of
good results of complexation reaction in all cases. Subse-
quently, complexing properties towards samarium ion were
investigated for nanohybrids 6, 11, 12, 13 and 15. The results
clearly show that the amount of complexed metal heavily
depends on the structure of the polymeric shell (Table 4
and Fig. 9).
Nanoparticles with block copolymeric shell complexed
a
greater amount of samarium ions than MNP with
homopolymeric shells. Nanohybrids 13 and 15 occurred to be
the least efficient chelating nanohybrids (with approx.
samarium ion content 4.5 and 10% respectively).
The IR spectra of MNP aer complexation reaction clearly
picture structural changes. Primarily, shi of C]O stretching
band towards lower wavenumbers (from 1712 to 1590 cmꢁ1) is
observed.
3.5. Polymer modied nanoparticles as magnetically
separable complexing agents
Furthermore, small peak at around 1540 cmꢁ1 which corre-
sponds to characteristic C]C bond in acetylacetonate
complexes has occurred (Fig. 10).
For the investigation of chelating properties of MNP with
polymeric shells three different lanthanide ions (Er3+, Sm3+,
Nd3+) were chosen (Fig. 8).
TGA and DSC analyses for the MNP with lanthanide ions
were performed and are presented in Fig. 11. Lower weight loss
observed on the TGA curve of complexes is associated with the
lanthanide residuals. The best results of complexation reaction
of samarium ions were observed in the case of nanohybrids with
homopolymeric shell obtained with monomer 2. The changes
derived from complexes formation were also observed on DSC
heating curves. Additionally, nanoparticles covered by block
copolymers with samarium ions were investigated. The results
In the complexation reactions only nanoparticles with
homopolymeric and block copolymeric shells were tested.
Furthermore, to compare complexing properties of different
kind of chelating agents towards lanthanide ions (erbium,
samarium and neodymium) nanoparticles 4 and 5 were used.
Simultaneously, complexation reactions with lanthanides and
nanohybrids 10 were conducted in order to investigate the
dependence of complexing properties on polymeric shell
structure (Table 3).
The results show that azide groups (present in the homo-
polymeric shell of MNP 4) have minor ability to complex
lanthanide ions than MNP with block copolymeric shell with
Table
3 Content of complexed lanthanide ions calculated by
SEM/EDX (values are in mass%)
Compound\metal ion
Er3+
Sm3+
Nd3+
MNP@PM1 (4)
MNP@PM2 (5)
MNP@PS-block-PM1 (10)
10.66 ꢂ 0.37
7.93 ꢂ 0.14
7.37 ꢂ 0.03
7.49 ꢂ 0.55
12.95 ꢂ 1.06 10.24 ꢂ 0.48
Fig. 9 Content of samarium ions in different polymeric nanohybrids
(left) and an example of SEM/EDX spectra (right).
1.40 ꢂ 0.41 21.03 ꢂ 0.59 10.88 ꢂ 0.83
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mild shi of the maximum or, in some cases, extinction of the
maximum is observed (see ESI†). In the luminescence spectra
three emission peaks are observed. One emission peak at
694 nm, which is common for all of modied nanoparticles,
corresponds to inuence of exciting light with magnetic core.
Two others are directly associated with the type of the com-
plexing ion. For the neodymium ions strong peak at 340 nm is
observed, and the other weaker at 310 nm. For erbium ions two
peaks occur with almost the same intensity (at 306 and 332 nm).
The luminescence spectrum of samarium ions complexed
with MNP 5 is similar to the neodymium one but the peak at
around 340 nm is less intense. It was proven that luminescence
spectra do not depend on the structure of complexing agent
(they are similar for all of synthesized nanohybrids). For the rest
of the investigated samarium complexes, the small broad peak
around 600 nm can be observed (Fig. 12). The intensity of this
peak corresponds to the amount of complexed samarium ions –
the highest emission was observed for MNP 10 with Sm3+ ions
(samarium content around 21%).
Fig. 10 ATR FT-IR spectra of MNP after reaction with lanthanides.
Fig. 11 TGA (left) and DCS (right) heating curves for lanthanide
complexes of MNP 5.
4. Conclusions
In conclusion, new types of nanohybrids were synthesized.
These nanohybrids consist of magnetic cores and polymeric
shells which are covalently bonded to the surface. Therefore,
they are very stable and resistant to washing off. In addition,
these polymeric shells possess chelating properties. The three
different chelating monomers were synthesized and used to
form polymeric shells around magnetic cores by RAFT/MADIX
polymerization. Also, the inuence of post-modication of
polymeric shell on its properties was investigated. It was proven
that chemical modication of the azide groups in the polymeric
shells affects their complexation properties. Unexpectedly, the
best complexing properties towards lanthanide ions exhibit
nanoparticles with block copolymeric shell consist of styrene
and 4-vinylbenzylazide what was conrmed by SEM/EDX and
luminescence spectroscopy. Despite the fact that these nano-
hybrids do not possess the acetylacetone moiety, they are very
good complexing agents. Since complexes of azides and ion
metals are heavily explosive,26 their formation on the MNP
surface appeared to be a very good alternative to the traditional
methods. Furthermore, the easy method of introducing acety-
lacetone groups on the surface of MNP which can be further
used for formation of acetylacetone-based catalysts/complexes
was presented. An important feature of such catalysts/
complexes is the extremely easy separation form the reaction
mixture. Regardless of the way of the synthesis of polymeric
shell around MNP, the magnetic measurements revealed rela-
tively good magnetic properties for all nanohybrids.
obtained by the DSC method are similar to the SEM/EDX
investigations, the highest change in weight loss was observed
in the case of MNP 10 complex with samarium (see ESI†).
It is proven that acetylacetone derivatives form complexes
with lanthanides which poses luminescent properties.25 The
emission colour highly depends on type of lanthanide but is
independent of the metal ion environment, e.g. samarium
complexes emit orange light but erbium and neodymium
complexes has near infrared luminescence.4 UV-VIS and lumi-
nescence studies show slight changes that occur aer
complexation reaction of lanthanide ions. In the UV-Vis spectra,
Acknowledgements
This work was partially nanced by Polish National Science
Centre, project no. NCN-2011/03/B/ST5/02691. Analyses were
performed in Centre of Synthesis and Analysis BioNanoTechno
of University of Bialystok. The equipment in the Centre of
Synthesis and Analysis BioNanoTechno of University of
Fig. 12 Luminescence spectra of nanoparticles with homopolymeric
shell consist of monomer 1 with different lanthanide ions (top) and an
extended region (550–800 nm) of spectra for all samarium complexes
with MNP, normalized to 1, (bottom).
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Bialystok was funded by EU, as a part of the Operational 14 M. Destarac, Macromol. React. Eng., 2010, 4, 165–179.
Program Development of Eastern Poland 2007–2013, project: 15 (a) A. Z. Wilczewska and K. H. Markiewicz, Macromol. Chem.
POPW.01.03.00-20-034/09-00 and POPW.01.03.00-20-004/11.
The authors are grateful to Dr hab. Emilia Fornal for LC-MS
analysis.
Phys., 2014, 215, 190–197; (b) L. Wang, M. Cole, J. Li,
Y. Zheng, Y. P. Chen, K. P. Miller, A. W. Decho and
B. C. Benicewicz, Polym. Chem., 2014, 6, 248–255; (c)
D. Hua, J. Tang, L. Dai, Y. Pu, X. Cao and X. Zhu, J.
Nanosci. Nanotechnol., 2009, 9, 6681–6687; (d) G. Huang,
Z. Sun, H. Qin, L. Zhao, Z. Xiong, X. Peng, J. Ou and
H. Zou, Analyst, 2014, 139, 2199–2206; (e) Y. He, Y. Huang,
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