Incorporation of superparamagnetic nanoparticles into poly(urea-urethane) nanoparticles by step growth interfacial polymerization in miniemulsion

Accepted Manuscript Title: Incorporation of superparamagnetic nanoparticles into poly(urea-urethane) nanoparticles by step growth interfacial polymerization in miniemulsion Author: Viviane Chiaradia Alexsandra Val´erio Paulo E. Feuser D´ebora de Oliveira Pedro H.H. Ara´ujo Claudia Sayer PII: DOI: Reference:

S0927-7757(15)30054-6 http://dx.doi.org/doi:10.1016/j.colsurfa.2015.06.035 COLSUA 19992

To appear in:

Colloids and Surfaces A: Physicochem. Eng. Aspects

Received date: Revised date: Accepted date:

27-4-2015 16-6-2015 18-6-2015

Please cite this article as: Viviane Chiaradia, Alexsandra Val´erio, Paulo E.Feuser, D´ebora de Oliveira, Pedro H.H.Ara´ujo, Claudia Sayer, Incorporation of superparamagnetic nanoparticles into poly(urea-urethane) nanoparticles by step growth interfacial polymerization in miniemulsion, Colloids and Surfaces A: Physicochemical and Engineering Aspects http://dx.doi.org/10.1016/j.colsurfa.2015.06.035 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

INCORPORATION OF SUPERPARAMAGNETIC NANOPARTICLES INTO POLY(UREA-URETHANE) NANOPARTICLES BY STEP GROWTH INTERFACIAL POLYMERIZATION IN MINIEMULSION

Viviane Chiaradiaa, Alexsandra Valério a,Paulo E. Feusera, Débora de Oliveiraa, Pedro H. H. Araújoa,Claudia Sayera*

a

Department of Chemical Engineering and Food Engineering, Federal University of Santa Catarina (UFSC), Florianópolis, SC 88040-900, Brazil.

Corresponding author: E-mail: [email protected] Graphical abstract

1

HIGHLIGHTS 

Magnetite magnetic nanoparticles coated with oleic acid (MNPs-OA) were synthesized.



MNPs-OA were incorporated in poly(urea-urethane) NPs by interfacial polymerization.



Increasing the content of MNPs-OA increased PUU particle diameter.



After encapsulation, magnetic PUU NPs presented superparamagnetic behavior.

ABSTRACT Superparamagnetic materials encapsulated in a polymeric matrix are interesting for several applications, including biomedical, separation, and biotechnology and enzyme immobilization.

In

this

work,

superparamagneticpoly(urea-urethane),

PUU,

nanoparticles were obtained by interfacial miniemulsion polymerization. Magnetite nanoparticles presenting superparamagnetic behavior were obtained by co-precipitation method and after the synthesis themagnetic nanoparticles, MNPs, were coated with oleic acid, OA, to provide a hydrophobic surface. The synthesis of PUU nanoparticles was performed using 1,6-hexanediol as polyol and IPDI as diisocyanate.The MNPs-OA were incorporated in-situ during the interfacial miniemulsion polymerization. PUU with MNPs-OAwere

characterized

by

Fourier

transform

infrared

spectroscopy, 2

thermogravimetric analysis,electromagnetic vibrating sample magnetometry, VSM, and transmission electron microscopy.Results showa high encapsulation efficiency and VSM analysis showed that PUU with MNPs-OA still presented superparamagnetic behavior after the encapsulation step.

Keywords:Magnetic nanoparticles; Poly(urea-urethane); Encapsulation;Miniemulsion polymerization.

3

1. Introduction Magnetic nanoparticles (MNPs) have remarkable electromagnetic properties and superparamagnetic behavior under a critical diameter (up to 20 nm) [1].Magnetite MNPs are biocompatible and have been used for biomedical applications including magnetic resonance imaging (MRI), contrast enhancement[2,3]and hyperthermia [4]. The encapsulation of MNPs in a polymer shell increases the possibilities of MNPs applications due to several advantages as the polymer shell protects the MNPs; improves stability against aggregation preserving the material in the range of superparamagnetism (single magnetic domain); and the polymer shell can be further functionalized or loaded with a drug [5].Among the applications of MNPs encapsulated in a polymer shell, the most featured ones are: biomedical applications, including cellular therapy, diagnostic applications[6,7], MRI contrastagents[8], hyperthermia [9], drug delivery [10] and for enzymes immobilization[11–14]with application in biocatalysis[15] including biodiesel production [16,17] andenzymatic synthesis of flavors[18]. Co-precipitation

[18–20]

thermal

decomposition[21]and

microemulsion[22]techniques have been reported for MPNs synthesis. The coprecipitation is the most commonly employed technique presenting several advantages as simplicity and high efficiency of the chemical reaction [23]. However, the magnetite MNPs synthesized by the co-precipitation technique are hydrophilic, therefore, MNPs surfaces have to be hydrophobized prior to encapsulation in a non-polar polymer. Several techniques can be applied for the in-situ encapsulation of MNPs during the polymer synthesis including emulsion polymerization[24], inverse emulsion polymerization[25],

inverseminiemulsion

polymerization[26,27]and

direct

miniemulsion polymerization[1,28,29].The polymer shells were composed mostly by

4

polymers obtained by free radical chain-growth polymerization, like polystyrene and copolymers, poly(methyl methacrylate), polyacrylamide, etc. However, there are several other polymers with very interesting properties that are obtained by step-growth polymerization, like polyurethane (PU) and poly(urea-urethane) (PUU), that could be used to encapsulate MNPs. PU and PUUcan be synthesized with many different monomers and have several applications as foams[30], coatings [31],enzyme immobilization [32],nanocarriers for anticorrosive agents [33]and for drug delivery systems [34,35]. One of the few works describing the encapsulation of MNPs by step-growth polymerization is the one of Park and co-workers[36]describing the synthesis ofphase change material (PCM) nanocapsulescontaining magnetite MNPswith a paraffin core and polyurea shell formed by interfacial polymerization. Results showed that the MNPs were localized in the polyurea shell layer due to the Pickering effect. The authors observed that the MNPs-PCM nanocapsules were responsive to external magnetic fields, although the magnetization properties were not measured, as the MNPs had the function of increasing the thermal conductivity of the polyurea, whereas the polymer shell avoided the leakage of the paraffin. PUUparticles can be obtained through different polymerization methods, such as inverse emulsion interfacial polymerization[37], that generates particles in the micrometric range. For the synthesis of PUU particles in the submicrometric rangeemulsion–diffusion process[38],interfacial miniemulsion polymerization[39], inverse

interfacial

miniemulsion

polymerization[40–42]

and

miniemulsion

polymerization [32,43–45]were applied.Miniemulsion polymerization hasthe advantage of being a very versatile techniquewhere the locus of polymerization is inside the submicrometric monomer droplets which act as “nanoreactors” [46]. The nanodroplets

5

containing the hydrophobic reactants are formed after a high-shear been applied to the reaction medium and are stabilized againstmolecular diffusion degradation, also known asOstwald

ripening,and

coalescence

by the

presence

of acostabilizerand

a

surfactant.Despite all the flexibility and applications of polyurethane and poly(ureaurethane), the encapsulation of magnetite MNPs by a PUU shell was not reported previously in the literature. In this work,superparamagnetic MNPsare encapsulated in a PUU shell by interfacial miniemulsion polymerization. MNPs are synthesized by the co-precipitation technique and functionalized with oleic acid (OA) to allow the dispersion of MNPs in the organic phase prior to the miniemulsification. PUU miniemulsion polymerization was conducted using isophoronediisocyanate (IPDI) in the dispersed phase and 1,6hexanediol as polyol in the continuous phase. Magnetic PUU nanoparticles were analyzed by Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TGA), magnetometry (VSM) and transmission electron microscopy (TEM).

2.Materials and methods 2.1.Materials Magnetite (Fe3O4) nanoparticles were synthesizedusing distilled water (H2O), ferric chloride (FeCl3.6H2O), ferrous sulfate (FeSO4.7H2O), ammonia hydroxide (NH4OH), and oleic acid, OA, (C18H34O2)all purchased from Vetec.Poly(urea-urethane) nanoparticles were prepared using isophoronediisocyanate (IPDI, 98%,) and 1,6hexanediol (C6H14O2) as monomers,both from Sigma-Aldrich.Sodium dodecyl sulfate (SDS, Vetec) was used as surfactant, cyclohexane (Sigma-Aldrich) was used as solvent for the IPDI monomer and Crodamol GTCC, a fully saturated triglyceride mainly

6

consisting of esters of caprylicacid (C8) and capric acid (C10) obtained from coconut oilpurchased from Alfa Aesar,was used as costabilizer[45]in some reactions.

2.2. Methods 2.2.1.Synthesis of magnetite nanoparticles Fe3O4 nanoparticles wereobtained by adapting a classical co-precipitation method [47,48].FeCl3.6H2O (5g) and FeSO4.7H2O (6g) were dissolved in 140 ml of distilled water using a mechanical stirrer (800 rpm) andNH4OH (11ml) was subsequently quickly added.One hour after the synthesis of MNPs, OA(20 ml) was addedto protect them against aggregation and to modify their surface for subsequent encapsulation, as shown in Figure 1.The MNPs coated with oleic acid (MNPs-OA) wereseparated by applying an external magneticfield and repeatedly washed with ethanol to remove the excess of OA.

2.2.2.Encapsulation of magnetite in poly(urea-urethane)nanoparticles by interfacial miniemulsion polimerization The procedure used to prepare PUU nanoparticles with MNPs was based on the step growth miniemulsionpolymerizations as described byValério and co-workers[45] to synthesize pure PUU nanoparticles. In these reactions IPDI was used as diisocyanate and was solubilized in the dispersed phase, whereas,1,6-hexanediol and SDS, used respectively as polyol and surfactant were solubilized in the continuous aqueous phase. The concentrations of IPDI and polyol wereevaluatedat two different NCO:OHmolar ratios (1.5:1 and 2.5:1) and the use of Crodamol GTCC as co-stabilizer in the dispersed phase

was

investigated.

The

formulations

employed

in

theminiemulsion

polymerizations are shown in Table 1. After mixing both phases, coarse emulsions were

7

prepared by mechanical stirring for 20 minutes and in sequence these emulsions were sonifiedusing an ultrasonic probe (Fisher-Scientific-UltrassonicDismembrator 500, 400 W) for 180 s at 70% power intensity to prepare the miniemulsions. Two different approaches were evaluated for the addition of the MNPs-OA. In the first one, MNPsOA were dispersed in cyclohexane and dripped into the reaction mediumduring sonication. In the second methodology, MNPs-OA were added directly to the organic phaseand this phase was dispersed in an ultrasound bath prior to mixing with the aqueous phase and preparation of the miniemulsion. MNPs concentrations 5, 10 and 30 wt% (in relation to IPDI) were tested. Polymerizations were conducted at a constant temperature of 70 °C for 3 h.

2.2.3 Characterization of the magnetite nanoparticles 2.2.3.1 Fourier Transform Infrared Spectroscopy Fourier Transform InfraredSpectroscopy (FTIR) was used to verify the completion of the step polymerization evaluating the consumption of NCO group and formation of urea and urethane bonds.After polymerization, the latex was centrifuged at 8,000 rpm for 10 minutes (Eppendorf AG 22331 70 Wcentrifuge) and the supernatant was removed.For these analyses, samples were compacted with potassium bromide (KBr) and analyzed in a range of 3200-400 cm-1.

2.2.3.2 Thermal decomposition Thermal decomposition was studied by thermogravimetric analysis (TGA, STA 449 F3 Jupiter, NETZSCH).After polymerization, the latex was centrifuged at 8,000 rpm for 10 minutes (Eppendorf AG 22331 70 W centrifuge) and the supernatant was

8

removed. Approximately 10 mg of each sample was weighed in a platinum pan and heated from 25 to 800°C with a nitrogen flow rate of 20 mL/min.

2.2.3.3 Magnetic properties Magnetic characteristics of MNPs-AO and PUU-magnetite nanoparticles were measured at 300 K using anelectromagnet vibrating sample magnetometer (3473-70, VSM). After polymerization, the latex was centrifuged at 8,000 rpm for 10 minutes (Eppendorf

AG

22331

70 W

centrifuge)

and

the

supernatant

was

removed.Approximately 4 mg of each sample was weighed in a glass capsule vertically fixed between two coils. The applied magnetic field was varied in a range from 20 to 20 kOe and measured at room temperature.

2.2.3.4 Morphology and particle size Transmission Electron Microscopy (TEM, JEOL, JEM 2100F) at 100 kV wasemployed to verify the nanoparticles morphology, average particle size and size distribution.The magnetic fraction of the latexes was separated with a magnet and diluted in distilled water (1:100). In sequence, one drop of the diluted samplewasplaced on aparlodium-coated copper grid and dried at room temperature. The particle size distribution, number (Dp,n) and volume (Dp,v) average particle diameters were calculated based on image analysis (SizeMeter®) of TEM images by counting at least 450 particles for each sample. In addition, the intensity average diameters of monomer droplets (Dg) and of polymer particles (Dp) was measured by dynamic light scattering (DLS; Zetasizer Nano S, from Malvern). Latexes were diluted in distilled water (1:10) and the final values were the average of two measurements.

9

3 Results and discussion Magnetite MNPswere synthesized by the co-precipitation method with a diameter between 5-15 nm (Figure 2)being smaller than the magnetite critical size for superparamagnetism[49].The MNPs were coated with oleic acid (MNPs-OA)turning the nanoparticles surface more hydrophobicallowing theirdispersion in organic monomers as IPDI. The TGA analysis of the MNPs-OA (Figure 3, curve d) showstwo distinct stages, the first one between 200 and 260 °C, and the second one between260 and 480 °C. The first stage corresponds to free oleic acid and the second one corresponds to oleic acid chemisorbed onto the magnetite MNPs due to the interaction between the carboxylate head and the metal atom. The weight fraction of magnetite in MNPswas 68%. Two different methodologies were evaluated for the addition of MNPs-OA to the organic phase. In the first methodology, MNPs-OA were added during sonication, and in the second methodology, MNPs-OA were added to the organic phase before sonication.The miniemulsion remained stable after the incorporation of the MNPs-OA to the organic phase and during the whole polymerizations. In these miniemulsion polymerizations using 1,6-hexanediol as polyol, the diol was dispersed in the aqueous phase and the IPDI in the dispersed phase, inside the droplets, and the polymerization occurs at the oil:water interfacebetween the functional hydroxyl groupsfrom the 1,6hexanediol and isocyanate from IPDI forming urethane bonds. In addition to this main reaction, part of the isocyanate groups may also react with water molecules forming amine groups that in turn quickly react with other isocyanate groups forming urea bonds.

10

The amount of MNPs-OA that was effectively incorporated into PUU nanoparticles was determined by TGA analysis. Figure 3 (curves b and c) shows TGA analysis of PUU with MNPs-OAusing the same formulation (reaction M3), but different methodologies for the addition of MNPs-OA. Bellow 250 °C, all the samples had a slight weight loss, due to removal of physically adsorbed water molecules and other components. The degradation of PUU without MNPs (Figure 3, curve a) is characterized by two mass reduction stages, at 260 and 400 °C, associated to the earlier soft segment decomposition, associated with polyol components degradation and the later

hard

segment

decomposition,

associated

with

isocyanate

components

degradation[30].TGA analysis of PUU with 10 wt% MNPs-OA showed a similar behavior for both methodologies of MNPs-OA addition (Figure 3, curves b and c). In these cases, the weight loss was shifted towards slightly higher temperatures when compared with pure PUU due to the higher stability in the presence of MNPs-OA. The weight fraction of magnetite in PUU-MNPs coated with oleic acid was 31% when MNPs-OAwere added during sonication and 34% when MNPs-OA were added before sonication. The mass fraction of magnetite in PUU nanoparticles as observed in TGA was higher than the initial magnetite/monomer ratio since the TGA analyses were performed after centrifugation of the PUU-MNPs latex. During centrifugation PUU nanoparticles without MNPs-OA migrate to the supernatant due to their lower density when comparedto PUU nanoparticles containing MNPs. Gravimetric analysis of the supernatant and of the precipitate indicated that, respectively, 6, 16 and 57%of PUU was in the precipitate together with the MNPs for 5, 10 and 30 wt% of MNPs in relation to IPDI. Therefore, the precipitate that was characterized by TGA contained a higher amount of MNPs than the initial MNP/monomer ratio. As both MNPs-OA addition

11

methodologies resulted in similar encapsulation efficiency, the next reactions were performed only with the addition of MNPs directly to the organic phase, before sonication. Fourier Transform IR Spectroscopy (FTIR) was used to verify the completion of the step polymerizations in miniemulsion applied to pure PUU and PUU/MNPs.Figure 4a shows the spectrum of the pure PUU (reaction M0)and Figure 4b shows the spectrum of the PUU/MNPs of the reaction M2 with 5 wt% of MNPs-OA in relation to IPDI.The absence of the absorption band with peak location at 2270 cm-1, corresponding to isocyanategroup (N=C=O), confirms the total consumption of the isocyanate groups during the miniemulsion polymerization for pure PUU and PUU/MNPs.The absorption bands with peak locations at 1763and 1741 cm-1 are attributed to stretching vibration of, respectively, C=O urethane groups and the absorption bands with peak locations at 1698 and 1693 -N-H urea groups,identifying the poly(urea-urethane) formation for reactions M0 and M2.Similar results are reported in relation to PUU formation and isocyanateconsumptionafter miniemulsionpolymerizationusing castor oil and poly(Ɛcaprolactone) (PCL) as polyols and IPDI as diisocyanate[45].In addition, in reaction M2, the characteristics bands at 631 and 584 cm-1corresponding to stretching vibration of Fe-O bond of Fe3O4can be observed in the spectra of synthesized magnetic polyurethane nanoparticles, as shown in Figure 4b. TEM images of the PUU with MNPs-OA that are attracted by a magnet are show in Figures 5 and 6. Tem images(Figure 5a) of PUUnanoparticles with 5wt% of MNPs-OA (reaction M2)showedfew particles containing a high number of MNPs, whereas most of the particles is composed of pure PUU.When the amount of MNPs was increased to 10 wt% (reaction M3), PUU particle size increased together with the fractionof PUU particles containing MNPs, as shown in Figure 5b.TEM images of

12

reactions obtained using 10 wt% MNPs-OAand17wt% of crodamol(reaction M4) showed a high number of PUU particles withMNPs-OA,as observed in Figure 6a.Whenthe amount of MNPs-OA was increased to 30 wt% (reaction M5)with 17wt% of crodamol in relation to organic phase, TEM analysis showed nanoparticles with high encapsulation level in most PUU nanoparticles (Figure 6b).In addition, no free MNPs were observed in the TEM images, though a small fraction of MNPs remained at the reactor wall after sonication.The fact that the reaction of IPDI with 1,6-hexanediol occurred at the interface forming a PUU shell around the droplet may have contributed for this encapsulation reducing the mobility of the MNPs-OA towards the aqueous phase. Table 2 shows the intensityaverage droplets diameter (Dg) and the intensity average particles diameter (Dp) and polydispersity index (PdI) measured by DLS.As shown in Table 2,the incorporation of MNPs-OA to the organic phase increased Dg and PdIdue to the increased viscosity of the dispersed phase. The higher viscosity led to an increased resistance to droplet deformation and breakage during the miniemulsification step resulting in largerdroplets with a broader distribution. In all reactions, Dg and Dp were quite similar, which means that the miniemulsion was stable during the reaction and that the droplets (and droplets interface) were the main polymerization locus as would be expected in a miniemulsion polymerization system. Therefore, the resulting PUU nanoparticles Dp and PdIwere affected by the incorporation of MNPs-OA, increasingDp from 100.5 nm (pure PUU nanoparticles-reaction M0) to 146.6 nm (5 wt% of MNPs-OA), 177 nm (10 wt% of MNPs-OA) and 241.2 nm (30 wt% of MNPsOA). The DLS results corroborate those of the TEM analyses and the intensity average diameters measured by DLS are bigger than the volume average diameters

13

determined based on TEM images, since the intensity average is affected more by the presence of some bigger particles than the volume average.As shown in Table 3, reaction M5 with 30 wt% of MNPs-OA resulted in the largest number average particle size (Dp,n184.3 nm) when compared with reaction M4 (10 wt% of MNPs-OA) with Dp,nof 115.5 nm.Figure 7 shows the particle size distribution (PSD) of reactions M4 and M5, shown in the Table 3. Both distributions were unimodal, however, the PSD of reaction with 10 wt% of MNPs-OA presented the largest number of particles in the range between75-125 nm whereas for the reaction with 30 wt% of MNPs-OA most of the particles were in the range of 125-200 nm. Magnetic materials are characterized by their ability to respond to an external magnetic field. In this work, the field dependent magnetic properties of magnetite MNPs-OAand PUU with MNPs-OA nanoparticles were measured by VSM at 300 Kas illustrated in Figure 8. The main magnetic parameters, such as coercive force, Hc, remanent magnetization,Mr,saturation magnetization, MS, and squareness ratio, Mr/MS, are listed in Table 4. The Msof magnetite MNPs-OA was 73.5 emu/gFe3O4and the low values of Hc(0.162 Oe)and Mr/Ms ratio (2.99x10-7) of MNPs-OAindicated superparamagnetic behavior.This means that each particle of MNPs-OA corresponds to a single crystal domain presenting only one orientation when a magnetic field is applied [28]. This occurs due to the very small particle size of the synthesized MNPs-OA (5-15 nm). The value of Ms(73.5 emu/g Fe3O4) was lower than the value of89 emugfound for bulk magnetite [1]possibly due to the partial formation of other materials like γFe2O3(maghemite)or α-Fe (ferrite)as magnetite MNPs present pyrophoric behavior due to their high surface area, and can oxidize in contact with air[50,51]. The Msof the PUU with 10 wt% magnetite MNPs-OA was 35.66 emu/g Fe3O4(Figure 8). The decrease in saturation magnetization can be attributed to the dense 14

coating of the non-magnetic polymer, or because during the sonication and polymerization, some of the Fe3O4converts to other iron oxides types without magnetization or with low saturation magnetization (Ms), such as

-Fe2O3 or α-Fe

reducing the content of superparamagnetic material (Fe3O4)[1]. Nevertheless, the PUU nanoparticles containing 10 wt% of MNPs-OA showed typical superparamagnetic behavior at room temperature, with absence of hysteresis loop, very low Mr/Ms ratio (5.04x10-7) and small Hc values (0.186 Oe).The superparamagnetic properties of PUU particles containing MNPs-OA are very important for several applications that require the NPs to be dispersed in an aqueous phase in the absence of an external magnetic field. It implies that without an external magnetic field, their overall magnetization value is randomized to zero, preventing the agglomeration of the particles. When an external magnetic field is applied, the PUU NPs are attracted to the magnet being segregated from the aqueous phase (Figure 9).

4. Conclusions Fe3O4 nanoparticles with superparamagnetic behavior were obtained by coprecipitation method. Oleic acid as coating formed a hydrophobic surface on the Fe3O4nanoparticles allowing the dispersion in the hydrophobic monomer (IPDI). Magnetic poly(urea-urethane) (PUU) nanoparticles were successfully prepared by interfacial miniemulsion polymerization when 1,6-hexanediol was used as polyol and the incorporation of a large number of Fe3O4 nanoparticles into PUU was achieved. FTIR results indicated that the Fe3O4 and PUUare present in the formed nanoparticles. In addition, through TEM and DLS analysis it was possible to see that the particle diameter increases with an increase in theamount of MNPs-OA. TGA analysis indicated that PUU with MNPs-OA contained up to 34 wt% of Fe3O4. According to

15

magnetization analysis PUU with MNPs-OA have a high magnetic response with Ms of 35.66 emu/g Fe3O4 and with superparamagnetic behavior.

Acknowledgments The

authorswouldliketothank:

Conselho

Nacional

de

Desenvolvimento

Científico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for financial support;Laboratório Central de Microscopia Eletrônica da UFSC (LCME-UFSC) for TEM images;andLaboratório Multiusuário de Caracterização

Magnética

de

Materiais

(LMCMM-UFSC)

for

themagnetizationmeasurements. References

[1]

K. Landfester, L.P. Ramirez, Encapsulated magnetite particles for biomedical application, J. Phys. Condens. Matter. 15 (2003) 1345–1361. doi:10.1088/09538984/15/15/304.

[2]

R. Weissleder, a. Bogdanov, E. a. Neuwelt, M. Papisov, Long-circulating iron oxides for MR imaging, Adv. Drug Deliv. Rev. 16 (1995) 321–334. doi:10.1016/0169-409X(95)00033-4.

[3]

C. Chouly, D. Pouliquen, I. Lucet, J.J. Jeune, P. Jallet, Development of superparamagnetic nanoparticles for MRI: effect of particle size, charge and surface nature on biodistribution., J. Microencapsul. 13 (1996) 245–255. doi:10.3109/02652049609026013.

[4]

D. Chan, D. Kirpotin, P. Bunn, Synthesis and evaluation of colloidal magnetic iron oxides for the site-specific radiofrequency-induced hyperthermia of cancer, J. Magn. Magn. Mater. 122 (1993) 374–378. doi:10.1016/0304-8853(93)91113L.

[5]

K. Landfester, C.K. Weiss, Encapsulation by Miniemulsion Polymerization, Adv. Polym. Sci. (2010) 14–49. doi:10.1007/12.

[6]

S.F. Medeiros, a. M. Santos, H. Fessi, A. Elaissari, Stimuli-responsive magnetic particles for biomedical applications, Int. J. Pharm. 403 (2011) 139–161. doi:10.1016/j.ijpharm.2010.10.011.

16

[7]

A. Akbarzadeh, M. Samiei, S. Davaran, Magnetic nanoparticles: preparation, physical properties, and applications in biomedicine, Nanoscale Res. Lett. 7 (2012) 144–157. doi:10.1186/1556-276X-7-144.

[8]

E. Illés, M. Szekeres, E. Kupcsik, I.Y. Tóth, K. Farkas, A. Jedlovszky-Hajdú, et al., PEGylation of surfacted magnetite core-shell nanoparticles for biomedical application, Colloids Surfaces A Physicochem. Eng. Asp. 460 (2014) 429–440. doi:10.1016/j.colsurfa.2014.01.043.

[9]

P.B. Shete, R.M. Patil, B.M. Tiwale, S.H. Pawar, Water dispersible oleic acidcoated Fe3O4 nanoparticles for biomedical applications, J. Magn. Magn. Mater. 377 (2015) 406–410. doi:10.1016/j.jmmm.2014.10.137.

[10] S.T. Tan, J.H. Wendorff, C. Pietzonka, Z.H. Jia, G.Q. Wang, Biocompatible and biodegradable polymer nanofibers displaying superparamagnetic properties, ChemPhysChem. 6 (2005) 1461–1465. doi:10.1002/cphc.200500167. [11] Y. Ren, J.G. Rivera, L. He, H. Kulkarni, D.-K. Lee, P.B. Messersmith, Facile, high efficiency immobilization of lipase enzyme on magnetic iron oxide nanoparticles via a biomimetic coating., BMC Biotechnol. 11 (2011) 1–8. doi:10.1186/1472-6750-11-63. [12] N. Sohrabi, N. Rasouli, M. Torkzadeh, Enhanced stability and catalytic activity of immobilized amylase on modified Fe3O4 nanoparticles, Chem. Eng. J. 240 (2014) 426–433. doi:10.1016/j.cej.2013.11.059. [13] K. Atacan, M. Özacar, Characterization and immobilization of trypsin on tannic acid modified Fe3O4 nanoparticles, Colloids Surfaces B Biointerfaces. (2015) 1– 10. doi:10.1016/j.colsurfb.2015.01.038. [14] J. Wang, D. Wu, G. Zhao, M. Li, Y. Li, Y. Han, et al., Reversible immobilization of glucoamylase onto magnetic polystyrene beads with multifunctional groups, Process Biochem. 49 (2014) 845–849. doi:10.1016/j.procbio.2014.02.009. [15] I. Mahmood, I. Ahmad, G. Chen, L. Huizhou, A surfactant-coated lipase immobilized in magnetic nanoparticles for multicycle ethyl isovalerate enzymatic production, Biochem. Eng. J. 73 (2013) 72–79. doi:10.1016/j.bej.2013.01.017. [16] D.T. Tran, C.L. Chen, J.S. Chang, Immobilization of Burkholderia sp. lipase on a ferric silica nanocomposite for biodiesel production, J. Biotechnol. 158 (2012) 112–119. doi:10.1016/j.jbiotec.2012.01.018. [17] W. Xie, N. Ma, Immobilized lipase on Fe3O4 nanoparticles as biocatalys for biodiesel production, Energy & Fuels. 23 (2009) 1353–1374. [18] M. Khoobi, S.F. Motevalizadeh, Z. Asadgol, H. Forootanfar, A. Shafiee, M.A. Faramarzi, Polyethyleneimine-modified superparamagnetic Fe3O4 nanoparticles for lipase immobilization: Characterization and application, Mater. Chem. Phys. 149-150 (2015) 77–86. doi:10.1016/j.matchemphys.2014.09.039.

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[19] C.-H. Kuo, Y.-C. Liu, C.-M.J. Chang, J.-H. Chen, C. Chang, C.-J. Shieh, Optimum conditions for lipase immobilization on chitosan-coated Fe3O4 nanoparticles, Carbohydr. Polym. 87 (2012) 2538–2545. doi:10.1016/j.carbpol.2011.11.026. [20] X. Zhang, Y. Wang, S. Yang, Simultaneous removal of Co(II) and 1-naphthol by core–shell structured Fe3O4@cyclodextrin magnetic nanoparticles, Carbohydr. Polym. 114 (2014) 521–529. doi:10.1016/j.carbpol.2014.08.072. [21] N. Andhariya, R. Upadhyay, R. Mehta, B. Chudasama, Folic acid conjugated magnetic drug delivery system for controlled release of doxorubicin, J. Nanoparticle Res. 15 (2013) 1416–1428. doi:10.1007/s11051-013-1416-9. [22] M.A. Malik, M.Y. Wani, M.A. Hashim, Microemulsion method: A novel route to synthesize organic and inorganic nanomaterials., Arab. J. Chem. 5 (2012) 397– 417. doi:10.1016/j.arabjc.2010.09.027. [23] P. Tartaj, M.P. Morales, T. González-Carreño, S. Veintemillas-Verdaguer, C.J. Serna, Advances in magnetic nanoparticles for biotechnology applications, J. Magn. Magn. Mater. 290-291 (2005) 28–34. doi:10.1016/j.jmmm.2004.11.155. [24] N. Yanase, H. Noguchi, H. Asakura, T. Suzuta, Preparation of magnetic latexparticles by emulsion polymerization of styrene in the presence of a ferrofluid, J. Appl. Polym. Sci. 50 (1993) 765–776. [25] Y. Chen, Z. Qian, Z. Zhang, Novel preparation of magnetite/polystyrene composite particles via inverse emulsion polymerization, Colloids Surfaces A Physicochem. Eng. Asp. 312 (2008) 209–213. doi:10.1016/j.colsurfa.2007.06.052. [26] A.P. Romio, H.H. Rodrigues, A. Peres, A. Da Cas Viegas, E. Kobitskaya, U. Ziener, et al., Encapsulation of magnetic nickel nanoparticles via inverse miniemulsion polymerization, J. Appl. Polym. Sci. 129 (2013) 1426–1433. doi:10.1002/app.38840. [27] Z.Z. Xu, C.C. Wang, W.L. Yang, Y.H. Deng, S.K. Fu, Encapsulation of nanosized magnetic iron oxide by polyacrylamide via inverse miniemulsion polymerization, J. Magn. Magn. Mater. 277 (2004) 136–143. doi:10.1016/j.jmmm.2003.10.018. [28] S. Lu, J. Forcada, Preparation and characterization of magnetic polymeric composite particles by miniemulsion polymerization, J. Polym. Sci. Part aPolymer Chem. 44 (2006) 4187–4203. doi:10.1002/pola. [29] T. Staudt, T.O. Machado, N. Vogel, C.K. Weiss, P.H.H. Araujo, C. Sayer, et al., Magnetic polymer/nickel hybrid nanoparticles via miniemulsion polymerization, Macromol. Chem. Phys. 214 (2013) 2213–2222. doi:10.1002/macp.201300329. [30] M. Zhang, H. Pan, L. Zhang, L. Hu, Y. Zhou, Study of the mechanical, thermal properties and flame retardancy of rigid polyurethane foams prepared from 18

modified castor-oil-based polyols, Ind. Crops Prod. 59 (2014) 135–143. doi:10.1016/j.indcrop.2014.05.016. [31] D.K. Chattopadhyay, K.V.S.N. Raju, Structural engineering of polyurethane coatings for high performance applications, Prog. Polym. Sci. 32 (2007) 352– 418. doi:10.1016/j.progpolymsci.2006.05.003. [32] E.P. Cipolatti, A. Valério, G. Nicoletti, E. Theilacker, P.H.H. Araújo, C. Sayer, et al., Enzymatic Immobilization of Candida antarctica lipase B on PEGylated poly ( urea-urethane ) nanoparticles by step miniemulsion polymerization, J. Mol. Catal. B. Enzym. 109 (2014) 116–121. doi:10.1016/j.molcatb.2014.08.017. [33] V. V. Gite, P.D. Tatiya, R.J. Marathe, P.P. Mahulikar, D.G. Hundiwale, Microencapsulation of quinoline as a corrosion inhibitor in polyurea microcapsules for application in anticorrosive PU coatings, Prog. Org. Coatings. 83 (2015) 11–18. doi:10.1016/j.porgcoat.2015.01.021. [34] G. Morral-Ruíz, P. Melgar-Lesmes, M.L. García, C. Solans, M.J. García-Celma, Polyurethane and polyurea nanoparticles based on polyoxyethylene castor oil derivative surfactant suitable for endovascular applications, Int. J. Pharm. 461 (2014) 1–13. doi:10.1016/j.ijpharm.2013.11.026. [35] P. Gentile, D. Bellucci, A. Sola, C. Mattu, V. Cannillo, G. Ciardelli, Composite scaffolds for controlled drug release: Role of the polyurethane nanoparticles on the physical properties and cell behaviour, J. Mech. Behav. Biomed. Mater. 44 (2015) 53–60. doi:10.1016/j.jmbbm.2014.12.017. [36] S. Park, Y. Lee, Y.S. Kim, H.M. Lee, J.H. Kim, I.W. Cheong, et al., Magnetic nanoparticle-embedded PCM nanocapsules based on paraffin core and polyurea shell, Colloids Surfaces A Physicochem. Eng. Asp. 450 (2014) 46–51. doi:10.1016/j.colsurfa.2014.03.005. [37] F. Salaün, G. Bedek, E. Devaux, D. Dupont, L. Gengembre, Microencapsulation of a cooling agent by interfacial polymerization: Influence of the parameters of encapsulation on poly(urethane-urea) microparticles characteristics, J. Memb. Sci. 370 (2011) 23–33. doi:10.1016/j.memsci.2010.11.033. [38] H. Souguir, F. Salaün, P. Douillet, I. Vroman, S. Chatterjee, Nanoencapsulation of curcumin in polyurethane and polyurea shells by an emulsion diffusion method, Chem. Eng. J. 221 (2013) 133–145. doi:10.1016/j.cej.2013.01.069. [39] A. Valério, M. Fortuny, A.F. Santos, P.H.H. Araújo, C. Sayer, Poly(UreaUrethane) Synthesis by Miniemulsion Polymerization Using Microwaves and Conventional Polymerization, Macromol. React. Eng. 9 (2015) 48–59. doi:10.1002/mren.201400029. [40] D. Crespy, M. Stark, C. Hoffmann-Richter, U. Ziener, K. Landfester, Polymeric nanoreactors for hydrophilic reagents synthesized by interfacial polycondensation on miniemulsion droplets, Macromolecules. 40 (2007) 3122–3135. doi:10.1021/ma0621932. 19

[41] E.M. Rosenbauer, K. Landfester, A. Musyanovych, Surface-Active monomer as a stabilizer for polyurea nanocapsules synthesized via interfacial polyaddition in inverse miniemulsion, Langmuir. 25 (2009) 12084–12091. doi:10.1021/la9017097. [42] C. Herrmann, D. Crespy, K. Landfester, Synthesis of hydrophilic polyurethane particles in non-aqueous inverse miniemulsions, Colloid Polym. Sci. 289 (2011) 1111–1117. doi:10.1007/s00396-011-2430-z. [43] F. Tiarks, K. Landfester, M. Antonietti, One-step preparation of polyurethane dispersions by miniemulsion polyaddition, J. Polym. Sci. Part A Polym. Chem. 39 (2001) 2520–2524. doi:10.1002/pola.1228. [44] F. Gaudin, N. Sintes-Zydowicz, Poly(urethane-urea) nanocapsules prepared by interfacial step polymerisation in miniemulsion. The droplet size: A key-factor for the molecular and thermal characteristics of the polymeric membrane of the nanocapsules?, Colloids Surfaces A Physicochem. Eng. Asp. 384 (2011) 698– 712. doi:10.1016/j.colsurfa.2011.05.050. [45] A. Valério, S.R.P. da Rocha, P.H.H. Araújo, C. Sayer, Degradable polyurethane nanoparticles containing vegetable oils, Eur. J. Lipid Sci. Technol. 116 (2014) 24–30. doi:10.1002/ejlt.201300214. [46] K. Landfester, Miniemulsions for Nanoparticle Synthesis, Top. Curr. Chem. 227 (2003) 75–123. doi:10.1007/b10835. [47] G.W. Reimers, S.E. Khalafalla, PRODUCTION OF MAGNETIC FLUIDS BY PEPTIZATION TECHNIQUES, US3843540-A, 1974. [48] P.E. Feuser, L.D.S. Bubniak, M.C.D.S. Silva, A.D.C. Viegas, A.C. Fernandes, E. Ricci-Junior, et al., Encapsulation of magnetic nanoparticles in poly(methyl methacrylate) by miniemulsion and evaluation of hyperthemia in U87MG cells, Eur. Polym. J. (2015) article in press. doi:10.1016/j.eurpolymj.2015.04.029. [49] a B. Salunkhe, V.M. Khot, S.H. Pawar, Magnetic hyperthermia with magnetic nanoparticles: a status review., Curr. Top. Med. Chem. 14 (2014) 572–594. doi:10.2174/1568026614666140118203550. [50] S. Si, A. Kotal, T.K. Mandal, S. Giri, H. Nakamura, T. Kohara, Size-controlled synthesis of magnetite nanoparticles in the presence of polyelectrolytes, Chem. Mater. 16 (2004) 3489–3496. doi:10.1021/cm049205n. [51] S. Sun, H. Zeng, Size-controlled synthesis of magnetite nanoparticles, J. Am. Chem. Soc. 124 (2002) 8204–8205. doi:10.1021/ja026501x.

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Table 1 Formulations of miniemulsion polymerizations.* Reactants and conditions M0 M1

M2

M3

M4

M5

IPDI (g)

4.9

2.21

4.9

4.9

4.9

4.9

1,6-hexanediol (g)

1.07

1.05

1.07

1.07

1.07

1.07

Cyclohexane (ml)

5

2

5

5

5

5

0.6

0.2

0.6

0.6

0.6

0.6

Crodamol (g)

-

-

-

-

1.08

1.28

MNPs-OA (g)

-

0.11a

0.24 a

0.49b

0.49 c

1.5 d

2.5:1

1.5:1

2.5:1

2.5:1

2.5:1

2.5:1

SDS (g)

Molar ratio (NCO:OH) *

All miniemulsions were prepared with 20 ml of water; 5 wt%, c 10 wt% and d 30 wt% in relation to IPDI: MNPs-OA added before sonication; b 10 wt% in relation to IPDI with two methodologies: MNPs-OA added during sonication and added before sonication. a

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Table 2 Intensity average diameter of droplets (Dg) and particles (Dp) of pure PUU and PUU with different contents of MNPs-OA and Polydispersity index (PdIg and PdIp) measured by DLS. Samples Dg (nm) PdIg Dp (nm) PdIp Pure PUU (reaction M0)

91.6±1.9

0.143

100.5±1.5

0.174

PUU 5wt% MNPs-OA (reaction M2)

133.3±1.8

0.144

146.6±1.2

0.149

PUU 10wt% MNPs-OA (reaction M4)

172.0±0.1

0.208

177.0±0.8

0.209

PUU 30wt% MNPs-OA (reaction M5)

263.3±9.6

0.325

241.2±5.9

0.323

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Table 3 Number and volume average particle diameters (obtained by TEM) and intensity average particle diameter (obtained by DLS) of reactions M4 and M5. Average diameter PUU 10 wt% MNPs-OA PUU 30 wt% MNPs-OA (reaction M4) (reaction M5) Number (nm)

115.5

184.3

Volume (nm)

154.7

218.1

Intensity (nm)

177.0

241.2

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Table 4 Magnetic properties of MNPs-OA and PUU withMNPs-OA (reaction M4)*. Hc(Oe Mr Ms Mr/Ms(x1 Sample ) (emu/g Fe3O4) (emu/gFe3O4) 0-7) MNPs-OA 0.162 73.5 0.022 2.99 PUU-MNPs coated with OA* 0.186 35.66 0.018 5.04

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Figure Captions: Fig. 1.Schematic representation of the magnetite nanoparticles (MNPs) preparation coated with oleic acid. Fig. 2.TEM image of MNPs coated oleic acid. Fig. 3. TGA thermograms of (a) reaction M0 (pure PUU), (b) reaction M3 (MNPs-OA added during sonication), (c)reaction M3 (MNPs-OA added before sonication), and (d) MNPs-OA. Fig.4.FTIR spectra of PUU nanoparticles synthesized by step miniemulsion polymerization using (a) 1,6-hexanediol/IPDI, reaction M0 and (b) and 1,6hexanediol/IPDI/MNPs, reaction M2. Fig.5.TEM images of PUUnanoparticles with MNPs-OA (a) 5wt% of MNPs-OA, reaction M2and (b) 10wt% MNPs-OA (added before sonication), reaction M3. Fig.6.TEM images of the PUUnanoparticles with MNPs-OA (a) 10wt% MNPs-OA, reaction M4and (b)30wt% MNPs-OA, reaction M5. Fig.7. Particle size distribution, based on TEM images, of (a) PUU nanoparticles with 10 wt% MNPs-OA, reaction M4, and (b) PUU nanoparticles with 30% MNPs-OA, reaction M5. Fig.8.Magnetization curves of (a) MNPs-OA, and (b) PUU with 10wt% MNPs-OA, reaction M4(MNPs-OA added before sonication). Fig. 9. PUU with MNPs-OA in distilled water without application of an external magnetic field and with application of an external magnetic field.

25

Fig. 1. Schematic representation of the magnetite nanoparticles (MNPs) preparation coated with oleic acid.

Fig. 2.TEM image of MNPs coated oleic acid.

26

Fig. 3. TGA thermograms of (a) reaction M0 (pure PUU), (b) reaction M3 (MNPs-OA added during sonication), (c)reaction M3 (MNPs-OA added before sonication), and (d) MNPs-OA.

Fig. 4.FTIR spectra of PUU nanoparticles synthesized by step miniemulsion polymerization using (a) 1,6-hexanediol/IPDI, reaction M0 and (b) and 1,6hexanediol/IPDI/MNPs, reaction M2.

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Fig. 5.TEM images of PUUnanoparticles with MNPs-OA (a) 5wt% of MNPs-OA, reaction M2and (b) 10wt% MNPs-OA (added before sonication), reaction M3.

Fig. 6. TEM images of the PUUnanoparticles with MNPs-OA (a) 10wt% MNPs-OA, reaction M4and (b)30wt% MNPs-OA, reaction M5.

28

Fig. 7. Particle size distribution, based on TEM images, of (a) PUU nanoparticles with 10 wt% MNPs-OA , reaction M4, and (b) PUU nanoparticles with 30% MNPs-OA, reaction M5.

Fig. 8.Magnetization curves of (a) MNPs-OA, and (b) PUU with 10wt% MNPs-OA, reaction M4 (MNPs-OA added before sonication).

29

Fig. 9. PUU with MNPs-OA in distilled water without application of an external magnetic field and with application of an external magnetic field.

30