WO2016022012A1

WO2016022012A1 - Fluorescent nanocomposite materials based on modified clay and uses

Info

Publication number: WO2016022012A1
Application number: PCT/MA2015/000013
Authority: WO
Inventors: Rachid Bouhfid; El Mokhtar Essassi; Abou El Kacem QAISS; Mehdi Mohammed MEKHZOUM
Original assignee: Moroccan Foundation For Advanced Science, Innovation & Research (Mascir)
Priority date: 2014-08-08
Filing date: 2015-08-10
Publication date: 2016-02-11
Also published as: MA37274A1; MA37274B1

Abstract

The present invention relates to a novel fluorescent nanocomposite material based on polymer and on clay modified by different range of surfactants derived from 2-styrylbenzothiazole having a 'donor-acceptor' molecular architecture having both fluorescent properties and good heat stability.

Description

Fluorescent nano-composite materials based on modified clay and applications

FIELD OF THE INVENTION

The present invention relates to a novel polymeric and clay-based fluorescent nano-composite material modified by a variety of surfactants derived from 2-styrylbenzothiazole having a donor-acceptor molecular architecture having both fluorescent properties. and good thermal stability.

STATE OF THE ART

Because of its abundance in nature, its particular structure and its chemical composition, clay has attracted significant interest from the engineering and scientific point of view. Clay minerals are frequently used to prepare nano-composites and nowadays much work is available on this subject [1-8].

Incorporation of clay in polymer matrices leads to nanomaterials with improved properties such as dimensional stability, heat resistance, gas permeability, and mechanical properties [9]. The main methods used to incorporate inorganic additives into matrices; in-situ polymerization and melt compounding. [10]. A key factor in the preparation of nano-composites is to compatibilize the matrix and the charge, which will affect the nanostructure (intercalated / exfoliated) and, consequently, the factors that control the polymer / clay interface, contributes to the design of systems for high value-added applications. Because most polymers are hydrophobic, modification of the clays by surfactants having a hydrophobic group improves adhesion to the interface. One of the most common methods of modification is the introduction of an ammonium or phosphonium salt, carrying a suitable organic function, into the intermediate space by a cation exchange reaction [11]. -13]. In addition, Ennajih et al. [14] have prepared new polypropylene nano-composites with a thermally stable benzimidazolium salt-derived surfactant used for the organic modification of clays. Thus, the evaluation of clay-surfactant-polymer interactions for a group of heat-stable surfactants and clays could provide a useful basis for the design and selection of suitable clays.

In recent decades, the design of materials with fluorescent properties has attracted great attention because of their potential applications in many advanced technologies [15]. However, a number of fluorescent nanomaterials, including quantum dots (QD) [16], up-converting nanoparticles [17], nanoparticles based on fluorescent polymers [18,19] and doped silica dyes ( DDSNs) [20], have already been reported in the literature. On the other hand, nanocomposite polymer-clay materials, which contain fluorescent organic dyes intercalated in the silicate of montmorillonite clay layers, have so far been limited to a few studies [21]. Many classes of fluorescent organic dyes have found their application in science and technology. The best known are xanthes, coumarins, naphthalimides, cyanines, various aryl-azoles, acridines and phenoazines [22]. With these considerations, we have hereinafter synthesized a series of benzothiazole-based coloring salts with a "push-pull" type structure; a system conjugated with thermally stable donor and acceptor end groups that can withstand manufacturing and produce fluorescent nanocomposites with higher intensities compared to pure benzothiazolium salts. Several of these systems containing benzothiazole derivatives with a donor-rc-acceptor configuration have already been synthesized and extensively studied for several decades because of their potential applications in molecular electronics and probing biological fluorescence [23]. Currently, to the best of our knowledge, benzothiazole derivatives have not been applied as intercalated dyes to develop polymer-clay nanocomposite materials that may have fluorescent properties. BRIEF DESCRIPTION OF THE FIGURES

Figure 1. NMR Spectrum ¹ ! surfactant

Figure 2. ¹³ C NMR spectrum of the surfactant d

Figure 3. Cation Exchange Reaction

Figure 4. Fluorescence curves of MMT-benzothiazolium cations

Figure 5. Fluorescence curves of nanocomposites

Figure 6. Fluorescence curves of nanocomposites

Figure 7. Fluorescence curves of the nanocomposites

DESCRIPTION OF THE INVENTION

The montmorillonite used is a commercial product that is MMT-Na (Cloisite Na ⁺ ), Southern Clay Products, with an interfolar distance of 1.17 nm.

Several benzothiazolium salts have been employed whose structures are of structure below:

The effect of fluorescence on the clay-reinforced polymer, as well as any interactions of the hydrophilic head of the benzothiazolium salt and the hydrophobic tail of the ethyl group with the clay sheets on the thermal stability and the interlayer distance has been studied.

Various methods have been described in the literature for preparing benzothiazolium salts and specifically 3-ethyl-2- (substituted p-o-styryl) benzothiazolium iodide. Generally these reactions are carried out in two stages. The first step consists of a quaternization reaction carried out in fusion or with a solvent (acetonitrile). The alkylated product thus obtained is condensed in a second step in the presence of (ethanol or acetic acid as solvent and pyridine or piperidine as catalyst) with various substituted aromatic benzaldehydes.

It has been found that these different techniques used are long, expensive, and require purification of the isolated products with low yields.

On our part, we have obtained the benzothiazolium salts, in 2 stages with an excellent yield and without the use of solvent or catalyst.

The first step is the alkylation or quaternization reaction, reacting 2-methylbenzothiazole with ethyl iodide in dimethylformamide (DMF). The reaction is refluxed for 4 to 5 hours to give 2-methylbenzothiazole substituted in the 1-position in excellent yield (Scheme). The protocol of this step is new in comparison with the literature.

In a second step, the alkylated product thus obtained is treated with various aromatic benzaldehydes which are substituted by the fusion reaction (without solvent). The reaction is carried out with stirring at reflux between 100 and 150 ° C. (scheme). At the end of the reaction a single product is obtained, resulting from the condensation of 3-ethyl-2-methyl-1,3-benzothiazol-3-ium with the corresponding benzaldehydes, leading to the formation of benzothiazolium salts. However, this reaction is carried out in the presence of solvents and / or catalysts.

Comp. R Comp. R a 4-OCH 3 h 2 -Cl 4 -CH 3 i 2-OH c 4 -Br j 4 -CO d 4 -IC k 2 -F e 2 -No ₂ 1 4-C ₄ H ₉ f 2 -OCH 3 m 4-F g 4-OH n H

Example of preparation of surfactants

A solution of 2-methylbenzothiazole (3.35 g, 22.45 mmol) and iodoethane (12.50 g, 80.15 mmol) in DMF (5 mL). The mixture was refluxed at 90 ^° C. for 4 to 5 hours. After cooling, the desired salt collected by filtration under reduced pressure and washed several times with diethyl ether and ethanol. After drying under vacuum. Ether and ethanol were removed at a time. The process was repeated one to three times to obtain a white solid crystal with a yield of 95%.

A solution was stirred of 3-ethyl-2-methyl-1,3-benzothiazolium iodide (5,61 mmol) and substituted p / o-benzaldehydes (16.83 mmol) at 100-150 ° C for 5-7 h. After completion of the reaction, the reaction mixture was slowly cooled in most cases solidifies or becomes a thick semi-solid mass, the crude product was recrystallized with methanol, washed with absolute ethanol and dried.

The structures of the compounds were elucidated based on spectroscopic IR, NMR ^1! -! and ¹³ C. Thermogravimetric analysis and derivatives of the benzothiazolium salt curves show that the decomposition occurs in 2 steps for the compounds ag Table 1 except for the case of the compound b or the decomposition occurs in a single step, while the degradation of salts occurs in 2 stages. This can be explained by the presence of the aromatic styryl group substituted with different groups. The main thermal decomposition of surfactants occurs from 228 to 314 ° C (Table 1).

Table 1. Thermal properties of surfactants derived from benzothiazolium

Tymax: The temperature at the maximum rate of decomposition.

Clays are hydrophilic ores which, by chemical treatment can be made organophilic, likely to be compatible with conventional organic polymers.

We used cation exchange as a method of organophilic modification. The substitution is carried out in a mixture of water and acetonitrile; because the swelling of the clay facilitates the insertion of benzothiazolium ions into the galleries interfolaires. After filtration of the slurry and drying of the clay, the presence of benzothiazolium ions on the surface of the slips, primary particles, and aggregates, gives the clay an organophilic character. In addition, their intercalation between the platelets causes a slight increase in the interfolar distance this is due to the short chain of the ethyl group, and forget the fluorescent character of the benzothiazolium salts which subsequently makes the organophilic clays fluorescent.

The characterization of the samples resulting from the organophilic treatment of clay, was carried out by using different techniques: X-ray diffraction (XRD), thermogravimetric analysis (ATG), Fourier transform infrared spectroscopy (FTIR) , UV-visible spectroscopy and fluorescence spectroscopy.

Binary nanocomposites containing by weight (1, 2, 5%) of MMT-surfactant and polystyrene (PS) and were prepared by melt blending, at the processing temperature of the chosen matrix.

The characterization of the materials obtained was carried out through different techniques: X-ray diffraction to study their structures, thermogravimetric analysis (TGA) will allow an evaluation of their thermal stability, UV-visible spectroscopy will determine the length excitation wave and fluorescence spectroscopy allows to study the fluorescent properties.

After synthesizing surfactants, we are interested in the development of fluorescent organophilic clays, using cationic salts previously prepared, to see the effect of the ethyl group in position 1 and also of the benzothiazolium cation on thermal stability and distance. interfolar (d ₀₀ i), and the effect of fluorescent dye on sodium clay. For this purpose we have studied benzothiazoliums having a methoxyl group, a methyl group of the halide, nitro, hydroxyl groups at the 4 and 2 positions of the styryl aromatic ring with a chain containing 2 carbons of the benzothiazolium cation. Example of preparation of modified clay:

In a 500 ml flask containing a magnetic bar, 1.5 g of sodium montmorillonite are dispersed in 300 ml of a water: acetonitrile solution (1: 1) with vigorous stirring. The suspension was heated to 80 ° C, after 2 hours of stirring a solution of dye (1.5CEC) in acetonitrile was added to the mixture. Stirring was continued for 24 h at 80 ° C. The organic clay (MMT-Bzt) was isolated by centrifugation, washed with a water-acetonitrile mixture (1: 1) and then with a solution of acetonitrile ( 2 times) and dried at 80 ° C. for 10 h before being ground.

The IR spectra make it possible to highlight the presence of certain vibration bands characteristic of clays functions, as well as that of organic matter by the appearance of the different absorption bands corresponding to benzothiazolium ions.

In the spectrum of the modified CMM, the presence of characteristic bands of the MMT-Na (OH valence vibration band for Al (OH) at 3625 cm ^-1 , and that of deformation at 912 cm, are particularly noted. ¹ deformation bands Al-O-Si and Si-O-Si groups at 513 cm ¹ and 430 cm ^-1, respectively, as well as the characteristic bands of the intercalated surfactant: valence vibration bands of the group (CH). ₂ ) and (CH ₃ ) of the short chain around 2921 cm ¹ and 2852 cm ^-1 , thus the different vibration bands of the functions (methoxyl, hydroxyl, etc.)

FTIR spectroscopy analysis confirmed the presence of benzothiazolium ions in cation-exchanged clays.

The DRX makes it possible to evaluate the different periodicities and more particularly in our case, the periodicity d ₀ oi (making it possible to obtain the distance between the sheets of the clay) according to the nature of surfactants and the length of the alkyl chain.

We noted a widening of the interfolar space of the modified montmorillonite, illustrated by a significant displacement of the diffraction plane (001) towards the smaller angles. Indeed, the substitution of interfolar cations by benzothiazolium ions causes spacing of the interfolar space due to cation exchange. On the other hand, the interfolar distance is similar for the surfactants obtained.

The results obtained by XRD for montmorillonite sodium treated with the different types of benzothiazolium salts are presented in Table 2.

Table 2. Values of the periodicity d ₀ oi (nm) of montmorillonite treated with different benzothiazolium salts

Benzothiazolium cations increase the interfolar distance from 1.17 nm to 1.68 nm (MMT-Na). This is due to the short chain of 2 carbons, the organization of benzothiazolium ions in the interfolar space, as well as the amount of organic matter exchanged.

Table 3 summarizes the results of ATG for montmorillonite modified with different benzothiazolium salts, using the 5% mass loss as an indicator of the thermal stability of the modified clays. Table 3: The residual mass of clay at different temperatures

The polystyrene / modified clay nanocomposites were prepared by melt extrusion. The diffractograms show that there is no relative peak in the MMT-organophile, indicating that the MMT-organophile may be fully dilaminated and exfoliated in the polypropylene matrix.

The samples analyzed a, f and g (5%) by XRD were studied by thermogravimetric analysis and compared to the pure matrix ATG.

According to the different fluorescence spectra and the emission wavelengths of surfactants, modified clays and nano-composite films (Table 4), it can be seen that the intensity of the fluorescence increases when we go from surfactant to nano-composite films, this is the phenomenon of fluorescence hence λ _βχ <A _em - Indeed, the longer the emission wavelength increases, the more the fluorescence increases and consequently in time towards the visible light .

Table 4. Fluorescent properties of surfactants, modified clays and nano-composite films surfactant modified clay Film 1% Film 2% Film 5%

(Ex) (Em) (Ex) (Em) (Ex) (Em) (Ex) (Em) (Ex) (Em) a 466 505 409 575 413 554 410 557 415 572 f 464 517 409 531 395 522 410 528 409 536 g 481 575 465 589 430 551 434 552 440 556

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Claims

Claims:

Fluorescent nano-composite based on thermoplastic polymer and clay, characterized in that the clay is modified by an amphiphilic molecule chosen from the family of 1-alkyl-2-stylbenzothiazolium.

Fluorescent nano-composite according to claim 1, characterized in that

the clay is selected from the smectite family.

3. Nano-composite fluorescent according to claim 1 and 2, characterized in that the clay is modified by intercalation.

Fluorescent nanocomposite according to claims 1 to 3, characterized in that

R 1 is C _n H _{2n +} 1 with n = 1-20; C _n H _2n -OH with n = 1-4; or C _n H 2n-SO ₃ H with n = 1 to 4;

- R ₂ is H, Cl, CH ₃ , NO ₂₎ CN, SO ₃ H, Br, NH ₂ or CO ₂ H;

R ₃ is H, Cl, CH ₃ , NO ₂ , CN, SO ₃ H, Br, NH ₂ or CO ₂ H;

X ^" is CI ^" , Br ^" , I ^" , CH ₃ SO ₄ ^" , C ₆ H ₅ SO ₃ ^" , or CH ₃ COO ^" .

Fluorescent nano-composite according to Claims 1 to 4, characterized in that the amphiphilic molecules are chosen from:

Ri = C ₂ H 5

R ₂ = H

And R ₃ = 4-OCH 3; 4-CH3; 4-Br; 4-CI; 2-NO2; 4-OH; 2-OCH 3.

Fluorescent nano-composite according to Claims 1 to 5, characterized in that the amphiphilic molecules are prepared in two steps:

a first step of preparation of the amphiphilic molecules is a quaternization of 2-methylbenzothiazolium with ethyl iodide in Ν, Ν-dimethylformamide.

a second step of preparation of the amphiphilic molecules is carried out by fusing 2-methylbenzothiazolium with the substituted aromatics without the use of a solvent.

7. Nano-composite fluorescent according to claims 1 to 6, characterized in that the polymer matrix is chosen from the following thermoplastic polymers:

polypropylene

polyethylene

polystyrene

polysaccharide

Polyamide

8. Nano-composite fluorescent according to claims 1 to 7, characterized in that the integration of the clay in the polymer matrix is carried out by melt extrusion.