Solvent Free Cationic Copolymerization of 2-Chloroethyl vinyl ether with Styrene , Catalyzed by Maghnite-H + , a Green Catalyst

Maghnite-H+ (Mag-H), proton-exchanged Montmorillonite, catalyzed the cationic copolymerization of 2-Chloroethyl Vinyl Ether (CEVE) with Styrene (St) in a solvent free system. The objective is to synthesize an end-group functionalized copolymer. The advantage of the Mag-H lies in its capacity to solve ecological (green catalyst) and economic problems, and also to the fact that the reactions are carried out under moderate conditions, solvent free and at room temperature. A kinetic study was carried out, and the products obtained were characterized using different methods of analysis, including IR, 1H and 13C NMR and viscosimetry.


INTRODUCTION
Polyvinyl ethers are viscous gum to rubbery solids used for a wide variety of technological and industrial applications; they are particularly employed in manufacturing additives and nanometer membranes.They are used in telecommunications, in the synthesis of nonlinear optical (NLO) materials 1 , and also in electronics, in the production of light emitting diodes (LEDs) 2 .Chloroethyl Vinyl Ether (CEVE) is one of the most popular industrial products.CEVE is a special product because it possesses the functional group chloroethoxy that offers extremely varied possibilities for chemical modification and for anchoring functional groups.Hashimoto et al. employed CEVE as a starting material for preparing 2-vinyloxyethyl phthalimide by substituting the chlorine atom with potassium phthalimide.It was also used as a raw material in the synthesis of divinyl ethers 3,4 .
Herein, we propose to use smectite clay, called Maghnite-H + 20 , as an efficient and recyclable green heterogeneous catalyst for the cationic copolymerization of Chloroethyl Vinyl Ether with Styrene at room temperature.The polymerization of vinyl ethers is widely known and has been used for a long time 26 ; this chemical reaction can only occur by a cationic mechanism.This is the case of Mag-H + which can initiate the polymerization reactions only cationically [19][20][21][22][23][24] .Moreover, Mag-H + presents several advantages, among which are its high efficiency, easiness of handling, recyclability, high capacity to operate under mild conditions, and eco-friendliness.

Methodology Copolymerization of 2-Chloroethyl Vinyl Ether with Styrene using Maghnite-H +
Proton exchanged Montmorillonite clay called "Maghnite-H + " (Mag-H) is a non-toxic catalyst that was prepared according to the procedure reported in the literature 19,20 .

Bulk copolymerization of CEVE with
Styrene was carried out in a heterogeneous system, at room temperature, using a percentage, by weight relative to monomers, of Mag-H + as a catalyst (scheme 1).Copolymerization was carried out with different mole fractions (x = n CEVE /n ST + n CEVE ), in several crimp tubes 7 .The mixture prepared was stirred with a magnetic stirrer for a specific period of time.Then, a given quantity of methylene chloride was added and the mix obtained was dried under vacuum in order to eliminate Mag-H + which precipitates in methanol.Finally, the copolymer was isolated and dried before analysis.The experimental conditions used are described in Table 1.
In a previous study on CEVE and St polymerization, with Mag-H + (3% by weight) as catalyst, reaches maximum yield after 6 hours of reaction 22,24 .

Apparatus
In order to characterize our products, analytical techniques such as 1 H-NMR, 13 C-NMR and IR were used.Viscosimetry was employed for the kinetic reactions.

H-NMR and 13 C-NMR
The proton and carbon NMR spectra were recorded on a Bruker AC 300MHZ apparatus.This technique allowed identifying the products obtained.The analysis was carried out in deuterated chloroform.

Infrared IR
ATR-FTIR absorption spectra were recorded on an Alpha Bruker ATR-FTIR spectrometer, in a range extending from 400 to 4000 cm -1 .

Characterization
Three mole fractions, 0.2, 0.5 and 0.8 were analyzed by 1 H NMR and one by 13 CNMR spectroscopy.Fig. 1 and 2 show 1 H NMR spectrums and Fig. 3 shows 13 C NMR spectrum.

RESULTS AND DISCUSSION
The 1 H NMR analysis indicates the presence of the main protons corresponding to the (CEVE-Styrene) copolymer.The 1 H NMR spectrum of the copolymer is almost the same to that reported in the literature by Cramail 27 .Peaks (i,h), observed between 5.2 and 5.80 ppm, correspond to H-vinyl of styrene of the chain end.
The number of CEVE and St units per chain in copolymer and Mn were determined by 1 H NMR (Fig. 2) from the ratio, on the one hand, between the -CH2-CH2-Cl methylene protons, the CH-O methine proton and aromatic proton of styrene and, on the other hand, between the aromatic proton of styrene and H-vinyl of styrene of the chain end.Results are shown in Table 2. Results show that in this copolymerization, CEVE is much more reactive than styrene.Values of r l = 36, r 2 = 3, and 66 ≥ r 1 ≥ 9, 0.125 ≥ r 2 ≥ 0.01were reported respectively by Brown and Pepper 28 and Kanoh et al., 29 for this system.Figure 4 shows the ATR-FTIR spectrum of the copolymer.The FTIR spectra indicate the presence of St and the CEVE units.As for the St repeating unit, aromatic C-H stretching occurs between 3000 and 3105 cm -1 , aromatic C=C stretching occurs at about 1600 cm -1 and St absorption of the out-of-plane ring deformation band occurs at about 700 cm -1 .Concerning the CEVE repeating unit, spectrum illustrates bands corresponding to C-Cl bond at about 660 cm -1 and C-O-C stretching of vinyl ether between 1090 and 1110 cm -1 .FTIR results from CEVE with St copolymerization showed that characteristic absorbance bands at about 700 cm -1 , the strongest IR band of St unit, and at 660 cm -1 , IR band of CEVE unit, could be used to follow the evolution of each unit in copolymer.Indeed, the comparison, between the intensities of absorption bands at 660 and 700 cm -1 , shows the great difference between the reactivities of St and CEVE (Fig. 4, B and Table 3).

Viscosimetric analysis
In order to understand the physical nature of the copolymers obtained, the evolution of their intrinsic viscosities was followed, in the solution of dichloromethane, at a temperature of 25 °C.The results obtained are grouped in Figure 6.

Kinetic study
The aim of the present study is to vary the amount of catalyst in order to examine its influence on the course of the living copolymerization.

Effect of the amount of Maghnite-H + on the yield
This study aims to know the behavior of our copolymer system, namely (2-Chloroethyl Vinyl Ether -Styrene) + Maghnite-H +

Description of experiment
In order to determine the effect of the amount of the catalyst on the yield, three (03) series of experiments were conducted, by varying the percentages of the amount of Mag-H, as 1%, 2% and 3%.The results obtained are presented in Figure 5.  Figure 5 shows the effect of the amount of Mag-H on the copolymerization rate of CEVE with Styrene Indeed, using various amounts of Mag-H + , 1, 2, and 3 % by weight, the copolymerization was carried in bulk at room temperature.The copolymerization rate increased with the amount of Mag-H + , in which the effect of Mag-H + as a cationic catalyst of the copolymerization is clearly shown.Similar results are obtained by Beloufa et al., 30 and Bouchama et al., 31 in, respectively, the copolymerization of 1,3,5-trioxane with 1,3-dioxolaneand e-caprolactone with tetrahydrofuran catalyzed by Mag-H + .This increase in yield is due to an increase in the number of ''initiating active sites'' responsible of inducing polymerization, a number that is proportional to the amount of catalyst.

Effect of the amount of Maghnite-H + on intrinsic viscosity
The different samples obtained from the different experiments were subjected to the viscosimetric analysis.The results are shown in Fig. 6.As is shown, on the one hand, the increase of the catalyst amount led to the decrease of intrinsic viscosity.This is comparable to that of the most active catalyst systems.The explanation for the decreased of intrinsic viscosity is that the chain transfer reaction rate is faster than that of the propagation reaction.On the other hand, the decrease in the quantity led to the increase of the intrinsic viscosity, this is due to the high reactivity of CEVE which leads to the formation of oligomers 22 .From the results obtained, it can be said that the intrinsic viscosity decreases as the amount of Maghnite-H + goes up.Moreover, the intrinsic viscosity increases with increasing percentage (%) of the most reactive comonomer.In this case, styrene (r 1 = 160) is more reactive than CEVE (r 2 = 0.07), and this difference in reactivity between the two monomers is due to the fact that the two types of active centers react with the most reactive monomer.The reaction mixture is therefore enriched with styrene, which is more reactive than CEVE.This causes the yield to decrease, while the intrinsic viscosity increases.

Proposed mechanism
The copolymerization is proposed undertaking in a way as shown in Scheme 2. Mag-H performs as an environmentally friendly solid catalyst.It was regarded as an initiator an activator [19][20][21][22][23][24]31 . The opolymerization of CEVE with St is initiated, firstly, by proton addition from Mag-H to CEVE (Eq.1), due to the most reactivity of CEVE compared to the St, and the Maghnite takes place as counter-ion.Propagation then takes place by conventional cationic mechanism (Eq.2).Secondly, reaction between growing macrocation and St occurs (Eq.3).The copolymerization ends by proton transfer to St and/or to Maghnite produced by unsaturation as shown in the termination reaction (Eq.4).

Initiation Propagation Termination
We suppose that there was formation of a double bond at the end of the chain of the copolymer by spontaneous transfer.
The kinetic study of cationic copolymerization in the presence of Mag-H + makes it possible to draw the following conclusions

CONCLUSION
The main goal was the synthesis of copolymers using an environmentally friendly solid catalyst.Our study aimed particularly at

Fig. 5 .
Fig. 5. Influence of the amount of Maghnite-H + on the yield, during the copolymerization of the (CEVE -Styrene) system

Copolymerization of CEVE with Styrene
+

Table 3 : Comparison between the intensities of absorption bands at 660 cm -1 and 700 cm -1
I: intensity of absorption bands