INTRODUCTION:

Well-known methods of the synthesis of oxidation-reduction polymers, redox polymers, are based on the interaction of quinones with polyvinylaromatic compounds^1-6. In addition, an important phase of the process is a preliminary activation of aromatic nucleus. Reactive CH₂Cl, NH₂, OH and other groups were introduced to it. In order to obtain chloromethylated copolymers, it has been carried out chloromethylation of copolymers with high toxic monochlorodimethyl ether.The synthesis of aminocopolymers consists of 2 phases: nitration of copolymers of styrene and DVB with mixture of HNO₃ and H₂SO₄ and subsequent reduction of nitrocopolymers to aminoderivatives by SnCl₂ in concentrated HCl^5,7-9. This substantially complicates the synthesis of redox polymers. Therefore, we have studied the possibility of the synthesis of quinoid oxidation-reduction polymers without activation phase of benzene ring¹⁰.

Method is based on Hill and Adams studies¹¹. They indicated that interaction of the aromatic compounds with quinones under conditions of Friedel-Crafts reaction leads to the formation of diarylhydroquinones. And quinoid group serves as an acceptor of the part of separating hydrogen:

The displacement reaction with formation of monoderivatives does not occur. 2,5-diarylhydroquinones easily transforms into the appropriate diarylquinones at oxidation of Fe³⁺in acetic acid, chromic acid, and other oxidants, and also excess of quinone itself:

Hydrogen sulfide, aromatic compound itself, benzene and other catalysts are used in this reaction as solvents. Chloride aluminum and other catalysts react with quinones forming stable complexes. They are released as far as the process goes.

MATERIAL AND METHODS:

Copolymers of styrene and divinylbenzene (DVB) were previously washed with methyl alcohol in Sohxlet apparatus. 1,2- and 1,4-Quinones (Q) of “pure” mark were recrystallized from ethyl alcohol or cleaned by sublimation with a melting point of 105 and 116ºC, respectively.

1,2- and 1,4-Naphthoquinones (NPhQ) of “pure” mark were reprecipitated from benzene and ethyl alcohol with a melting point of 267 and 158ºC, respectively. Anthraquinone (AQ) of “pure” mark after cleaning had melting point of 286 ºC.

Catalysts AlCl₃ of “pfs” mark, waterless sublimated; ZnCl₂ and SnCl₄ of “pfs” mark were dried to constant weight in vacuum oven; SnCl₄ was distillated under the vacuum by selecting fraction that boils at 41-42 ºC/1,60 kPa, n_D²⁰=1,1457.

Synthesis of redox polymers was carried out in three-necked reactor by condensation of polystyrene or copolymers of styrene and DVB in the medium of freshly distillated solvents at the temperature of 7-100ºC during 1-8 hrs. Copolymers were washed off from unreacted components by decantation, then by methyl alcohol in Sohxlet apparatus. Soluble samples were reprecipitated from benzene into sulphuric ether twice. The redox capacity of reduced samples was determined in the argon atmosphere under 0,1N solution of Fe₂(SO₄)₃. The reduction of polymers was carried out by alkali solution of sodium dithionite. They were washed off consequently with oxygenless diluted sulfuric acid, then by oxygenless bidistilled water until absence of reducer ions in the filtrate (according to non-disappearing pink color KMnO₄).

Oxidized-reduced potentiometric titration of the reduced polymers was carried out on a titrometer of the firm Mettler-Toledo in a thermostated cell in the argon flow by solution of Ce(SO₄)₂in sulfuric acid, standartized with 0.1N solution of Na₂S₂O₃ in the presence of a calomel electrode with a smooth platinum electrode at the temperature of 25ºC. As mediator in the case of cross-linked redoxpolymers, 1/30N solution of Fe³⁺ in a buffer of K₂SO₄+H₂SO₄ at pH 0.6-0.7 was used¹.

IR-spectra of samples were taken on a spectrophotometer “Specord M-80/M85” in tablets with KBr (200 mg of KBr + 1 mg of substances).

Results and discussion:

The influence of solvents nature on interaction reaction of quinones with сopolymers of styrene and DVB has been studied. It was shown that the process takes place only in those solvents in which formation of quinone-catalyst complex and dissolution or swelling of the initial polymer occurs. In addition, reaction mixture acquires typical color for every complex.

A change in outward appearance of granules and character of IR-spectra of condensation products of quinones with copolymers of styrene and DVB were observed only in dichloroethane (DChEt) and nitrobenzene. In other solvents the reaction did not occur. Due to the strong toxicity of nitrobenzene further study was carried out in DChEt.

The changes in IRS in comparison with spectra of the initial quinones are observed for all forming complexes of quinone-catalyst. For example, a comparison study of the IR-spectrum of 1,4-Q complex with AlCl₃catalyst (fine-dispersed black-blue powder) and initial quinone was carried out. It was established that spectra of complex is characterized by: displacement of the absorption band of valence vibrations C=O to 1765 (against 1735 cm^-1); a significant broadening of quinoid absorption and its shifting to the low-speed range to 1635 (against 1650 cm^-1); occurrence of the absorption tract at 1210 cm^-1of significant density that is characterized by valence vibrations of phenolic CO; occurrence of strong band at 1505 cm^-1that is typical for flat vibrations of skeleton of aromatic ring. The obtained data confirms the formation of quinone-catalyst complex. The appearance of new 1505 and 1210 cm^-1bands in its spectrum evidences about more aromatic character of the formed compound and decrease of unsaturation of the initial diketone. It occurs because of the participation of C=O in complex formation. The same pattern is observed for the 1,2-Q.

The results of the elemental analysis confirm the obtained data. It was founded, %: C 30,27; H 1,83; Cl 41,6; Al 13,5. It was calculated for C₆H₄O₂. AlCl₃, %: C29,69; H 1,65; Cl 40,02; Al 11,13.

The benzene ring of NPhQ decreases the energy of the system and weakens 1,4- or 1,2- conjugation in quinoid cycle of compound. It occurs because of the inclusion of one double bonds of Q into the aromatic ring of NPhQ. As a result of this, the changes in the character of spectra at complex formation with haloids of metals do not have such expressed character as in the case of 1,4- and 1,2-Q. In the lesser degree this effect appears in molecule of AQ.

The study of the sequence for combining the reagents has indicated that there is a need for the simultaneous presence of quinoid compounds and catalyst in reaction mixture that again confirms the interaction of Q with copolymer through the stage of formation of complex (tab.1).

As shown, in case of simultaneous addition of Q and catalyst into the reaction mixture, the coloring of granules is much deeper (initial polymer is matted), absorption intensity of quinoid band and oxidation-reduction capacity of final products is higher than at gradual addition of the catalyst.

Different correlations of the initial components were studied. It was showed that the excess of catalyst is not desired as in this case many additive products are formed and unreacted catalyst remains. Deletion of the unreacted catalyst from the reacting medium creates additional difficulties. Graphic chartof catalyst concentrations from the quantity of introducing into the polymers of quinoid groups is obtained at two different temperatures (fig. 1).

Fig. 1. Influence of the concentration of catalyst at 7⁰ (1) and 82^O (2) on the intensity of quinoid absorption (D, %) of product of interaction of complex with copolymer of styrene and DVB.

It is clear that they pass through maximum that corresponds to the presence in the reacting medium of 0,5 moles of catalyst to 1 mole of quinone. The increase of the quantity of Q to 1 basis-mole of polymer from 0,5 to 2 moles shows that intensity of quinoid band in the polymer is increasing. However, using more than 1 mole of quinone leads to the polymerization of the excess Q. In addition, polyquinone (black powder) forms which has in IR-spectrum wide band of absorption in the area of 1645 cm^-1. A high reactivity of Q and possibility of its polymerization in the presence of different catalyst (anionic, cation and etc.) are referenced by authors¹². This also confirmed by the temperature dependence which we obtained as shown in fig. 2: interaction of Q with polymers of styrene and DVB takes place equally well at different temperatures (both at 0^оС and at the temperature of solvent boiling).

Fig. 2. The influence of the reaction temperature of the complex with copolymers of styrene and DVB on the intensity of quinoid absorption (D, %) of polymer.

In order to obtain redoxpolymers, a correlation of polymers:catalyst:quinone, which is equal to 1:0,5:1 is taken. IR-spectra of products of condensation of quinones with polystyrene or copolymers of styrene and DVB are characterized by appearance of intensive absorption band in the area of 1665 cm^-1.

The data of quantum-chemical analysis suggests the following types of interaction of Q with model R^q particles (nucleophils, electrophils and radicals) in the presence of chloride aluminum (fig. 3). According to the data of enthalpy of the mentioned reactions, the last one is reacted with more probability with quinone than with hydroquinone. At formation of complex, the electron density is changed from Q molecule to AlCl₃and the symmetry in electron density distribution in Q is violated. Under the influence of polarization of σ-skeleton of Q by the complex formator, π-electronic level in Q decreases, increasing its π-acceptor properties.

At further interaction with model particles the preference is given to nucleophilic reagents and formed σ-complex has a structure of “a” type (fig. 3). Values of enthalpies of the reaction evidences about preferred participation of Q in reaction with AlCl₃rather than with hydroquinone and that primarily all α-atoms of the ring interact.

Polymers, which are obtained on the basis of copolymers, do not swell in the water and at conversion from oxidized into the reduced form change colour from brown to grey. The introduction of sulfo- and phosphoric acid groups on the basis of earlier described methods¹ considerably increases hydrophylic property of net-shaped redoxites.

The redox capacity of samples composes of 0,5-1,4 mg-eqv/g, cation-exchange capacity – 1,2-2,3 mg-eqv/g. Values of normal oxidation-reduction potentials (E_o1/2,mV) approach to literary¹ (tab. 2), and for all redoxites the introduction of acid groups promotes certain increase of potential. This can be explained by appearance of additional protons at the expense of “internal pH”. “Internal pH” is caused by ionogenic groups, and its value is considerably smaller than in external solution¹³. It causes regular increase of potential because in the oxidation-reduction process deletion of electron should be accompanied by the loss of one proton.

CONCLUSION:

Thus, the study of interaction of quinones with copolymers of styrene and DVB showed the possibility in principle of obtaining the oxidation-reduction polymers in one stage. This eliminates a need for obtaining the chloromethylated or aminated derivatives of polymers. There is no need in toxic reagents (monochlorodimethyl ether), in conducting the processes in aggressive mediums and stringent conditions of synthesis (nitration and reduction of polymeric materials). With the help of quantum-chemical calculations, a mechanism of interaction of quinone with polyarenes is revealed. The process is running through the stage of activation of quinone by catalyst. At first there forms π- and then σ-complex. The expected course of reaction has been confirmed by the data which was acquired by elemental analysis, IR-spectroscopy, acid-base and oxidation-reduction potentiometric titration.

Table 2 Oxidation-reduction characteristics of polymers on the basis of different quinones and copolymers of styrene and DVB (8%)

Quinone

ORC,

mg-eqv/g

E_o1/2, mV

-SO₃H

-PO(OH)₂

1,4-Q

1,2-Q

1,4-NPhQ

1,2-NPhQ

1,3

1,0

0,9

0,7

0,5

704

740

410

425

147

710

747

420

440

150

715

745

417

435

155

Fig. 3. Enthalpies of reaction of quinone with model Rq particles: anions (-), cation (+) or radicals (*) in presence of chloride aluminum (A).

ABBREVIATIONS:

ORC oxidation-reduction capacity (mg-eqv/g)

DVB divinylbenzene

DChEt dichloroethane

Q 1,2- or 1,4-benzoquinone

NPhQ naphtoquinone

AQ antraquinone

IRS infrared spectroscopy

D intensity, %

C concentration, mole

T temperature, ^oC

REFERENCES:

1. Cassidy HG, Kun KA. Oxidation-reduction polymer (Redox polymers). Interscience Publishers, New-York. 1965.

2. Cassidy HG. Oxidation-reduction polymers. Makromol.Review. J.Polym.Sci. Pt. D. 6;1972: 1-16.

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Received on 27.01.2012 Modified on 12.02.2012

Asian J. Research Chem. 5(5): May 2012; Page 616-619