INTRODUCTION:

Researchers’ interest to allylic resins has considerably increased in recent years. This is so because of their exclusive physical and electric properties, high hemo- and thermal stability. However, it is known¹ that allylic monomers are hard to polymerize under the free-radical mechanism, and they offer polymers with low molecular weight and low yields. The main reason of it is low reaction ability of allylic monomers in the polymerization reactions, which is caused by the structure of the monomer itself, and, namely, because of the presence of –CH₂– groups in α-position in relation to double linkage. The separation of α-hydrogen by a growing active radical with formation of a little active allylic radical СН₂=СН-·CН-R, stabilized by internal interface, means destruction both material, and a kinetic chain (degradation chain transfer on a monomer)². One of the ways to suppress the degradation chain transfers is a procedure under high pressure or at high temperatures. However technologically it is not always convenient.

Other approaches are promising as well, and, namely, the change of monomer’s structure with the purpose of its "activation" by introducing electron-accepting substitutes to the initial compounds [2, 3]. As a result, there is a polarization of allylic groups, which is caused by displacement of electronic density (π-electrons) of double linkage, and, accordingly, monomer’s polymerization ability emerges or substantially increases.

At the same time it is important, that electron-accepting substitute should be directly attached to the atom of nitrogen. At removal of the substitute on 1 or 2 carbon atoms N- substituted allylamines not polymerize.

Considering the above, we have used a 1,4-benzoquinone (Q), which is a strong nucleophile⁴ because of the structure of 1,4-nonsaturated diketone, as an electron-accepting substitute in allylamine (АА). This approach significantly simplifies preparation of polymers on the АА basis. Thus, it is known, for example, that synthesis of vinyl monomers, which contain quinoid groups, includes 4-5 stages⁵.

We have studied the polymerization of allylic derivatives of Q in various conditions depending on the nature and concentration of the solvent, monomer, catalyst, temperature mode, duration of process. The structure and the basic properties of polymers was studied.

MATERIAL AND METHODS:

We have recrystallized Q of the "pure" qualification from methanol, and, after the purification, it had melting point of 116°С⁴.

We have used AA of the "chemical pure" qualification of the "Veb Berlin-Chemie-Adlershof” firm (Boiling point - 54,5 ^oС, n_D²⁰ 1,4205) without preliminary purification, and N,N-dimetilformamid (DMF), methyl and ethyl alcohols, sulfuric and petroleum ethers were purified by methods⁶. A benzoyl peroxide (BP) was dissolved in acetone and precipitated by absolute methyl alcohol (M.p.106-108 °С)⁷.

Synthesis of quinoid derivatives of АА with Q was carried out by their condensation in the organic solvents at room temperature⁸. The synthesized monomers represent finely-dispersed powders of cherry color that are soluble in organic solvents and insoluble in water and petroleum ether. The data of the elemental analysis, IR-, ¹H and ¹³C NMR-spectroscopy confirms the formation of products of interaction of Q with AA.

For monosubstituted monomer С₉Н₉NО₂, %: it is calculated C 65,66; Н 5,95; N 8,58; it is found C 66,25; Н 5,52; N 8,58. For disubstituted monomer С₁₂Н₁₄N₂О₂: it is calculated C 66,05; Н 6,42; N 12,84; it is found C 66,10; Н 6,36; N 11,95.

IR-spectrum of the samples are characterized by the presence of absorption bonds (sm^-1) in the field of 1630 – valence frequencies С=О, 3280 and 1544 – valence and deformation frequencies of amino groups, 1472 and 3010 – deformation and valence frequencies -С=С, 1352 – valence frequencies =С-N-groups.

In ¹³С nuclear magnetic resonances-spectrum of the product of АА and Q interaction, there present a small shift of a signal (ppm) of the carbon, which is connected with NН₂-group, to the weaker field with 44,364 to 44,590. Shifts of the carbon of vinyl groups (СН₂ =) to the weaker field from 113,306 to 118,063, and another carbon (=СН-) – to the stronger field from 139,388 to 130,926 are observed. Additionally, there appeared signals: 150,504 - carbons of quinoid rings and 178,156 - a signal, which is indicative of carbonyl groups of quinoid rings.

In PMR - spectrum of the product of АА (¹Н²НС=С³НС⁴НN⁵H) and Q interaction, there present a small shift of the signal (ppm) to the weaker field from 5,02 to 5,28; ²Н moves to the weak field from 5,02 to 5,149; ³Н – to the stronger field from 5,95 to 5,825; ⁴Н from 3,29 to 3,808, i.e. the protons of the nearby methylene group are shifting more strongly to the weaker field under the influence of the electron-accepting substitute – Q. The signal, which is indicative ²NH-groups (1,41), disappears, and there appeared signals -NH – 3,770. Also signals of protons of quinoid rings 6,650 are observed.

The content of double linkage is defined according to the Knoppe method⁹, constituted 99,3 %.

The polymerization of monomers was carried out as follows: the calculated amount of the monomer (10-50 mol/l), the initiator (0,04-0,30 mol/l), and the solvent (DMF) were loaded into ampoules, blown with argon, sealed, thoroughly shaken up and placed in the thermostat heated to certain temperature (75-87 ^oC – at radical initiation, 7-28 ^оС – at cationic initiation). Upon termination of the reaction (0,5-21h) ampoules were taken out, quickly cooled with cold water with ice, the content was poured out into a methanol, the precipitation was filtered, dissolved in DMF, precipitated with diethyl ether, dried at first on air, and then in vacuum-drying box at 40-50 °С. The polymer yield constituted 20-88 %.

We have studied the kinetics of the polymerization by the polarographic method. The polarograms were registered by the universal polarograph PU-1, with the use of a mercury-drop electrode with the capillary characteristic at the opened chain m^2/3t1/6=4,38 min^2/3sec^-1/2. A saturated calomel electrode was used as a reference. The oxygen from solutions was removed by blowing of current argon for 5 minutes. Experiments were carried out in the thermostat cell at 25±0,5°С. Polarography was carried out at the background of phosphate buffer with рН 7,4 in 25%-DMF, concentration of substances constituted 10-3 mol/l as in these conditions the waves most convenient for the analysis turn out. On an investigated site the background gives a signal of a residual current 0,2 μА.

The process course was judged based on the amount of unreacted monomer. The calculated amount of the monomer, initiator, solvent were loaded into ampoules, and then were thoroughly shaken, one ampoule was left for a polarography analysis (a zero point), and the others were placed in the thermostat, which was heated to required temperature. After a certain time, we have taken the ampoules one by one, then quickly cooled them down with cold water with ice, collected samples for the polarography research, which was carried out at the background of phosphate buffer with рН 7,4 and 25%-DMF(reduction of С=O-groups) and at the background of 0,2М LiCl solution and 25%-DMF (reduction of double linkage).

The viscosity measurement was carried out in the capillary viscosimeter Ubellode at temperature 25°С in the DMF; the determination of the polymers’ static exchange capacity (SOC) – according to methods [10], oxidation-reduction capacity (ОRC) polymers – according to methods⁵.

IR-spectrum of samples was registered on the spectrophotometer "Specord М-80/M85" in tablets with КВг. ¹H и ¹³С NMR spectrums were registered on spectrometer “Mercury-300“ of the VARIAN company with the working frequency of 300 MHz. Melting point of samples were determined on the TU-25-11-1144-84 apparatus.

Solubility of polymers were studied in the alifatic, cyclic, chlorinated hydrocarbons, polar solvents at room temperature.

RESULTS AND DISCUSSION:

Introduction of quinoid groups to the AA structure was carried out under the following scheme:

СН₂ = СН–СН–NН₂ + Q àСН₂=СН–СН₂–NН–Q (AA - Q)

2CH₂=CH – СН–NН₂ + Q à СН₂=СН–СН₂–NН–Q–NH–CH₂–CH=СН₂ (AA–Q–AA)

Interaction of АА with Q is proceeding through transformation stage of the quinoid systems to aromatic, with formation of the addition product of replaced hydroquinones at the intermediate stage as a result of enolization, which further are oxidized into quinones. The latter, in turn, can attach again amine under the same scheme to disubstituted product [4]. Thus, АА with Q form both mono- (M.p. 168^oС), and disubstituted (M.p. 171^oС) monomers with a yield, accordingly, of 75 and 88 %.

Table 1. Potentials of half wave АА and it mono- and disubstituted quinoid derivatives

Monomer	Е_1/2 reduction >С=О, В*						Е_1/2 >С=C<, В**
	40% Ethanol			20% DMF			40% Ethanol	20% DMF
	I	II	III	I	II	III
АА	-	-	-	-	-	-	-1,49	-1, 41
1,4-Q	-0,11	-	-1,20	-0,07	-0,22	-1,30	-	-
АА-1,4-Q	-0,19	-0,55	-1,22	-0,16	-0,52	-1,17	-1,89	-1,94
АА-1,4-Q-АА	-0,17	-0,54	-1,13	-0,13	-0,47	-1,11	-1,97	-2,10

С _mon= 4^.10^-3 mol/l; * - phosphatic buffer solution with рН 7,4; **- 0,2 М LiCl.

Table 2. Optimum conditions of polymerization of derivatives АА and Q by radical* and cationic** initiation (C_mon=0,1531 mole/l) and some characteristics of polymers

Monomer	Catalyst%	Т,⁰С	Time, h	Yield,%	[η], dl/g	SEC	ОRC exp./theor.
Monomer	Catalyst%	Т,⁰С	Time, h	Yield,%	[η], dl/g	mq-eqv/g
АА-Q*	7,0	87	21	59,0	1,21	7,9	3,3/12,3
АА-Q-АА*	7,0	87	21	57,8	1,73	9,6	7,1/9,2
АА-Q-Q**	5,4	7	0,5	86,9	2,70	10,8	6,0/12,3
АА-Q-АА**	5,4	7	0,5	84,7	2,46	10,3	8,1/9,2

The choice of polarographic method for studying of kinetic of polymerization of monomers is due to its speed, accuracy and high sensitivity. The data of polarographic behavior of mono- and disubstituted derivatives АА and Q, and namely, the reduction of >С=О-group and double linkage (>С=С <), is presented in the tab. 1.

Comparison of Е_1/2 of the first wave of Q and derivatives both in the aqueous-alcoholic medium, and in the DMF shows that in derivatives it moves in negative area and is indicative of oxidation-reduction ability of the compound. Possibly, the presence of free electronic pair of nitrogen atoms in the AA molecule increases electronic density to >С=О-group bands of connected Q, and as a result its reduction on a mercury drop electrode becomes difficult and the redoх ability slightly worsens.

In addition, the decrease of Е1\2 of > C=C <- bonds of allylic derivatives of 1,4-Q in comparison with initial АА evidences about increase of electronic density on it. In its turn, it increases their ability to polymerization.

Modification of АА with Q leads to redistribution of electronic density and displacement of π-electronic cloud to electron acceptor substitute. In turn, such displacement leads to decrease of the degree of a mutual overlapping of clouds of double linkage of π-electrons, its polarization and to decrease of energetic expenses for opening of double linkage of АА. As a result, reaction ability of a polymeric radical raises. This is shown by a shift to the negative area of a half-wave potentials of reduction of double linkage of quinoid derivatives АА in the background of 0,2 M НС1 in comparison with an initial АА (tab. 1) and fairly easy involving of monomers in radical polymerization, unlike allyl compounds, which do not polymerize well at radical initiation^2,3.

For many nonlimiting monomers dependence between Е_1/2 reduction of double linkage and the ability to polymerization was established. It is observed in this case as well. Since polarographic indexes are defined by the size of electronic density on double linkage, under Е_1/2of its reduction it is possible to judge about its susceptibility to polymerization of monomer. This may serve as an additional information source about the activity of the formed polymeric radical. The more negative values has Е_1/2 reduction of double bond, the better polymerize a monomer. Shift of the potential to the negative area can be caused by redistribution of electron density and energetic levels in a molecule, which causes internal rotation of its separate parts around σ-bonds, and leads to change of a spatial structure and the further stabilization of the structure.

The obtained optimum conditions of synthesis of polymers on a basis of mono- and disubstituted derivatives of АА and Q by radical and cationic initiation method, and also some characteristics of samples are presented in tab. 2.

As shown in tab. 2, with cationic initiation the temperature (7 against 87^оС) and duration of the process (0,5 against 21 h) are significantly lower. In this process polymers with higher yield (to 87 against 59 %) and higher molecular mass are formed ( 2,7 against 1,7 dl/g). Accordingly, SEC and ORC parameters are higher in the samples that are obtained by cationic initiation. It follows from the obtained data that in synthesising of redox polymers on the basis of quinoid derivatives of AA it is more preferable to use cationic catalysts instead of radical.

Radical initiation of monomers was carried out in the presence of PB, cationic – in the presence of hydrochloric acid. With these catalysts, polymers with high molecular weight and good yields are formed.

In the course of research of radical and cationic polymerizations of monomers with the polarographic method, kinetic curves of polymerizations of mono- and disubstituted derivatives of АА and Q (fig. 1 and 2) have been received. We have judged the reaction process based on the content of unreacted monomer. This data is comparable with gravimetric method where a process course judged by the quantity of formed highmolecular compounds.

Fig.1.Conversion of mono- (а) and disubstituted (b) derivatives of AA and Q expense by radical polymerization depending on temperature: 75 (1), 80 (2), 87°С(3).

Fig. 2. Conversion of mono- (а) and disubstituted (b) derivatives of AA and Q expence by cationic polymerization depending on temperature: 7 (1), 14 (2), 21 (3), 28°С (4).

From the logarithmic dependence of polymerization velocity on an initiator concentration and linear dependence of lgС of monomers on the duration it was established that process proceeds as a reaction of the first order. From graphic dependences of link from 1/Т we have defined the angle of slope of straight lines, and calculated the energy of activation of polymerization under the following formula:

Е=4,571.|tgα|.x,

Where, α is a slope of angle of a straight line to the abscissa axis; x is the ratio of scales of abscissa and ordinate axes. The data is resulted in tab. 3.

From the kinetic curves received at different temperatures under the equation of the first order we have calculated constants of the speed of processes. Kinetic characteristics and pre-exponential multipliers k_о were calculated from the Arrhenius equation kо=к.е-Е/RT (tab. 3).

Table 3. Kinetic characteristics of polymerization of mono- both disubstituted derivatives of АА and Q at radical and cationic initiation

Monomer

Т,К

K, sec^-1

lnk

Е_аkt,

кJ/mol

Radical initiation

АА-Q

347

353

359

1,92^.10^-3

2,97^.10^-3

4,63^.10^-3

-2,89

-2,75

-2,56

47,3

АА-Q-АА

347

353

360

4,58^.10^-3

4,95^.10^-3

5,30^.10^-3

-2,56

-2,53

-2,49

66,1

Cationic initiation

АА-Q

280

287

294

301

6,75^.10^-4

6,16^.10^-4

5,65^.10^-4

5,10^.10^-4

-3,17

-3,21

-3,25

-3,29

-8,7

АА-Q-АА

260

287

294

9,02^.10^-4

7,05^.10^-4

5,87^.10^-4

-3,05

-3,15

-3,22

-19,3

It has been established that at cationic initiation monomers AA-Q and AA-Q-AA are easily enough involved in reaction of polymerization without presence in system of radical initiators or additional influences on it. It was shown, that for achievement of maximum yield of polymers on the basis of AA-Q, larger quantity of hydrochloric acid (0.238 mol/l^-1) is required than for AA-Q-AA (0.142 mol/l^-1). Maximum permissible concentration of AA and AA-Q-AA at their polymerization in the DMF solution is 40 g/l^-1. The use of more concentrated solutions of monomers for polymerization is impossible because of their limited solubility in DMF.

The optimum duration of reaction (fig. 2а) is 0.5-1h. At the same time the yield of polymers on the basis of AA-Q and AA-Q-AA are accordingly 88 % and 85 %. For both monomers the polymer yield almost linearly falls with temperature growth in the studied interval of temperatures. From kinetic curves it is established that cationic polymerization in the initial stage is a reaction of the first order on concentration of a monomer. On this basis, the constants of velocity at different temperatures are calculated, and from the dependences of Arrhenius equation energy of activation process for AA-Q and AA-Q-AA (see table 3) are found.

Table 4. Characteristic bands of absorption (ν, sm^-1) of Q, АА, their derivatives and polymers on their basis

Compound	=СН₂	>С=С<	С=С	νNH	σNH	>С-N	>С=О
АА	918, 980	-	3040	3408(NH₂)	1584	-	-
Q	-	1590	-	-	-	-	1650
АА-Q	922, 986	1498	3040	3285	1548	1350	1652
(АА-Q)_n	-	1502	-	3280	1549	1332	1635
АА-Q-АА	925, 981	1496	3040	3262	1570	1330	1642
(АА-Q-АА)_n	-	1500	-	3260	1545	1329	1650

As can be seen from the data of the table, value of the energy of activation of cationic polimerization of AA-Q and AA-Q-AA are negative. It is known^I1 that for cationic polymerizations total energy of activation of E_s, which is determined by the speed, is equal:

E_s = E_i + E_g- E_b,

Where, E_i, E_g and E_b – energy of activation of reactions of initiation, growth and chain breakage.

It is possible to explain negative sizes of the E_s, assuming that E_g is small, and Е_b large. It happens in the event when breakage reaction represents interaction of solvate ionic pairs. Usually the E_s of cationic polymerizations lies in region from -42 to 63 kJ/mol. These are corresponded by the found values of energy of activation.

Thus, on the basis of the data of the elemental analysis, polarography, IR-spectroscopy, the structure of end-products was identified. In IR-spectrum (tab. 4) of quinoid derivatives of АА there remains characteristic absorption bonds of >С=О-groups (1652 sm^-1); their small displacement to the area of smaller frequencies (1635 sm^-1) is observed, and, at the same time, in А-Q-АА it is insignificant. Moreover, there appears the bond of absorption, which is corresponding to the -C-N- group (1350-1329 sm^-1), and frequencies, that are indicative of a primary amino group and С=С double bonds, disappear. In view of the fact that absorption bonds of σNH and of double carbon-carbon bond >С=С< are located in close area, we have judged concerning the unsaturation of polymers based on non-flat deformation and valency frequencies of С-Н bonds of vinyl groups =СН₂(920, 985 and 3040sm^-1). The latter are practically absent in the obtained polymers.

CONCLUSION:

Thus, it is shown that introduction of quinone in a molecule of allylamine essentially raises its ability to polymerization, and cationic initiation of monomer is more perspective, because such indicators as temperature and duration of process substantially decrease. The yield and molecular mass of polymers thus increases.

Abbreviations:

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

SEC static exchange capacity (mg-equ/g)

[η] characteristic viscosity, dl\g

E_akt energy of activation

E_1/2 potenzial of half-waves

AA allylamine

Q 1,4-benzoquinone

AA-Q monosubstituted monomer

AA-Q-AA disubstituted monomer

DMF dimethylformamide

BP benzoil peroxide

IK infrared spectroscopy

NMR nuclear magnetic resonance spectroscopy

B volt

REFERENCES:

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Received on 17.11.2011 Modified on 12.12.2011

Asian J. Research Chem. 5(1): January 2012; Page 93-97