Synthesis and properties of new polyazines—I

European Potlmer Journal Vol. 17. pp. 197 Io 201

0014-:~057 81 '0201-0197502.(~0/0

© Pcrgarnon Press Lid 1981. Printed in Grcal Britain

SYNTHESIS AND PROPERTIES OF NEW POLYAZINES--I MARIANA PASTRAVANU,MARIA DUMITRIU and TAT1ANA LIXANDRU Department of Organic Chemistry', Polytechnic Institute of Jassy, R-6600-Jassy, Rumania

(Receiced 3 May 1979) Abstract--New polyazines were synthesized by the polycondensation of hydrazine with acenaphthenequinone, 5-chloroacenaphthenequinone, 5-nitroacenaphthenequinone and 5,6-dinitroacenaphthenequinone. The influences of the catalyst and quinone/hydrazine mole ratio on the yield of soluble and insoluble compounds, as well as on the viscosity of a solution of the polymer in DMF, were studied. Some electrophysical properties as well as the polyazine behaviour under heating were also studied by thermogravimetrical analysis.

INTRODUCTION Heterochain polymers show important properties and have numerous applications. Since ~-dicarbonylic compounds can lead to conjugated systems, they are particularly important for obtaining polyazines and polyazomethines. The polyazines easily eliminate nitrogen with formation of thermostable polyolefines [1,2], a property useful for preparing poroplastes [3-5]. The present paper reports the synthesis of new polyazines and some of their characteristic properties. Acenaphthenequinone and derivatives (5-chloroacenaphthenequinone, 5-nitroacenaphthenequinone and 5,6-dinitroacenaphthenequinone) were used as ~-dicarbonylic components; the influence of the substituent on both monomer reactivity and polymer properties was examined. EXPERIMENTAL

Materials Acenaphthenequinone-Merck Schuchard product, m.p. 248-253. The pure compound, recrystallized from m-xylene, melted at 261'. 5-Chloroacenaphthenequinone was synthesized by oxidation of 5-chloroacenaphthene [6] and was recrystallized from an acetic acid/water mixture: m.p. 218 °. 5-nitro- and 5,6-dinitroacenaphthenequinone were prepared by nitration of acenaphthenequinone [7, 8]. After recrystallization from acetic acid, the melting points of 5-nitro- and 5,6-dinitro-acenaphthenequinone were 218 and 300 ° respectively. Hydrazine hydrate-LOBA-ChemieWien-Fischamend product, 100~ p.a. The i.r. and ESR spectra were recorded on specord-i.r. 71 and ART 5 apparatus, respectively. The thermograms were recorded by means of a J. Paulik, F. Paulik, L. Erdey MOM Budapest apparatus.

Polycondensation procedure 0.02mol (quinone/hydrazine hydrate l/2mol ratio) or 0.01 mol {quinone/hydrazine hydrate 1/1 mol ratio) hydrazine hydrate were added to 0.01 mol quinone dissolved in 40-70 ml of glacial acetic acid (the amount depending on the solubility of the quinone). The reaction mixture was refluxed with stirring for 10 hr. After 2-3 hr, the polymer began to separate. The insoluble polymer was filtered and the soluble portion isolated from the filtrate by the addition of water.

The insoluble products were purified by repeated washings with hot xylene and those soluble in acetic acid by washings with hot xylene and ethanol to remove unreacted reagents. Some characteristics of the synthesized polymers are listed in Tables 1 and 2. RESULTS AND DISCUSSION

1. Synthesis and the molecular structure of the polymers Acenaphthenequinone reacts with hydrazine in alcoholic solution with formation of monohydrazone or azine [9]. Since acenaphthenequinone and hydrazine are bifunctional, the formation of macromolecular compounds is also possible. By carrying out the polycondensation of acenaphthenequinone and its derivatives with hydrazine under various conditions, the optimum parameters for obtaining polyazines have been settled. The reaction was performed both in the presence and the absence of catalyst, at quinone/hydrazine 1/1 and 1/2 tool ratios. Hydrazine hydrate was used in order to avoid the destructive action of hydrazine on the polymer [5]. An optimum reaction time of 10hr was found. The polymers were obtained as reddish-brown, light-brown or dark-brown amorphous powders. Some characteristics depending on the reaction conditions, are listed in Tables 1 and 2. Tables 1 and 2 show that the acenaphthenequinone derivatives can lead to both soluble and insoluble fractions. Acenaphthenequinone leads only to insoluble compounds; soluble products are formed probably in very small amounts and have not been separated. It may also be noticed that the addition of catalytic amounts of sulphuric acid leads to higher polymer yields, since acid catalysis favours the polycondensation. As the polycondensation of dicarbonylic compounds with diamines is practically complete in the presence of a large excess of diamine [10], the working quinone/laydrazine mol ratio was 1/2; the yields were higher than those obtained with a mol ratio of 1/1, both soluble and insoluble fractions. The reaction of acenaphthenequinone and its mand p-phenylenediamine substituted derivatives [11] 197

198

MARIANAP.~STR~.VANU,MARIA DUMITRIUand TATIANALlXANDRU

=

C - - C

:

N-

N

=

n RI

R2

Table 1. Characteristics of soluble polyazines i.r. absorptions

No.

Rt

R2

Catalyst

1 2 3

H H H

CI C1 C1

H2SO4 -H2SO,

4 5

H H

NO 2

--

6 7

NO2 NO2

NO2 NO2 NO2

H2SO4 -H2SO4

= C

~

-" N -

Quinone hydrazine mol ratio

Yield (%)

1/l 1/2 1/2 1/2 1/1 1/1 1/1

58.04 82.79 39.47 27.81 20.29 39.49 20.29

I

Melting point (°C)

vC - - N - - (cm- 1) Appearance

Amorphous, Amorphous, 265 decomp. Amorphous, Amorphous, 280 Amorphous, 291 Amorphous, >290 Amorphous,

I

fight brown light brown light brown brown brown light brown light brown

1650 1650 1650 1650 1650 1650 1650

N=

n

R

R2

Table 2. Characteristics of insoluble polyazines i.r.

absorptions

No.

R~

R2

1

H

H

2

H

H

3

H

4

H

5

H

H CI CI

6

H

CI

H H NO2 NO 2

NO2 NO 2 NO2 NO 2

7 8 9 10

PA = polyazine.

Catalyst

Quinone/ hydrazine mol ratio

, Yield % Total PA~ol + PAin,o] PAinsoI

1/1

70.09

70.09

H2SO,

1/1

79.44

79.44

H2SO,

1/2 l/l 1/2

95.60 40.62 16.16

95.60 98.66 98.95

H2SO4

1/2

56.69

96.16

l/2 1/1 i/1 1/1

1.66 41.09 30.72 41.09

29.47 61.38 70.21 61.38

H2SO, H2SO4

Melting point (°C) 260 decomp. 269 decomp. 296 292 297 decomp. 297 decomp. > 296 280 >290 > 290

r I

vC=N--

Appearance

(cm -~)

Amorphous, reddish-brown

1650

Amorphous, reddish-brown

1650

Amorphous, reddish-brown Amorphous, dark-brown Amorphous, reddish-brown

1650 1650 1650

Amorphous, dark-brown

1650

Amorphous, Amorphous, Amorphous, Amorphous,

1650 1650 1650 1650

dark-brown brown dark-brown brown

199

Synthesis and properties of new polyazines--I results in only insoluble polymers. This might be explained by the fact that hydrazine shows greater reactivity than m- and p-phenylenediamine, a reactivity favourable for formation of compounds of low molecular weights which separate from the reaction medium as they form. In the resulting oligomers, the n-electron delocalization on the conjugated system also diminishes the reactivity of dicarbonylic endgroups [10, 12] reducing the possibility of continuing the polycondensation. The molecular weights of the polymers were not determined because of their insolubility in common solvents. For the compounds soluble in DMF, the intrinsic viscosities were measured (see Table 3). The data in Table 3 show the intrinsic viscosity to be higher for the products obtained in the presence of H/SO4 for both soluble and insoluble fractions, confirming that H2SO4 favours the formation of compounds of higher molecular weights in high yields. The insoluble products have, of course, higher molecular weights. The values of intrinsic viscosities of the polyazines under study are comparable to those of benzyl- [5] and isophthalaldehyde- [13] polyazines. The polyazine structure of the synthesized compounds was confirmed by elemental analysis and i.r. spectral measurements. All i.r. spectra show the absorptions characteristic of the Vc=r~ (1650cm-1), C - - O and NH valence vibrations. These bands indicate the presence of C = N bond formed by polycondensation as well as of the carbonyl and amino endgroups. The absorption bands at 1560cm -~ (amide II), 1700cm -1 (amide I) and 2850-2950cm -1 (sym. and asym. C - - H in ~ C H 3 ) indicate the acylation of the terminal amine groups (the reaction was carried out in glacial acetic acid). All spectra show the bands characteristic of the aromatic ring and of the substituents in dicarbonylic compounds (1340cm -~ vNO2 sym. and 1530cm -1 vNO2 asym.). The i.r. spectra and elemental analysis data confirm the following polyazinic structure of the polymers:

~

N- N=

R, R2

RI ,

R2 -

RI =

Hi

R2 :

Cl

Rr =

H;

R2 =

NO,?.

RI ,

R2 =

Table 3. Intrinsic viscosities quinone/hydrazine mol ratio I/1

No. 1 2 3 4 5

Rl H NO2 NO 2

NO2 NO2

R2

NO2 NO2 NO2 NO 2

NO2

Intrinsic viscosities Catalyst Compound (It/] dl/g) H2SO4 Soluble Soluble H2SO 4 Soluble -Insoluble H2SO4 Insoluble

From this point of view, the reactivity of the dicarbonylic component decreases in the following order: 5-nitroacenaphthenequinone > 5,6-dinitroacenaphthenequinone > acenaphthenequinone > 5chlororoacenaphthenequinone, as was found by calculating the atomic charges on the carbonylic carbon atoms by the EHT method (Extended Hfickel Theory)

[14]. 2. Properties of polyazines Thermal stability. The thermal behaviour was examined by thermodifferential analysis in the 20-1000 ° temperature range, at a heating rate of 10°/min in air. The weight losses as a function of temperature are given in Table 4. The thermal stability of the polymers depends to a great extent on both the stability of the structural unit and the linkages between these units within the macromolecular chain. Furthermore, the alternating double bond system and the bulky substituents, conferring rigidity to the system, also cause increased thermal stability [15]. By examining the thermal stabilities of polyazines, thermodestruction was found to begin at temperatures within the 18(~205 ° range, comparable to those for the monomers [16]. In the first stage, sudden nitrogen elimination takes place (15.4~,0 weight losses compared to 15.774 nitrogen content, Fig. 1) with formation of stable polyenes which then decompose at higher temperatures (250-800 °) during the second and third thermodestruction stages. The easy nitrogen elimination during the first stage might be explained by means of azo-azinic tautomerism =N--N~-~- ~ - - N = N - [17]. The slower nitrogen elimination for the 5,6-dinitroacenaphthenequinone polyazine might be caused by the strong electron withdrawing effect of the two nitro groups causing shift of the tautomeric equilibrium to the azinic form. Electrophysical properties. Due to their extended alternating double bond system, the polyazines show electrical conductivity and paramagnetic properties.

H

NO 2

The polycondensation involves nucleophilic addition of hydrazine to the dicarbonylic component followed by elimination. The initial nucleophilic addition to one of the carbonyl groups depends on the electrophilicity of the carbonylic carbon, determined in turn by the nature of the substituent and by the molecular symmetry.

OH H2N--NH 2 + ~-~C~---O.

H',~.

+

+

H2N--NH---C--C-----O ,

I I

-~-C-.-----O

,." H 2 N - - N H 2

I I

+OH 2 ~ H2N--NH

~

r I • H2N--N~-----------C------C~---O.. ~ H2N--N~

I I

0.039 0.031 0.044 0.048 0.102

--C~--O .

H,O

-"

f I

(C ~ N - - N = li

I

1 C~C~----O /.1

P

200

MARIANAPASTR.~VANU,MARIADUMITRIUand TATIANALIXANDRU Table 4. Thermal properties of polyazines I

Stages of thermal degradation II III Weight Temperature Weight Temperature Weight losses range losses range losses T~t (%) (°C) Tui" (%) (°C) Trot (%)

Td* (°C)

Temperature range (°C)

Polyazines from: 1 Acenaphthenequinone

205

205-266

230

14.0

266-398

330

4.6

398-805

2

Chloroacenaphthenequinone

200

200-305

260

41.6

305-416

368

10.1

416-780

3

Nitroacenaphthenequinone

180

180-248

224

22.8

248-395

305

22.5

3954i50

4

Dinitroacenaphthenequinone

197

197-407

322

27.2

407-700

548

73.0

No.

Polymer

* T~--initial temperature of weight loss. + TI, Tu, Tin--temperature of the maximum destruction rate for stages I, II and III (from DTG curves).

I00

15.4%

o

72.1%

i

I

I

I

I

I

I

I

I00

200

300

400

500

600

700

800

~ 1

900

°C Fig. 1. Thermogram of acenaphthenequinone polyazine.

Table 5. Electrophysical characteristics of polyazines

No. R~

R~

Conductivity Concentration of 55 ° AE unpaired electrons Catalyst (ohm -1 cm -1) ( e V ) (spins/g)

1

H

H

H2SO4

2 3 4 5 6

H H H NO2 NO2

H C1 NO2 NO2 NO2

--

H2SO4 H2SO,I. -H2SO4

3.51'10-1a 7.35' 10-1s 4.21.10-14 6.43' 10-1'* 3.04"10 -la

0.672 0.514 0.642 0.096 1.645

2.82"1021 8.45" 1020 4.52"1021 8.25'1021 1.25.1022 5.23" 1022

595

78.4 34.9

550

48.9

Synthesis and properties of new polyazines

~ 2 4

o

3

3t

50

201

The values of electrical conductivity (cr = 10 -15 10 -13 ohm -1 cm -~) and paramagnetic particle concentration (in the 102°-1022 spin/g range) for several polyazines (Table 5) confirm the semiconducting properties of these polymers.

33

32

I

CONCLUSIONS

~~l~;~l

The polycondensation of acenaphthenequinone and its substituted derivatives with hydrazine was studied; the optimum parameters for obtaining polyazinic macromolecular compounds were estabfished. Based on elemental analysis data and i.r. spectral measurements, a polyazinic structure was attributed to the products. Thermodifferential analysis indicated good thermal stability for the synthesized polyazines. The polyazines derived from acenaphthenequinone and its derivatives show semiconducting properties, electrical conductivity of the order 10-15-10 -13 o h m - 1 c m - 1 and paramagnetic particle concentration of 102°-1022 spin/g.

29

28

Ino27

2E

25

24 REFERENCES

22

~

I 25 3 3.I5

212

I

_--

I/Tx IO-3

Fig. 2. Electrical conductivity vs temperature. Polyazines from: 1--acenaphthenequinone with catalyst; 2--acenaphthenequinone; 3--chloroacenaphthenequinone with catalyst; 4--nitroacen.aphthenequinone with catalyst; 5-dinitroacenaphthenequinone. The electrical conductivity was measured for insoluble compounds, obtained at a I/1 quinone/hydrazine mol ratio, on pellets formed under a pressure of 10 t/cm 2. The runs were made within the 20-90 ° temperature range. Figure 2 shows that the exponential law of semiconductors holds: O"

=

~0 e AEi2kT o h m - t c m - 1 -

where a ~ro AE k

= = = =

conductivity at temperature T; conductivity at temperature T = ~ ; energy of activation; Boltzmann constant.

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