JOURNAL OF POLYMER SCIENCE: PART A-1 VOL. 7, 2481-2491 (1969)

Polymers with Quinoxaline Units. V. Polymers with Quinoxaline and Dioxin Units

RAIKER WOLF and C. S. MARVEL, Department of Chemistry, University of Arizona, Tucson, Arizona 85721

Synopsis Ladder or partly ladder polymers have been prepared by condensation of tetra-

phenols with tetrachloroquinoxaline compounds in melt, or in pyridine, naphthalene, and nitrobenaene reaction media. The poymers are dark-colored, powdery materials with good thermal stability. Some of the samples are slightly soluble in sulfuric acid, while others are completely insoluble. No other solvents were found.

INTRODUCTION

The condensation of tetrachloroquinoxaline derivatives with diamino-di- thiophenols' or diaminodiphenols2 is reported to form high molecular weight ladder polymers with quinoxaline and thiazine or oxazine recurring units, respectively. In a further continuation of this work, the condensation of tetrachloroquinoxaline derivatives with tetraphenols has been investigated and will be described in this paper. The replacement of the thiazine or oxazine unit,s by the symmetrical dioxin unit was expected to improve solubility and also to increase oxidative stability of the polymers, since no heterocyclic hydrogens are present.

RESULTS AND DISCUSSION

Model Reactions

The melt condensation between catechol and 2,3-dichloroquinoxaline is reported3 to form 9,10-diaza-11,12-dioxatetracene (I) and this can be con- sidered as a model reaction for the preparation of ladder-type polymers with quinoxaline and dioxin recurring units.

I

This reaction has been studied in several solvents in order to find proper conditions for a corresponding polymerization procedure. Compound I was formed in almost quantitative yields in basic solvents, such as pyridine

2481

2482 WOLF AND MARVEL

and N,N-diethylaniline, a t the reflux temperature. Some other high-boil- ing solvents, such as naphthalene or nitrobenzene, were also found to be suitable for the described reaction. Yields are not as high as in the case of basic solvents; however, they can be improved by addition of small amounts of base, as studied in the case of nitrobenzene-pyridine. I n other high-boiling solvents, such as dimethylacetamide, hexamethylphosphor- amide, or benzonitrile, the reaction could not be accomplished, and even the addition of pyridine did not succeed in a formation of I. Starting materials or unidentified reaction mixtures were obtained.

Model compound I1 was prepared from 2,3-dichloroquinoxaline arid tetrahydroxy-p-benzoquinone in both naphthalene and pyridine solution. Structure I1 was established by analysis; however, in the case of naph- thalene as a solvent, a remaining chlorine content of 1.02% indicates an incomplete reaction.

0

I1

Tetrafunctional Monomers

All monomers which have been used in the following investigations are listed in Table I. The compounds were prepared according to the litera- ture. Nitro- benzene and N,N-diethylaniline are sufficient solvents for all monomers except I11 and VII. All monomers, except V, which is extremely sensitive against oxidation, are stable in air or solution.

Pyridine is a good solvent for all of the described monomers.

Polymers

Polymers with quinoxaline and dioxin units have been prepared from the various tetraphenols and tetrachloroquirioxalirie compounds in pyridine, naphthalene, and nitrobenzene solution, and in melt. The new polymers are summarized in Table 11.

The solubility of these polymers was disappointing. Only sulfuric acid was found to be a fairly good solvent for some of the products, while others were only partly soluble or completely insoluble. Solubility in methanesulfonic acid was very poor, and no solubility was found in di- methylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, hexa- fluoroacetone sesquihydrate, formic acid, or trifluoroacetic acid.

In general, the solution viscosities of the polymers or their soluble por- tions are rather low, indicating low molecular weights. This is probably due to insufficient solubility of the growing macromolecules with ladder or partly ladder structure in the described solvents. In fact, a precipitation of polymeric material occurs soon after starting the reaction. The highest

2483 POLYMERS WITH QUINOXALINE UNITS. V

TABLE I Monomers

MP, NO. Compound Formula “C

0

I11

IV

V

VI

VII

VII I

IX

x

Tetrahydroxy-p- benzoquinone

3,3’,4,4’-Tetra- hydroxy diphenyl

1,2,4,5-Tetra- hydroxybenzene

2,3,6,7-Tetra- hydroxythi- anthrene

1,2,5,6-Tetra- hydroxy- anthraquinone

HO ”* OH

0

HO

HO

HO OH

2,3,7,8-Tetrachloro- 1,4,6,9-tetraaza- anthracene

2,2‘,3,3’-Tetra- chloro-6,6’-bis- quinoxaline

2,2‘,3,3‘-Tetra- chlor06,6 ‘-bis- quinoxalyl ether

>350

3’2 7

2 17-218

270-275

>350

325

2Y5

218

-

viscosity values were determined on polymers from 3,3‘,4,4’-tetrahydroxy- diphenyl. Melt polymerizations have been investigated with this mono- mer, and a light brown polymer with an [ ? I i n h of 0.35 was obtained from 2,2’,~~,3‘-tetmchlorc~-G,G’-diquinoxnlyl ether and 3,3’,4,4’-tetrnhydroxy- diphenyl, both monomers having melting points near 220°C.

A\\lost of the results of the elemental analyses (see Experimental) are in relatively good agreement with the values calculated from the probable formulas. While carbon analyses of some samples are poor, nitrogen is in

2484 WOLF AND MARVEL

m a 3 0 0 0 991

d - 4

0 0 . .

3

I s b-

+ + + U U U U

U U U U U

U x U

2

1 X

IV

IT’ +

1’111

XV

11

- + IX

Pyri

dine

N

itrob

enze

ne

0.25

0.

13

L

Poly

( [1,

4lB

enzo

diox

ino

[2,3

-b] [

1,4]

benz

odio

xino

[2’,

3/ : 5

,6]p

yraz

ino [2,3-g]quinoxaline-2,12-diyl)

r

-

Pyri

dine

XI?

IV

+ x

Py

ridi

ne

Mel

t

XV

II

T’+

171

1 Py

ridi

ne

Poly

( [2,

2’-b

i[ 1,

4] be

nzod

ioxi

no [2

,3-b

] qui

noxa

line]

-8,8

’-di

yl)

r

L

Poly

( [2,

2’-b

i [ 1,

4] be

nzod

ioxi

no “2

,341

quinoxaline]-8,8’-diyl-8’-oxy)

r 1

0.03

Bro

wn

Gol

d br

own

Lig

ht b

row

n L

ight

bro

wn

3 3 c FI

4

Bla

ck

Poly

( [1,

4] be

nzod

ioxi

no [2

,3-b

] pyr

azin

o [2

,3-g

] qui

noxa

line-

2,3

: 9,1

0-te

tray1

-9, 1

0-di

oxy)

(c

onti

nued

) 03

u1

2486 WOLF AND MARVEL

Y U U

>

U Y

J + c U

v

2 x x

8 z 2 .-

x + U

i) 3

x x

I'OLYMERS WITH QUINOXALINE UNITS. v 2487

Temperature "C

mers XV and XIV were prepared in pyridine solution, XVI in melt. Fig. 1 . TGA curves of (1) polymer Xi', (2) polymer XIV, and ( 3 ) polymer XVI. Poly-

2 0 0 400 600 R O O

Te,rp-.!Jture "C

Fig. 2. TGA curves of ( 1 ) polymer XI11 and ( 2 ) polymer X\?II. Both polymers were prepared in pyridine solution.

better agreement with the calculated values. Polymer XI, prepared in napththalene, has a chlorine content of 5.970/,, indicating incomplete ring closure. Polymer XIV, prepared in pyridine or nitrobenzene, also has high chlorine contents of 2.15 and 4.91y0, respectively. Chlorine malyses of the other samples are below 1%.

Thermogravimetric analyses on some of the samples, determined in helium at a heating rate of 180"C/hr, are shown in Figures 1 and 2 . Initial weight loss occurs a t about 500°C.

2488 WOLF AND MARVEL

EXPERIMENTAL

Materials

Catechol was sublimed before use. 2,3-Dichloroquinoxaline was pre- pared as described in the l i terat~re.~,f~

Tetrahydroxy-p-benzone. The dihydrate (Aldrich Chemical Co.) uas dissolved in hot dioxane, treated with molecular sieves and crystallized from dioxane.

ANAL. Calcd for C&OG: C, 41.90%; H, 2.34y0. Found: C, 41.95%; H,

3,3',4,4'-Tetrahydroxydiphenyl. 4Iodoveratrole was prepared as de- scribed.6 3,3',4,4'-Tetramethoxydiphenyl was synthesized by mixing 87 g of iodoveratrole with 90 g sand and heating under nitrogen to 220°C. Then 60 g copper bronze (Crescent Bronze Powder Co.) was added portion- wise. After 4 hr further stirring, the mixture was immediately poured into sand and extracted with hot methanol. Pale brown crystals of 3,3',4,4'-tetramethoxydiphenyl were obtained in 74% yield, mp 132°C (lit.' mp 130-132°C). This compound was demethylated as previously described." White crystals of 3,3',4,4'-tetrahydroxydiphenyl were ob- tained after sublimation; mp 227°C (lit.* mp 229-230°C). 1,2,4,5-Tetrahydroxybenzene. 1,2,4,5-Tetrahydroxybenzene was pre-

pared as describeds and crystallized from acetic acid; mp 217-218°C (lit.9 mp 215-220°C).

2,3,6,7-Tetrahydroxythianthrene was prepared as described,lO mp 270-275°C (lit."J mp 273°C). Crystallization from acetic acid did not yield a sharp melting material. 1,2,5,6-Tetrahydroxyanthraquinone was prepared as described in the

patent Orange colored needles were obtained by recrystal- lization from acetic acid.

2.46%.

Other Compounds.

ANAL. Calcd for CIrHsO6: C, 61.77%; H, 2.96%. Found: C, 61.47%; H, 3.10y0.

2,3,7,8-Tetrachlor0-1,4,6,9-tetraazaanthracene,~~ 2,2',3,3'-tetrachloro-6,- and 2,2 ', 3,3'-te trachloro-6, 6'-bisquinoxalyl ether were 6 '-bisquinoxaliie,

prepared as described in the literature.

Model Reactions

9,10-Diaza-11,12-dioxatetracene. The general procedure was to dis- solve (or mix) catechol (1.101 g; 0.01 mole) and 2,3-dichloroquinoxaline (2.011 g; 0.01 mole) with solvent. The concentration of starting materials was 30 wt-% in naphthalene, 5 wt-% in pyridine, and 10 wt-% in N,N- diethylaniline, nitrobenzene, and nitrobenzene-pyridine mixtures. The solutions were heated under nitrogen atmosphere with stirring to the reflux temperature and kept at this level for 6 hr in the case of pyridine arid for 12-22 hr in other solvents. The reaction mixture was cooled, methanol was added, and the product was filtered and washed with meth-

POLYMERS WITH QUINOXALINE UNITS. V 2489

anol. anol.

9,lO-Diaza-1 1712-dioxatetracene was recrystallized from 95% eth- The yield in naphthalene was 75%; mp 265°C (lit.3 mp 264-265°C).

ANAL. Calcd. for: CllHs0zN2: C, 71.1870; 11, 3.417,; N, 11.86%. Found: C, 71.46y0; H, 3.61%; N, 11.7170.

In pyridine the yield was 97y0; mp and mixed mp, 265°C. In N,N-dieth- ylaniline the yield was 96%; mp and mixed mp, 265°C. I n nitrobenzene the yield was 87Yc; mp and mixed mp, 265°C. In nitrobenzene- pyridine mixture (6: l ) ; the yield was 95%; mp and mixed mp, 265°C.

Veratrole (2.763 g, 0.02 mole), 2,3-dichloroquinoxaline (4.021 g; 0.02 mole) and pyridine hydrochloride (15 g, 0.13 mole) were mixed and heated under nitrogen and stirring to 200°C for 12 hrs. After cooling, a dark-colored solid was precipitated in water, filtered, and washed with hot water. After extraction with hot ethanol, 9,10-diaza-11,12-dioxatetracene was obtained in a 6% yield, mp 264°C; mixed mp 261-263°C.

Model Compound 11. Tetrahydroxy-p-benzoquinone (0.5163 g, 0.003 mole) and 2,3-dichloroquinoxaline (1.327 g, 0.0066 mole) were mixed with naphthalene (10 g) or dissolved in pyridine (50 ml). The mixtures were heated under nitrogen atmosphere and stirring to the reflux temperature for 16 hr. After cooling, the reaction products were precipitated in ethanol, filtered, washed with hot ethanol, and dried. The products were extracted with benzene for one day, then heated in vacuum to 300°C for 6 hr and finally extracted with ethanol for 2 days; mp >360"C. When the reaction was carried out in naphthalene, the yield was 82%.

62.00%; H, 2.46%; N, 13.99%; C1, 1.02y0.

When the reaction was carried out in pyridine, the yield was 95%.

The procedure in pyridine hydrochloride was as follows.

ANAL. Calcd for C22HsN4Os: C, 62.27%; 11, 1.82%; N, 13.21%. Found: C,

ANAL. Found: C, 62.18%; H, 2.70%; N, 13.89%; Cl,O.Sl%.

Polymers

The general procedure was as follows. Equimolecular amounts of monomers were dissolved or mixed with solvent. The concentration of monomers was 2070 in naphthalene, 1-3% in pyridine, and 3% in nitro- benzene. The mixtures were heated under a nitrogen atmosphere with stirring to reflux temperature and kept at this level for 16-24 hr in the case of pyridine and naphthalene as solvents, and for 30-60 hr in nitrobenzene. The mixtures were cooled, methanol was added, and the polymeric ma- terials were filtered, washed with hot methanol, and dried. After Soxhlet extraction with benzene (1 day), the samples were heated to 350°C in vucuo for 6 hr and finally extracted with alcohol for 1-2 days. Generally, yields were between 85 and 98%, calculated for a complete ring closure. Viscosities have been determined in sulfuric acid a t 30°C. Details for polymers XI-XX are given in Table 111.

TA

BL

E I1

1

XI

XI1

XI1

1 X

IV

xv

XV

I

XV

II

XV

III

XIX

xx

Cal

cula

ted

Foun

d Po

lym

eriz

atio

n E

mpi

rica

l Po

lym

er

solv

ent

llin

h (c

oncn

) fo

rmul

a C1

%

H,

%

"1 %

C

, %

H

, %

N

, %

-

Pyri

dine

N

apht

hale

ne

Nitr

oben

zene

Py

ridi

ne

Nitr

oben

zene

Py

ridi

ne

Pyri

dine

N

itrob

enze

ne

Pyri

dine

Py

ridi

ne

Mel

t Py

ridi

ne

Pyri

dine

Py

ridi

ne

Pyri

dine

0.09

(0.5

%7,

)8

0.06

(0.

30%

)b

0.11

(0.5

%)*

0

.6 (0

.03%

',)"

d 0.

25 (0

.40%

)"

0.13

(0.

5%P

0.22

(O.2

8%)9

0.

35 (0

.35%

)h

d 0.

06 (

0.5%

)a

0.09

(0.

4170

)k

0.11

(O.5

'%)"

0.4

(0.

02%

)r

0.03

(0.

04%

)'

55.5

1

62.5

5

60.2

9 67

.35

71.7

9 69

.42

60.7

5 63

.39i

64

.58

66.9

2

0.58

1.42

1.38

2.

06

2.58

2.

50

1.26

1.

90

1.36

1.

87

16.1

8

13.2

1

12.7

8 14

.28

11.9

6 11

.57

17.7

2 10

.56

12.5

5 10

.41

54.4

6 54

.59

54.2

0 68

.30

64.6

2 64

.84

65.7

4 63

.58

70.4

2 68

.11

68.4

2 61

.45

62.7

0 62

.81

65.6

7

2.30

1.

78

1.36

3.

10

2.50

2.

70

2.19

2.

33

2.90

2.

84

2.69

2.

22

2.34

1.

96

2.47

17.8

7 16

.45

16.8

4 15

.16

14.6

1 14

.72

14.7

2 14

.18

12.5

9 11

.89

11.2

5 17

.15

10.8

1 12

.96

10.6

6 __

____

a

Com

plet

ely

solu

ble.

b

40%

of

sam

ple

inso

lubl

e.

c 94

% o

f sa

mpl

e in

solu

ble.

d

Inso

lubl

e in

sul

furic

aci

d an

d ot

her

solv

ents

. * 2

0% o

f sa

mpl

e in

solu

ble.

f

96%

of

sam

ple

inso

lubl

e.

g 4

4% o

f sa

mpl

e in

solu

ble.

h

30%

of

sam

ple

inso

lubl

e.

i 92

% o

f sa

mpl

e in

solu

ble.

j

Als

o: c

alcu

late

d S,

12.

097,

; fo

und

S, 1

1.09

%.

5.97

2.15

4.

91

18%

of

sam

ple

inso

lubl

e.

POLYMERS WITH QUINOXALINE UNITS. V 2491

We are indebted to Dr. G. Ehlers, Air Force Materials Laboratory, Wright Patterson Air Force Base, for thermogravimetric curves.

This work was sripported by the Air Force Rlaterials Laboralory, Research and Tech- nology Division, Air Force Systems Commalid, Wright Patterson Air Force Base, Ohio.

References 1. M. Okada and C. S. Marvel, J . Polym. Sci. A-I, 6, 1259 (1968). 2. R. Wolf, M. Okada and C. S . Marvel, J . Polym. Sci. A-I, 6, 1503 (1968). 3. F. Lehrmann and C. Bener, Helv. Chim. Acta, 8,16 (1925). 4. Pvl. A. Phillips, J . Chem. SOC. 1928,2393. 5. G. W. H. Cheeseman, J. Chem. Soc., 1955,1804. 6. H. 0. Wirth, 0. Konigstein, and W. Kern, Ann., 634,101 (1960). 7. K. Seer, Monatsh., 34,647 (1913). 8. E. Spaeth and K. Gibian, Monatsh., 55,348 (1930). 9. R. Nietzki and F. Schmidt, Chem. Rer., 21,2374 (1788).

10. K. Fries, H. Koch, and H. Stukenbrock, Ann., 468,172,182 (1928). 11. Farbenfabriken Bayer, Ger. Pat. 96364 (1897). 12. Farbenfabriken Bayer, Ger. Pat. 103988 (1898). 13. H. Jadamus, F. De Schryver, W . DeWinter, and C. S. Marvel, J . Polym. Sci.

A-1,4,2831 (1966).

Received November 25, 1968