poly(arylene sulfides) with pendant cyano groups as high-temperature laminating resins

JOURNAL OF POLYMER SCIENCE: Polymer Chemistry Edition VOL. 11. 2793-2811 (1973)

Poly(ary1ene Sulfides) with Pendant Cyan0 Groups as High-Temperature Laminating Resins

IBRAHIM HADDAD, SHAUN HURLEY, and C . S. MARVEL, Department of Chemistry, The University of

Arizona, Tucson, Arizona 85721

synopsis

Poly(pheny1ene sulfidea) were synthesized from m-benzenedithiol and aromatic dibro- midm in a basic medium of potaasium carbonate in dimethylformamide or dimethylacetamide. The products obtained were slightly off-white with relatively low melting ranges and had inherent viscosities in the 0.2-0.4 dl/g range in hexamethylphosphoric triamide. Similar poly(pheny1ene sulfides) containing pendant cyano groups along the polymer chains were obtained by the use of 5 mole-% of either 2,Pdichlorobenmnitrile or 3,5di- chlorobenzonitrile. The products were similar to the pure polyphenyiene sulfides, efcept that they showed lower melting ranges and gave insoluble products when heated alone or in the presence of zinc chloride.

INTRODUCTION

Although many thermally stable polymers can be fabricated into fibers and films, the use of these materials as resins in laminating, molding, or coating applications often poses considerable proceasing and handling problems. Besides the required stability towards oxidative and hydrolytic degradation, polymers which are to be used as laminating resins must be low-melting or soluble in inert solvents in order to wet the surface of the coated or reinforced material and should show good adhesive properties. If the final polymeric resin is a crosslinked material, the crosslinking process should not be accompanied by the evolution of any gaseous or other volatile products, as these would cause voids that result in weak points in the final laminate or coating.

The work reported in this paper describes the preparation of polyphenylene sulfides and related polymers for use as thermally stable laminating resins. Poly(pheny1ene sulfides) have been previously reported in the likrature.'-S These polymers, however, did not possess either the 801u- bility or the low melting ranges required of a laminating resin, and thus a search for a poly(pheny1ene sulfide) with the proper properties was ini- tiated. The laminating resins were obtained in the precuring stage as poly-m,p-thiophenylenes substituted with cyano groups along the polymer chains and having softening ranges around 100°C. These laminating

@ 1973 by John Wiley & Sons, Inc.

2793

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m-d

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2796 HADDAD, HURLEY, AND MARVEL

resins were cured by heating at temperatures of 350-400°C or by heating to 290°C under nitrogen in the presence of zinc chloride, and it is thought that the crosslinking might proceed by the trimerization of the nitrile groups without the formation of any volatile side products. The products were determined to be crosslinked on the basis of their insolubility in hexamethylphosphoric triamide in which the noncrosslinked polymers were quite soluble and from infrared spectra that were similar to those obtained for the noncured polymers without the nitrile absorption. Conclusive evidence for the formation of the triazine molecules could not be obtained, as neither infrared nor proton NMR spectra could be effectively used in this determination.

RESULTS AND DISCUSSION

Model Reactions

It has been reported that potassium carbonate in N, N-dimethylformamide (DMF) provided a suitable medium for the reaction between an aromatic dithiol and an aromatic dihalide to give linear polymers with sulfide linkage^.^ However, the polymerizations which were of interest to this work were not reported. Model reactions were, therefore, carried out between thiophenol and various aromatic dibromidos in order to evaluate the feasibility of using potassium carbonate-DMF as the reaction medium for the corresponding polymerizations. It was also thought that potassium carbonate-DMF would provide a suitable medium for the reaction between polyphenylene sulfides containing thiol endgroups and 4-bromobenzonitrile to give nitrile end-capped polymers which could be used in the crosslinking experiments. Model reactions were, therefore, carried out between 4-bromobenzonitrile and thiophenol and m-benzcncdithiol.

The products of the model reactions along with the reaction conditions, yields and the respective physical properties are shown in Table I. Identi- fication of the products was achieved by infrared spectroscopy and by elemental analysis, the corresponding values of which are given in Table 11.

During the initial heating period of these reactions, a bright yellow color due to the thiophenoxy anion was formed. The intensity of this color usually decreased during the later stages of these reactions. This observa- tion was also true of the polymerization reactions described below.

As shown in Table I, the yields of all but two of the model compounds were reasonably high. This suggested that potassium carbonate-DMF should provide a suitable medium for the polymerization and endcapping reactions. Furthermore, i t appears that these reactions proceed by the expected nucleophilic aromatic substitution mechanism as, in each case, products with rearranged structures were not observed. It was, therefore, thought that the corresponding polymerizations would also proceed without positional isomerizations and thus give products of the desired structures.

POLYARYLENE SULFIDES 2797

TABLE I1 Elemental Analysis of Model Compounds

Model com-

pound8 Formula c, % H, % s, % N, % 2 Ci8HiaSz Calcd

Found 3 CiBHi4Sz Calcd

Found 4 CZ~HIBSZ Calcd

Found 5 CzzH1Sz Calcd

Found 6 CzaHi~Sz0 Calcd

Found 7 CiaH9NS Calcd

Found 8 C Z ~ H I ~ N ~ S Z Calcd

Found

73.48 73.32 73.48 73.35 77.84 77.95 76.76 76.91 74.61 73.42 73.93 74.18 69.77 69.99

4.76 4.78 4.76 4.90 4.87 5.14 4.65 4.62 4.66 4.69 4.27 4.50 3.49 3.49

21.78 21.74 21.78 21.78 17.30 17.13 18.61 18.77 16.58 16.39 15.17 6.64 15.25 6.79 18.71 8.14 18.27 8.21

8 Compound number corresponds to model compound number in Table I

Polymerization Reactions Poly(pheny1ene sulfides) with various struc-

tures were prepared in potassium carbonateDRIF, and some of their properties were determined. These investigations were carried out in order to determine the most suitable backbone for the poly(pheny1ene sulfide) which was eventually to be substituted with nitrile groups and crosslinked to give the final cured laminate.

The compoistion of the various poly(pheny1ene sulfides) obtained along with the reaction conditions and results of polymerizations of m-benzenedithiol (MBDT) with various dibromo compounds are given in Table 111. Elemental analysis data of the various polymers are given in Table IV.

As with the model compounds, a bright yellow color was observed during the initial stages of the reaction, which slowly changed to a light brownish color as the reaction proceeded. At the end of the reaction, the reaction mixture was cooled, and the polymers were obtained by precipitation with acidic water-methanol solution. With the exception of polymers PVII, PVIII, and PIX, all the polymers obtained werc stirred in a large volume of ether to dissolve the low molecular weight fractions and possibly any unreacted starting materials. Polymer PVII was precipitated from benzene, and polymers PVIII and PIX were extracted with boiling ethanol during the final purification stages.

As indicated in Table 111, the polymers were generally obtained in fairly high yields. As seen from the model reaction involving bis(p-bromophenyl) ether, i t is quite obvious that the displacement of the bromine atom by the thiophenoxy anion is quite difficult, and a polymer with this structure could be more readily prepared from m-dibromobenzene and 4,4'- bis(pheny1 ether) dithiol.

Poly(pheny1ene Sulfides).

TA

BL

E I11

Po

lym

erss

9 ?

5.60

77

mD

BB

80

12

.70

24

8.7

110-

120

0.1

? "2 U

U

Poly

mer

g

(mol

e)

g (m

ole)

b m

l g

(mol

e)

hr

g "0

dl

/&

3

Dib

rom

o co

m-

MB

DT

, po

und,

D

MF,

K

&O

a,

Tim

e, Y

ield

, M

p,

?inh

,

(0.0

4)

9.43

41

(0.0

92)

(0.0

4)

DS

G4

PI

5.60

60

pDB

B

80

12.7

0 24

7.

7 11

0-14

0 0.

15

5 (0

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9.

4290

(0

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) U

(0

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9

PI1

..

E 50

3.

97

24

2.5

240-

250

-

4.72

59

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25)

(0.0

29)

c F 4.

114

DB

BP

70

9.84

24

8.

81

160-

190

-

PIIT

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(0

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2.84

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PIX

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00'

(0.0

1)

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5.71

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6.56

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2.36

18

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22

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a A

ll po

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ns w

ere

run

at 1

50-1

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. b

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rom

oben

zene

; DB

BP

= 4

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ibro

mob

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nyl;

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1,4

-dib

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onap

htha

lene

; D

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is(p

- br

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1)et

her.

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mel

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1.


TABLE IV Polymer Analyses

Polymer Repeating

Unit

PI

PI1

PI11

PIV

PV

PVI

PVII

PVIII

PIX

Analysisa

c, % H, % s, % Br, % Calcd 66.67 3.70 29.63 - Found 63.42 3 .54 27.28 5 .51 Calcd 66.67 3.70 29.63 - Found 66.21 3 .73 28.45 1.75 Calcd 66.67 3.70' 29.63 - Found 63.88 3.56 26.91 5.24 Calcd 73.97 4.11 21.92 - Found 70.85 4 .12 19.98 5.00 Calcd 70.78 3.94 25.20 - Found 69.13 3 .92 24.16 2.28 Calcd 72.18 3.76 24.06 - Found 71.95 3 .80 23.85 < 0 . 3 Calcd 70.13 3.90 20.78 - Found 64.66 3.85 18.65 8.10 Calcd 70.13 3 .90 20.78 - Found 67.56 3.84 20.18 <0 .3 Calcd 70.13 3 .90 20.78 - Found 67.06 4.34 18.84 -

* The bromine endgroups affect the analysis for carbon, hydrogen, and sulfur.

The structures of the polymers obtained were confirmed by elemental analysis (Table IV) and by infrared spectroscopy. As in the case of the model reactions, no positional isomerism on the aromatic ring is expected and the polymerizations are belicved to proceed via the nucleophilic displacement mechanism.

As would be expected, the melting ranges of the poly(pheny1ene sulfides) and related polymers (Table 111) are dependent upon their respective structures. Polymers PI11 and PIX have the most regular structure and were found to possess the highest melting ranges. This phenom- enon was most visible from results obtained from polymer PIV and PV which were obtained from a mixture of two different dibromo compounds. These results reveal that the incorporation of further m-thiophenylene units along the polymer chains has a rather large effect on the physical characteristics of the polymer and that a control over the melting range could be achieved by varying the amounts of the various dibromo compounds used.

The softening behavior of polymers PI, PI1 and PI11 have been studied.a These polymers exhibited distinct melting points and displayed a two-stage penetration on the softening apparatus. Generally, these penetrations occurred close to or at somewhat lower temperatures than the melting ranges reported in Table 111. In the case of polymer PI, DTA showed two distinct endotherms at 85-90°C and at 120°C which are apparently two crystalline melting points. It was, t,herefore, suggesteda that two different crystalline forms are present and that the same behavior was observed with


poly-p-thiophenylene samples obtained from Dow and Phillips Petroleum (Ryton) chemical companies.8

Isothermal aging of some of the polymers were run in a small furnace in an atmosphere of noncirculating air, and the samples were aged a t temperatures of 200, 300, 350, and 400°C. The results of these experiments are shown in Table V. All the polymers except PI11 melted and darkened a t 200°C. At the com- pletion of the isothermal aging the polymers turned into black solids that could not be separated from the walls of the glass containers, which indi- cates the good adhesion properties of these polymers even after heating at 400°C.

This behavior was exhibited by PI11 a t 300°C.

TABLE V Isothermal Aging of Poly(pheny1ene Sulfides) and Related Polymers

Weight loss, % Polymer 6 days a t

(Table 111) 200°C 8 days at

300°C 7 days at 9 days at

350°C 400°C

PI 0.34 PI1 0.41 PI11 6.65 PIV 1.48 PV 1.53 PVI 1.56

4.5 1.95

13.3 4.96 3.08 2.32

21.8 67.8 7.07 77.0

16.0 84.4 8.8 49.3 9.6 66.0

17.28 -

a Aged for 5 days.

The solubility of the polymers vaned considerably with structure. In general, the polymers did not dissolve in cold organic solvents but some of them did dissolve when heated but precipitated out when the solution was cooled. All polymers were, however, very slowly solubilized in cold hexamethylphosphoric triamide, and solutions used in viscosity measure- ments were prepared by initially dissolving the polymer in the hot solvent and allowing the solution to cool to room temperature.

Effect of Polymerization Conditions on the Molecular Weight of Poly- (mpthiophenylene). From the results of the polymerizations carried out earlier it was decided that the backbone of poly-m,p-thiophenylene would be the most suitable one to use in experiments involving the preparation of poly(pheny1ene sulfides) containing nitrile groups. This choice was based on the availability of starting materials, the better solubility and low melting range of this polymer. The results of experiments run to determine the reaction conditions under wnich the poly-m,pthiophenylene of highest molecular weight could be obtained are given in Table VI. Elemental analysis data obtained for these polymers are shown in Table VII.

During polymerization 1, 2, 3, and 4, the polymers were observed to precipitat'e from the reaction media and to coagulate. Since the premature precipitation was believed to result in lower molecular weight polymers, reactions 5 and 6 were carried out using more dilute solutions. Less precipi-

TA

BL

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I E

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Poly

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Con

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Wei

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ioD

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lene

from

MB

DT

and

DD

BB

~

Poly

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eriz

atio

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BD

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PD

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Solv

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Tem

p, "

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Tim

e, h

r M

p, "

CC

ll

inht

dll

d

1

2 3 4 5 6 7 8 9 10

11

5.60

60

2.84

34

2.84

16

2.84

35

2.84

25

2.84

52

2.84

01

2.85

40

2.85

29

2.84

11

2.84

71

9.42

90

4.71

97

4.72

30

4.72

71

4,72

49

4.72

94

4.72

01

4.73

02

4.72

78

4.72

24

4.73

18

DM

F

80

DM

F

40

DM

F

40

DM

F

40

DM

F

80

DM

F

80

DM

Ac

40

DM

Ac

40

HM

P

40

NM

eP

40

Sna

40

12.7

0

6.35

6.35

6.35

6.35

6.35

6.35

6.35

6.35

6.35

6.35

150-

155

150-

155

150-

155

150-

155

150-

155

150-

155

165-

170

165-

170

190-

195

170-

175

170-

175

24

48

72

96

48

72

48

72

72

48

48

110-

140

110-

130

105-

125

100-

125

110-

125

100-

120

100-

120

105-

140

110-

130

120-

135

85-9

0

0.15

0.26

0.40

0.24

0.13

0.15

0.41

0.33

0.28

0.26

0.12

MB

DT

= m

benz

ened

ithio

l; PD

BB

-dib

rom

oben

zene

. b

DM

F =

dim

ethy

lform

amid

e;

DM

Ac

= d

imet

hyla

ceta

mid

e; H

MP

= h

exam

ethy

lpho

spho

ric t

riam

ide;

NM

eP =

N-m

ethy

lpyr

rolid

one;

Sn

=

0 T

he m

eltin

g ra

nges

repo

rted

wer

e ru

n in

cap

illar

ies

and

are

unco

rrec

ted.

d

Vis

cosi

ties w

ere

obta

ined

at 3

0°C

in 0

.5%

sol

utio

n of

the

poly

mer

in h

exam

ethy

lpho

spho

ric

tria

mid

e.

sulfo

lane

.


TABLE VII Elemental Analysis of Poly-mpthiophenylene Samplesa

Analytical data Found

Polymerization c, % H, % s, 70 Br, 70 1 2 3 4 5 6 7 8 9

10 11

66.21 65.89 77.32 66.10 66.02 66.09 65.92 65.64 65.67 66.11 62.45

3.73 3.63 3.75 3.75 3.72 3.66 3.74 3.63 3.72 3.62 3.92

28.45 29.12 29.35 29.85 29.70 29.58 29.87 29.93 28.00 29.38 28.64

1.75

0.93 <0 .3

<0 .3 < 0 . 3 <0.3 -

a Anal. calculated for (C&S)n: C, 66.67%; H, 3.70%; S, 29.63%.

tation and no coagulation occurred during these runs, however, the products obtained exhibited lower viscosities and thus lower molecular wiights.

As indicated in Table VI, an increase in molecular weight was obtained when the reaction time was raised from 24 to 72 hr. When the reaction time was raised to 96 hr, a drop in the molecular weight was observed. No plausible explanation could be given for this unexpected behavior.

Dimethylacetamide, hexamethylphosphoric triamide, pyridine, N- methylpyrrolidone, sulfolane, quinoline, and diphenyl ether were used in the polymerization reactions replacing dimethylformamide as the solvent. No polymerization occurred when diphenyl ether and pyridine were used, and only dimethylacetamide was found to be more effective than dimethylformamide. For that reason dimethylacetamide was used in the reactions involving the preparation of polyphenylene sulfides containing pendant cyan0 groups.

Synthesis of Poly(pheny1ene Sulfides) Containing Nitrile Groups. After the selection of poly-m,pthiophenylene as the polymer whose backbone was to be used in the preparation of the nitrile-containing poly(pheny1ene sulfides), experiments were run to determine the best method by which such nitrile groups can be introduced into the polymer system. Three different methods to introduce the nitrile groups were attempted. The first involved end-capping the polymer chains with nitrile groups, while the two other methods involved substituting the nitrile groups along the polymer chains.

A poly-m,p-thiophenylene, presumably containing only nitrile endgroups was prepared by the reaction of the initial poly-m,p-thiophenylene with excess mbenzendithiol in KzCOrDMF followed by the reaction of the newly formed polymer with 4bromobenzonitrile. That a polymer containing nitrile groups was obtained was shown by elemental analysis and infrared spectroscopy which indicated the presence of nitrile groups after


the polymer was vigorously stirred in a large volume of ether to remove 4-bromobenzonitrile. However, elemental analysis also indicated the presence of bromine which showed that the end-capping was incomplete.

TWO techniques were used to introduce nitrile groups along the polymer backbone. The first involved the bromination of the initial poly-m,p- thiophenylene with bromine, followed by treatment of the brominated polymer (mp 205-225°C) with cuprous cyanide. The final product showed a distinct nitrile absorption in the infrared spectrum, however, elemental analysis showed that a substantial amount of bromine was still left. This polymer was bright yellow, did not dissolve in all solvents tested, and turned dark brown when heated around 200°C but did not melt when heated up to 500°C. It could not be determined whether the insolubility of the polymer and its inability to melt is an inherent property of the polymer or whether it is due to crosslinking that might have occurred during its preparation.

.The second technique to introduce nitrile groups along the polymer chains involved the use of a small molar per cent of a nitrile containing comonomer. In this method, a poly(pheny1ene sulfide) containing pendant cyano groups was prepared from m-benzenedithiol, 95% dibromobenzene, and 5% 2,4dichlorobenzonitrile or 3,5-dichlorobenzonitrile. The polymers were prepared in dimethylacetamide and potassium carbonate, since in this medium the highest molecular weight poly-m,p-thiophenylene was obtained (Table VI). The polymers were stirred in ether in the final purification stages and were found to lose between 15-2074, of their weight believed to be low molecular weight fractions. The polymers melted at ranges about 20" C lower than the corresponding pure poly-m,p-thiophenylene of comparable inherent viscosity. The structures of the polymers were determined by infrared spectroscopy which showed a nitrile absorption at 2245 cm-l and from elemental analysis which gave results that were within the allowed limits of the theoretical values.

Br 100% 95% 5%

100% 95% 5%

Thermogravimetric analysis of polymers PX and PXI are shown in Figs. Isothermal aging of the polymers I V ~ B carried in a small furnace

The results of 1 and 2. in air and the results of this test are shown in Table VIII.


2o

Linear polymer - - - - Cronalinkcd polymer -

T e p . (OC)

1 I I I I I I I

isothermal aging and TGA seem to indicate that these polymers possess good thermal stability.

It has been reported in the litera- ture that compounds containing nitrile groups can be trimerized in the presence of an acid catalyst or simply under pressure and heat to give s-triazine molecule^.^ Because triazine molecules are known to have a fairly high thermal stability, they would be appropriate constituents in the final laminate structure. For this reason poly(pheny1ene sulfides) containing cyano groups were synthesized.

Synthesis of Crosslinked Polymers.

TABLE VIII Isothermal Agmg of the Nitrilecontaining and Crosslinked Polymers

Cumulative Weight Loss, yo Polymep 10 days at 300°C 8 days at 350°C

PX PXI PXII PXIII PXIIa PXIIIa

3 .7 3.9 2 .4 2.9 2 .3 1.5

16.2 18.6 19.8 19.6 13.2 15.8

a Polymers PXIIa, PXIIIa were crosslinked polymers washed to remove zinc chloride.


Teap. (OC)

I I I I I I I 100 200 300 400 500 600 700 800 900

Fig. 2. TGA (- -) of linear poly(pheny1ene sulfide) (PXI) and (-) of the corresponding polymer PXIII crosslinked with zinc chloride. Heating rate AT = 3"C/min; atmosphere, N2: flow rate, 98 cc/min.

Crosslinking of the polymer with nitrile endgroups was carried out, but very little crosslinking occurred. This was believed to be due to the incomplete end-capping of the polymer chains as well as to the low concentration of nitrile groups making the trimerization statistically unfavorable.

The synthesis of polymers PX and PXI was carried out after the failure of the polymer with nitrile endgroups to give a crosslinked product. Cross- linking of these polymers (PX and PXI) was carried out under nitrogen at 350-40O"C without catalyst or a t 290°C in the presence of zinc chloride. Initial attempts to cure PX in a carver press a t 250-300°C and 15,000 psi resulted in a soluble polymer, however further attempts to cure the same polymer a t temperatures in excess of 350" and under nitrogen resulted in a completely insoluble product. A fiber cloth was then impregnated with about 34% of its weight of a nitrile-containing poly-m,p-thiophenylene and the soft laminate obtained, when heated in a carver press a t 350-400°C with occasional application of about 10,000 psi, produced a black, hard but slightly flexible laminate without any appreciable weight loss.

Crosslinking of polymers PX and PXI with zinc chloride was carried out, since the curing process in this case can be achieved at lower temperatures (290-300" C). Because zinc chloride is so hygroscopic, the amount of this catalyst used could not be determined exactly; however, about 7% by weight was used. Initial heating of PX at 210°C and under


nitrogen failed to produce any crosslinking of the polymer chains and yielded a product that was soluble in hexamethylphosphoric triamide in which the original linear polymer dissolved quite readily. Further heating of the polymer a t 290°C for 24 hr produced an 89% insoluble polymer, PXII. Trimerization of polymers PX and PXI was then carried out by heating in the presence of zinc chloride and under nitrogen a t 210°C for 12 hr followed by heating a t 290°C for 24 hr. The product obtained by heating PX was 870/, insoluble and that obtained from PXI (PXIII) was 76'% insoluble. These results seem to indicate that PXI is probably more difficult to crosslink than PX, and it is believed that this could be due to the presence of the nitrile groups in the more crowded ortho positions.

A T: 2.5°C/min Abospbere: Static A i r

Linear polymer - - - - - Crosslinked polymer -

Tenp. (''2)

I I I I I I I I 300 350 400 200 2" 50 100 150

Fig. 3. Softening under load (--) of linear poly(pheny1ene sulfide) PX and (--) of polymer PXII crosslinked with zinc chloride. Heating rate AT = 2.5"C min; atmosphere, static air.

Identification of the products as the result of trimerization and not charring was indicated by the infrared spebtrum of the final products which were identical to those obtained for the starting materials without the nitrile absorption and by elemental analysis which gave values very close to the expected ones. Further evidence for the crosslinking was supplied by the Ehlers-Fisch softening behavior technique, in which a comparison of the amount of penetration under load and a t different temperatures was made between the linear and crosslinked polymers. Figures 3 and 4 show that the crosslinked polymers were less penetrable than the linear polymer a t higher temperatures, which suggests that some curing of the linear polymer was achieved.


The crosslinked products were dark brown, almost black, and showed excellent glass adhesion which made it difficult to obtain the crosslinked polymers free of glass particles for use in the various tests. A convenient method for obtaining the polymer free of glass particles involved the coating of the inner walls of the glass tube with aluminum foil followed by the removal of the foil from the crosslinked product by reaction with dilute hydrochloric acid.

Thermogravimetric analysis of samples of the crosslinked polymers still containing zinc chloride are shown in Figures 1 and 2. The results of isothermal aging of the untreated crosslinked polymers (PXII and PXIII) as well as those washed with hexamethylphosphoric triamide and

A T: 2.5'C/min Atmosphere: Static Air

Tenp. (OC)

I I I I I I I 50 100 I50 200 250 300 350 100

Fig. 4. Softening under load of polymer PXIII crosslinked with zinc chloride. Heating rate A T = 2.5"C; atmosphere, static air.

water to remove zinc chloride are shown in Table VIII. These results show that the crosslinked polymers possess a rather high thermal stability. A comparison of these results with those obtained for the linear polymers show that zinc chloride-free crosslinked polymers possessed the highest thermal stability while the untreated crosslinked polymers possessed the lowest thermal stability. These results seem to indicate that zinc chloride could be the reason behind the excessive weight loss in that it might be enhancing the oxidation and hence degradation of the polymer.

A laminate was prepared from PX on glass fiber in the presence of zinc chloride. The curing was run a t 250°C under about 15,000 psi and produced a hard but slightly flexible laminate.


EXPERIMENTAL

Commercially obtained samples of thiophenol, bromobenzene, and m- dibromobenzene were dired and then fractionally distilled before use. Similarly samples of 4-bromothiophenol, p-dibromobenzene, 1,4-dibro- monophthalene, bis-p-bromophenyl ether and 4-bromobenzonitrile were recrystallized.

DMF dried over magnesium sulfates and DMAc and HMPA were dried over calcium hydride before distillation.

The polymerization solvents were dried and distilled before use.

rn-Benzenedithiol

m-Benzenedithiol was obtained by the reduction of m-benzenedisulfonyl chloride with zinc amalgam in sulfuric acid. The methods employed for the amalgam preparation and the reduction have been reported by Caesar.'O The only modifications made to the reported procedure were concerned with the workup. The reaction mixture was filtered under gravity and the solid material was washed with distilled water then ether. The dithiol was extracted from the aqueous filtrate with ethyl ether. The ether extracts were combined and dried over magnesium sulfate. Ether was then removed by rotary evaporation, and the crude dithiol was distilled under reduced pressure on a Vigreux column to give the pure dithiol, bp 98"C/2.2 mm, in yields ranging from 60 to 80%.

H, 4.28%; S, 44.88%. ANAL. Calcd for CeHcS2: C, 50.70%; H, 4.23%; S, 45.07%. Found: C, 50.61%;

4,4'-Diphenyl Ether Dithiol

This dithiol was prepared by the use of a prcedure reported in the litera- ture." After initial workup, the crude product was sublimed three times (96-98"C/0.05 mm) to give a white crystalline product; mp, 101-103°C (uncorr.); lit., 103-104°C.

H, 4.47; S, 27.17%. ANAL. Calcd for C12HlOOS2: C, 61.65%; H, 4.27; S, 27.35%. Found: C, 61.59%;

Model Reactions

All model reactions were carried out in three-necked flasks fitted with a reflux condenser and a drying tube. A 15% molar excess (based on thiol concentration) of K&03 was generally employed. All reaction mixtures were initially worked up in a similar manner. The DMF was removed under reduced pressure, and dilute HC1 was then added to the remaining slurry. The aqueous mixture was extracted with benzene and the combined extracts after washing with water, drying over magnesium sulfate and filtration was rotor evaporated to remove benzene and leave the crude model compounds behind. The pure model compounds were then obtained by distillation or recrystallization as indicated in Table I.


After the initial workup, the model compound obtained in reaction 8 was distilled under reduced pressure and distillate was dissolved in ether. The resulting solution was then extracted with 20% aqueous NaOH, 20% HC1 and 10% aqueous NaHC03, and the light yellow solution was dried over anhydrous sodium sulfate. After removal of the ether, the yellow oil which solidified was rccrystallized from ethanol.

Polymerizations

All polymerizations were run under nitrogen in a three-necked flask fitted with a condenser and a mechanical stirrer. Since all polymerizations were carried out similarly, only a sample polymerization is described here.

Into a 200-ml, three-necked flask equipped with a mechanical stirrer, a reflux condenser, and a nitrogen bubbler were placed 2.8401 g (0.02 mole) of m-benzenedithiol, 4.7201 g (0.02 mole) of p-dibromobenzene, 6.35 g (0.046 mole) of potassium carbonate, and 40 ml of dimethylacetamide. The reaction mixture, which turned light yellow, was stirred, and the temperature of the oil bath was raised to 160°C and maintained between 160 and 170°C for 48 hr. After cooling to room temperature, the reaction mixture was poured with stirring into a cold solution of 800 ml of methanol, 400 ml of water, and 100 ml of concentrated hydrochloric acid. The solid that formed was filtered and washed well with water and methanol. The dry solid was then stirred well in 1.5 liter of ether, filtered, and dried in vucuo. The off-white solid obtained weighed 3.7 g (89yo yield) and softened a t 100-120°C. A 5% solution of the polymer in hexamethylphosphoric triamide gave an inherent viscosity of 0.41 dl/g.

The preparations of the polymers containing pendant cyan0 groups were carried out similarly. Polymer PX was prepared from 2.8457 g (0.02 mole) of m-benzenedithiol, 4.4827 g (0.0190 mole) of p-dibromobenzene, 0.1722 g (0.0010 mole) of 2,4dichlorobenzonitrile, and 6.35 g (0.046 mole) of potassium carbonate in 40 ml of dimethylacetamide and was obtained in 84y0 yield after stirring in ether.

ANAL. Calcd for (CIZHSZ)O.X, (CI~H~NSZ)~.~~, , : C, 66.52%; H, 3.68%; S, 29.49% N, 0.27%. Found: C, 66.30%; H, 3.60%; S, 29.71%; N, 0.30%.

Polymer PXI was prepared from 2.8447 g (0.020 mole) of m-benzenedithiol, 4.4831 g (0.0190 mole) of p-dibromobenzene, 0.1725 g (0.0010 mole) of 3,5-dichlorobenzonitrile, and 6.35 g (0.046 mole) of potassium carbonate in 40 ml of dimethylacetamide and was obtained in 82% yield after stirring in ether.

ANAL. N,0.27%.

Calcd for (C~zH&)o.gs, [CI~H~NSZ)~.OS,,: C, G6.52%; H, 3.68%; S, B.49% Found: C,66.33%; H,3.80%; S,29.43%; N,0.25%.

Crosslinking Reactions

Crosslinking of PX. A 0.5 g sample of PX was mixed wyell with 0.035 g The resulting mixture of zinc chloride by the use of a mortar and pestle.


was then added to a test tube with a side-outlet and equipped with a nitrogen inlet. Under nitrogen, the contents of the tube were heated a t 210°C for 12 hr followed by raising the temperature to 290°C and maintaining it a t this temperature for 24 hr. The black solid obtained (PXII) was found to be 89% insoluble when stirred in hexamethylphosphoric triamide for 24 hr and gave an infra;ed spectrum that corresponded to that obtained for PX without the cyano absorption.

C, 65.72%; H, 353%; N, 0.34y0; S, 29.17%. ANAL. Calcd for PXII: C, 66.52%; H, 3.68%; N, 0.27%; S, 29.49%. Found:

Crosslinking of PXI. Crosslinking of PXI was carried similarly as that The crosslinked product PXVI was only 76% insoluble in hexa- of PX.

methylphosphoric triamide.

ANAL. Calcd for PXIII: C, 66.52%; H, 3.68%; N, 0.27%; S, 29.49’%. Found:

Preparation of Laminates. Laminates were prepared by impregnating three pieces of E glass 181 glass fiber cloth with a solution of the polymer with or without zinc chloride in hexamethylphosphoric triamide, followed by evaporation of the solvent under partial vacuum. The soft laminates thus obtained were placed in a carver press and heated under pressure for 24 hr to give dark colored hard laminates.

C, 66.34%; H, 3.6370; N, 0.22%; S, 29.47%.

We gratefully acknowledge the Air Force Materials Laboratory, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio, for the financial support of this work.

We are indebted to Dr. G. F. L. Ehlers, Air Force Materials Laboratory, WrighbPatter- son Air Force Base, for the thermogravimetric analysis and to Dr. R. K. Fisch, of the same laboratory, for the softening curves.

We are also indebted to Dr. V. D. Todd of Koppers for a generous supply of m-benzenedisulfonyl chloride.

References 1. R. Lenz, C. E. Handlovits, and H. Smith, J . Polym. Sci., 58,351 (1962). 2. C. E. Handlovitz, Macrmlecular Synthesis, 3,131 (1969). 3. J. Edmonds and H. W. Hill, U.S. Pat. 3,354,129 (1962). 4. A. L. Blank, Makromol. Chem., 140,83 (1970). 5. Handbook of Chemistry and Physics, Chemical Rubber Publishing Co., Cleveland,

6. J. R. Campbell, J . Org. Chem., 29, 1830 (1964). 7. C. S. Marvel and J. Wilbur, unpublished results. 8. G. A. Loughran, G. F. L. Ehlers, and K. R. Fisch (Wright-Patterson Air Force Ma-

9. Z. Rappoport, The Chemistry of the Cyan0 Group, Interscience, New York, 1970,

10. P. Caesar, Organic Synthesis, Call. Vol. ZV, Wiley, New York, 1963, pp. 693-697. 11. P. C. Dutta and D. Mandel, J . Indian Chem. Sac., 33,54 (1956).

Ohio, 52nd ed., 1971-1972.

terials Laboratory), private communications.

p. 410.

Received July 6, 1973 Revised August 9, 1973

poly(arylene sulfides) with pendant cyano groups as high-temperature laminating resins

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