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Synthesis and certain properties of soluble polyphenylene sulphides
Synthesis and properties of soluble polyphenylene sulphides
2783
copolymer acquires an increased concentration of D H P P units, indicating that the latter is more reactive t h a n DVCH. I n the preparation of the copolycarbonates from phosgene, AIPC and D H P P it is found t h a t the ratio of units with phosgene and AIPC radicals is the same as the original ratio of the corresponding reactants. I n the mixed polycarbonates from DPC and DPHMI (Table) the dependence of copolymer composition on the composition of the original mixture of bisphenols has a point of inflexion at a concentration of DPHMI in the reactant mixture of about 50 mole %. Up to this concentration the concentration of D P H M I radicals in the copolymer is higher than the concentration of D P H M I in the react a n t mixture. After the equimolar concentration of D P H M I ra~licals in the copolymer has been reached the concentration of this bisphenol in the copolymer deviates a little from that of the linear azeotrope. This situation leads to the conclusion t h a t the rate constants of polycondensation of the cardic bisphenols D P H M I and DPC are of similar magnitude under conditions in which the reaction rate is kinetically controlled. This is indicated also by the average rate constant of copolycondensation of 1.34. I t was found that as the concentration of DPHMI units in the copolymer is increased both the temperature and strength characteristics of the polycarbonates are raised. The high alkali resistance of the copolymer, in comparison with a polycarbonate based on DHPP, is also noteworthy. Translat~ by E. O. I>HILLLPS REFERENCES
1. B. JACKSON and I. CALDWELL, Khimiya i tekhnol, polimerov 7: 141, 1964 2. T. BRUSON, 5. Amer. Chem. Soc. 67: 726, 1945 3. D. VORLANDER and O. KOCH, Ber. 62: 540, 1929
SYNTHESIS AND CERTAIN PROPERTIES OF SOLUBLE POLYPHENYLENE SULPHIDES* V. A. SERGEYEV, V. K. S m T m o v , V. I. NEDEL'KII~ a n d V. V. KORSHAK Institute for Elemento-Organic Compounds, Academy of Sciences, U.S.S.R. (Received 6 July 1974) Soluble and fusible polarylene sulphides have been synthesized by the polycondensation of halogen substituted aromatic compounds with anhydrous sodium sulphide. I t has been shown that disruption in the degree of ordering of the poly* Vysokomol. soyed. A17; No. 11, 2420--2424, 1975.
2784
V. A. SERGEYEV 85 a~.
merle chains leads to an increase in the solubility of the polyphenylene sulphides. IR, NMR spectroscopy and X-ray structural analysis, as well as a comparative assessment of the physico-chemical properties, have been used to establish that the polyphenylene sulphides based on dihalogenbenzenes have a linear structure. An ionic mechanism for the polycondensation of dihalogenbenzenes with sodium sulphide is put forward and discussed. IgVESTIGATORS have given considerable attention recently to polymers of the polyphenylene sulphide type and to the production of thermally stable and heatresistant materials based on them [1-5]. Work of this type is, however, found predominantly in the patent literature [1-4], and information about the features of the synthesis of polyphenylene sulphides is very limited. I n this connection, it was of interest to study in rather more detail the process of obtaining polyarylene sulphides with various structures and to investigate their properties. Polyarylene sulphides are known to have been obtained by the high temperature polycondensation of polyhalogen derivatives of aromatic compounds with anhydrous sodium sulphide in solution in N-methylpyrrolidone-2 [1]. The polymers obtained previously by this method had high melting points and limited solubility at room temperature in high melting point polar organic solvents. I n order to obtain polyarylene sulphides with better solubility, it seemed to us that it would be interesting to use, as the initial dihalogen-aromatic compounds, compounds which would contain substituents in the aromatic ring or whose polyeondensation would give rise to polymeric products with a branched structure. We therefore selected as the initial compounds, 1,4-dibromodurol and 1,3,5tri-(4-bromophenol)benzene. For comparison, we also obtained and investigated the properties of the polyarylene sulphides based on 1,4-dichlor- and 1,4-dibromobenzene. The Table shows the conditions of synthesis and certain properties of the products obtained. I t m a y be seen that, for polycondensation in solution in N-methylpyrrolidone-2 at 250°C for 8 hr, the overall yield of the reaction products depends principally on the structure of the initial polyhalogenated aromatic compound and amounts to 63-69~, with the exception of an overall yield of 9 0 ~ (experiment 5), obtained for the product based on 1,3,5-tri-(4-bromophenol)benzene: as distinct from the other products, which were completely soluble when heated in N-methylpyrrolidone-2, hexamethylphosphortriamide, diphenylsulphide and other similar solvents, this product dissolved only partially in these solvents. The proportion of the soluble fraction was determined by boiling the specimens in dimethylformamide (DMF) for 1 hr. It was found from the data obtained that the polyarylene sulphide based on 1,4-dibromodurol (experiment 4) was completely soluble in DM_F. This m a y be explained by the fact that this polymer contains methyl groups as pendant substituents in the aromatic ring and these obviously reduce the intermolecular interaction between the polymeric chains, unlike the polymer based on 1,4-dibromobenzene which does not have substituents in the benzene ring. A similar
12,500
235 260
100 100 18
69 63 90
250 250 275
580
5.035 16,675
280 280
31 27
63 66
Mol. w*.
250 250
time, hr
1,4-Dichlorbenzene 1,4-Dibromobenzene 1,4-Dibromobenzene + 1,3,5-tri-(4-bromophenyl)benzene (20: 1) 1,4-Dibromodurol 1,3,5-Tri-(4-bromophenyl)-benzene
ing point, oC
Soft(~n-
T, °C
Yield, °/o fraction total soluble in DMF
Starting monomers
Reac tion
* This corresponds to the point of intersection of the tangents to the branches of the thermomechanical curve.
Experiment number
halogen
1.42
1.17
11.42 1-28 9.95
S
27.74 27.61
22-04 13.34 10.66
H
3.81 3.68
3.55 7.70 3.71
C
65.24 65.17
63.73 72-41 58"9
Chemical analysis, ~o
C O N D I T I O N S OF SYI~TTHESIS~ Y I E L D A N D C E R T A I N P R O P E R T I E S OF T H E P O L Y M E R S
m
O M~
i"
2786
V. A. S~:Ra:~YEVet al.
reduction in the intermolecular interaction clearly occurs also when the regularity of the polymeric chain structure is disrupted by the introduction of a comparatively small number of branch sections into the structure of the polymer. Thus, in order to obtain a polyarylene sulphide based on 1,4-dibromobenzene that would be completely soluble in DMF, it is sufficient to introduce into the polymeric molecule one mole of a branching agent, namely, 1,3,5-tri-(4-bromophenyl)benzene, for every twenty moles of the initial 1,4-dibromobenzene (experiment 3). The strongly branched polymer obtained from 1,3,5-tri-(4-bromophenyl) benzene gives only 18% of products soluble in DMF (experiment 5). With the formation of the polyarylene sulphides based on 1,4-dichlor-and 1,4-dibromobenzene as examples (experiments 1 and 2), it was shown that the overall yield of the reaction products, the yield of the fraction soluble in DMF and the temperature for the start of softening have approximately the same values for these two polymers. However, the polyarylene sulphide based on 1,4-dibromobenzene has a molecular weight of 13,700 (calculated from the bromine concentration in the product), as distinct from a molecular weight of 5000 for the polyarylene sulphide based on 1,4-dichlorbenzene, calculated from the concentration of chlorine atoms. This may clearly be explained by the rather greater reactivity of bromine substituted aromatic compounds during the polyeondensation with sodium sulphide. As distinct from the polyphenylene sulphides based on 1,4-dichlor- and 1,4-dibromobenzene (experiments 1 and 2), which begin to soften at around 280°C, the branched polyphenylene sulphide based on a mixture of 1,4-dibromobenzene and 1,3,5-tri-(4-bromophenyl)benzene (experiment 3) and the polymethyl-substituted polyphenylene sulphide based on durol have somewhat lower softening points, namely, 235 and 260°C respectively. According to the X-ray structure analysis data, the polyphenylene sulphides based on 1,4-dihalogenobenzenes and durol are crystalline products with a high degree of order, as distinct from the copolymer (experiment 3) and the polymer based on 1,3,5-tri(4-bromophenyl) benzene, which have much lower degrees of crystallinity. This fact, and also the high softening points and limited solubility in organic solvents, form the basis for assuming that the polymers based on 1,4-dihalogen derivatives (experiments 1,2,4) have a predominantly linear structure which favours the molecular chains' having a high packing density. The I R and NMR spectra of the polymers were recorded as indicators of their structure. The I R spectra of all the polyarylene sulphides synthesized by us exhibited absorption bands in the region of 680 cm -1, characteristic of the valency vibrations of the phenyl-sulphur bond, and in the regions 1570 and 1470 cm -1, attributable to deformation vibrations of the same bonds. The I R spectra of the polymethyl-substituted polyphenylene sulphide have absorption bands in the regions 2870-3000 and 1465 cm -1, characteristic respectively of the valency vibrations of methyl groups and those of C and H atoms of
Synthesis and properbies of soluble polyphenylene sulphides
2787
benzene rings: for the copolymer based on a mixture of 1,4-dibromobenzene and 1,3,5-tri-(4-bromophenyl) benzene (experiment 3), there are absorption bands in :the regions of 820 and 880 cm -1, characteristic respectively of 1,4-di- and 1,35-trisubstituted benzene rings. I n order to confirm the structure proposed for the polyphenylene sulphides based on 1,4-dihalogenobenzenes, we compared the IR spectra of a branched polyphenylene sulphide (based on 1,4-dichlorbenzene, sulphur and Na carbonate [4]) and a linear polyphenylene sulphide (based on the p-bromophenolate of sodium [3]) with the IR spectrum of the poly-l,4-phenylene sulphide that we had synthesized from 1,4-dichlorbenzene and sodium sulphide (see Figure).
I
I
I
I
l
I
/0
I
8
wlO-%m-tG
IR spectra of: /--linear and and 2--branched polyphenylene sulphides; and 3--the polymer based on 1,4-diehlorbenzene and sodium sulphide. It may be seen that the IR spectrum of the poly-p-phenylene sulphide based on 1,4-dichlorbenzene and anhydrous sodium sulphide is similar to that of the linear product from the polycondensation of sodium p-bromothiophenolate. The band corresponding to the out-of-plane deformation vibrations of the 1,4substituted benzene ring in the polyphenylene sulphides occurs in the region of 820 cm -1, and the band at 1400 cm -1 is characteristic of the planar positioning of the benzene rings. A feature distin~mishing the polymer synthesized by us from the branched polyphenylcne sulphide obtained in [4] is the absence of a band at 860 cm -1, characteristic of 1,2,4-substituted benzene rings. The IR spectroscopic data of the poly-p-phenylene sulphide obtained by us from 1,4-dichlorbenzene and anhydrous sodium sulphide agree well with the NMR spectra recorded in solution in DMF: no appreciable splitting of the signal from the phenyl protons, which would be characteristic of 1,2,4-substituted benzene rings, was observed in the spectra. The results of I R and NMR spectroscopy, X-ray structural analysis and also
2788
V. A. SERa~YEV et o~.
the comparative assessment of the physico-chemieal properties thus confirm t h a t the polyphenylene sulphides obtained by the reaction of dihalogenobenzenes with sodium sulphide have a linear structure. The formation of a linear polyphenylene sulphide from the polycondensation of dihalogenobenzenes with sodium sulphide (reaction 1) is a feature distinguishing this process from the polycondensation of dihalogenobenzenes with sulphur and sodium carbonate (reaction 2), as a result of which branched polymers m a y be formed. This m a y obviously be explained from two causes. A sodium polysulphide with the general formula Na~S~ is known to be formed during reaction (2) as an intermediate product [5]. The reaction between a dihalogenobenzene and sodium polysulphide m a y occur both by an ionic and also by a free radical mechanism, the free radical mechanism being preferred at elevated temperatures [5]. 200 - - 3 6 0 °
Na..,Sx •
* Na~S 4- Sx_z
CI
CI
J
J
c!
cl
I
a reaction which also le ads to chain branching. Secondly, whereas reaction (2) occurs in the melt, reaction (1) occurs in solution in a polar organic solvent. The solvent evidently has a substantial effect on the course of the polycondensation. On the one hand, it increases the mobili W o f the initial monomers and this gives rise to more selective substitution in the benzene ring, and on the other hand, the polar solvent will clearly cause dissociation of the sodium monosulphide, thus favouring the occurrence of the polyeondensation of the dihalogenobenzene with the sodium sulphide by an ionic mechanism. Thus the use of sodium monosulphide and a polar organic solvent in reaction (1) will make the ionic reaction mechanism to be preferred. In the general form, t h e polycondensation of sodium sulphide with a dihalogenobenzene m a y be represented by the following scheme: X--O-X
-}- Na~S--, X - - ~ - - S - N a +
X--~---~--S-Na + + X - - ~ - - X - - ,
X--~--S--O--X
d- NaX + NaX etc.
or
2 X--~--~---S-Na + --, X - -~~ - ~ , - - S - - /\ f_-_~/ -. - S - N a + + NaX etc. where X is a halogen atom. A sodium 4-halogenthiophenolate is probably formed in the first stage of t h e polyeondensation of dihalogenoaryls with sodium sulphide; this then reacts with the initial dihalogenobenzene molecule and the formation of a p-substitut~t di-
Synthesis a n d properties of soluble polyphenylene sulphides
2789
halogen derivative of diphenylsulphide thus occurs. In its turn, the 4,4'-dihalogendiphenyl sulphide and sodium sulphide form a sodium thiophenolate, and SO on. Sodium sulphide was made anhydrous b y the method given in [6]. 1, 3, 5-tri-(4-bromophenyl) benzene was synthesized b y a method similar to t h a t in [7]. 20 g (0.1 mole) of p-bromaeetophenone and 18 g (0.12 mole) of orthoformie ester were dissolved in 50 ml of chloroform a n d dry HC1 was passed through the reaction mixture, with stirring, for 8 hr at 20°C. The residue that precipitated was recrystallized from chloroform; yield, 40%, melting point 263-264°C (melting point in the literature, 265°C [7]). Polyarylene sulphides was synthesized as in [8], h u t the addition of 1 mole of alurninlum chloride to the reaction mixture for each 1.5 mole of durol enabled us to do away with the use of intense solar illumination: melting point 198.5-199°C (melting point in the literature, 199-200°C [8D. 1,4-Dibromodurol was synthesized b y the method given in [8], b u t the addition to the reaction mixture of 1 mole of aluminium chloride for each 1.5 mole of durol enabled us to avoid the use of intense solar radiation; melting point, 199-200°C [8]. The polyphenylene sulphides were synthesized b y the method suggested in [1]. Anhydrous sodium sulphide and the halogen derivative were loaded into an autoclave that had been purged with nitrogen. N-methylpyrrolidone-2 was used as the solvent. The reaction mixture was heated to 250-275°C and held at this temperature for 8 hr. After being cooled, the reaction products were precipitated in alcohol, the precipitate left was washed with water and alcohol and then dried at 60°C in vacuum to constant weight. The I R spectra of the polymers synthesized were recorded with a UR-20 speetrophotometer in the range 400-3600 cm -1. The polymer specimens were prepared b y pressing as tablets with KBr.
Translated by G. F. MODLEN REFERENCES 1. J. T. EDMONTS and H. W. HILL, U.S. Pat. 3354129, 1967: RZhKhim., 7C406, 1969 2. R. W. LENZ and C. E. HAUDLOWITS, J. Polymer Sei. 43: 167, 1960 3. R. W. LENZ, C. E. HAUDLOWITS and W. K. CARRINGTON, U.S. Pat. 3274165, 1966; RZhKhim. 3C229, 1968 4. A. D. MACCALLUM, U.S. Pat. 2513188, 1950; Chem. Abstrs. 8465a, 1950 5. R. W. LENZ a n d W. K. CARRINGTON, J. Polymer Sci. 41: 333, 1959 6. Yu. V. KORYAKIN, Chistyye khimicheskiye reaktivy (Pure Chemical Reagents). p. 385, GNTI, 1947 7. G. F. WOODS and M. S. DEPT., Chem. Abstrs. 60: 6197a, 1964 8. O. KORCZUUSKI, Ber. 35: 869, 1902
2783
copolymer acquires an increased concentration of D H P P units, indicating that the latter is more reactive t h a n DVCH. I n the preparation of the copolycarbonates from phosgene, AIPC and D H P P it is found t h a t the ratio of units with phosgene and AIPC radicals is the same as the original ratio of the corresponding reactants. I n the mixed polycarbonates from DPC and DPHMI (Table) the dependence of copolymer composition on the composition of the original mixture of bisphenols has a point of inflexion at a concentration of DPHMI in the reactant mixture of about 50 mole %. Up to this concentration the concentration of D P H M I radicals in the copolymer is higher than the concentration of D P H M I in the react a n t mixture. After the equimolar concentration of D P H M I ra~licals in the copolymer has been reached the concentration of this bisphenol in the copolymer deviates a little from that of the linear azeotrope. This situation leads to the conclusion t h a t the rate constants of polycondensation of the cardic bisphenols D P H M I and DPC are of similar magnitude under conditions in which the reaction rate is kinetically controlled. This is indicated also by the average rate constant of copolycondensation of 1.34. I t was found that as the concentration of DPHMI units in the copolymer is increased both the temperature and strength characteristics of the polycarbonates are raised. The high alkali resistance of the copolymer, in comparison with a polycarbonate based on DHPP, is also noteworthy. Translat~ by E. O. I>HILLLPS REFERENCES
1. B. JACKSON and I. CALDWELL, Khimiya i tekhnol, polimerov 7: 141, 1964 2. T. BRUSON, 5. Amer. Chem. Soc. 67: 726, 1945 3. D. VORLANDER and O. KOCH, Ber. 62: 540, 1929
SYNTHESIS AND CERTAIN PROPERTIES OF SOLUBLE POLYPHENYLENE SULPHIDES* V. A. SERGEYEV, V. K. S m T m o v , V. I. NEDEL'KII~ a n d V. V. KORSHAK Institute for Elemento-Organic Compounds, Academy of Sciences, U.S.S.R. (Received 6 July 1974) Soluble and fusible polarylene sulphides have been synthesized by the polycondensation of halogen substituted aromatic compounds with anhydrous sodium sulphide. I t has been shown that disruption in the degree of ordering of the poly* Vysokomol. soyed. A17; No. 11, 2420--2424, 1975.
2784
V. A. SERGEYEV 85 a~.
merle chains leads to an increase in the solubility of the polyphenylene sulphides. IR, NMR spectroscopy and X-ray structural analysis, as well as a comparative assessment of the physico-chemical properties, have been used to establish that the polyphenylene sulphides based on dihalogenbenzenes have a linear structure. An ionic mechanism for the polycondensation of dihalogenbenzenes with sodium sulphide is put forward and discussed. IgVESTIGATORS have given considerable attention recently to polymers of the polyphenylene sulphide type and to the production of thermally stable and heatresistant materials based on them [1-5]. Work of this type is, however, found predominantly in the patent literature [1-4], and information about the features of the synthesis of polyphenylene sulphides is very limited. I n this connection, it was of interest to study in rather more detail the process of obtaining polyarylene sulphides with various structures and to investigate their properties. Polyarylene sulphides are known to have been obtained by the high temperature polycondensation of polyhalogen derivatives of aromatic compounds with anhydrous sodium sulphide in solution in N-methylpyrrolidone-2 [1]. The polymers obtained previously by this method had high melting points and limited solubility at room temperature in high melting point polar organic solvents. I n order to obtain polyarylene sulphides with better solubility, it seemed to us that it would be interesting to use, as the initial dihalogen-aromatic compounds, compounds which would contain substituents in the aromatic ring or whose polyeondensation would give rise to polymeric products with a branched structure. We therefore selected as the initial compounds, 1,4-dibromodurol and 1,3,5tri-(4-bromophenol)benzene. For comparison, we also obtained and investigated the properties of the polyarylene sulphides based on 1,4-dichlor- and 1,4-dibromobenzene. The Table shows the conditions of synthesis and certain properties of the products obtained. I t m a y be seen that, for polycondensation in solution in N-methylpyrrolidone-2 at 250°C for 8 hr, the overall yield of the reaction products depends principally on the structure of the initial polyhalogenated aromatic compound and amounts to 63-69~, with the exception of an overall yield of 9 0 ~ (experiment 5), obtained for the product based on 1,3,5-tri-(4-bromophenol)benzene: as distinct from the other products, which were completely soluble when heated in N-methylpyrrolidone-2, hexamethylphosphortriamide, diphenylsulphide and other similar solvents, this product dissolved only partially in these solvents. The proportion of the soluble fraction was determined by boiling the specimens in dimethylformamide (DMF) for 1 hr. It was found from the data obtained that the polyarylene sulphide based on 1,4-dibromodurol (experiment 4) was completely soluble in DM_F. This m a y be explained by the fact that this polymer contains methyl groups as pendant substituents in the aromatic ring and these obviously reduce the intermolecular interaction between the polymeric chains, unlike the polymer based on 1,4-dibromobenzene which does not have substituents in the benzene ring. A similar
12,500
235 260
100 100 18
69 63 90
250 250 275
580
5.035 16,675
280 280
31 27
63 66
Mol. w*.
250 250
time, hr
1,4-Dichlorbenzene 1,4-Dibromobenzene 1,4-Dibromobenzene + 1,3,5-tri-(4-bromophenyl)benzene (20: 1) 1,4-Dibromodurol 1,3,5-Tri-(4-bromophenyl)-benzene
ing point, oC
Soft(~n-
T, °C
Yield, °/o fraction total soluble in DMF
Starting monomers
Reac tion
* This corresponds to the point of intersection of the tangents to the branches of the thermomechanical curve.
Experiment number
halogen
1.42
1.17
11.42 1-28 9.95
S
27.74 27.61
22-04 13.34 10.66
H
3.81 3.68
3.55 7.70 3.71
C
65.24 65.17
63.73 72-41 58"9
Chemical analysis, ~o
C O N D I T I O N S OF SYI~TTHESIS~ Y I E L D A N D C E R T A I N P R O P E R T I E S OF T H E P O L Y M E R S
m
O M~
i"
2786
V. A. S~:Ra:~YEVet al.
reduction in the intermolecular interaction clearly occurs also when the regularity of the polymeric chain structure is disrupted by the introduction of a comparatively small number of branch sections into the structure of the polymer. Thus, in order to obtain a polyarylene sulphide based on 1,4-dibromobenzene that would be completely soluble in DMF, it is sufficient to introduce into the polymeric molecule one mole of a branching agent, namely, 1,3,5-tri-(4-bromophenyl)benzene, for every twenty moles of the initial 1,4-dibromobenzene (experiment 3). The strongly branched polymer obtained from 1,3,5-tri-(4-bromophenyl) benzene gives only 18% of products soluble in DMF (experiment 5). With the formation of the polyarylene sulphides based on 1,4-dichlor-and 1,4-dibromobenzene as examples (experiments 1 and 2), it was shown that the overall yield of the reaction products, the yield of the fraction soluble in DMF and the temperature for the start of softening have approximately the same values for these two polymers. However, the polyarylene sulphide based on 1,4-dibromobenzene has a molecular weight of 13,700 (calculated from the bromine concentration in the product), as distinct from a molecular weight of 5000 for the polyarylene sulphide based on 1,4-dichlorbenzene, calculated from the concentration of chlorine atoms. This may clearly be explained by the rather greater reactivity of bromine substituted aromatic compounds during the polyeondensation with sodium sulphide. As distinct from the polyphenylene sulphides based on 1,4-dichlor- and 1,4-dibromobenzene (experiments 1 and 2), which begin to soften at around 280°C, the branched polyphenylene sulphide based on a mixture of 1,4-dibromobenzene and 1,3,5-tri-(4-bromophenyl)benzene (experiment 3) and the polymethyl-substituted polyphenylene sulphide based on durol have somewhat lower softening points, namely, 235 and 260°C respectively. According to the X-ray structure analysis data, the polyphenylene sulphides based on 1,4-dihalogenobenzenes and durol are crystalline products with a high degree of order, as distinct from the copolymer (experiment 3) and the polymer based on 1,3,5-tri(4-bromophenyl) benzene, which have much lower degrees of crystallinity. This fact, and also the high softening points and limited solubility in organic solvents, form the basis for assuming that the polymers based on 1,4-dihalogen derivatives (experiments 1,2,4) have a predominantly linear structure which favours the molecular chains' having a high packing density. The I R and NMR spectra of the polymers were recorded as indicators of their structure. The I R spectra of all the polyarylene sulphides synthesized by us exhibited absorption bands in the region of 680 cm -1, characteristic of the valency vibrations of the phenyl-sulphur bond, and in the regions 1570 and 1470 cm -1, attributable to deformation vibrations of the same bonds. The I R spectra of the polymethyl-substituted polyphenylene sulphide have absorption bands in the regions 2870-3000 and 1465 cm -1, characteristic respectively of the valency vibrations of methyl groups and those of C and H atoms of
Synthesis and properbies of soluble polyphenylene sulphides
2787
benzene rings: for the copolymer based on a mixture of 1,4-dibromobenzene and 1,3,5-tri-(4-bromophenyl) benzene (experiment 3), there are absorption bands in :the regions of 820 and 880 cm -1, characteristic respectively of 1,4-di- and 1,35-trisubstituted benzene rings. I n order to confirm the structure proposed for the polyphenylene sulphides based on 1,4-dihalogenobenzenes, we compared the IR spectra of a branched polyphenylene sulphide (based on 1,4-dichlorbenzene, sulphur and Na carbonate [4]) and a linear polyphenylene sulphide (based on the p-bromophenolate of sodium [3]) with the IR spectrum of the poly-l,4-phenylene sulphide that we had synthesized from 1,4-dichlorbenzene and sodium sulphide (see Figure).
I
I
I
I
l
I
/0
I
8
wlO-%m-tG
IR spectra of: /--linear and and 2--branched polyphenylene sulphides; and 3--the polymer based on 1,4-diehlorbenzene and sodium sulphide. It may be seen that the IR spectrum of the poly-p-phenylene sulphide based on 1,4-dichlorbenzene and anhydrous sodium sulphide is similar to that of the linear product from the polycondensation of sodium p-bromothiophenolate. The band corresponding to the out-of-plane deformation vibrations of the 1,4substituted benzene ring in the polyphenylene sulphides occurs in the region of 820 cm -1, and the band at 1400 cm -1 is characteristic of the planar positioning of the benzene rings. A feature distin~mishing the polymer synthesized by us from the branched polyphenylcne sulphide obtained in [4] is the absence of a band at 860 cm -1, characteristic of 1,2,4-substituted benzene rings. The IR spectroscopic data of the poly-p-phenylene sulphide obtained by us from 1,4-dichlorbenzene and anhydrous sodium sulphide agree well with the NMR spectra recorded in solution in DMF: no appreciable splitting of the signal from the phenyl protons, which would be characteristic of 1,2,4-substituted benzene rings, was observed in the spectra. The results of I R and NMR spectroscopy, X-ray structural analysis and also
2788
V. A. SERa~YEV et o~.
the comparative assessment of the physico-chemieal properties thus confirm t h a t the polyphenylene sulphides obtained by the reaction of dihalogenobenzenes with sodium sulphide have a linear structure. The formation of a linear polyphenylene sulphide from the polycondensation of dihalogenobenzenes with sodium sulphide (reaction 1) is a feature distinguishing this process from the polycondensation of dihalogenobenzenes with sulphur and sodium carbonate (reaction 2), as a result of which branched polymers m a y be formed. This m a y obviously be explained from two causes. A sodium polysulphide with the general formula Na~S~ is known to be formed during reaction (2) as an intermediate product [5]. The reaction between a dihalogenobenzene and sodium polysulphide m a y occur both by an ionic and also by a free radical mechanism, the free radical mechanism being preferred at elevated temperatures [5]. 200 - - 3 6 0 °
Na..,Sx •
* Na~S 4- Sx_z
CI
CI
J
J
c!
cl
I
a reaction which also le ads to chain branching. Secondly, whereas reaction (2) occurs in the melt, reaction (1) occurs in solution in a polar organic solvent. The solvent evidently has a substantial effect on the course of the polycondensation. On the one hand, it increases the mobili W o f the initial monomers and this gives rise to more selective substitution in the benzene ring, and on the other hand, the polar solvent will clearly cause dissociation of the sodium monosulphide, thus favouring the occurrence of the polyeondensation of the dihalogenobenzene with the sodium sulphide by an ionic mechanism. Thus the use of sodium monosulphide and a polar organic solvent in reaction (1) will make the ionic reaction mechanism to be preferred. In the general form, t h e polycondensation of sodium sulphide with a dihalogenobenzene m a y be represented by the following scheme: X--O-X
-}- Na~S--, X - - ~ - - S - N a +
X--~---~--S-Na + + X - - ~ - - X - - ,
X--~--S--O--X
d- NaX + NaX etc.
or
2 X--~--~---S-Na + --, X - -~~ - ~ , - - S - - /\ f_-_~/ -. - S - N a + + NaX etc. where X is a halogen atom. A sodium 4-halogenthiophenolate is probably formed in the first stage of t h e polyeondensation of dihalogenoaryls with sodium sulphide; this then reacts with the initial dihalogenobenzene molecule and the formation of a p-substitut~t di-
Synthesis a n d properties of soluble polyphenylene sulphides
2789
halogen derivative of diphenylsulphide thus occurs. In its turn, the 4,4'-dihalogendiphenyl sulphide and sodium sulphide form a sodium thiophenolate, and SO on. Sodium sulphide was made anhydrous b y the method given in [6]. 1, 3, 5-tri-(4-bromophenyl) benzene was synthesized b y a method similar to t h a t in [7]. 20 g (0.1 mole) of p-bromaeetophenone and 18 g (0.12 mole) of orthoformie ester were dissolved in 50 ml of chloroform a n d dry HC1 was passed through the reaction mixture, with stirring, for 8 hr at 20°C. The residue that precipitated was recrystallized from chloroform; yield, 40%, melting point 263-264°C (melting point in the literature, 265°C [7]). Polyarylene sulphides was synthesized as in [8], h u t the addition of 1 mole of alurninlum chloride to the reaction mixture for each 1.5 mole of durol enabled us to do away with the use of intense solar illumination: melting point 198.5-199°C (melting point in the literature, 199-200°C [8D. 1,4-Dibromodurol was synthesized b y the method given in [8], b u t the addition to the reaction mixture of 1 mole of aluminium chloride for each 1.5 mole of durol enabled us to avoid the use of intense solar radiation; melting point, 199-200°C [8]. The polyphenylene sulphides were synthesized b y the method suggested in [1]. Anhydrous sodium sulphide and the halogen derivative were loaded into an autoclave that had been purged with nitrogen. N-methylpyrrolidone-2 was used as the solvent. The reaction mixture was heated to 250-275°C and held at this temperature for 8 hr. After being cooled, the reaction products were precipitated in alcohol, the precipitate left was washed with water and alcohol and then dried at 60°C in vacuum to constant weight. The I R spectra of the polymers synthesized were recorded with a UR-20 speetrophotometer in the range 400-3600 cm -1. The polymer specimens were prepared b y pressing as tablets with KBr.
Translated by G. F. MODLEN REFERENCES 1. J. T. EDMONTS and H. W. HILL, U.S. Pat. 3354129, 1967: RZhKhim., 7C406, 1969 2. R. W. LENZ and C. E. HAUDLOWITS, J. Polymer Sei. 43: 167, 1960 3. R. W. LENZ, C. E. HAUDLOWITS and W. K. CARRINGTON, U.S. Pat. 3274165, 1966; RZhKhim. 3C229, 1968 4. A. D. MACCALLUM, U.S. Pat. 2513188, 1950; Chem. Abstrs. 8465a, 1950 5. R. W. LENZ a n d W. K. CARRINGTON, J. Polymer Sci. 41: 333, 1959 6. Yu. V. KORYAKIN, Chistyye khimicheskiye reaktivy (Pure Chemical Reagents). p. 385, GNTI, 1947 7. G. F. WOODS and M. S. DEPT., Chem. Abstrs. 60: 6197a, 1964 8. O. KORCZUUSKI, Ber. 35: 869, 1902