On the polymerization of acetylenic derivatives—XXXVII

European Pol vmer Journal Vol. 17, pp. 689 to 693, 1981 Printed in Great Britain. All rights reserved

0014-3057 81'060689-05202.000 Copyright © 1981 Pergamon Press l.td

ON THE POLYMERIZATION OF ACETYLENIC DERIVATIVES--XXXVII ISOMERIZATION OF POLYARYLACETYLENES THROUGH THEIR CYCLIC HALONIUM IONS

Cis-trans

C. I. SIMIONESCU,Sv. DUMITRESCU,V. PERCEC and M. GR1GORAS "Petru Poni" Institute of Macromolecular Chemistry, 6600 Jassy, Romania (Received 9 October 1980)

Abstract Cyclic halonium ions of high cis polyarylacetylenes were isolated. Pure trans potyarylacetylenes [polyphenylacetylene, poly(:~-ethynylnaphthalene), poly(fl-ethynylnaphthalene), poly(N-ethynylcarbazole), poly(3-ethynylphenanthrene)and poly(9-ethynylanthracene)] were obtained after the halogen was recovered from these compounds.

INTRODUCTION Previous papers reported the synthesis and structural characterization of cis and trans isomers of polyphenylacetylene (PPA) [1, 2], poly(c~-ethynylnaphthalene) (PosEN) [3, 4], poly(/~-ethynylnaphthalene) (P/~EN) (5), poly(N-ethynylcarbazole) (PEC) [6], poly(3-ethynylphenanthrene) (PEP) [7] and poly(9-ethynylanthracene) (PEA) [1,8,9]. Their thermal [10], paramagnetic [ 11, 12] and electrical [ 13] properties depend on polymer configuration which determines the effective conjugation length and polymer crystallinity. In a previous paper [14] we studied the thermal cis-trans isomerization of PPA and showed that it is accompanied by intramolecular cyclization, aromatization and chain scission. Recently Woon and Farona [15] reported the synthesis and some properties of cyclic halonium ions of PPA. This paper refers to a study of cis-trans isomerization of PPA, P~EN, P/3EN, PEC, PEP and PEA through their halonium halide. This method allowed the first synthesis of pure trans polyarylacetylenes. EXPERIMENTAL The cis isomers of polyarylacetylenes were synthesized by the polymerization of the corresponding acetylenic derivatives with Ziegler-Natta catalysts, according to published methods: PPA [2], P~EN [3], P/~EN [5], PEC [6], PEP I-7] and PEA [1]. Only in the case of PPA, the cistrans isomerization was studied for both cis structures i.e. cis-cisoidal (crystalline and insoluble) and cis-transoidal (amorphous and soluble). For the other polymers, only the cis-cisoidal insoluble and crystalline structures were studied. The PEC structure consists of cis-cisoidal and cistransoidal stereoblocks. This polymer is crystalline and insoluble. The cis cisoidal structures of PEP and PEA are insoluble but amorphous. All polyarylacetylenes having a trans-cisoidal structure are amorphous and soluble in aromatic or halogenated solvents. The halogenation reactions were carried out as follows: the solid polymer was added to a 10~o chlorine solution in CC14 (the chlorine content was in excess relative to polymer structure unit). After 24 hr at room temperature, CC14 and chlorine were removed on a rotovapor. The resulting polymer was several times washed with hexane and then 689

dried at room temperature in vacuum. Part of this polymer was then several times washed with acetone to remove the ionic chlorine, and finally vacuum dried. RESULTS AND DISCUSSION It is accepted that the electrophilic halogenation of olefins involves first a cyclic halonium ion intermediate, followed by nucleophilic attack of a second molecule of halogen, always from the back side. When the back side of this halonium ion is sterically blocked, the ionic intermediate can be isolated [15]. The first example of a stabilized bromonium ion was reported by Wynberg et al. [16], who succeeded in isolating the bromonium bromide derivative of adamantylidene adamantane. More recently Woon and Farona [15] reported the second example of stabilized halonium ions, viz. the bromonium bromide and chloronium chloride derivatives of polyphenylacetylene. The halogenation of cis isomers of a few polyarylacetylenes led to cyclic halonium ions of the corresponding polymers also. The halogen addition to the conjugated double bonds was reversible. When treated with acetone, recovery of the parent polymer was achieved, but it had a trans structure. The halogenations carried out with large excess of chlorine in CC14 and long reaction times (24 hr) take place in two steps, viz. cyclic ion formation and substitution of chlorine in the aromatic pendant groups of the polyarylacetylenes. The halonium halide structures were indicated by the comparison of the elemental composition of the halogenated product with that of the polymer recovered by acetone treatment. The chlorine content decrease after acetone treatment (Table 1), indicating cyclic halonium ion formation. The unremoved chlorine of the polymer provides evidence for the covalent bonded chlorine. Assuming all the unremoved chlorine is covalently bonded to aromatic polymer rings, the average formulae of halogenated polymers were obtained by elemental analysis. The ionic halogen was also found (Table 1~. As shown in Table 1, by increase of the size of the polyarylacetylene aromatic substituent (i.e. by increase of the

690

C.I. SIMIONESCUet al.

Table 1. Elemental analysis of: (a) chloronium chloride derivatives of cis polyarylacetylenes; and (b) the polymers recovered by acetone treatment of the chloronium chloride derivatives

(a) No. Polymer Structure 1 2 3 4 5 6 7

PPA PPA P~EN PflEN PEC PEP PEA

c-c

c t c-c c-c c-c/c-t c-c c-c

(b)

(a)

(b)

C~

H%

Clio

C~o

H~o

Clio

Formula

Formula

63.18 63.60 61.20 62.70 60.21 66.18 65.21

3.45 3.52 2.65 2.82 2.50 2.70 2.64

33.27 32.60 36.02 34.32 31.80 31.20 31.73

73.92 76.08 67.18 69.38 64.52 70.18 68.02

4.02 4.20 2.92 3.12 2.72 2.90 2.78

21.82 19.70 29.72 27.40 27.22 27.02 29.01

(CaHs.2CI0.a)3.2CI 2 (CaH5.3Clo.7)2.9C12 (CI 2H6.2CIl.a)3.,I.CI 2 (C12H6.4.C11.6)3.2C12 (C14HvNCI2.o)4.0C12 (C16H7.gCI2.1)s.3CI2 (C16HT.TC1/.3)5.aC12

CaHs.2C10.8 CsHs.3Clo.7 C12H6,2C11. a C12H6.4Cll. 6 C14HTNCI2, O C16H7.9C12.1 C16H7.7C12. 3

c-c = ci~cisoidal structure; ~ t = cis-transoidal structure; c-c/c-t = cis-cisoidal/cis-transoidal stereoblocks structure.

steric hindrances due to the substituent volume), there is a reduction in the number of the polymer chain double bonds changed into cyclic chloronium ion. At the same time, due to the decrease of the aromatic character of the substituent, the amount of covalent bonded halogen increases. After ionic chlorine was removed, all the polymers become soluble and amorphous (except for the case of PEA which is not completely soluble) and present a trans-cisoidal structure. This structure was shown by NMR and i.r. spectroscopy. By NMR and chemical analysis, it was verified that the covalent halogen was not obtained by halogen addition at the main chain double bonds. This kind of addition would lead to tertiary labile chlorine. Both the reaction with AgNO3 and with NEts did not show the presence of tertiary chlorine in the halogenated polymers. NMR analysis also did not reveal methinic hydrogen in the polymer chain. The halogen substitution at the aromatic rings was indicated in all cases by i.r. spectroscopy, and also by u.v. spectroscopy in the case of PEA. The cis-cisoidal (insoluble) and cis-transoidal (soluble) PPA structures show bands characteristic of cis configurations at 630, 735 and 884 cm-1 (Fig. la). The polymers obtained by acetone removal of ionic chlorine are soluble and do not show these bands, but show a new peak at 819cm -1 (Fig. 2a) assigned to 1,4-disubstituted benzene. The i.r. spectra of cis-cisoidal (insoluble and crystalline) P~tEN do not differ significantly from those of the trans-cisoidal amorphous and soluble polymers. After isomerization through cyclic halonium ions, P~EN becomes soluble and shows the band characteristic of 1,2,3,4-tetrasubstituted benzene at 822 cm(Fig. lc, d). The cis-cisoidal (crystalline and insoluble) PflEN shows the band of cis configurations at 900 cm- 1 and bands characteristics of 1,2- and 1,3,4-substituted benzene at 740 crn- ~ and at 900 and 850 cm- 1 respectively. The isomerized polymer is soluble and has no bands at 900 and 850 cm-~ (Fig. 2a, b). The bands at 740 and 814 cm- ~ provide evidence for 1,2-disubstituted and 1,2,3,4-tetrasubstituted benzene. The PEC structure of cis-cisoidal and cis-transoidal stereoblocks shows two bands specific of cis configurations at 880 and 1000cm -1 as well as the bands of 1,2-disubstituted benzene at 720 and 744 cm-1 (Fig. 2c). The cis specific bands disappear after isomerization; the absorption of 1,2-disubsti\

tuted benzene bands decrease and in addition at 791 and 860orn - a the peaks of 1,2,4-trisubstituted benzene appear (Fig, 2d). All these bands confirm the cis-trans isomerization of PEC and the halogenation of carbazole ring in the 3,6-positions. The i.r. spectra of cis-cisoidal structures of PEA and PEP do not differ significantly from those of the trans-cisoidal polymers. The i.r. spectra of the halonium derivatives and of the polymers recovered from halonium derivatives show in both cases halogenation of the aromatic groups. Unisomerized PEA shows the i.r. band characteristic of 9-substituted anthracene (730, 785, 835 and 875 cm-1) (Fig. 3a). After isomerization the polymer has bands characteristic of polysubstituted anthracene (750, 800 and 890cm -1) (Fig. 3b). The anthracene substituted positions after halogenation are 9, 10, 4 and 5. u.v. Absorption spectroscopy presents further evidence for halogenation of anthracene group (Fig. 4). The parent PEA shows the n - n* absorption characteristic of 9-substituted anthracene at 250-394 nm (Fig. 4a). The halogenation of 10 position shifts this absorption up to 410nm (Fig. 4b). After the chlorine was removed from cyclic halonium ions of PEA, the polymer become partially soluble only. This means that the isomerization is not complete, because of the low content of chloronium ions in the polymer (Table 1). The cis-cisoidal PEP shows i.r. characteristics of 3-substituted phenanthrene (740, 800 and 835 cm -a) (Fig. 3c). After isomerization, the polymer becomes soluble and shows a new band (760 era- ') assigned to disubstituted phenanthrene in the 9 and 10 positions (Fig. 3d). The thermal cis-trans isomerization was indicated for all cis polyarylacetylenes by an exothermal maximum in their DSC or DTA curves I10]. Except for PEA, the other polymers obtained from cyclic halonium salts do not show in their DSC curves the exothermal phenomenon of cis-trans thermal isomerization, meaning that they have been completly isomerized through their halonium salts. When the halogenations were carried out with chlorine in amounts less than that added by the conjugated double bonds as cyclic halonium ions, and at low reaction times (under 20 min) only the cis-trans isomerization takes place, without halogenation of the aromatic ring. This fact could be easily confirmed in the case of cis-transoidal PPA. The polymer halogenation was carried out in the NMR sample tube, by successive

On the polymerization of acetylenic derivatives.--XXXVII

691

/

1'

900

850

Io4.

Y,,,,,

1' i

-g f, #

900

800 700 600 Wavenumber, om-1

Fig. 1. i.r. Spectra (KBr pellets) of: (a) cis-cisoidal PPA; (b) trans cisoidal PPA obtained from PPA halonium salts; (c) cis cisoidal P:tEN; and (d) trans-cisoidal P~EN obtained from P~EN halonium salts.

791 I

I

I

I

1000 900 800 700 Wavenum bet cm-I Fig. 2. i.r. Spectra (KBr pellets) of: (a) ciscisoidal PflEN; (b) trans-cisoidal PflEN obtained from PflEN halonium salts; (c) cis-cisoidal/cis-transoidal stereoblocks structure of PEC; and (d) trans-cisoidal PEC obtained from PEC halonium salts.

692

C.I. SIMIONESCUet al.

t-4

35 875

¢.-, ~30

trans isomerization through halonium salts without ring halogenation was also indicated for the eis-cisoidal structures of PosEN and PflEN. On the other hand, increase of the size (and in the same time the reactivity of aromatic groups) of the polymer-pendant aromatic groups makes the formation of cyclic halonium ions competitive with the halogenation of the aromatic ring, even at low chlorine contents. As already shown in previous papers [2, 3, 5, 6-9], the polymerization of arylacetylenes in the presence of Ziegler catalysts, phosphine, arsine and stibine complexes of group VIII transition metals, as well as by thermal polymerization, occurs with cis opening of the triple bond. Trans polymer sequences result from cis-trans thermal isomerization, which takes place especially during the propagation reaction, being initiated and propagated by heat derived from the following sources: (a) unremoved heat of polymerization; (b) a high polymerization temperature (as in thermal or phosphine polymerization); (c) the exothermic process which occurs when the catalytic system is destroyed. At least in the case of PPA, cis-trans thermal isomerization is accompanied by intramolecular cyclization, aromatization and polymer chain scission [11, 14, 17, 18]. These side reactions prevent determination of the real molecular weight of the so-called trans polymer obtained by thermal isomerization of an insoluble cis-cisoidal polymer, and also prevent study of the physical properties of the real trans polymer. The cis-trans isomerization of arylacetylenes through cyclic halonium ions affords the possibility of synthesis of pure trans polymer starting from the corresponding high cis polymers, at least in the cases of PPA, PosEN and PflEN. The electrical properties of the polyarylacetylenes cyclic halonium ions will be presented in another paper.

890 750 I

1000

I

800

~

600

39/.

Wovenumber, cm-~ Fig. 3. i.r. Spectra (KBr pellets) of: (a) cis-cisoidal PEP; and (b) trans-cisoidal PEP obtained from PEP halonium salts.

addition of various amounts of CC1 a chlorine solution (5.4 x 10 -2 tool/l) into the PPA (CC14) solution. The cis--transoidal PPA has 3 protonic resonances centred at 6 = 5.82 ppm (1 cis polyenic proton), 5 = 6.70 ppm (aromatic proton) and 6 = 6.85 ppm (4 aromatic protons) (Fig. 5) [2]. The cis content of the studied PPA, by a published method [2], is 92%. As shown in Fig. 5, by increasing the amount of chlorine added to the PPA solution, the area of the 5 = 5.82 ppm signal decreases. The decrease of PPA cis content, as a function of amount of chlorine in solution, is given in Fig. 6, where the initial cis content is considered to be 100%. The resulting polymer was precipitated with hexane; after washing with acetone, the i.r. spectrum showed the benzene ring is monosubstituted. The cis-

2,0 2' 0

L

275

300

I

325

I

350

LO0

I

450

Wavelength, nm

Fig. 4. U.V. absorption spectra (CHCIs solution) of: (a) trans-cisoidal PEA obtained by thermal isomerization of cis-cisoidal PEA; and (b) trans-cisoidal PEA obtained from PEA halonium salts.

On the polymerization of acetylenic derivatives--XXXVll

693

Ioo 9o 8C -to

N6o ~ 5c

g U

4£

u

~c 2£ I¢ o

i Chlorine ,tool %

Fig. 6. Decrease of the PPA cis content as a function of added chlorine (sample presented in Fig. 5).

4. 5. 6. 7.

8. 9. 10. I

I

i

8

7

6

5

B, ppm Fig. 5

Fig. 5. [~ H ] N M R spectra (CC14, HMDS) of cis-transoidal PPA (920/0 initial cis content) solution with various chlorine contents.

11.

12. 13. 14.

R EFERENCES

15.

1 C. I. Simionescu, S. Dumitrescu, I. Negulescu, V. Percec, M. Grigora~, I. Diaconu, M. Leanc~ and L. Gora~, Vysokomolek. Soedin. A-16, 790 (1974) (English transl. Polym. Sci. U.S.S.R. A-16, 911 (1974). 2. C. I. Simionescu, V. Percec and S. Dumitrescu, d. Polym. Sci. Polym. Chem. Ed. 15, 2497 0977). 3. C. I. Simionescu, S. Dumitrescu, V. Percec, I. Negulescu and I. Diaconu, International Symposium on Mac-

16. 17. 18.

romolecules (Edited by O. Harva and C. G. Overberger), p. 201. Wiley, New York (1973). C. I. Simionescu, S. Dumitrescu and V. Percec, Polym. J. 8, 313 (1976). C. I. Simionescu, S. Dumitrescu and V. Percec, Polym. J. 8, 139 (1976). S. Dumitrescu, V. Percec and C. I. Simionescu, J. Polym. Sci. Polym. Chem. Ed. 15, 2893 (1977). C. I. Simionescu, S. Dumitrescu, M. Grigora~ and I. Diaconu, International Symposium on Macromolecules, Madrid. Preprint I. 5-14 (1974); C. I. Simionescu, S. Dumitrescu and M. Grigora~, Eur. Polvm. J. 14, 1051 (1978). C. I. Simionescu, S. Dumitrescu, M. Grigora~ and I. Negulescu, 4th Symposium on Polymers, Varna, 4-6 October. Preprints I. 5-13 (1973). C. I. Simionescu, S. Dumitrescu, M. Grigora~ and I. Negulescu, J. Macromolec. Sci.-Chem. A13, 203 (1979). C. I. Simionescu, S. Dumitrescu, V. Percec and M. Grigora~, Rev. roum. Chim. 22, 1105 (1977). C. I. Simionescu, S. Dumitrescu and V. Percec, S. R. Romania-U.S.A. Seminar on Polymer Chemistry (Edited by O. Vogl and C. I. Simionescu), p. 209. Wiley, New York (1978). S. Dumitrescu, V. Percec and C. I. Simionescu, Rev. roum, Chim. 23, 1303 (1978). V. Percec, G. Ioanid, S. Dumitrescu and C. I. Simionescu, Plaste Kautch. 25, 222 (1978). C. I. Simionescu and V. Percec, J. Polym. Sci. Polym. Chem. Ed. 18, 147 (1980). P. S. Woon and M. F. Farona, J. Polym. Sci. Polym. Lett. Ed. 13, 567 (1975). J. Strating, J. H. Wieringa and H. Wynberg, J. ('hem. Soc. Chem. Commun. 907 (1969). C. I. Simionescu and V. Percec, J. Polym. Sci. Polym. Lett. Ed. 17, 421 (1979). C. I. Simionescu and V. Percec, Main lecture presented at International Symposium on Macromolecular Chemistry, Tashkent, 17-21 October, Abstracts, Vol. I, p. 71 (1978) J. Polym. Sci. Polym. Syrup. Ed. 67, 43 (1980).