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Synthesis of polyphenylmethine by dechlorination of benzene trichloride
SYNTHESIS OF POLYPHENYLMETHINE BY DECHLORINATION OF B E N Z E N E TRICHLORIDE* Yr. G. KRYAZHEV, V. B. PETRINSKA and E. I. BRODSKAYA Ir k u t s k Institute of Organic Chemistry, Siberian Section of the U.S.S.R. Academy of Sciences
(Received 16 July
1968)
T ~ polycondensation of compounds containing three labile substituents on the same carbon a t o m or with two labile substituents on each of two contiguous carbon atoms can in principle result in formation of polyenes, as indicated by the following general equation: Y
X
n X--C--X-4- n Y--~--Y
I
I
R
\RR]~
R Y X
,
,
n X--C--C---Y R The suggested formation of polyenes and not crosslinked polymers with saturated chains by polycondensation of such polyfunctional compounds should be favoured by the following factors: 1) The gain in energy as a result of formation of a conjugated system. 2) A higher rate of intramolecular elimination in the growing chain, in comparison with condensation, which must ensure rapid removal of side groups t h a t could be involved in branching and crosslinking of the polymer molecules, for example r . . . . .
-~lo
I
if" . . . . . . .
X~ - ~ - X
"1o
+ Y
.........
..,
. _ ~r . . . .
,¥
....
-~ . . . .
"It" .......
L
- -
"t
J
---~ . . - - C - - C - - - C - - C . . . . . --~
C=C--C=C ....
Dilution of the reaction mixture and the presence of fairly bulky substituents R, creating steric hindrance to chain branching, produce a favourable ratio of intra- to intermolecular elimination. 3) When complexing agents are present--suitable orientation of the molecules undergoing orientation and additional gain in energy due to complex formation with the growing polyene chain, which is very susceptible to donor-aceeptor interactions. I t has
* Vysokomol. soyed. A l l : No. 12, 2609-2614, 1969.
2964
Synthesis of polyphenylmethine
2965
been shown in a number of papers (reference [1] for example) that complex formation can have a decisive effect on the course of a polymerization reaction. The above observations give grounds for hoping that the suggested principle of polycondensation with formation of polyenes ("polyene condensation") will prove to be a fruitful and convenient method for preparation of polymers with a system of conjugated double bonds. As an illustration of the possibilities opened up b y polyene condensation we present in this paper results obtained from dechlorination of benzyl trichloride (phenyltrichloromethane) (BTC), which b y polyene condensation produces polypehenylmethine (PPM), with the same structure as the already known polytolane [2], which is the polymer formed from diphenylacetylene:
oo,.
-7 °-)
As a dechlorinating agent we used metallic lithium in tetrahydrofuran (THF). The choice of reactants was dictated b y the desire to satisfy to the greatest possible extent the conditions enumerated above for predominance of polyene condensation, i.e. b y the complex-forming tendency of lithium T H F and the organolithium compounds formed as intermediates in dechlorination, b y conducting the reaction in solution and as a result of the large bulk of the phenyl radical. These factors do not of course completely eliminate the possibility of formation of branched structures, but study of the structure of the P P M obtained confirms its identity with polytolane and shows that it is not branched to any significant extent. The reaction of lithium with BTC in T H F at temperatures from --7 to ÷ 60 ° produces in yields of 80-85~o (of theory) light- or reddish-brown polymers, which, like polytolane, are soluble in benzene, CC14, ChC13, dioxan, T H F and other organic solvents, and insoluble in aliphatic hydrocarbons and alcohols. These products of polyene condensation are however only partially soluble in ether and acetone, which are solvents for polytolane. This is evidently a result of the higher molecular weight of our polymers (Table). These polymers give the E P R signal characteristic of polyenes, namely a narrow singlet, corresponding to a concentration of unpaired electrons of 1017_101s g - 1, and they have an electrical conductivity of 10-14-10-15 o h m - 1 cm- 1 at 20 °, with an energy of activation for conductivity of 1.5-2.0 eV. The infrared spectra of all the samples of P P M (Fig. 1) are almost identical with the spectrum of polytolane [2]. The slight differences (the appearance of some new bands not present in the spectrum of polytolane), due to side reactions, will be explained below. The spectra do not show the background of absorption in the 700-1800 cm -1 region characteristic of branched polyconjugated structures [4].
2966
Y u . G. KRYAZHEV et al.
I n order t o o b t a i n P P M with a deliberately p r o d u c e d b r a n c h e d s t r u c t u r e 50 moles ~ of CC14, calculated on the BTC, was a d d e d to the reaction mixture. T h e s p e c t r u m o f t h e resulting polymer, which was soluble a n d practically identical in e l e m e n t a r y composition, electrical c o n d u c t i v i t y a n d E P R signal with the p r o d u c t of h o m o p o l y c o n d e n s a t i o n o f BTC, contains t h e b a c k g r o u n d o f a b r a n c h e d structure. The ultraviolet s p e c t r u m of PPI~I is similar to t h a t of polytolane, w i t h t h e b a t h o c h r o m i c shift characteristic of polyenes with superposition of t h e a b s o r p t i o n of the benzene ring a t a b o u t 240 m/l. I n contrast to polytolane, which gives practically no absorption b e y o n d 400 m/~, the a b s o r p t i o n region of P P M e x t e n d s to 500 m/~. Thus the average length o f the c o n j u g a t e d sequences in P P M is n o t less, b u t is possibly greater, t h a n polytolane [5]. I t is obvious t h a t if the P P M h a d a highly b r a n c h e d structure, which would preclude a high p r o p o r t i o n of polyene blocks of this length, the ultraviolet s p e c t r u m should contain a sharp m a x i m u m a t 240-260 m/l, corresponding to absorption b y the benzene ring, w i t h o u t a welldefined b a t h o c h r o m i e shift. I t is seen from the d a t a p r e s e n t e d in the Table t h a t polyene condensation o f B T C in the presence of lithium gives a high yield of polymer. R e m o v a l of CHARACTERISTICS OF POLYMERS OBTAINED BY DECHLORII~'ATIOI~ OF CONDITIONS
BTC
UNDER VARIOUS
(Experiments 1-8 were carried out in an atmosphere of nitrogen containing 0.5~z~ of 02, and experiments 9 and 10 in argon) Experimental conditions EXl~v.
No. 1
2 3
temperature, °C --
7
reaction time, [ / br 6
Product of ex )t. 1, subsequently kept for 14 hr at 20° 2O 1
4
20
2
5
20
3
6
20
4
7
20
5
8
20
20
9
10
20 20
Elementary composition I
5 20
C
I-I
C1
82"89 90.53 90.25 85.78 85.42 86.21 86-68 90.35 90"20 91-56 91.11 90.35 90.47 89"44 89-62 92"48 92-20 90.38 90.07
5.17 5.97 5.88 4.96 4.86 5.74 5.37 5.70 5.97 5.60 5-81 6"07 5-90 5.63
10.30 10-49 Trace 4.71 4.58 3.28 3.24 1.21 0.83 Trace
5.99 5.94
5.88 6.04 6.03
theory, % 62 80
5500 9000
31
3200
62
5000
76
6500
83
8000
85
8000
86
8000
83
9000
83
12,000
Synthesis of poIyphenylmethine
2967
samples during the course of reaction revealed the increase in molecular weight with time, characteristic of a polycondensation reaction. The reaction is practically complete in 4 hr at 20 °, and after that time no significant increase in the yield or molecular weight of the polymer occurs. An the polymers in the Table show an increase in the diffuseness of the infrared spectrum with increase in molecular weight. The degree of dechlorination is strongly dependent on the reaction temperature. Whereas the polymer contains only ~ 5 % of chlorine after 1 hr at 20 °, after 6 hr at --7 ° it contains more than 10% of chlorine, which corresponds on the average to two atoms of chlorine to every seven carbon atoms in the polymer chain. I f this polymer is kept in contact with lithium in T H F at room temperature almost complete dechlorination of the polymer occurs, with simultaneous increase in molecular weight• Thus further treatment of the polymer with lithium causes further condensation of the polymer molecules and intramolecular dechlorination. Experiments 3-6 show that the same processes occur in the polycondensation o f BTC at 20 °. The formation of P P M can involve various intermediate stages:
~
3
LI -CIx~ +C6H5CCI3
oCo
• "--CCI
CCt,7--C CI 2
CCI
CCI
CCI. . . .
CC!~CCI
....
C
C
C
'C
':",-'C
C. . . .
The possibility of formation of P P M as a result of polymerization of diphenylacetylene can be eliminated because it was shown b y separate experiments t h a t diphenylacetylene does not polymerize in T H F in the presence of lithium, or when the lithium-BTC or lithium-BTC-PPl~I systems are present. Polycondensation of dichlorophenylethylene cannot be the main reaction route, because b y this route the formation of products of high molecular weight with relatively high chlorine content, as occurs at low temperatures or in the early stages of the process, would be impossible. Under the given conditions one might expect the formation and polymerization o f phenylchloroearbene [6], b u t the increase in molecular weight with time indicates the predominance of polycondensation of BTC or of carbene oligomers
2968
Yu. G. K-RYAZHEVet al.
b y the Wurtz reaction, with parallel intramolecular dechlorination of the polymer molecules with formation of polyene blocks. In view of the fact that dechlorination b y lithium involves the substitution of lithium for chlorine [4] the reaction system must contain polymer molecules containing lithium. It is well known that organolithium compounds readily combine with oxygen and C02, to form the corresponding alcohols and carbonyl compounds, and b y means of water or an alcohol the lithium can be replaced b y hydrogen. Side reactions of this kind during polymerization and isolation
~0o [
.~ 20
gO 0
i _
3200
I
2800 2000
I
l
1600
r
~
1200
,
1
800 %),ore-/
FTG. 1. Infrared spectra of polymers:/--experiment 7, 2--experiment 9 (see Table).
of the polymer provide an obvious explanation of the slight deviation of the results of micro-analysis from the calculated composition, and the presence in the infrared spectrum of P P M of the bands at 1680 and 1720 cm -1 assigned to the C = 0 group, and in the 2800-3000 cm -1 region, characteristic of CH in saturated hydrocarbon groups. The presence of the latter is obviously also due to retention of a certain amount of T H F in the polymer as a result of complex formation or of addition of T H F to the organolithium groups at the ether bond [7]. This is confirmed b y the presence in the spectrum of P P M of a weak, broad maximum corresponding to the C - - O - - C group in the 1000-1300 cm -1 region. The suggestion that the intermediate organolithium polymer reacts with impurities in the system is confirmed b y the higher molecular weight, lower oxygen content and absence of C = O groups from polymers prepared in an atmosphere of argon with no access of air and under conditions in which the polymer pr6cipitates (see experiment 9 and Fig. 1). The spectrum of P P M clearly shows the bands of the skeletal vibrations of the benzene ring at 1445 and 1495 cm -1 (Fig. 1). However, the ratio of the intensities of these bands varies with reaction time. This is explained b y superposition of the vibrations of saturated hydrocarbon groups on the 1445 em -x band. Hence the ratio of the intensities of these bands can be used to estimate the relative proportions of the above-mentioned groups in the polymer. It is seen
Synthesis of polyphenylmethine
2969
f r o m Fig. 2 t h a t the c o n t e n t o f s a t u r a t e d C H g r o u p s passes t h r o u g h a m i n i m u m d u r i n g t h e course of the reaction. T h e initial fall in this q u a n t i t y is explained b y decrease in the q u a n t i t y of lithium c o m b i n e d in t h e polymers, as a result
0.9( 0,
07
06
~
3
J
51 T/me
I~
201 , hp
Fie. 2. Variation in the quantity of saturated CH groups in the polymer during polyene condensation of BTC. DI and D2 are the optical densities of the absorption bands at 1445 and 1495 em -1 respectively. of intra- a n d intermolecular elimination o f Li. The s u b s e q u e n t increase in t h e c o n t e n t of s a t u r a t e d g r o u p s is e v i d e n t l y due to addition of T H F . EXPERIMENTAL Benzyl trichloride, chemically pure grade, was redistilled in vacuo before use, n~ 1.5584,
m.p. 4-75% b.p. 221 °. Tetrahydrofuran, was dehydrated over sodium and redistilled immediately before use. Preparation of polyphenylmethine. Five hundred millilitres of THF and 98 g of BTC
were placed in a four-necked flask, provided with a stirrer, gas inlet tube and thermometer. After nitrogen (or argon) had been blown through the mixture for 15 min and the chosen temperature had been reached, freshly prepared lithium turnings were added in portions such that the temperature of the reaction mixture did not exceed the desired temperature, the system being continuously swept out with nitrogen (argon). All the required amount of lithium (I1 g) was added within a period of 1 hr. Stirring was continued for 5-6 hr and 25 ml samples were removed at regular intervals. The polymer was precipitated by methanol, purified by five reprecipitations from dioxan by methanol and dried in vacuo at 40 °. The electrical conductivity of the polymers was measured in vacuo (10-8 mm) by means of a U-l-2 amplifier at 50 V. The samples were compressed in a quartz capillary under a pressure of 1000 kg/cm 2. The molecular weight was determined by the thermoelectric method [8], from the VPO temperature maximum in solutions of the polymers in chloroform, using MT-54 thermistors and a precision of thermostatic control of ! 0"005°. The infrared spectra were recorded in a UR-10 spectrophotometer, with specimens in the form of pellets of the polymers compressed with KBr (5 mg in 400 mg of KBr). CONCLUSIONS (l) B y t h e e x a m p l e o f t h e dechlorination of benzyl trichloride b y lithium in t e t r a h y d r o f u r a n it is s h o w n t h a t it is possible t o prepare polyenes b y poly-
2970
S . G . ENTELIS et a/.
condensation of compounds containing three labile substituents on the same carbon atom. (2) Soluble polyphenylmethine, with a structure and properties similar to •those of the polymer from diphenylaeetylene, was obtained. The yield and molecular weight of the polymer obtained by polycondensation of benzoyl trichloride are considerably higher than those of the polymer from diphenylacetylene. Translated by E. O. PHILLIPS REFERENCES 1. V. A. KABANOV and V. P. ZUBOV, ZhVKhO im. Mendeleyeva 7: 131, 1962 2. P. P. KISILITSA, M. I. CHERKASHIN and A. A. BERLIN, Izv. Akad. N a u k SSSR, set. khim., 1959, 1967 3. O. Yu. OKHLOBYSTIN, Uspekhi khimii 36: 34, 1967 4. Yu. Sh. MOSHKOVSKII, N. D. KOSTROVA and A. A. BERLIN, Vysokomol. soyed. 3: 1969, 1961 (Translated in Polymer Sci. U.S.S.R. 3: 6, 1057, 1962) 5. I. A. DRABKIN, V. I. TSARYUK, M. I. CHERKASHIN, P. P. KISILITSA, M. G. CHAUSER, A. N. CHIGIR' and A. A. BERLIN, Vysokomol. soyed. A10: 1727, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 8, 1998, 1968) 6. 0. M. NEFEDOV and V. I. SHIRYAYEV, Zh. obshch, khim. 37: 1223, 1967 7. K. A. KOCHESHKOV and T. V. TALALAYEVA, Sinteticheskie m e t o d y v oblasti metal. loorganicheskikh soyedinenii litiya, natriya, kaliya, rubidiya i tseziya (Synthetic Methods in the Field of Organometallic Compounds of Lithium, Sodium, Potassium, Rubidium and Caesium). Izd. Akad. N a u k SSSR, 1949 8. Ye. Yu. BEKHLI, D. D. NOVIKOV and S. G. ENTELIS, Vysokomol. soyed. AP: 2754, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 12, 3117, 1967)
ANALYSIS OF COPOLYMER COMPOSITION BY INFRARED SPECTROPHOTOMETRY* S. G. ENTELIS, E. F. VAINSHTEINand I. V. KUI~rANENKO Institute of Chemical Physics, U.S.S.R. A c a d e m y of Sciences
(Received 10 October 1968)
VARIOUSmethods, such as infrared spectroscopy, radiospectroscopy etc., are used for determining the composition of copolymers. Infrared spectrophotometrie methods of analysis are the most universal, but extensive application of these involves difficulties in the decipherment of the spectra of copolymers, which is usually done by analysis of the spectra of the corresponding homopolymers. Therefore, even for ethylene-propylene copolymers, which have received through * Vysokomol. soyed. A l l : No. 12, 2615-2623, 1969.
(Received 16 July
1968)
T ~ polycondensation of compounds containing three labile substituents on the same carbon a t o m or with two labile substituents on each of two contiguous carbon atoms can in principle result in formation of polyenes, as indicated by the following general equation: Y
X
n X--C--X-4- n Y--~--Y
I
I
R
\RR]~
R Y X
,
,
n X--C--C---Y R The suggested formation of polyenes and not crosslinked polymers with saturated chains by polycondensation of such polyfunctional compounds should be favoured by the following factors: 1) The gain in energy as a result of formation of a conjugated system. 2) A higher rate of intramolecular elimination in the growing chain, in comparison with condensation, which must ensure rapid removal of side groups t h a t could be involved in branching and crosslinking of the polymer molecules, for example r . . . . .
-~lo
I
if" . . . . . . .
X~ - ~ - X
"1o
+ Y
.........
..,
. _ ~r . . . .
,¥
....
-~ . . . .
"It" .......
L
- -
"t
J
---~ . . - - C - - C - - - C - - C . . . . . --~
C=C--C=C ....
Dilution of the reaction mixture and the presence of fairly bulky substituents R, creating steric hindrance to chain branching, produce a favourable ratio of intra- to intermolecular elimination. 3) When complexing agents are present--suitable orientation of the molecules undergoing orientation and additional gain in energy due to complex formation with the growing polyene chain, which is very susceptible to donor-aceeptor interactions. I t has
* Vysokomol. soyed. A l l : No. 12, 2609-2614, 1969.
2964
Synthesis of polyphenylmethine
2965
been shown in a number of papers (reference [1] for example) that complex formation can have a decisive effect on the course of a polymerization reaction. The above observations give grounds for hoping that the suggested principle of polycondensation with formation of polyenes ("polyene condensation") will prove to be a fruitful and convenient method for preparation of polymers with a system of conjugated double bonds. As an illustration of the possibilities opened up b y polyene condensation we present in this paper results obtained from dechlorination of benzyl trichloride (phenyltrichloromethane) (BTC), which b y polyene condensation produces polypehenylmethine (PPM), with the same structure as the already known polytolane [2], which is the polymer formed from diphenylacetylene:
oo,.
-7 °-)
As a dechlorinating agent we used metallic lithium in tetrahydrofuran (THF). The choice of reactants was dictated b y the desire to satisfy to the greatest possible extent the conditions enumerated above for predominance of polyene condensation, i.e. b y the complex-forming tendency of lithium T H F and the organolithium compounds formed as intermediates in dechlorination, b y conducting the reaction in solution and as a result of the large bulk of the phenyl radical. These factors do not of course completely eliminate the possibility of formation of branched structures, but study of the structure of the P P M obtained confirms its identity with polytolane and shows that it is not branched to any significant extent. The reaction of lithium with BTC in T H F at temperatures from --7 to ÷ 60 ° produces in yields of 80-85~o (of theory) light- or reddish-brown polymers, which, like polytolane, are soluble in benzene, CC14, ChC13, dioxan, T H F and other organic solvents, and insoluble in aliphatic hydrocarbons and alcohols. These products of polyene condensation are however only partially soluble in ether and acetone, which are solvents for polytolane. This is evidently a result of the higher molecular weight of our polymers (Table). These polymers give the E P R signal characteristic of polyenes, namely a narrow singlet, corresponding to a concentration of unpaired electrons of 1017_101s g - 1, and they have an electrical conductivity of 10-14-10-15 o h m - 1 cm- 1 at 20 °, with an energy of activation for conductivity of 1.5-2.0 eV. The infrared spectra of all the samples of P P M (Fig. 1) are almost identical with the spectrum of polytolane [2]. The slight differences (the appearance of some new bands not present in the spectrum of polytolane), due to side reactions, will be explained below. The spectra do not show the background of absorption in the 700-1800 cm -1 region characteristic of branched polyconjugated structures [4].
2966
Y u . G. KRYAZHEV et al.
I n order t o o b t a i n P P M with a deliberately p r o d u c e d b r a n c h e d s t r u c t u r e 50 moles ~ of CC14, calculated on the BTC, was a d d e d to the reaction mixture. T h e s p e c t r u m o f t h e resulting polymer, which was soluble a n d practically identical in e l e m e n t a r y composition, electrical c o n d u c t i v i t y a n d E P R signal with the p r o d u c t of h o m o p o l y c o n d e n s a t i o n o f BTC, contains t h e b a c k g r o u n d o f a b r a n c h e d structure. The ultraviolet s p e c t r u m of PPI~I is similar to t h a t of polytolane, w i t h t h e b a t h o c h r o m i c shift characteristic of polyenes with superposition of t h e a b s o r p t i o n of the benzene ring a t a b o u t 240 m/l. I n contrast to polytolane, which gives practically no absorption b e y o n d 400 m/~, the a b s o r p t i o n region of P P M e x t e n d s to 500 m/~. Thus the average length o f the c o n j u g a t e d sequences in P P M is n o t less, b u t is possibly greater, t h a n polytolane [5]. I t is obvious t h a t if the P P M h a d a highly b r a n c h e d structure, which would preclude a high p r o p o r t i o n of polyene blocks of this length, the ultraviolet s p e c t r u m should contain a sharp m a x i m u m a t 240-260 m/l, corresponding to absorption b y the benzene ring, w i t h o u t a welldefined b a t h o c h r o m i e shift. I t is seen from the d a t a p r e s e n t e d in the Table t h a t polyene condensation o f B T C in the presence of lithium gives a high yield of polymer. R e m o v a l of CHARACTERISTICS OF POLYMERS OBTAINED BY DECHLORII~'ATIOI~ OF CONDITIONS
BTC
UNDER VARIOUS
(Experiments 1-8 were carried out in an atmosphere of nitrogen containing 0.5~z~ of 02, and experiments 9 and 10 in argon) Experimental conditions EXl~v.
No. 1
2 3
temperature, °C --
7
reaction time, [ / br 6
Product of ex )t. 1, subsequently kept for 14 hr at 20° 2O 1
4
20
2
5
20
3
6
20
4
7
20
5
8
20
20
9
10
20 20
Elementary composition I
5 20
C
I-I
C1
82"89 90.53 90.25 85.78 85.42 86.21 86-68 90.35 90"20 91-56 91.11 90.35 90.47 89"44 89-62 92"48 92-20 90.38 90.07
5.17 5.97 5.88 4.96 4.86 5.74 5.37 5.70 5.97 5.60 5-81 6"07 5-90 5.63
10.30 10-49 Trace 4.71 4.58 3.28 3.24 1.21 0.83 Trace
5.99 5.94
5.88 6.04 6.03
theory, % 62 80
5500 9000
31
3200
62
5000
76
6500
83
8000
85
8000
86
8000
83
9000
83
12,000
Synthesis of poIyphenylmethine
2967
samples during the course of reaction revealed the increase in molecular weight with time, characteristic of a polycondensation reaction. The reaction is practically complete in 4 hr at 20 °, and after that time no significant increase in the yield or molecular weight of the polymer occurs. An the polymers in the Table show an increase in the diffuseness of the infrared spectrum with increase in molecular weight. The degree of dechlorination is strongly dependent on the reaction temperature. Whereas the polymer contains only ~ 5 % of chlorine after 1 hr at 20 °, after 6 hr at --7 ° it contains more than 10% of chlorine, which corresponds on the average to two atoms of chlorine to every seven carbon atoms in the polymer chain. I f this polymer is kept in contact with lithium in T H F at room temperature almost complete dechlorination of the polymer occurs, with simultaneous increase in molecular weight• Thus further treatment of the polymer with lithium causes further condensation of the polymer molecules and intramolecular dechlorination. Experiments 3-6 show that the same processes occur in the polycondensation o f BTC at 20 °. The formation of P P M can involve various intermediate stages:
~
3
LI -CIx~ +C6H5CCI3
oCo
• "--CCI
CCt,7--C CI 2
CCI
CCI
CCI. . . .
CC!~CCI
....
C
C
C
'C
':",-'C
C. . . .
The possibility of formation of P P M as a result of polymerization of diphenylacetylene can be eliminated because it was shown b y separate experiments t h a t diphenylacetylene does not polymerize in T H F in the presence of lithium, or when the lithium-BTC or lithium-BTC-PPl~I systems are present. Polycondensation of dichlorophenylethylene cannot be the main reaction route, because b y this route the formation of products of high molecular weight with relatively high chlorine content, as occurs at low temperatures or in the early stages of the process, would be impossible. Under the given conditions one might expect the formation and polymerization o f phenylchloroearbene [6], b u t the increase in molecular weight with time indicates the predominance of polycondensation of BTC or of carbene oligomers
2968
Yu. G. K-RYAZHEVet al.
b y the Wurtz reaction, with parallel intramolecular dechlorination of the polymer molecules with formation of polyene blocks. In view of the fact that dechlorination b y lithium involves the substitution of lithium for chlorine [4] the reaction system must contain polymer molecules containing lithium. It is well known that organolithium compounds readily combine with oxygen and C02, to form the corresponding alcohols and carbonyl compounds, and b y means of water or an alcohol the lithium can be replaced b y hydrogen. Side reactions of this kind during polymerization and isolation
~0o [
.~ 20
gO 0
i _
3200
I
2800 2000
I
l
1600
r
~
1200
,
1
800 %),ore-/
FTG. 1. Infrared spectra of polymers:/--experiment 7, 2--experiment 9 (see Table).
of the polymer provide an obvious explanation of the slight deviation of the results of micro-analysis from the calculated composition, and the presence in the infrared spectrum of P P M of the bands at 1680 and 1720 cm -1 assigned to the C = 0 group, and in the 2800-3000 cm -1 region, characteristic of CH in saturated hydrocarbon groups. The presence of the latter is obviously also due to retention of a certain amount of T H F in the polymer as a result of complex formation or of addition of T H F to the organolithium groups at the ether bond [7]. This is confirmed b y the presence in the spectrum of P P M of a weak, broad maximum corresponding to the C - - O - - C group in the 1000-1300 cm -1 region. The suggestion that the intermediate organolithium polymer reacts with impurities in the system is confirmed b y the higher molecular weight, lower oxygen content and absence of C = O groups from polymers prepared in an atmosphere of argon with no access of air and under conditions in which the polymer pr6cipitates (see experiment 9 and Fig. 1). The spectrum of P P M clearly shows the bands of the skeletal vibrations of the benzene ring at 1445 and 1495 cm -1 (Fig. 1). However, the ratio of the intensities of these bands varies with reaction time. This is explained b y superposition of the vibrations of saturated hydrocarbon groups on the 1445 em -x band. Hence the ratio of the intensities of these bands can be used to estimate the relative proportions of the above-mentioned groups in the polymer. It is seen
Synthesis of polyphenylmethine
2969
f r o m Fig. 2 t h a t the c o n t e n t o f s a t u r a t e d C H g r o u p s passes t h r o u g h a m i n i m u m d u r i n g t h e course of the reaction. T h e initial fall in this q u a n t i t y is explained b y decrease in the q u a n t i t y of lithium c o m b i n e d in t h e polymers, as a result
0.9( 0,
07
06
~
3
J
51 T/me
I~
201 , hp
Fie. 2. Variation in the quantity of saturated CH groups in the polymer during polyene condensation of BTC. DI and D2 are the optical densities of the absorption bands at 1445 and 1495 em -1 respectively. of intra- a n d intermolecular elimination o f Li. The s u b s e q u e n t increase in t h e c o n t e n t of s a t u r a t e d g r o u p s is e v i d e n t l y due to addition of T H F . EXPERIMENTAL Benzyl trichloride, chemically pure grade, was redistilled in vacuo before use, n~ 1.5584,
m.p. 4-75% b.p. 221 °. Tetrahydrofuran, was dehydrated over sodium and redistilled immediately before use. Preparation of polyphenylmethine. Five hundred millilitres of THF and 98 g of BTC
were placed in a four-necked flask, provided with a stirrer, gas inlet tube and thermometer. After nitrogen (or argon) had been blown through the mixture for 15 min and the chosen temperature had been reached, freshly prepared lithium turnings were added in portions such that the temperature of the reaction mixture did not exceed the desired temperature, the system being continuously swept out with nitrogen (argon). All the required amount of lithium (I1 g) was added within a period of 1 hr. Stirring was continued for 5-6 hr and 25 ml samples were removed at regular intervals. The polymer was precipitated by methanol, purified by five reprecipitations from dioxan by methanol and dried in vacuo at 40 °. The electrical conductivity of the polymers was measured in vacuo (10-8 mm) by means of a U-l-2 amplifier at 50 V. The samples were compressed in a quartz capillary under a pressure of 1000 kg/cm 2. The molecular weight was determined by the thermoelectric method [8], from the VPO temperature maximum in solutions of the polymers in chloroform, using MT-54 thermistors and a precision of thermostatic control of ! 0"005°. The infrared spectra were recorded in a UR-10 spectrophotometer, with specimens in the form of pellets of the polymers compressed with KBr (5 mg in 400 mg of KBr). CONCLUSIONS (l) B y t h e e x a m p l e o f t h e dechlorination of benzyl trichloride b y lithium in t e t r a h y d r o f u r a n it is s h o w n t h a t it is possible t o prepare polyenes b y poly-
2970
S . G . ENTELIS et a/.
condensation of compounds containing three labile substituents on the same carbon atom. (2) Soluble polyphenylmethine, with a structure and properties similar to •those of the polymer from diphenylaeetylene, was obtained. The yield and molecular weight of the polymer obtained by polycondensation of benzoyl trichloride are considerably higher than those of the polymer from diphenylacetylene. Translated by E. O. PHILLIPS REFERENCES 1. V. A. KABANOV and V. P. ZUBOV, ZhVKhO im. Mendeleyeva 7: 131, 1962 2. P. P. KISILITSA, M. I. CHERKASHIN and A. A. BERLIN, Izv. Akad. N a u k SSSR, set. khim., 1959, 1967 3. O. Yu. OKHLOBYSTIN, Uspekhi khimii 36: 34, 1967 4. Yu. Sh. MOSHKOVSKII, N. D. KOSTROVA and A. A. BERLIN, Vysokomol. soyed. 3: 1969, 1961 (Translated in Polymer Sci. U.S.S.R. 3: 6, 1057, 1962) 5. I. A. DRABKIN, V. I. TSARYUK, M. I. CHERKASHIN, P. P. KISILITSA, M. G. CHAUSER, A. N. CHIGIR' and A. A. BERLIN, Vysokomol. soyed. A10: 1727, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 8, 1998, 1968) 6. 0. M. NEFEDOV and V. I. SHIRYAYEV, Zh. obshch, khim. 37: 1223, 1967 7. K. A. KOCHESHKOV and T. V. TALALAYEVA, Sinteticheskie m e t o d y v oblasti metal. loorganicheskikh soyedinenii litiya, natriya, kaliya, rubidiya i tseziya (Synthetic Methods in the Field of Organometallic Compounds of Lithium, Sodium, Potassium, Rubidium and Caesium). Izd. Akad. N a u k SSSR, 1949 8. Ye. Yu. BEKHLI, D. D. NOVIKOV and S. G. ENTELIS, Vysokomol. soyed. AP: 2754, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 12, 3117, 1967)
ANALYSIS OF COPOLYMER COMPOSITION BY INFRARED SPECTROPHOTOMETRY* S. G. ENTELIS, E. F. VAINSHTEINand I. V. KUI~rANENKO Institute of Chemical Physics, U.S.S.R. A c a d e m y of Sciences
(Received 10 October 1968)
VARIOUSmethods, such as infrared spectroscopy, radiospectroscopy etc., are used for determining the composition of copolymers. Infrared spectrophotometrie methods of analysis are the most universal, but extensive application of these involves difficulties in the decipherment of the spectra of copolymers, which is usually done by analysis of the spectra of the corresponding homopolymers. Therefore, even for ethylene-propylene copolymers, which have received through * Vysokomol. soyed. A l l : No. 12, 2615-2623, 1969.