Mechanism of formation and properties of polytrichlorobutadiene-polystyrene paired polymers at high conversion

158

V . V . KORSI-IAKet al.

samples heated to 120-140°C did not exceed 20~o, but upon further heating at still higher temperatures decomposition commenced as evidenced by the formation of secondary products. Translated by M. KUBIN

REFERENCES 1. V. A. ZHORIN, Yu. V. KISSIN, Yu. V. LUIZO, N. M. FRIDMAN and N. S. YENIKOLOPYAN, Vysokomol. soyed. A18: 2677, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 12, 3057, 1976) 2. V. A. ZHORIN, Yu. K. GODOVSKII and N. S. YENIKOLOPYAN, Vysokomol. soyed. A24: 953, 1982 (Translated in Polymer Sci. U.S.S.R. 24: 5, 1073, 1982) 3. V. A. ZHORIN, A. Yu. SHAULOV and N. S. YENIKOLOPYAN, Vysokomol. soyed. B19: 841, 1977 (Not translated in Polymer Sci. U.S.S.R.) 4. A. N. KRYUCHKOV, V. A. ZHORIN, S. S. LALAYAN, E. V. PRUT, V. G. NIKOL'SKII, Yu. M. BUDNITSKII, M. S. AKUTIN and N. S. YENIKOLOPYAN, Vysokomol. soyed. AfA: 184, 1982 (Translated in Polymer Sci. U.S.S.R. 24: 1, 211, 1982) 5. V. A. ZHORIN, N. Ya. RAPOPORT, A. N. KRYUCHKOV, L. S. SHIBRYAYEVA and N. S. YENIKOLOPYAN, Vysokomol. soyed. A25: 578, 1983 (Translated in Polymer Sci. U.S.S.R. 25: 3, 679, 1983) 6. Z. A. ROGOVIN, Khimia tseUyulozy (Chemistry of Cellulose). 508 pp., Khimiya, Moscow, 1972 7. V. L SHARKOV, Usp. khimii 36: 313, 1967 8. A. SHARPLi~.g, In: Tsellyuloza i eye proizvodnye (Cellulose and Cellulose Derivatives), Vol. 2, p. 304 (Eds. N. M. Bikales and L. Segal) Mir, Moscow, 1974 9. I. Z. YEMEL'YANOVA, Khimiko-tekhnicheskii kontror gidroliznykh proizvodstv (Chemical and Technical Control of Industrial Hydrolysis), pp. 39, 128, Lesn. prom-st', Moscow, 1976 10. A. V. OBOLRNSKAYA, V. P. S H C ~ L E V , G. A. AKIM, E. L. AKIM, N. L. KOSSOVICH and L Z. YEMEL'YANOVA, Prakticheskie raboty po khimii drevesiny i tselyulozy (Practical Exercises in Chemistry of Wood and Cellulose). pp. 131, 290, Lesn. prom-st', Moscow, 1965 11. V. L SHARKOV, O. A. DMITRIEVA and N. P. POTAPOVA, Zh. prikl, khimii 34: 1133, 1961

PolymerScienceU.S.S.R.VoL 29, No. 1. pp. 158-165,1987 Printedin Poland

0032-3950/87$10.00+.00 © 1988PergamonJournalsLtd.

MECHANISM OF FORMATION AND PROPERTIES OF POLYTRICHLOROBUTADIENF~ POLYSTYRENE PAIRED POLYMERS AT HIGH CONVERSION* V. V. KORSHAK, I. I. VOINTSEVA, A. :P. SUPRUN, A. A. ASKADSKII a n d G. L. SLONIMSKII A. N. Nesmeyanov Institute of Metal-Organic Compounds, U.S.S.R. Academy of Sciences (Received 24 June 1985) At advanced stages of the synthesis of paired polymers of poly-l,l,2-trichlorobutadiene-1,3 with polystyrene (PS) under the conditions of a Friedet-Crafts reaction, the unequal macromo* Vysokomol. soyed. A29: No. 1, 140-146, 1987.

Formation and properties of polytrichlorobutadiene-polystyrene paired polymers

159

lecular coils already paired at earlier reaction stages further react by means of the fragments t h a t h a v e s o far been unaffected by the reaction. Hardly soluble or insoluble paired polymers are formed in this process. In parallel with the Friedel-Crafts reaction, dehydrochlorination of the polytrichlorobutadiene component of the paired macromolecules occurs at advanced reaction stages, although it is partly inhibited by the main reaction. The paired polymers isolated at high conversion differ from conventional crosslinked polymers by the circumstance that their glass transition temperature decreases with increasing conversion. CHEMICAL reactions occurring in solution between two different polymer molecules by means of functional groups situated along their chains lead to the formation of polymacromolecular compounds called "paired polymers". In [l], the kinetics and mechanism of paired polymer formation between poly- 1,1,2-trichlorobutadiene-l,3 (PTCB) and PS at early reaction stages were described and it was shown that in the first stage, an inter-macromolecular reaction takes place between two different polymers leading to the formation of a small number of chemical bonds (N l ~ ) between them. In this process, a fully soluble paired polymer A is formed. In the second stage, an intramolecular reaction develops, proceeding within a single pair of previously bound macromolecular coils and increasing the number of chemical bonds between them; in this process the reaction rate increases, conversion reaches 10 ~o and the paired polymer A is transformed into the paired polymer B, of the same composition and molecular mass, easily soluble in a number of solvents, but insoluble in CCI,. In the further process, the reaction rate sharply decreases and the kinetic curve reaches a plateau (Fig. 1 in [1]). Evidently reaction by the same mechanism becomes impossible because the chemical bonds between PTCB and PS hinder their further interpenetration and therefore also the intramolecular reaction [2]. However, the reaction does not stop, but develops further leading to the formation of hardly soluble or insoluble coloured products C and D, preventing studies of the reaction kinetics at high conversion by the refractometric method used in [1]. In the present work, the features of the reaction between PTCB and PS were studied at high conversion when gel is formed in the system. PTCB of M= 150,000, [t/]=0.90 dl/g in benzene at 25° was used in this work; found (calculated), %: C 31.00 (30.51), H 1.88 (1.92), CI 67.11 (67.57); PS of M=400,000, [t/]=1.2 dl/g; found (calculated), %: C 91.76 (92-30), H 7-70 (7"91). Nitrobenzene was dried over P205 and vacuum distilled. Preliminary experiments have shown that PS does not undergo substantial changes in the presence of AICI3 under the selected reaction conditions ([AIC13]=0"3 mole/mole PTCB, C0-3 Jo, 20°, 24 hr): yield PS 97%, found, ~: C 91.03, H 7.21, [r/]=l.10 dl/g. PTCB under these conditions undergoes dehydrochlorination with the formation of a partly insoluble coloured product. Therefore parallel with the study of the formation of the PTCB-PS paired polymers, the process of PTCB dehydrochlorination was studied under the same conditions, but in the absence of PS. The solutions of PTCB and of the equimolar polymer mixture (PTCB with PS) in nitrobenzene, prepared for a series of experiments, were placed in conical flasks, air was expelled by inert gas, the flasks were thermostated and a calculated amount of AICI3catalyst in nitrobenezene was introduced. The reaction mixture was shaken for concentration homogenization, and then the reaction was let to proceed without stirring. In the course of the reaction, darkening and thickening of the reaction __

o/

V.V. KORSHAKet al.

160

mixture was observed, with subsequent gel formation. The reaction was stopped at various times by the addition of aqueous and acidic methanol. The polymers were separated in the form of swollen gel of orange-red colour by chloroform extaction in a Soxhlet apparatus until disappearance of nitrobenezene odour; the traces of unreacted polymers, and the chloroform soluble fractions A and B were also removed in this process. In the experiments requiring the separation of the fractions C and D, the gel was heated in tetrachloroethane and the fraction C was separated from the solution. For the determination of the gravimetric swelling degree of the reaction products, ms[md (m, and rna are the masses of the swollen and dry gel, respectively), the chloroform swollen gels were weighed immediately after the Soxhlet extraction, and then after vacuum-drying at 50°. Density of the obtained polymers was determined by density matching of polymer films in Thoulet liquid at 20°. Thermomechanical measurements were made at punch pressure of 0.08 MPa.

Based on the mechanism of the Friedel-Crafts reaction [3], A1C13 introduced into a solution of the PTCB-PS mixture, may be expected to primarily separate the labile allylic chlorine atom from various sterically best accessible units of the PTCB macromolecule (i.e.units situated at the surface of the coil), resulting in complex formation +

--CHz--CH-~-CCI--CCI~--+AIC13~--CH2--CH~CCI--CCI--AICI4

The anion A1CI4 can further abstract a proton either from a PS macromolecule, or from a PTCB methylene group. In the first case this leads to a Friedel-Crafts reaction and chemical bond formation between the PTCB and PS macromolecules according to the scheme +

--CH2--CH=CC1--CCI--+--CH2--CH--~--CH2--CH=CC1--CC1--

(1)

I

--CH2--CH--

In the second case either inter-chain (scheme (2)) or intramolecular (scheme (3)) dehydrochlorination of PTCB will occur: CCI2--CCI = CH--CH2--CCI2--CCI= C H - - C H z - -

-HCI

--CH2--CH=CCI--CC12--CH2--CH=CCI--CCI2---CCI2--CCI~ CH--CH--CClz--CCI-~-CH--CH2--

(2)

I

- - C H 2 - - C H = CCI--CCI--CH2--CH= CC1--CCI2--HCI

- - C H 2 ~ C H = CCI--CCI2--CHz--CH= CCI--CClz---CH=CCI--CCI=

~=CH--CH=CCI--CCI~-CH-(3)

In [1, 4] it was established that PTCB dehydrochlorination processes are not important in the initial stages of the studied reaction: the polymers A and B are completely soluble and are of white or light yellow colour. The activation energy values in the first and second stages (stages I and II, respectively) are equal to 96.1 and 37.6 kJ/mole, i.e. are considerably lower than the activation energy of PTCB dehydrochlo-

Formation and properties of polytriehlorobutadiene--polystyrene paired polymers

161

rination which is equal to 130.4 kJ/mole [5]. Thus in the early stages the polymers react practically only by a Friedel-Crafts reaction (scheme (1)). Analysis of the temperature dependence of the reaction rate constants at higher conversion (experimental data of [1]) indicated that here Ea increases up to 150 kJ/mole, i.e. it becomes commensurable with Ea of PTCB dehydrochlorination. Consequently, at high conversion, three parallel competing transformations are possible: a FriedelCrafts reaction and interchain and intramolecular dehydrochlorination of the polytrichlorobutadiene part of paired macromolecules; the first two reactions will increase the number of chemical bonds between paired macromolecules and lead to network formation, whereas the reaction according to scheme (3) will lead to the appearance of the orange-red polymer colour due to polyene structure formation [6, 7]. In order to evaluate the contribution of each of these reactions to the process of paired polymer formation at high conversion, dehydrochlorination of PTCB (in absence of PS) and paired polymer formation (in the presence of PS) were studied in parallel. In these experiments, a number of substantial differences in the course of these reactions was revealed (Table 1). In PTCB dehydrochlorination in the absence of PS, TABLE 1. YIELD AND PROPERTIESOF GEL FORMEDBY PTCB DEHYDROCHLORINATION(IN THE ABSENCE

OF PS) AND DURING PAIRED POLYMER FORMATION(IN THE PRESENCE OF PS)

(Co = 3 ~, [AICI3I=0"3 mole/mole PTCB, 20°) Gel m~/ma yield, xl0 -3 %

Time, rain I Initial mixture 20 40 60 120

0 98 91 96 100

•

CI, %

g/cPl~13 K

in presence of PS 40"98 I 1'346 5"1 37"291 1"240 4"6 37'09I t'260 3"8 38"21/ 1-286 3"0 37-48! 1-360 -

Gel mJFrld yield, xl0 -a

0.677 Jl 0.64211 0"653 II O'666 I 0"705

~ 27 68 67 83

8'2 6"3 5"4 4'4

C1,

Colqver- t p,

sion, g/cma K Vo in absence of PS 67"11 0 1.570 0.653 65-69 15'9 1"428 0.600 65"34 19"8 1.422 0.599 60"97 68"7 1"345 0"605 59"84 81"7 1"312 0'578

gel yield gradually increases with time, reaching a maximum of ~ 80 ~; in the presence of PS, gel yield very quickly reaches ~ 100 ~. The swelling ability of dehydrochlorinated PTCB (ms/md) is considerably higher than that of the paired polymers obtained after the same reaction time. During PTCB dehydrochlorination, chlorine content decreases uniformly with degree of conversion. In [8] it was shown that the transformation of PTCB under the conditions of a Friedel-Crafts reaction occurs by way of the loss of one of the allylic chlorine atoms. As in the original PTCB the theoretical chlorine content is equal to 67.56 ~, and after the loss of one chlorine atom it should be equal to 58.67~o, the theoretical decrease of chlorine content at I00 ~ conversion by any mechanism should be equal to 8"9~o. The experimentally found chlorine loss in the limit (after 120 rain) reaches 7.27 ~; consequently the total content of dehydrochlorinated units amounts to 81.7~.

162

V. V, KORSnAKet al. I I

I00

4

35

2 5O

I

100

Z00

FIG. 1

I00

T°

2OO

28

I

I

I

20

I

12

I

I

20 o 4

Fro. 2

FIG. 1. Thermomechanical curves of initial (1) and dehydrochlorinated PTCB (2), PS (3), mechanical mixture of PTCB with PS (1 : 1) (4) and paired polymers (5--8) (fractions A, B, C, D) respectively. FIG. 2. Diffractograms of films of PS (1) and of paired polymers isolated 3 (2); 4.5 (3); 8 (4) and 17 hr (5) after start of reaction. For determining the degree of conversion in PTCB dehydrochlorination by the inter-chain process, the glass temperature of the generated network Tg was experimentally determined and theoretically calculated by the method of [9] assuming that one HCI molecule is removed from two PTCB units and one crosslink per unit is formed (scheme (2)). The calculation has shown that at 100 70 conversion by scheme (2), T= of the polymer should reach 237 °. Actually for the polymer isolated at the highest conversion it is equal to 60 ° (Fig. la) (T= of the initial trI'CB is 55°), corresponding to 4.8 7o conversion, i.e. a very loose network is formed. Further it was considered that simultaneously with inter-chain dehydrochlorination, also intramolecular PTCB dehydrochlorination may occur, in which one HCI molecule is removed from each PTCB unit (scheme (3)). Above it has been shown that the overall conversion amounts to 81.77o, of which 4.87O corresponds to inter-chain dehydrochlorination, so that 76.9~ of total conversion is to be ascribed to intramolecular dehydrochlorination. Table 1 demonstrates that in the presence of PS, chlorine loss in the polymer reaches the limiting value ('~3"57o) already at the initial stage and does not change further; this limiting value is considerably higher than the corresponding value in the absence of PS after the same reaction time (~ 1.4 7o). An analogous calculation of total conversion shows that the limiting chlorine loss corresponds to 38 70 conversion, which is considerably lower than in the absence of PS. This indicates inhibition of the PTCB dehydrochlorination process in the presence of PS a n d t h e importance of the reaction of paired polymer formation in tho first reaction moments, in agreement with the kinetic data [1].

Formation and properties of poiytrichiorobutadiene-polystyrene paired polymers

163

The cited experimental data indicate that similar the initial reaction stages, even at high conversion the dominating mechanism is the Friedel-Crafts reaction which can here occur only between already pair-bound macromolecular coils. This is supported by X-ray analysis data: the diffractogram of the soluble paired polymer B exhibits two maxima characteristic of PS (Fig. 2); consequently in the paired macromolecules formed at the initial reaction stages, domains untouched by the reaction are preserved [10]. At the later reaction stages the individual peaks characteristics of PS gradually disappear, indicating participation of PS fragments in paired macromolecules in the proceeding reaction and formation of a uniform, practically structureless system in the final stage. By performing the reaction in a more dilute solution where it proceeds much more slowly, two reaction products could be separated at high conversion: the sparingly soluble paired polymer C and the insoluble polymer D (Table 2). In the course of the reaction, polymer C is fxrst produced and accumulated (stage liD: this is of bright orange colour and it is soluble in hot polar solvents. The formation of polymer C is accompanied by the reduction of the sol-fraction indicating that primarily the macromolecules with the highest It//, i.e. fraction B [4], are transformed into gel. TABLE 2 .

Y I E L D OF PAIRED POLYMER FRACTIONS AT HIGH CONVERSION

(Co = 2 %, [AlClal= 0"3 mole/mole PTCB, 20°) Reaction stage II IIl III

Time, Gel Gel fraction [r/] Reaction Time, Gel Gel fraction yield, hr yield, yield, ~ dl/g stage hr yield, % C D C D (sol) III 100 3'0 0 - ] 2"28* 8"0 73 IV 75 25 10"0 86 4'5 12 100 t 2"20 100 IV 100 6'0 16 100 1"25 17'0

[~] dl/g (sol) 0"78 0"82

* F o r f r a c t i o n B.

Evidently in the third stage, similarly as in the first one, the intermacromolecular reaction occurs, leading to the formation of single chemical bonds between already pair-bound macromolecules (in this process conversion increases by 0-7 ~)

B

B

C

D

These single chemical bonds can be broken relatively easily: after dissolution in boiling tetrachloroethane and reprecipitation in ethanol, polymer C is easily soluble in cold chloroform, i.e. it has been transformed back to polymer B. In Table 2 it is shown that at stage IV where the gel yield is nearly quantitative, polymer C is transformed into the insoluble polymer D. A special experiment has been performed where the reaction was interrupted at the stage of polymer B formation; polymer A and the initial homopolymers were extracted with CC14. The purified polymer B was redissolved in nitrobenzene and AIC13 was added; in due time, the polymers C

164

V.V. KORSHAKet al.

and D were separated. This experiment proves that the transformation of the paired polymers B ~ C ~ D can take place without the participation of the initial polymers, i.e. the paired macromolecules PTCB-PS participate in the reaction. The Friedel-Crafts reaction in stage IV can best be described as an intramolecular reaction of the second kind (in contrast to stage I1), leading to an increased number of chemical bonds between already pair-bound different macromolecules (scheme (4)). This is in agreement with the observed values of density and of the packing coefficient K of the polymers separated at various reaction stages. K was calculated by the method of [11], respecting the changes of the chemical structure of the polymers caused by the described chemical transformations and their contribution to total conversion. Table 1 shows that K decreases at the initial moment of paired polymer formation, and later increases with increasing conversion, i.e. a tightening of the paired polymer structure is observed; this is in contrast to the dehydrochlorination of PTCB where K steadily decreases in the course of the reaction, i.e. a loosening of the structure occurs. Density of the polymers changes in t h ~ a m e manner. Thermomechanical studies of paired polymers isolated at various reaction stages revealed that fractions A and B (soluble paired polymers) are characterized by increased T8 as compared to the mechanical mixture and to the initial components (Fig. lb). On transition to the hardly soluble fraction C and to the insoluble fraction D, an unexpected decrease of Tg is observed; the reason of this is so far unclear and further studies are needed. Thus at the late stages of the reaction between the pair-bound polymers PTCB-PS, two competing chemical reactions proceed, with roughly equal activation energy: a Friedel-Crafts reaction and dehydrochlorination of the polytrichlorobutadiene part of the paired macromolecules, leading to the formation of coloured, hardly soluble and insoluble products C and D. In the third stage, the intermacromolecular Friedel-Crafts reaction (of the second kind) and the intramolecular PTCB dehydrochlorination predominate; in the fourth stage, the intramolecular Friedel-Crafts reaction (of the second kind) and intermolecular PTCB dehydrochlorination are dominant. Based on our previous studies and on the results of the present work it is necessary to specify the term "paired polymer": by this term we designate the reaction product of two types of different macromolecules bound by covalent bonds along their chains with the formation of polymacromolecules. The polymacromolecule of a paired polymer may contain various numbers of chemically bound initial different macromolecules. In the simplest case a polymacromolecule may consist of one macromolecule of type 1 and one macromolecule of type 2. In more complicated cases, the polymacromolecule may consist of one macromolecule of type 1 and two macromolecules of type 2, or vice versa, of two macromolecules of type 1 and one macromolecule of type 2. When the macromolecule consists of four initial macromolecules, the number of combinations increases; the following combinations are possible: 1132, 2~22, 3~12, where l, 2 and 3 are the numbers of macromolecules in the polymacromolecule; the indices ! and 2 designate the macromolecule type. When the macromolecule contains in initial macromolecules of type 1 and 2, then the possible combinations will be /

Formation and properties of polytrichlorobutadiene-polystyrene paired polymers

165

11 (n - 1)2, 2x ( n - 2)2 . . . . . ( n - 1)112 Thus the p o l y m e r s built o f t w o types o f different m a c r o m o l e c u l e s will be design a t e d as " p a i r e d " , i n d e p e n d e n t o f the n u m b e r n o f m a c r o m o l e c u l e s constituting the polymacromolecule. ]~n [1] it was shown t h a t by selection o f synthetic m e t h o d , p a i r e d polyn~ers could be p r e p a r e d with p o l y m a c r o m o l e c u l e s consisting o f o n l y two different m a c r o m o l e c u l e s a c c o r d i n g to the a b o v e classification these can be designated as 1112. A c c o r d i n g to the results o f the p r e s e n t w o r k , at late r e a c t i o n stages these p o l y m a c r o m o l e c u l e s consisting o f two different m a c r o m o l e c u l e s m u t u a l l y react f o r m i n g larger p o l y m a c r o m o l e c u l e s o f type (n/2)~(n/2)2. G e l is f o r m e d at n ~ ~ .

Translated by D. DOSKO~ILOVA REFERENCES

1. V. V. KORSHAK, A. P. SUPRUN, I. I. VOINTSEVA, B. B. MUSTAFAYEVA, G. L. SLONIMSKII, A. A. ASKADSKII, T. M. BIRSHTEIN and Ye. N. KANEVA, Vysokomol. soyed. A26:111, 1984 (Translated in Polymer Sci. U.S.S.R. 26: 1, 123, 1984) 2. B. VOLLMERT and H. STUTZ, Angew. Macromolec. Chemie 20: 276, 71, 1971 3. A. TERNEI, Sovremennaya organicheskaya khim;ya, p. 604, Mir, Moscow, 1981 4. V. V. KORSHAK, A. A. ASKADSKII, I. I. VOINTSEVA, B. B. MUSTAFAYEVA, A. P. SUPRUN and G. L. SLONIMSKII, Vysokomol. soyed. A23: 1001, 1981 (Translated in Polymer Sci. U.S.S.R. 23: 5, 1116, 1981) 5. G. S. POL'SMAN, L. V. GINZBURG, A. S. KUZMINSKII, A. M. MEDVEDEVA, A. A. SOKOLOVSKII, A. S. SHASHKOV, T. A. SOBOLEVA and A. B. BELYAVSKII, In: Kinetika i mekhanism polireaktsii (Kinetics and Mechanism of Polyreactions) Vol. 5, p. 61, Budapest, 1969' 6. C. DECKER, Europ. Polymer J. 20: 149, 1984 7. V. I. KASATOCHKIN, A. A. BERLIN and Z. S. SMUTKINA, Izv. AN SSSR, Ser. Khim., 1003, 1965 8. I. I. VOINTSEVA, A. S. SHASHKOV and A. P. SUPRUN, Vysokomol. soyed. A20: 1640, 1978 (Translated in Polymer Sci. U.S.S.R. 20: 7, 1851, 1978) 9. A. A. ASKADSKII, Yu. I. MATVEYEV, A. V. PASTUKHOV, B. A. ROZENBERG, T. I. PONOMAREVA, N. A. SHCHEGOLEVSKAYA and A. S. MARSHALKOVICH, Vysokomol. soyed. A25: 56, 1983 (Translated in Polymer Sci. U.S.S.R. 25: 1, 64, 1983) I0. V. V. KORSHAK, G. L. SLONIMSKII, A. A. ASKADSKII, O. G. NIKOL'SKII, A. P. SUJ~RUN, I. I. VOINTSEVA, B. B. MUSTAFAYEVA, Ye. M. BELAVTSEVA and L. G. RADCHENKO, Vysokomol. soyed. A26: 1929, 1984 (Translated in Polymer Sci. U.S.S.R. 26: 9, 2158, 1984) 11. A. A. ASKADSKII and Yu. I. MATVEYEV, Khimicheskoye stroyenie i fizicheskie svoistva polimerov (Chemical Structure and Physical Properties of Polymers), p. 103, Khimiya, 1983