Effect of the medium on polymerization of acrylonitrile

Effect of the medium on polymerization of acrylonitrile

2118 T. S. YATSIMIRSK&YAand Yu, L. SPIRn~T 8. I. I. ZHUKOV, I. Ya. PODDUBNYI and A. V. LEBEDEV, Sb. Issledovaniya v oblasti vysokomolekulyarnykh soy...

416KB Sizes 0 Downloads 3 Views

2118

T. S. YATSIMIRSK&YAand Yu, L. SPIRn~T

8. I. I. ZHUKOV, I. Ya. PODDUBNYI and A. V. LEBEDEV, Sb. Issledovaniya v oblasti vysokomolekulyarnykh soyedinenii (Investigations in the Field of High Molecular Weight Compounds). Izd. AN SSSR, 238, 1949 9. R. L. SCOTT, W. C. CARTER and M. MAGAT, J. Amer. Chem. Soc. 71: 220, 1949 10. M. BAER, J. Polymer Sci. A2: 429, 1964 11. M. WALES and S. RENFELD, J. Polymer Sci. 62: 179, 1962 12. T. FUJIMOTO, N. OZAKI and M. NAGASAWA, J. Polymer Sci. AS: 2259, 1965 13. H. L. HSIEH, J. Polymer Sci. A3: 163, 1965 14. L. LOCHMANN and I). L1M, J. Organomet. Chem. 28: 153, 1971 15. W. J. TREPKA, J. A. FAVRE and R. J. SONNENFELD, J. Organomet. Chem. 55: 221, 1973 16. I). MARGERISON and V. A. NYSS, J. Chem. Soc. 3065, 1968 17. A. R. SAMOTSVETOV, I. Yu. KIRCHEVSKAYA, L. A. GRIGOR'YEVA and V. P. SHATALOV, Vysokomol. soyed. AIS: 1839, 1973 (Translated in Polymer Sci. U.S.S.R. 15: 8, 2070, 1973) 18. R. V. BASOVA, A. R. GANTMAKHER and S. S. MEDVEDEV, Dokl. AN SSSR 158: 876, 1964

EFFECT OF THE MEDIUM ON POLYMERIZATION OF ACRYLONITRILE* • T. S. YXTS~n~S~rA and Y r . L. SPrats Institute of the Chemistry of High Molecular Weight Compounds, L~r.S.S.R. Academy of Sciences

(Received 22 September 1975) A study was made of polymerization kinetics of aerylonitrilo (A_N) in dimethylformamide, methylpyrrolidone and a dilute, saturated magnesium perchlorate solution. Kinetic constants were determined using pulse photolysis of the initiator. I t was found that polymerization of AN in a dilute saturated magnesium porchlorate solution is homoKeneous up to a ratio of AN to magnesium perchlorate of six. I t was assumed that ct~ngos in the activity of the monomer a n d growing radical in reactions of chain extension a n d rupture are due to the co-ordination effect of solvated ions, producing a variation in activation entropy of these reactions.

IT was shown in m a n y studies [1-3] t h a t the type of solvent has a marked effect on kinetics of homogeneous polymerization of aeryloaitrile (AN). Bamford et aL [4] found t h a t the addition of metal salts to organic solvents accelerates polymerization as a result of increasing the rate constant of chain extension due t o the formation of a complex between the monomer and salt. Similar effects caused b y the addition of ZnC12 were explained [5] by an increase in the rate constant * Vysokomol. soyed. AI8: No. 8, 1850-1854, 1976.

Effect of medium on polymerization of acrylonitrilo

21 lib

o f extension a n d in a n o t h e r s t u d y [ 6 ] - - b y a r e d u c t i o n of the rate o f chain r u p t u r e . The m o s t considerable change in t h e rate o f p o l y m e r i z a t i o n is observed on t r a n s i t i o n f r o m organic solvents to c o n c e n t r a t e d dilute salt solutions. These changes. are also explained b y complex f o r m a t i o n . I t is a s s u m e d t h a t in dilute zinc chloride solutions a complex is f o r m e d b e t w e e n t h e CN g r o u p of a P A N radical a n d salt [7] a n d in the case of dilute s o d i u m t h i o c y a n a t e solutions [8] on the o t h e r h a n d , b e t w e e n t h e double b o n d a n d rhodanide. Absolute rate constants o f chain extension a n d r u p t u r e were d e t e r m i n e d during p o l y m e r i z a t i o n o f A N in dilute m a g n e s i u m perchlorate solutions [1] a n d it was f o u n d t h a t the c o n s t a n t of extension ke a n d r u p t u r e k r increases considerably, c o m p a r e d with p o l y m e r i z a t i o n in organic solvents. P o l y m e r i z a t i o n is also accelerated b y o t h e r s a l t s - - l i t h i u m bromide, calcium t h i o c y a n a t e , etc. [9]. The cause of the accelerating a c t i o n o f these v e r y different salts is n o t clear .The e x p l a n a t i o n s proposed are conflicting a n d inconclusive. Difficulties in i n t e r p r e t i n g the effect of m e d i u m are largely due to the v a r i a b i l i t y of results concerning t h e i n t e r a c t i o n o f A N w i t h the m e d i u m a n d discrepancies in rate c o n s t a n t s of chain extension a n d r u p t u r e o b t a i n e d b y various a u t h o r s [10]. This s t u d y was u n d e r t a k e n t o determine kinetic c o n s t a n t s of p o l y m e r i z a t i o n o f A N in various m e d i a using pulse photolysis o f the initiator a n d to explain t h e m e c h a n i s m o f the effect o f m e d i u m . AN" was treated stepwise with 10~o Na0H, 10~/o phosphoric acid, washed with water, dried with calcium chloride and distilled in a column. Before the experiments AN was~ partially polymerized while heating with 1~/o AID and condensed in a dilatometer in vacuum. Methylpyrrolidone was treated with alkali in vacuum, distilled over calcium hydride and recondensed in vacuum in a dilatometer. DMF was boiled with toluylened~i-isoeyanate for 6 hr and distilled twice. The magnesium perchlorate (MPC) used was analytically pure. The rate of polymerization was determined dilatometric~lly. AID was used as thermo- and photo-initiator, of which the rate constant of thermal decomposition is independent of t h e solvent [l 1]. AID is sparingly soluble in MPC solution. The rate constant of decomposition of AID in MPC solution was determined from the rate of nitrogen liberation at 75°. The constant derived (8.6× l0 -e see -1) practically agreed with the constant of decomposition in other solvents, which is evidence of the absence of the effect of MPC on the decomposition of AID. Values of ke and k*r were calculated from the rate of polymerization of A ~ at a rate of initiation given by the thermal decomposition of AID with an effectiveness of 0.7. The ratio of ke//Cr was determined from results of post-polymerizatlon by pulse photolysis of AID, according to the relation [12]:

ke/kr =,dMI2/M In (Ix/I~), where AMx2=(AMx--.dMs)/n; AMx and AM2 are polymer yields in 7 rain (time of thermostat,ic control) with a number of pulses n : l0 of intensities Ix and 12, respectively. The duration of the pulse was 0.002 sec. The rate of polymerization showed a linear dependence on monomer concentration, in accordance with results in the literature [7]. The order of the rate of polymerization in relation to the rate of initiation was examiped according to the variation of the rate ofpolymerization and light intensity and found to be 0.5, which agrees with results in t h e literature [3].

T. S. YATSIMIRSKAYAand Yu. L. SPn~IN

2120

S u m m a r i z e d results are t a b u l a t e d . Results concerning polymerization o f A N in D M F are close to results previously described [13] a n d s o m e w h a t differ f r o m t h o s e o f a n o t h e r s t u d y [3]. T h e r e p l a c e m e n t of D M F b y m e t h y l p y r r o l i d o n e slightly KINETIC

PARAMETERS

OF POLYMERIZATIOI~

OF ~1~

IN DIFFERENT

SOLVENT

4t

o i

Solvevt

cD

.

×

×

•°

×

X

ke

IcrX X 10-T

x~ mole/l. 1 2 3 4 5 6

7 8 9

10

DMF Methylpyrrolidone Mg.

20 20 30 20 30

2-54 2.57 3.76 1.89 5'4

• (C10,)"

30

6.65

• 12HsO

30 8.0 30 8.6 30 8.8 30

8"95

D w

2.5 3.6 5.0 5.9 6.3 6.5

10.2 1.27 0.027 0"79 5.7 1.66 0.044 1.17 L1.6 8.6 0.051! 5"35 4.7 4.2 0.19s 2"35 3.1 -0.21 3.3 3.4 3.0 2-5 3.1

3.0

0"68 0.98 5.04 2.23

L/mole. s e o 0.011

3.6 6.15

200 3201

5.3 5.2

8.4 310 0.012 5.29 7400

3.7 1400

0.019 0.029

---

24.4 --

0.121

* Polymerization in experiments 1-8 takes place by a homogeneousmechanism,in experimenta9, 10--bya heterogeneous mechanismwith the separation of the polymer. ~Vot¢. [M] is the concentration of AN; [I] - concentration of AID; w--rate of polymerization. increased the value o f he a n d related constants which m a y , evidently, be explained b y t h e weak inhibition of p o l y m e r i z a t i o n o f aerylonitrile with DMF. P o l y m e r i z a tion of A N in a dilute solution o f MPC takes place w i t h m u c h higher values o f h e a n d br, c o m p a r e d w i t h organic solvents, however, w i t h a qualitative a g r e e m e n t results differ m a r k e d l y f r o m results o f a n earlier p a p e r [1], in which it was f o u n d t h a t a t 50 ° be--~65,000 a n d br----47 × 108 l./mole.sec. Based on existing views [7, 8] it could be assumed t h a t the strong increase in constants in p o l y m e r i z a t i o n in dilute MPC is caused b y complex f o r m a t i o n b e t w e e n MPC b o t h with a m o n o m e r a n d a radical. According to a n earlier t h e o r y concerning t h e r e a c t i v i t y o f radicals a n d monomers [14] it m a y be assumed t h a t a n increase o f electronegative properties of the nitrile group owing to i n t e r a c t i o n with t h e m e d i u m reduces t h e r e a c t i v i t y of t h e m o n o m e r a n d increases t h e r e a c t i v i t y of the radical. The r a t e o f p o l y m e r i z a t i o n c a n be increased w i t h a n increase of k e if t h e radical forms a complex t o a n increased e x t e n t , c o m p a r e d with the m o n o m e r , so t h a t chain extension takes place in the form of addition of the free m o n o m e r to a complex c o m b i n e d radical. I f we assume t h a t all R radicals are combined a n d m o n o m e r M is free, according t o t h e relation [14]: bR~---- ]co e x p (-~- 1 . 6 e ~ - 0.35eM-- crew)

Effect of medium on polymerization of aerylonitrile

2121

where e represents the Alfrey-Price polar parameters for R and M, respectively and the value of eB with an over 20-fold increase of the value of ke observed experimentally, should increase from e~----1.2 to eR~-2.3. This increase of e is only possible with strong interaction and is unlikely in this case. The cause of strong increase of kr also remains obscure with this variation of e since the proposed increase in the reactivity of the radical due to complex formation should increase steric hindrances in rupture, i.e. reduce the value of kr. The accelerating effect of M'PC is only apparent in saturated dilute solutions. Although dehydrated IV[PC dissolves in AN, polymerization takes place under heterogeneous conditions the same way as without MPC.

60-

"~

4o

-

20-

I

I

20

qO

I

60 Mg(Ct 0~) 2 .12 HzO , vol %

Fro. 1. Solubility of AI~ in mixtures of a dilute saturated MPC solution a n d water at 25%

The interaction of AN with dilute solutions of MPC was examined by several methods. The variation of the solubility of AN in the mixture of a saturated solution of Mg(C104)~" 12H~O and water is shown in Fig. 1, which indicates t h a t on increasing the concentration of the saturated MPC solution to 50%, the solubility of AN increases markedly and becomes infinite in the 75-80% range. This shows that the interaction of MPC with AN is not stoichiometric. The simultaneous interaction of both ions is important for solubility since the solubility of AN in aqueous saturated solutions of MgCl~ and NH4CI04 is low and and polymerization of AN takes place by a heterogeneous mechanism. An interesting relation was established when studying the effect of the ratio of monomer and Mg(CI04)~- 12 H20 on the phase condition of the system. The polymerization system remains homogeneous up to a ratio Of 5.9 (Table). On increasing the ratio to 6.3 polymerization takes place with the separation of the polymer. The yalue of ke/k ~ is higher in a homogeneous system. These results indicate that a MPC molecule can co-ordinate up to six PAN units. A solution of M-PC (0.0077 mole) and AN (0.0077 mole) in water (0.83 mole) freezes at --3.58 °, which corresponds to the complete dissociation of MPC and

2122

T. S. YATSIMIRSKAYA and Y u . L. SP~RX~

the absence of complex formation between salt ions and AN. This result is in agreement with the low equilibrium constant ( ~ 1 0 -4 ) of complex formation between acetonitrile and various salts in dilute solutions [15]. On mixing in a calorimeter 0.5 ml AN with 1.5 ml saturated MPC solution practically no temperature change was observed which points to a low energy of interaction. 2J

22

23

~ ~

22

Z8

22~f0 -z

h b C

f

FIG. 2. IR spectra: a-c--MPC solution in A_~ with a molar ratio of AN : M-PC of 25; 12;

7, respectively (saturated solution); d--pure AN; e--AN in DMF; f--ZnC1, solution in A~.; g--AN in dilute saturated MPC with an initiator after blending; h--PAN in aqueous saturated MPC with an initiator, the system was brought to a high degree of polymerization. An absorption band is observed at 2278 cm -1 in I R spectra of an anhydrous MPC solution in AN, which is evidence of a shift of absorption frequency of the --C-ffiN group absorbing at 2240 cm -1 and proves the formation of a complex between the nitrile group of the monomer and a salt cation. In I R spectra of a dilute saturated solution of MPC t h e absorption band of the nitrile group is shifted by ~ 10 cm -1 to the short wave range, compared with absorption in a pure monomer. Further, diffusion absorption is observed at frequencies higher t h a n "2240 cm -1, which increases during polymerization of AN (Fig. 2). These samll changes evidently point to a weak interaction between the nitrile group at the hydrogen bonds and the medium. I t was found [16] t h a t the viscosity of a dilute 60% zinc chloride solution increases on adding up to 8% AN to the system. A band is observed at 2270 cm -1 in the I R spectrum of this system. Viscosity also increases somewhat in the system studied by us on adding up to 90//0 AN (Fig. 3), which is evidence of the interaction between solution components.

Effect of medium on polymerization of acrylonitrilo

2123

Thus, results concerning solubility, cryoscopy and heat of mixing prove t h a t AN is unable to displace a water molecule from the solvate sheath of Mg =+ or CIO~ ions. At the same t i m e I R spectroscopic and viscosity results indicate some interaction between AN a n d ions solvated with water. These results suggest ~ rel l"02q i'Oi6

1. 008 I. oo0

I

2

I

I

I

I

I

10 [AN2, .ol. %

I

I

I I¢

FIG. 3. Relation between the relative viscosity of an aqueous saturated MPC solution and A~ concentration. t h a t values of be and k r in a saturated dilute MPC solution increase in the absence o f strong interactions of the t y p e of complex formation between AN and salt ions and these are not superimposed on existing systems of radical polymerization. Results suggest the following reaction mechanism. In a saturated MPC solution all water molecules are combined and the solution is most probably highly ordered and approximates to the crystalline state. AN molecules (not more t h a n six per salt molecule) are co-ordinated by ions with retention of solution regularity, which is confirmed b y an increase in the viscosity of the system on adding the monomer. Solution ordering is expressed by a reduction in volume accessible to reagents, which increases concentration in the inter-ionic space a n d corresponds to a formal increase in rate constants. A further factor which contributes to an increase of constants m a y be the favourable orientation of reagents under weak ionic interaction increasing pre-exponential factors in rate constants. To confirm these assumptions it is desirable to investigate the struct u r e of salt solutions. Translated by E. S~,~m~ REFERENCES

1. 2. 3. 4. 5. 6. 7.

J. ULBRICHT, J. Polymer Sei. C16: 3747, 1968 E. F. WHITE and M. J. ZISSELL, J. Polymer Sei. AI: 2189, 1963 A. F. REVZIN and Kh. S. BAGDASAR'YAN, Zh. fiz. khimii 18: 1042, 1964 C. H. BAli[FORD and A. D. JENKINS, Prec. Roy. See. A241: 364, 1226, 1957 M. IMOTO, T. OTSU and S. SHEM:IZU, Makromolek. Chem. 65: 194, 1963 M. YOS~ffnA and K. TANAUCHI, Chem. High Polymer Japan 20: 221, i963 M. YOSI~[IDA and K. TANAU~B[I, Kobunshi Kagaku, 20: 545, 1963

2124

T.G.

K--A~aOV

8. A . L. B O R T N I C H U K , A . D. S T E P U K H O V I C H a n d I. S. R A B I N O V I C H , Methdunarodnyi

9. 10. U. 12. 13. 14. 15. 16.

simpozium po khir.ni.'cheskim voloknam (International Symposium on Chemical Fibres). Kalinin, 1974 A. F. NIKOLAYEV, Sinteticheskiye polimery i plasticheskiye massy na ikh osnove (Synthetic Fibres and Plastics Made from Them). Izd. "Nauka", 1969 Spravochnik po khimii polimerov (Handbook on the Chemistry of Polymers). Izd. "Naukova dumka", 1971 Kh. S. BAGDASAR'YAN, Teoriya radikal'noi polimerizatsii (Theory of Radical Polymerization). Izd. "Nauka", 1966 Yu. L. SPIRIN and T. S. YATSIMIRSKAYA, Teoretich. i eksperiment, khimya 4: 849, 1968 N. COLEBOURNE and E, COLLINSON, Trans. Faraday Soc. 59: 1357, 1963 Yu. L. SPIRIN, Uspekhi khimii 38: 1201, 1969 V. GUTMAN, Khimiya koordinatsionnykh soyedinenii v nevodnykh rastvorakh (Chemistry of Co-ordination Compounds in Anhydrous Solution~). Izd. "Mir", 1971 ZENJIRO MOMIYAMA and AKIRA YAMAMOTO, J. Maeromolec. Sci. A4: 1649, 1970

INHIBITION OF THERMAL OXIDATIVE BREAKDOWN OF POLY-4-METHYLPENT-1-ENE* T. G. KHAI~T+AROV S. M. Kirov State University, Azerbaijan

(Received 23 October 1975) A kinetic study was made of the initial stage of thermal oxidation of poly-4-methylpent-l-ene (PMP) at different temperatures and initial oxygen pressures. An empirical relation was established between the induction period, temperature and oxygen pressure. The activation energy" and other kinetic parameters of the initial stage of oxidation of PMP were determined. A study was made of the relation between the induction period of thermal oxidation of PMP and temperature and the concentration of antioxidants: phenyl-fl-naphthylamine (AO-I), 2,2'-methylene-bis-(4-methyl-6tert. butylphenol) (AO-II), KBr, K1 and S. It was shown that in PMP AO-I behaves as a "weak" antioxidant and the effect of AO-II is lower in this polymer than in PE and PP, i.e. the effect of the antixidant also depends on polymer structure. I t was established that KBr, KI and S antioxidants function at temperatures higher than 250 ° .

IT IS k n o w n t h a t p o l y - 4 - m e t h y l p e n t - l - e n e (PM~P) has a high melting p o i n t (240°). Therefore, this p o l y m e r is processed a n d o p e r a t e d a t c o m p a r a t i v e l y high t e m p e r a t u r e s , which results in intensive oxidation. The inhibition of t h e r m a l o x i d a t i v e b r e a k d o w n o f P M P over a wide r a n g e of t e m p e r a t u r e is o f interest. A s t u d y was therefore m a d e of t h e inhibiting a c t i o n of some organic a n d inorganic antioxidants. * Vysokomol. soyed. AI8: No. 8, 1855-1858, 1976.