Kinetics of radical polymerization of 1-vinyl-1,2,4-triazole

Kinetics of radical polymerization of 1-vinyl-l,2,4-triazole

2529

:8. K. ITO, N. USAMI and Y. YAMASHITA, Polymer J. 11: 171, 1979 9. A. I. KUZAYEV, O. M. OL'KHOVA and S. G. ENTELIS, Vysokomol. soyed. A17: 2120, 1975 (Translated in Polymer Sci. U.S.S.R. 17: 9, 2447, 1975) 10. A. I. KUZAYEV, G. N. KOMRATOV, G. V. KOROVINA and S. G. ENTELIS, Vysokomol. soyed. A12: 1033, 1970 (Translated in Polymer Sei. U.S.S.R. 12: 5, 1169, 1970) 1. A. I. KUZAYEV and O. M. OL'KHOVA, (book): Mezhdunarodnyi simpozium po makromolckulyarnoi khimii: Tezisy kratkikh soobshchenii (International Symposium on Macremolecular Chemistry: Proceedings of Brief Reports). Nauka, Moscow, 2: 146, 1978.

~olymer Science U.S.S.R. Vol. 24, 1~o. 10, pp. 2529-2536, 1982 Printed in Poi~md

0032-3950/82 $7.50+.00 © 1983 Pergamon Press Ltd.

KINETICS OF RADICAL POLYMERIZATION OF 1-VINYL-1,2,4-TRIAZOLE* L . A. TATAROVA, T . G. YERM~KOVA, AL. AL. BERLIN, YE. F . RAZVODOVSK[[, V. A. LOPYREV, N . F . KEDRINA a n d N . S. YENIKOLOPYAN Institute of Chemical Physics, U.S.S.R. Academy of Sciences Institute of Organic Chemistry, U.S.S.R. Academy of Sciences

(Received 22 June 1981) Studies were made of kinetic features of radical polymerization of 1-xSnyl-1,2,4. triazole a n d the molecular weight variation of poly-l-vinyl-l,2,4-triazole in water, i n DMF and in DMAA. The rate of polymerization of the monomer in water and MW ~f the polymer obtained is higher than in other solvents. MW ofpoly- 1-vinyl-1,2,4-triazole is proportional to the concentration of the monomer. I t was shown that a typical feature; of polymerization, which is general tbr all the solvents studied, is the existence of a reaction rate for the initiator with a reaction order higher t h a n 0.5. The mechanism of monomolecular decay of macroradicals is discussed. The effective activation energy of polymerization was found.

Polymers of 1-vinyl-l,2,4-triazole (VT) have a complex of valuable properties [1]. The formation mechanism of these polymers was studied insufficiently [2]. This :paper seeks to examine kinetics of homogeneous radical polymerization of VT in protic and aprotic solvents. VT was polymerized in the presence of AID in water, in D/VIF, a n d in DM_~A at 50-90% T h e concentration of VT varied within the range of 0.5-6, of the initiator between 1 X 10 - 3 3 × 10 -"~mole/1.. Kinetics of polymerization were studied by dilatometry, calorimetry and .gr~vimetry. * Vysokomol. soyed. A24: No. 10, 2205-2210, 1982.

2530

L . A . TATAROVA ~ .L

Monomer prepared by methods previously described [3] was purifieddirectlybefore th~ experiment by repeated fractionaldistiUationin vacuum (b.p. 41°]10 Pa, n~ 1.5100). The purity of the monomer was mon/tored chromatographically using a Perkin-Elmer device (model 452, SE-30 fixed phase, helium being the carriergas and excess pressure being 50 kPa, 130°). The content of the main substance was 99-3-99.7%, D M I % D M A A , A I D was purified by standard methods. W a ~ r (twice distilled)was boiled in a quartz vessel directly

before filling the ampoules. Reagents were placed into ampoules in dry argon. The reactio~ mixture was degasified in vacuum. Polymers were separated by precipitation using an acetone-ethanol mixture and purified by reprecipitation using the same mixture from PVT solution in ]:))IF. Polymers prepared in water were separated by lyophilic drying at 20°, followed by reprecipitation from DMF into a mixture of acetone and ethanol, followed by drying in vacuum to constant weight. The coefficient of contraction was determined by comparing results of dilatometric an4 gravimetric methods (0-18:~0.01 ml/g). Calorimetric measurements were carried out using a DAK-I-I automatic differential calorimeter. Reproducibility of kinetic results obtained dilatometrically and ealorimetrically was within the range of 10%. Intrinsic viscosity of PVT was measured in water at 25° in an Ubelohde viscometer. Viscosity-average molecular weights were calculated using the Mark-Kuhn-Houwink equation derived by us for PVT' in water at 25° by the light-scattering method. 25° [t/]H,O= 5"44 × 10 -4

.,M0.64

Typical kinetic curves of polymerization of VT in water, DMAA, DMF a r e shown in Fig. 1. I t can be seen t h a t independent of the t y p e of solvent, t h e y are S-shaped. The induction period is independent of monomer concentration, b u t is inversely proportional to the concentration of the initiator. I t is m o s t likely t h a t traces of oxygen function as inhibiting impurity, which is r e m o v e d with difficulty from polar solvents. This assumption is supported by the f a c t t h a t on carrying out polymerization without previous degasification of t h e reaction mixture, the induction period increases considerably. I t follows from Fig. 1 t h a t the rate of polymerization of VT in water is higher t h a n in DMF and DMAA. I n the two latter solvents the rate of polymerization is practically identical. The molecular weight of P V T obtained by polymerizatiorL in water is also higher t h a n in DMF and DM_AA. For example, intrinsic viscosity of P V T obtained in water and DMAA, other conditions being equal, is 7.0. and 2.0 dl/g, respectively. The addition of water (over 5 × 10 -2 mole/1.) to polymerization in DMAA and DMF is also accompanied by an increase in the molecular weight of PVT. Similar effects were observed during polymerization of a n u m b e r of vinyl monomers with hetero-cycles containing nitrogen or with ionogenie groups in the side chain [4]. The reactivity of VT, apparently, increasea as a consequence of specific properties of solvation of the monomer and growing radical with water. Figure 2 shows the dependence of m a x i m u m rate of polymerization wmax on t h e initial concentration of the monomer [M]0. I t can be seen t h a t the reaction is of first order regarding monomer concentration, independent of the t y p e o f solvent. The dependence of the rate of polymerization on initiator concentration in logarithmic coordinates is shown in Fig. 3a. The order of the reaction rate f o r

Kinetics of radical polymerization of 1-vinyl-l,2,4-triazole

253I

i n i t i a t o r c o n c e n t r a t i o n d e p e n d s on t h e t y p e of s o l v e n t a n d is higher t h a n 0.5, t y p i c a l of r a d i c a l p o l y m e r i z a t i o n , in e v e r y case. F r o m t h e l o g a r i t h m i c d e p e n d e n c e o f t h e r a t e of p o l y m e r i z a t i o n on i n v e r s e t e m p e r a t u r e (Fig. 3b) t h e v a l u e o f effec4ive a c t i v a t i o n e n e r g y w a s assessed. N u m e r i c a l values o f t h e a c t i v a t i o n e n e r g y a n d t h e o r d e r of t h e r a t e o f p o l y m e r i z a t i o n for t h e c o n c e n t r a t i o n of t h e m o n o m e r a n d i n i t i a t o r are t a b u l a t e d . I t is t y p i c a l t h a t a v a r i a t i o n in t h e a c t i v a t i o n e n e r g y o f p o l y m e r i z a t i o n in different solvents is p r o p o r t i o n a l to t h e v a r i a t i o n o f t h e o r d e r o f r e a c t i o n r a t e for t h e initiator. This :regularity is, p r o b a b l y , due to t h e effect of t h e a c t i v a t i o n e n e r g y o f initiation. :J,~ ~ ~tOJ, m o/e /L. sec

_

o~ 1'0

q.//~

l

Xt

0.5

tO0 T[me,min

50

150

1

200

FIo. 1

3

5 {bl]o, mole/[.

Fro. 2

FIO. 1. Kinetic curves of polymerization of VT in wa.t~.r (1), in DMF (2) and in DMAA (3). [M]0=4 mole/1., [I]0----3× 10 -3 mo}e/l. 1;'i~. 2. Dependence of maximum rate of polymerizatiot~ of VT in DMF (1) in DMAA (2) and in H,O (3, 4) on [M]0. [I]0~-6 × 10 -3 (1, 4), 1 "< 16 -2 ,'2) c~nd 3 × 10 -3 mole/1. (3).

5+1o9 wm~, Emo/e/l..sec] a

2

2

l

F I

t 0.5

I l.O

I 1.5

a * loS [ q o , [ m o l e / l J

\×2 2"8 3"0 W3/T, X-'

Fro. 3. Dependence of log Wmaxon log[I]0 (a) and on 1/T (b) in polymerization of VT in DM.F (1), DMAA (2) and in water (3). [M]0=4mole/1., [1"]o-----3×10 -8 raole]l.

L. A. TAT~OVA e t a / .

2532

O~DER OF :t'J~.~ P~ATE OF POLYMERIZATION ~ VARIOUS SOLVE~TS

ACTIVATION ENERGY I ~

Order of the reaction rate Solvent

for t h e m o n o mer

for t h e initiai tor

E f f e c t i v e activation energy, kJ/mole

1 0.9 0.8

108±2 97±2 83+2

DMF H,0 DMAA

Therefore, a typical feature of radical polymerization of VT is the order o f the reaction rate which is close to first with respect to initiator concentration and is of first order for monomer concentration. I t is known that an increase in reaction order to one with respect to initiator concentration is observe4 for radical polymerization, which is complicated b y "degradative" chain transfer through the monomer (allyl polymerization ([5]}, or for inhibited polymerization [6, 7]. In these cases, however, an increase in reaction order for initiator concentration is accompanied b y a deviation from one of the reaction order for monomer concentration. In the case of polymerization of VT the inhibitor m a y be introduced with the monomer. Analysis of kinetic systems of polymerization bearing in mind various reactions of chain termination shows that the existence of a linear dependence of the rate of polymerization Wmax on initiator and monomer concentration agrees with the mechanism of monomolecular decay of active centres. Therefore, it m a y be assumed that in polymerization of VT apart from ordinary bimolecular chain termination, monomolecular decay of macroradicals is of considerable significance. In the case of DMF bimolecular termination, apparently, has no marked effect. In water and in DMAA chain termination evidently takes place b y both mechanisms. When there are two types of termination reaction the variation of the concentration of macroradicals (under stationary conditions) m a y be described b y the following equation: --

0,

(1)

where [R'] is the concentration of radicals, k01, b02 are reaction rate constants of molnomolecular and bimolecular termination, respectively, w~ is the rate of initiation. The proportion of bimolecular termination is characterized b y the ratio

(2) The order of reaction rate of initiator concentration m a y be expressed as follows: d In wp d In[R'] m---- d In w~

=

-

-

d in w~

(3)

Kinetics of radical polymerization of 1-vinyl-l,2,4-triazole

2533

Substituting in ratio (3) the formula for [R'] derived from formula (1), after a number of transformations we obtain re(l--m) y---(4) (2m-- 1) 8 From equation (4) the proportion of bimolecular termination for water (m-~0.9) is N 1 2 ~ , for DMAA (m=0.S) ~30%. Therefore, in polymerization of VT macromolecular decay of growing radicals predominates. I f bimolecular termination is ignored, the instantaneous degree of polymerization in this case will be determined by the velocity ratio of reactions of propagation and monomolecular termination k01

(5)

A corresponding formula for the integral average degree of polymerization Pn, according to the degree of transformation a, takes the form p~

kp[M]0~' k011og ( i - - a ) ' (6) where [M]0 is the initial monomer concentration. Analysis of equation (6) indicates that the number average degree of polymerization shows a linear dependence on the initial concentration of the monomer [M]0, decreases during polymerization and is independent of the initial concentration of the initiator. Figure 4 shows dependences of the number average degree of polymerization on the concentration of the initiator, monomer and polymer yield during polymerization in DM_F and in DMAA. I t can be seen t h a t the number average degree of polymerization is independent of initiator concentration and increases with an increase in VT concentration, which is in agreement with equation (6). However, the molecular weight of P V T remains constant until polymerization is completed. Therefore, the idea of monomolecular decay of macroradieals is insufficient for explaining the results obtained. Allowing for the slight effect of bimolecular termination does not qualitatively change the situation. Let us examine possible reactions of monomolecular termination in polymerization of VT. According to the structure of growing radical the reaction system of monomolecular termination m a y be represented as follows:

k0t N ~

~CH--¢H: --> N

N "

-~- ~ CH=CH:

2534

L.A.

CH2~CH ~ I N

TATAROVA e~ aJ.

N

"t-~ C H = G H ~

~

N(~

+

~

"CH2~CH:

f

N

I!

Both reactions result in the formation of a terminal double bond which m a y take part in subsequent polymerization or combine the growing radical forming a branched macromolecules b y the reaction CH=CH2

q- ' C H - - C H 2 ~ --" "~ C H - - C ~ d 2 - - C H - - C H ~

I N N

I N ....U

N

I_.__1

,~yO -J

' 3

tZ

I-

=J

7

I

b

,.J.

2 I

I

2

3

I ~ "r"

I

[I.1 o • I0~ mole/L

~

3

I

I

I

5

[H]o , mole/L C

I

I

i

I

I

I

I

I

FIG. 4. D e p e n d e n c e of P . on [I]0 (a), o n [M]0 (b), on ~ (e) in p o l y m e r i z a t i o n of VT. a: 1 - - D M F , 2 - - D M A A ([M]0=4molefl.), 3 - - D M F ( [ M ] 0 = 6 m o l e f l . ) ; b: 1 - - D M A A , 2 - - I ) M F ([I], = 6 × 10 -3 molefl.); c: 1--DM-F ([I]0=4 × 10 -a mole/L), 2 - - D M A A ([I0]----6 × 10 -s mole/L); [M]o= 4 mole/l.

Reaction (III) m a y be the cause of reduced solubility of high molecular weight P V T synthesized during polymerization in water. In the case of (II) the macromolecule with a terminal carbene bond m a y react with the monomer, solvent, initiator or with the radical giving an inactive maeromolecule. Considering reactions (I)-(III) the following kinetic system of polymerization of VT m a y be proposed: Initiation

Kinetics of radical polymerization of 1-vinyl-l,2,4-triazole

2535

--+2R; •

kx

Ro+M . . . . E" Chain propagation Chain termination by reactions (I) and (II)

R"k°L e + ~ ; Addition of a radical to a dead macromolecule with a terminal double bond by reaction (III) •

/¢p'

R + P - - - + R" Radical recombination

R"+ R

•

k0a

- - ~ P,

~vhere I, R~, R', R~, M, P are the initiator,primary, propagating and secondary (system (Ill)) radicals, monomer and polymer, respectively, f is the efficiency of initiation, k~, kl, k~, k01, k~, k02 being the rate constants of corresponding reactions. The equation system corresponding to the kinetic system, with a slight effect ,of bimolecular termination takes the form

--d[R']/dt=wi--kol[R" ]

(7)

--d[M]/dt=kp[M] [g'] dn/dt= wl--/cp[R In,

(8)

t

*

(9)

where w~ is the rate of initiation, n is the concentration of dead polymer chains. F r o m formula (7) [R']=w~/ko~ (10) Substituting ratio (10) into formula (9), after integration we obtain an equation for the concentration of chains

"w~t

(ll)

[M]=[M]°exp { -k-~-kol .w#}

02)

n=

:,- • 1--exp kp

From tbrmula (8)

w,t} where e is the degree of conversion.

(13)

2536

L.A.

TAT~OV~ e~ aL

Then, t h e n u m e r i c a l a v e r a g e degree o f p o l y m e r i z a t i o n m a y be expressed

using equations (11) and (13),

p_

1--exp -- k0~ "w~ [ M ] j = [Mq__0k. _ _ n

kox

(141

\ 1 _ exp { _ k01 k__~_~w---~t~]

When kp=k~ _

lCl

Pn = d ' [M]0

(15)

Therefore, the degree of polymerization Pn only depends on monomer coneentration, which is in satisfactory agreement with results of experiments, i.e. the addition of a dead polymer to growing radicals enables the constancy of MW to be explained during the process. Analysis of all experimental results suggests that kinetic regularities of radical polymerization of VT depend on the presence (in addition to bimoleeular) of a monomoleeular mechanism of decay of maeromoleeules. The effect of both mechanisms of termination depends on the type of solvent. Translated by E. SE~CtEI~E REFERENCES

l. L. A. TATAROVA, T. G. YERMAKOVA, V. A. LOPYREV, N. F. KEDRINA, Ye. F. RAZVODOVSK1/, A. A. BERLIN and N. S. YENIKOLOPYAN, U.S.S.R. Pat. 647311) Byul. izobret., 85, ]979 2. H. HOPFF and M. LIPPAY, Makromolck. Chem., 66: 157, 1963 3. L. P. MAKHNO, T. G. YERMAKOVA, Ye. S. DOlVININA, L. A. TATAROVA, G. G. SKVORTSOVA and V. A. LOPYREV, U.S.S.R. Pat. 464584, ByuU. izobret., 11, 66, 1975 4. V. A. KABANOV and V. A. TOPICHEV, Polimerizatsiya ioniziriyushchikhsya monomerov (Polymerization of Ionizing Monomers). Nauka, Moscow, 50, 1975 5. P. D. BARTLETT and F. A. TATE, J. Amer. Chem. Soc. 75: 1, 81, 1953 6. K. BAMFORD, U. BARB, A. JENKINS and P. ONION, Kinetika polimerizatsii vinilovykh soyedinenii (Kinetics of Polymerization of Vinyl Compounds). p. 274, Izd. inostr, lit., Moscow, 1961 ! 7. Kh. S. BAGDASAR'YAN, Teoriya radikal'noi polimerizatsii, 2-ye i d. isp. i dop., p. 147, Nauka, Moscow, 1966