Determining constants of decomposition of initiators in the polymer phase during polymerization of vinyl chloride

Polymerization of vinyl chloride

261

10. E. G. HOFFMANN, Z. Phys. Chem. 53: 179, 1943 11. L. V. VLADIMIROV, A. N. ZELENETSKII a n d E. F. OLEINIK, Vysokomol. soyed. A I g : 2104, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 9, 2413, 1977) 12. W. A. P. LUCK, Water, a Comprehensive Treatise, eel. 2, New York-London, 1973 13. S. F. BUREIKO a n d G. S. DENISOV, Sb. Molekulyarnaya spektroskopiya (Molecular Spectroscopy). LGU, 1973 14. R. P. TIGER, Sb. M e k h a n i z m y geteroliticheskikh reaktsfi (Heterolytic Reaction Mechanisms) Izd. " N a u k a " , 1976

Polymer ScienceU.S.S.R. Vol. 22, pp. 261-207.

© PergamonPress Ltd. 1980. Printed in Poland

0032-3950/80/0101-0261507.50/0

DETERMINING CONSTANTS OF DECOMPOSITION OF INITIATORS IN THE POLYMER PHASE DURING POLYMERIZATION OF VINYL CHLORIDE* V. G. MARINII~', D . •. BERT, V. V. ZHIL'TSOV, S. I . G. F . ZVERV.VA a n d E . P . RYBK1W

Kuc~ov,

(Received 28 November 1978) Q u a n t i t a t i v e ratios were derived to describe polymerization kinetics of vinyl chlor. ide in the polymer phase with constant composition. Using a special device in a wide range of t e m p e r a t u r e a n d phase composition, rate constants of decomposition were measured in the polymer phase of some initiators extensively used in the production of polyvinyl chloride a n d a relation established between this value and phase composition.

O~E of the typical symptoms of heterophase polymerization of vinyl chloride (VC) is the fact that elementary reactions of polymerization take place in two phases: monomer and polymer phases. When polymerization takes place in bulk or suspension, the polymer phase is a highly concentrated solution of PVC in VC. In the conversion range of 0.5-60% the composition of the polymer phase is retained practically unchanged (77% PVC and 23% VC) [1]. In the range of high conversions until the process is completed the composition of the polymer phase varies continuously with an increase in the degree of conversion towards a higher content of polymer component. It is evident that the viscosity of the polymer phase which changes as a result influences rate constants of all elemen* Vysokomol. soyed. A22: No. 1, 231-236, 1980.

262

V . G . MA~U~U~

t a r y reactions, includiug the r a t e c o . r a n t of t h e decomposition o f the i n i t i a t o r , /¢I.* T h e practical use of the m a t h e m a t i c a l model o f p o l y m e r i z a t i o n kinetics o f VC in bulk (suspension) requires the knowledge of a c t u a l k2 values in the whole range of conversion [1]. Constants of decomposition of initiators given in t h e literature [2, 3] a n d used for p o l y m e r i z a t i o n of VC c a n n o t be applied as ks values in t h e m a t h e m a t i c a l model of the process. This is due to t h e fact t h a t on the one hand, w h e n m e a s u r e d in i n e r t solvents the chemical n a t u r e of the m e d i u m [4] has a n effect, a n d on the other, these values are d e t e r m i n e d in low m o l e c u l a r weight liquids of m u c h lower viscosity. A t t h e same time well k n o w n m e t h o d s of determining constants of decomposition of initiators, which are based on analyses of c u r r e n t c o n c e n t r a t i o n of the initiator b o t h b y direct m e t h o d s [5] a n d using kinetic results [6], are inapplicable in those cases w h e n the :polymer p h a s e is the medium. This is due to the absence of reliable control over i n i t i a t o r c o n t e n t in t h e p o l y m e r a n d a v a r i a t i o n of viscosity characteristics of the p o l y m e r m e d i u m [7], occurring on increasing conversion. A n original m e t h o d was developed in this s t u d y for determining r a t e c o n s t a n t s o f decomposition of initiators in the p o l y m e r phase using t h e r m a l initiators widely applied in p o l y m e r i z a t i o n of VC ,such as a c e t y l c y c l o h e x y l s u l p h o n y l peroxide (ACSP) a n d e t h y l h e x y l p e r o x y d i c a r b o n a t e ( E H P D ) . The s t u d y was also aimed a t showing t h e d e p e n d e n c e of ks values on the composition of the p o l y m e r phase. A special device was used for polymerization in the polymer phase. A monomer previously freed from traces of oxygen was condensed through a value from a metering device of the vacuum system into a part of the apparatus, whmh is a cahbrated capillary. A polymer-initiator mixture was placed into the other part, an ampoule, which is joined to the first part via the capillary and valve. A f a r evacuation the apparatus was transferred to a thermostatically controlled dual device, consisting of two sections; the calibrated capillary" was placed in one of the sections and the ampoule, into the other. The temperature of of ~0.02 °. The the heat transfer agent in the sections of the thermostat was controlled with an accuracy compomtion of the polymer phase was gwcn by maintaining a certain monomer vapour pressure above it (p), this value being regulated by the temperature of the capillary containing the monomer; this pressure was always lower than the saturated vapour pressure of VC, P0, which corresponds to the temperature of the l~action ampoule. A KM-8 eathetometer was used to observe the loss of liquid monomer from the capillary, thus controlling consumption during polymerization. When preparing the initial samples for polymerization the imtiator was measured into the polymer phase, the polymer being kept in the initiator solution in the monomer in a closed vessel at a temperature of 0 °, followed by evaporation of the monomer. T o d e t e r m i n e r a t e constants of decomposition of the initiators in ~h~ p o l y m e r phase, q u a n t i t a t i v e ratios were derived w h i c h describe poly~aerizatt~za kinetics o n l y in the p o l y m e r phase w i t h c o n s t a n t comlxmition. * When denoting the constant of decompofition of the initiator index 2 here and subsequently indicates the ratio of parameters to the polymer phone when denoting other parameters in accordmace with notations previously ~ u : [ ~ [l].

Polymerization of vinyl chloride

263

The following equation holds good for the rate of weight variation of the l~olymer in this phase: dP2 dt

= k e , [M~] R~

(1)

"where P~ is the number of moles of the polymer at a given moment of time t, kel is the rate constant of chain extension in the polymer phase, [M2] and [R~] ~re the concentration of the monomer and the overall number of radicals in the polymer phase. Equation (1) indicates that the rate of polymerization in the polymer phase with constant composition is only determined by the number of radicals Rs zinee kez and [M,] remain unchanged during polymerization. The following equation is valid for the rate of variation of the total number ~)f radicals dR, kr, Rl dt = 2k2y205 V~- = 0 (2) where f2, kr2 and Q, are the effect of initiation, rate constant of rupture and the ~mount of initiator in the polymer phase of volume V2. With the joint solution of equations (1) and (2), bearing in mind that Qs =Qo~. e-e't, where Q0, is the initial proportion of the initiator in the polymer ]phase, we obtain d P~

/ 2k, f , Qo~e-Ic't

d--V=~e, [~,] ~--~r~

V,

(a)

The volume of the polymer phase V, may be presented as V~= v~ M~ + v~ P~

(4)

~vhere v~a and v~ are the molecular volumes of the monomer and polymer in the ]polymer phase, M, is the total number of moles of the monomer in the polymer ]phase and the weight fraction of the polymer a in the polymer phase may be ]presented as P, - - (5) M~+P2 Then, excluding V~ from equation (3) using equations (4) and (5) we derive the formula for the rate of weight variation of the polymer taking place as a result ~)f the polymerization of the monomer in the volume of the polymer phase with constant composition

/2k,/, Qo, / , _

P,(0)

d~ =k~'[~']V ~ P,(O)~ m t

P, .

,

/

where Pa (0) is the initial number of moles of the polymer.

~P,(o)

(6)

~64

V.G. MxRr~

et ed.

Let us introduce P2

x= -->~1;

P~ (0)

then equation (6) is transformed into a differential equation in relation to dx

----ae-k'~l~/x; x(O)= l

(7)

After integration of equation (7) we obtain

~/x--2=alk2 (1--e -~''12)

(8)

To determine k 2 values from experimental kinetic curves both the differeno ¢ial form of kinetic equation (7) and its integral form (8) may be used. To carry out calculations, it is convenient to present experimental kinetic curves in coordinates x-t. _As an example Fig. 1 shows kinetic curves for three different conditions of polymerization. 1. Determining k 2from the differential form of kinetic equation (7). After transformations logarithmic equation (7) becomes 2"3 l o g [ - - - - : 1=2"3 log a--

(9}

Diagrammatic relations plotted using ratio (9) according to results of kinetic cm'ves in Fig. 1 (the dx/dt value was found diagrammatically by differentiation) were straight lines in every case. From the tangent of the gradient of straight~ lines the value of k2 was determined. These relations are given in Fig. 2. 2. Determining k 2 from the integral form of kinetic equation (8). When using this method it is essential that the time of experiment exceeded a few times th~ half-life of the initiator. During this time the value of x practically reaches thelimiting value x~o=(l+a/k2)2; this value being known it is easy to l~lot th~ semi-logaritl~nic transformation of the ratio (8)

4X-1

log4L_4

k,

= -t

2

(10)

Analysis of kinetic curves in Fig. 1 using ratio (10) showed that in coordinates 2.3 log (x/x~--1)/(~/5oo--~/5) and t experimental points are situated on a straight, line, which passes through the origin of coordinates, in accordance with equation (10). The gradient of these straight lines k2/2 enables constant k S to be determined. The Table shows k2 values calculated from the differential (7) and integral (8) forms of the kinetic equation for different conditions of polymerization: dif-

Polymerization of vinyl chloride f e r e n t temperatures, types of initiator a n d polymer phase composition. I t follows from the Table t h a t k z values determined b y either m e t h o d s show s a t ~ f a c t o r y agreement, which is evidence of the v a l i d i t y of theoretical q u a n t i t a t i v e x

x

2.5

cL

=1

-

20

2O

1"6

I'G

oi o2 r, 3

2.1 l

80

I

,

80

2#0

I

I

2qo

80

I

I

240

Time ~ rain

]FIG. I. Kinetic curves of polymerization of VC in the polymer phase, the process talcing place with constant composition: a--70 °, initiator EHPD, p/po=0-95; b, c--60°; initiator ACSP, p/p0=0-95 (b) and 0.88 (c); initial content of the initiator in the polymer p h i . ~--0.028; b, c--0.125~/o; /--experimental points used for plotting kinetic curves; o r d i n a ~ from which kt values were calculated using formulae (7) (2), (8) (3). A

B

V C

I F

,.o -, #0

120

Time, rain F ~ . 2. D e ~ e n c o

200

-,.,

4O

120

180

Time, rain

of a = 2.3 log \d= d ; ! (Z) and B = 2.3 log 4~_.~_4~. x/~-(2) on time in poly-

merization of VO in the polymer phase: a-c--correspond to kinetic curves in Fig. 1; ordinates of points on straight lines were oMoulated from ordinates of kinetic curves in Fig. I, denoted by points 2 (I) and 3 (2), respectively. ~atios proposed, for t h e description of polymerization kinetics in the p o l y m e r phase w i t h c o n s t a n t composition a n d the accuracy of results of determining/¢~ values. An analysis of t a b u l a t e d results indicates t h a t k= values a n d a c t i v a t i o n

V.G. M~.m-~u~eta/.

266

energies Ea of the initiators examined depend on the coml~osition of the p o l y m e r phase for all the temperatures selected: with a reduction in the content of t h ~ monomer in the polymer phase, ]¢~ decreases and Ea increases. I ) E C O M P O S I T I O N R A T E CONSTANTS IN" TkLm P O L Y M E R P H A S E F O R

ACSP AND EHPD

INITIATOR~

A N D A C T I V A T I O N E N E R G I E S OF DECOMPOSITIOI~', D E T E R M I N E D F O R D I F F E R E N T C O N D I T I O N S O]~" P O L Y M E R I Z A T I O N OF V C

Initiator

Relative vapour pressure,

PIPe kCSP

~.HPD

]¢1× lOS, see

70°

Monomer content in the polymer phase, ~o 23.0 16.5 13.5 9.8 7-0 2.0 [2]

1.00t O.95 O.88 0.77 0.68 0.48 Benzenet

23.0 16.5 13.5 9.8 7.0 2-5 [3]

60"

15o"

method of calculation*

a

1.00t 0.95 0.88 0.77 0.68 0.48 Benzene:

I

I b

235 i -197 I - 186 185 173 174 158 166 153

la

Ib

77.4 67-0 58~0" 50.0 48.6

I

-62.5 60-0 52.6

72.0 52.4 51.0 42.0 36.1

25"9 21"0 17"0 15"1

--

25,200 25,700 26,600 27,800 27,600

48

385

60.3

a

E a of initiator decomposition, cal/mole

--

64.2 ----

25-2

--

19.6

--

16.4

--

15-4

--

11-3

--

5"4

24,300 24,600 26,500 28,400 32,70(~

-79.0

20.4

5"0

* a-differential; b - i n t e g r a l . 1" /:J values corresponding to a r e l a t i w vapour pressure of VC o f one, were obtained b y graphical extrapolation o f ~ ~ d u e s s h o w n in this Table a n d determined at relative pressures lower t h a n one. Results of decomposition constants of initiators in solvents, taken from results in the literature.

Regularities derived in the variation of decomposition constants of initiators and activation energies with a change in the composition of the p o l y m e r phase (viscosity) do not conflict with results well known from the literature [8, 9]. An increase in b 2 and a reduction in Ea with an increase in the content of t h e monomer in the polymer phase (reduction of viscosity) is, apparently, due t(~. the fact t h a t on the one hand the probability of radical yield from the "cell" b y rapid chain transfer to the monomer [8] increases and, on the other, the rot a r y motion of primary radicals formed during decomposition in the cell, becomes easier [9]. I t should be noted t h a t constants of decomposition determined b y otherauthors [2, 3] for the initiators studied in inert solvents (Table) are either somew h a t higher t h a n the k s values determined b y the authors for the polymer phase, or are close to these values. This fact m a y confirm t h a t medium viscosity andt ehemical structure influence decomposition constants of initiators. Trandated by E. S~um~

Polymerization of vinyl chloride

26T

REFERENCES

1. S. I. KUCHANOV and D. N. BORT, Vysokomol. soyed. AIS: 2393, 1973 (Translated i ~ Polymer Sci. U.S.S.R. 15: 10, 2712, 1973) 2. Ya. N. ZIL'BERMAN, Polucheniye i svoistva polivinilkhlorida (Preparation and Propcrties of PVC) Izd. "Nauka", 1968 3. M. YAMADA, K. KITAGAWA and T. KOMAI, Vinyls and Polymer 11: 38, 1971 4. Kh. S. BAGDASAR'YAN, Tcomya radikal'nm polimerizatsii (Theory of Radical Polymerization) Izd. "Nauka", 1969 5. N. M. E M A N I ~ L ' and D. G. KNORRE, Kurs khimlcheskoi kinetiki (Course of Chemical Kinetics) Izd. "Vysshaya shkola", 1969 6. G. V. KOROLEV, A. A. BERLIN and T. Ya. KEFELI, Vysokomol. soyed. 4: 1520, 196~' (Translated in Polymer Sci. U.S.S.R. 4: 3, 482, 1963) 7. G. P. GLADYSHEV and V. A. POPOV, Radlkal'naya polimerizatsiya pri gluboklkh~ stepenyakh prevrashcheniya (Radical Polymerization With High Degree of Transformation) Izd. "Nauka", 1974 8. P. Ye. MESSERLE, S. R. RAFIKOV and G. P. GLADYSHEV, I)okl. AN SSSR 166: 158, 1968 9. A. F. GUK and V. F. TSEPALOV, Kinet~ka i kataliz 12: 910, 1971