The study of kinetic features of the radical polymerization of styrene, initiated by o,o′-carbo-tert-butylperoxysuccinyl peroxide

Pblymer Science U.S,S.R. Vol. 24, 1~'o. 1, pp. 98-105, 1 9 8 2 Printed in Poland

0032-3950/82/010098-08507.5010 © 1982 Pergamon Press Ltd.

THE STUDY OF KINETIC FEATURES OF THE RADICAL POLYMERIZATION OF STYRENE, INITIATED BY o,o'-CARBO-tert-BUTYLPEROXYSUCCINYL PERO~:IDE* S. S. IvA~cc~v,v, N. G. PODOS~OVA, V. V. Ko~ovnT.~Ko, T. A. K~z~ETSOVX, E. G. ZOTrKOV and V. 1). :BVDTOV Okhtinsky "Plastpolimer" Scientific and Industrial Association

{Received 28 August 1980) The features of styrene polymerization, initiated by a tri-peroxide, having peroxide groups of differing thermal stability, have been studied using kinetic and (]PC methods. The conditions for maximum realization of the polymerization-polyrecombination mechanism during formation of the macromolecules have been determined. This results in an appreciable increase in molecular mass, whilst maintaining high polymerization rates. RADICAL polymerization, initiated by polyfunctional initiators of various structure, as has been shown in a series of papers in recent years [1-3] has a number of advantages compared with classical systems, in which monofunctional initiators are used. These advantages accrue from the formation during the polymerization of macroradicals or macromoleeules, containing peroxide groups capable of radical formation which complicate the macromolecule-forming mechan.ism by superimposing a polymerizatiou-polyrecombination mechanism [1]. This permits an appreciable increase in the molecular mass of the polymer and a simple synthesis of block copolymers of different type, whilst preserving a high polymerization rate [1]. Recently, a quantitative theory, interlinking kinetic parameters and MMD of the polymer product for such polymerization systems, was proposed [3, 4] and work appeared on the initiating effect of polyfunctional initiators, combining peroxy and azonitrile groups [5]. In this article, an experiment was undertaken, using calculation and GP(~ methods, to work out the features of styrene polymerization at various conversion stages with initiation by one of the available polyfunctional initiators~ with peroxy groups, which differ in their thermal stability. This was o,o'-carbotert-butylperoxysuccinyl peroxide (TSBP) [6, 7]. Styrene polymerization was carried out ih solution in ethyl benzene, monomer concentration 4 mole/1., initiator concentration varied in the range 0.005-0.01 mole/1. MMD analysis were carried out by GPC on a Waters GPC-501 chromatograph. Methyl ethyl ketone was used for elution: elution rate was 1.67 × 10 -~ * Vysokoraol. soyed. A24: No. 1, 84-90, i982. 98

Kinetic features of radical polymerization of styrene

99

ran/see. Sample concentration was 0.5 kg/m a, introduction time 60 see. Columns were filled with Korasyl, of type 3 X 10 -7 and 5 × 10-7 m. Calibration was with standard PS form the Waters company. MMI) parameters were calculated by the method of [8] and the chromatograms corrected by the method of [9]. The kinetic polymerization parameters and MMI) of the polymers were calculated using a kinetic scheme, taking account of the nature of the initiating radicals and their ultimate transformation. Thus the initiating reaction went according to the following scheme: I ~', 2R. I z'-~ R'.-f-R".

(radical generation by decomposition of TBSP through the diaeylperoxy groups)

(1)

(radical generation by decomposition of TBSP via the perester groups)

(2)

3M kp M.ff-M~. (radical formation from the monomer with thermal pa' ~, pa._t_R,," pa k, P'-kR""

initiation of polymerization)

(3)

(radical generation by breakdown of an "activated" PS molecule, containing 2 terminal peroxide groups)

(4),

(radical generation by breakdown of an "activated" PS molecule, containing one terminal peroxide group)

(5).

All types of radicals are converted into growing radicals on adding monomer. When compiling an MMD model, we did not pay attention to the difference ha reactivity of the various radicals and we assumed that the growth of all chains occurred with the same growth constant bp. Whether or not they contained peroxide groups, the chain termination reaction could be of three types: Pc-t-Pf k, p~+j

(with formation of inactive macromolecules)

P~'-kP~" ~', l~(+j

(with formation of "active" macromolecules, containing only one terminal peroxy group)

P~-kP]" ~°, P ~+j

(with formation of "active" macromolecules, with peroxy groups at both ends)

The model for styrene polymerization in presence of TBSP is described by the following scheme of material balance equations. dt d[I] =

dt

4[R.] - = 2k, f [I] dt

,l oj [R. ]--kp

-]

S. S. Iv~o~mv et al.

100

d[~'.] dt

= ~ A [ I ] - ~o [To] [ ~ ' - ] - ~

d ~ ~] d[P~.] -dt

dig"] -dt

[~

[lV.]

,-, a . 8,t & -k~[P ]+½~o 2 [P,-,'I [P, "]

= k,P~'+k,l~] ([P~_~.]--[e~.]}--ko[T]o[P~.] ~>> ~) oo

= k,A[I]+k, /Zc - i ([P~']+[P~]}--kJM] [Z".]--ko[T]o[R"]

d- [IK'] -

k~[M]~

dt

d[P.] - -

dt

= ks [Pa]-~-~p [M] {[P,-1 "]--[Pi

d[pa]

" ] } - - ] g o [ Y ] o [ P "]

~-1

d--7-=-~,[~*]+½ko 8=1 2 [P,'] [P,-,'] dips]

~-~

at ----½k°• [P,-] [P~-," ],

oo

where [Y]o= ~, {[P~']+[Pk']}, f -

efficiency of initiation.

k-o

Converting to differential equations for moments, we get dD.

at - A(2kJl+kJ,) [~--k0[~D..+k~,,+kp N1 [~+*},.--D,d dE,)

d t = k~,.+½k°{D+D},~ dK' dt

__ -

-

' ' + 1 }n--K~.] ' (k~,A[l']+lc,r.[M']2 )A +Ic2(Eo+ L~+ L.)--ko[Y]oK~+ICpM[{K

dL dt

k~.+½ko{D+K'}.

d~q~ d---i--= ½ko{X' +X;} {~ ~br n>O A= for n----O, oo

where

oo

~= Z

D~= Z ~ t ~ . ] ,

r--O

1¢--0

~ ,~'.],

co

oO

oO

r--O

r=O

#'--0

Kinetic features of radical polymerization of styrene

101

For the conclusion of the differential equations for moments, we used the following designations:

{A-l-1}n=An+nA~-~-

n(n--1)

2---~. A,~-2+ ...+Ao (n>~l) n(n--1)

{A + B }n= AnBo-t- nA n_lB1-~- - -

2!

An-IB2+... + AoBn

{A-~l}0~½A0

{A+B}°=½A.B. The above scheme of differential equations, supplemented by the first two material balance equations, was solved numerically on the EV3I by a specially developed program in the algorithmic language, FORTRAN. The solution was made for n-~O, 1, 2, 3. For this solution, the quasi-stationary principle was used i.e. the derivatives for D 0 and K; were assumed equal to zero and the corresponding differential equations substituted by algebraic ones. From the solution of the system of equations, the following expressions were obtained for polymerim~tion rate v, average/Sn, mean weight/Sw and z, the average P~ degree of polymeriT.ation.

P,,= P,o=

+

+ M; + Lz+

+ Lo+ M;+ Do) D,)/(EI + LI+ M; + DD

The following values of the rate constant of the component reactions were used to calculate the degree of conversion of monomer to polymer, (x, P~, P,p), kl----1"8× 10-4see -1, /~2=2"5× 10-6see -1, /¢p:583 1..mole-L see -~, /~0=1.2× 1t~s 1..mole-~.see-1 [10]. The polymerization of styrene in presence of TI3SP was compared with the analogous polymerization in the presence of a mixture of monofunetional peroxides--tauryl peroxide (LP) and tert-butylperben~oate (TBPB). This comparison emphasises the influence on polymerization of the polymerization-polyrecombinationmechanism of macromolecule formation. With the LP-TBPB mixture, k~ was taken as the decomposition rate constant of the peroxide, since monofunctional peroxides were used; also the calculation was made in 2 stages. In the first (up to x=0.3) x , / 5 and/Sw were claculated for a polymerization, in which LP was used as initiator and in the second (with x>0.3), for a process using TBPB. The choice of this critical value of conversion was explained by the fact that up to 30% conversion, styrene polymerization under the conditions used is initiated by LP; later on when the LP is exhausted, the decomposition of TBPB completes the initiation.

S. S. IvAz~OH~Vet (zZ.

102

I t can be seen from the data given in Figs. 1 and 2 t h a t calculated and experimental conversion-time, 25~-x and Pw-x ratios agree well. I t follows t h a t the suggested model permits a reliable calculation of the moments of MM]) for different degrees of initiation. .~-2

~

. ,.,-2

15

lO x

3

,5"

0.2 I

I

IO

20

FzG.

T~me,hp l

,

-. 0.2 .

O~ or

FzG. 2

FzG. 1. Curves showing the accumulation of polymer during styrene polymerization in presence of TBSP (1 and 3)and LP-TBPB mixtures (9); 1--[TBSP] = 0.005; 2--[LP]= 0.005 and [TBPBJ=0.0I mole/l., 90°. The points here and in Fig. 2 are experimental valuemthe continuous times are the calculated curves. FI(~. 3. Dependence of ~5w(1--3)and Pm,(d--6) on conversion in polymerization of styrene at 90~ in presence, of TBSP (1,3,4,6) and LP-TBPB mixtures (2,5). Initiator concentrations: 1,4 .-[TBSP] -=0.005; 3,6--[TBSP]----0.01, 2,5--[LP]=0.005 and [TBPB] -- 0.01 mole/]. A comparison of the properties of the calculated curves for styrene polymerization in the presence of TBSP and L P - T B P B mixtures shows t h a t the kinetic curves for polymer build-up in the conversion range studied agree for similar active oxygen concentrations (Fig. 1). The nature of the P n - x and 15w-x ratios, as would be expected, are different in form as well as quantitatively. The form o f the curve for L P - T B P B mixtures is characterized by maxima at x t> 0.4 at the same time as when in the curves with TBSP, in this range, there is observed an ~appreciable increase in the value of P a and especially of -Pw. We can fully explain the former type of curve, within the framework of classical radical polymerization theory. The increase in P , and Pw in the first

Kinetic features of radical polymerization of styrene

103

stage is connected with the decrease in the easily decomposed LP, whose decomposition at this point is determined b y the initiation rate. As the concentration of L P falls, so does the rate of radical formation. Accordingly an increase in the degree of polymerization would be anticipated. At x~>0.3, when initiation is determined b y T B P B decomposition, the rate of radical regeneration is hardly changed b u t the decrease in monomer concentration must lead to a reduction of degree of polymerization. This is why a slowing down in the growth o f / s n and Pw was registered in our results. The initiating effect of "activated" PS appeared during the polymerization of styrene in the presence of T B S P at x>0.3, as a resu It of w h i c h / 5 and/Sw increased.

3

100

l°s

1

0"5 I

O.3

• ,

~ 0.5 2

'

2"

0,3

13

.

.

0"1

04 0.2

0~/

Fro. 3

0.6

11

x

5° I 0"2

,

,

o.q

0"6 ~

Fro. 4

Fie. 3. Dependence of log P~/P°s, (1,3) and log P~/I=~ (2, 4) on monomer conversion at 90°at TBSP concentration 0.01 (1, 2) and 0.005 mole/1. (3, 4)./~ and P~ are the degrees of polymerization for corresponding conversions, ~fi~and P~ are degrees of polymerization with x=0.I. FIG. 4. Dependence of Pw(1-3) and Pn(l'-3") for degrees of monomer conversion at the following ratios of thermal stability of peroxy groups l--hi--k=; 2--k~k=. It is necessary to note t h a t a two-fold increase of T B S P concentration with the other conditions the same, appreciably decreases the growth of J3n and/~w with x >t 0.4 (Fig. 3); at the same time the polymerization rate is hardly changed (Fig. 1). It might be supposed t h a t there is a certain range of T B S P concentrations, in which use of the given initiator guarantees the maximum effect of increasing the degree of polymerization. To establish a correlation between the properties of the polyfunctional initiator and the M:MYD of the polymerization product, a model experiment was carried out, comprising the calculation of Pn and Pw values with different properties of thermostable groups and initiators. Figure 4 shows the calculated ratios of/~a and Pw to x for the following ratios of stability of peroxide groups:

104

S, S. IVA~CHEVa a/.

1) similar thermal stabilities, values of ]~1 and ks taken equal to 1.8 × 10-4sec-1; 2) different thermal stabilities, kl and ]~ values taken as 1.8)< 10-4sec -1 and 2.5 × 10-asec -1. Moreover, two variants were possible: a) kl~k~ and b) kl~]~ 2. The concentration of primary radicals formed b y decomposition of peroxy groups has a important significance for the calculation of the parameters of MMD. In order to keep it at a comparable level, in case 2b, the initial initiator level was doubmd, since the type of iniitator being examined contains one peroxy group having a decomposition velocity constant kl and a two peroxy groups which decompose with a velocity constant, ks. --I

~4-

a

b

-

I x/

0.2 0

2~ 0.2

I 0~t

I O.8

0

0.2

0"#

I-

0"6 X

FIG. 5. Dependence of log P'n[P~ on monomer conversion with initiator concentrations of 0-01 (a) and 0.005 mole/1. (b). Ratio of thermostability of peroxide groups: 1--kl----ka; 2--kl>ks; 3--kl
using a polyfunctional initiator, which has peroxide groups differing in thermaI stability. However, calculation indicates that during polymerization in isothermal conditions, when the predominantly labile peroxide groups w e r e decomposed, t h e degree of polymerization in case 2 m a y only be increased twice (Figs. 4 and 5). This is due to the fact that the stable peroxide groups w h i c h determine the occurrence of the polymerization-polyrecombination mechanism cannot be more than 10% decomposed. A change of initiator concentration in the model experiment, just as in practice when using TBSP, does not cause a change in the ratio of degree of polymerization with conversion but a large increase in the former would be expected with an initiator concentration of 0.005 mole/1. Thus the need to choose on initiator concentration and the corresponding temperature pattern when using polyfunctional initiators with peroxide grouFs of differing thermal stability must be considered for optimizing polymerization processes. To maximise the polymerization-polyrecombination mechanism, it is expedient to use those triperoxides with central labile and lateral stable initiating groups so that polymerization will proceed in a changed temperature pattern. favourable to decomposition of all peroxy groups. Transla2~ by C. W. C.¢PI"

Molecular weight a n d volume of spin probes

105-

I~EFEltEN¢~.$

1. S. S. IVANCHEV, Vysokomol. soyed. #.20: 1923, 1978 (Translated in Polymer Sei. U.S.S.R. 20: 9, 2157, 1978) 2. S. I. KUCHENOV, N. G. IVANOVA a n d S. S. IVANCHEV, Vysokomol. soyod. AI8: 1870, I976 (Translated in P o l y m e r Sei. U.S.S.R. 18: 8, 2141, 1976 3. V. A. IVANOV, S. I. KUCHENKOV and S. S. IVANCHEV, Vysokomol. soyod. A19: 1684, 1977 (Translated in Polymer Sei. U.S.S.R. 19: 8, 1923, 1977) 4. N. G. IVANOVA, S. S. IVANCHEV and N. M. DOMAREVA, Vysokomol. soyed. A18: 2788, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 12, 3190, 1976) 5. J. P I I R M A and L. P. H. CHOU, J. Appl. Polymer Sei. 24: 9, 2051 1979 6. S. S. IVANCHEV, V. V. KONOBALENKO, I. I. ARTIM and M. A. KOVBUZ, Dokl. A k a d . l%auk SSSR 250: 5, 1148, 1980 7. M. A. KOVBUZ, I. I. ARTIM, S. S. IVANCHEV a n d K. R. GORBACHEVSKAYA, Zh. organich, khimii 13: 2, 324, 1977 8. V. P. B U D T O V , N. G. P O D O S E N K O V A , E. G. ZOTIKOV, V. M. B E L Y A Y E V , Ye. N.

KISLOV and Yu. M. DZH/tLIASHVILI, Plast. massy, No. 2, 33, 1975 9. Ye. N. KISLOV, E. G. ZOTIKOV, N. G. PODOSENKOVA, Ye. L. PONOMAREVA a n d V. P. BUDTOV, Vysokomol. soyed. A20: 8, 1910, 1978 (Translated in Polymer Sci. U.S.S.R. 20: 8, 2147, 1978) 10. T. A. TOLPYGINA, V. I. G # L I R E I and S. S. IVANCHEV, Vysokomol. soyed. A14: 1027, 1972 (Translated in Polymer Sei. U.S.S.R. 14: 5, 1143, 1972); V. L. ANTONOVSKII, Organieheskie perekisnye initsiatory (Organic Peroxide Initiators) p. 242, Khilm'ya, 1972

Polymer Science U.S.S.R. Vol. 24, /qo. 1, pp. 105-110, 1982 Printed in Poland

0082-8950/82/010105-06507.5010, 1982 Pergalnon Press Ltd.

THE MOLECULAR WEIGHT AND VOLUME OF SPIN PROBES A N D THEIR EFFECTS ON THEIR ROTATION CAPACITY IN POLYMERS*: I. I. BARASHKOVA,A. L. KOVARSKIIand A. M. VASS~R~A~ Chemical Physics Institute, U.S.S.R. A c a d e m y of Sciences (Received 2 _November 1980)

The rotation c a p a c i t y of nitroxyl radicals of various molecular weights and volumes have been studied in n a t u r a l rubber at 313°K. The main factor determining the rotation of low mol.wt, particles in polymers is their volume (and not weight). The dimensiosns of the kinetic segment present in n a t u r a l rubber have been determined; it consists of about 4 monomer units at high temperatures. * Vysokomol. soyed. A24: No. 1, 91-95, 1982.