Polymerization of styrene, initiated by tertiary butyl perester

Polymerization of styrene

2267

merization constants r 1 and r 2, and this leads to copolymers of different chemical compositions being obtained from the same monomer mixture. (3) The regulating action of the heterogeneous catalyst leads to the formation of copolymers having a different chain microstrueture from copolymers of the same chemical composition but obtained under homogeneous conditions. Translated by G. MODLEN REFERENCES 1. G. ALFREY, ft. BORER and G. MARK, Sopolimerizatsiya. (Copolymerization.) Izd. in. lit., 1953 2. F. MAYO and F. LEWIS, J. Airier. Chem: Soc. 66: 1594, 1944 3. G. ODIAN, G. ACKER and A. ROSSI, J. Polymer Sci. 57: 661, 1962

POLYMERIZATION OF STYRENE, INITIATED BY TERTIARY BUTYL PERESTER* G . A . I~OSAYEV a n d T . V . R E I Z V I K t t Scientific Research I n s t i t u t e for Polymerized Plastics

(Received 9 December 1963)

IT HAS been shown in previous work [1, 2] that with the use of tertiary butyl peresters as initiators for the polymerization of styrene, a considerable increase is observed in the molecular weight of the polymers being formed during the process, whereas when diacyl peroxides (benzoyl peroxide) are used, this phenomenon does not take place. These results have been confirmed by other investigators [3]. However, the mechanism of the process remains as yet not completely clear. We suggest that to establish this, it is necessary to study the change in initiation efficiency during the polymerization of styrene by the given class of peroxide compounds, and to study the change connected with it, in the molecular weight of the polymers in the course of polymerization. The present work is devoted to this topic. EXPERIMENTAL Initial materials. Tertiary b u t y l peresters were synthesized t b y the reaction of the acid chlorides of aliphatic, aliphatic-aromatic and aromatic acids with t e ~ i a r y b u t y l hydroperoxide in a n alkaline medium at 10-20°C. The properties of the synthesized peresters are shown in the Table, and data on their decomposition is given in [4]. * Vysokomol. soyed. 6: No. 11, 2046-2050, 1964. t O. P. Samarina took part in the experimental work of synthesizing the peroxides.

2268

G.A. I~OSAYEVand T. V. REIZWKH

Styrene, freed from hydroquinone, was redistilled twice in a current of purified nitrogen:

1 467; d o, 09060. The polymerization of styrene was carried out at 90°C in ampoules in an atmosphere of purified nitrogen in the presence of 1% of the perester to the monomer weight. To determine the efficiency of initiation in the polymerization of styrene, peresters containing halide were used. The halide concentration in carefully reprecipitated polymer was determined by a modified SchSniger micro-method, which makes it possible to find halide in polymers in small quantities (0.5-0.01%). * RESULTS AND DISCUSSION

The kinetic curve for the suspension polymerization of styrene in the presence of t e r t i a r y b u ty l per-p-chlorbenzoate is shown in Fig. 1. The kinetic curves for the polymerization of styrene with all the other t e r t i a r y but yl peresters shown in th e Table have the same form. I00

80 C EGO Qa

4O

2O I

0

2

I

r

4 6 Time, hours

I,..

8

FIG. l. Kinetics of polymerization of styrene in the presence of tertiary butyl per-p-chlorbenzoate. F r o m the Figure it m a y be seen t h a t a marked acceleration in the polymerizat i o n of styrene starts at a degree of transformation of approximately 5 0 ~ . The molecular weight of the polymers obtained increases markedly when the degree of transformation mentioned is attained. When the monomer is almost completely converted, the molecular weight of polymer is twice as great as the molecular weight of polymers obtained with degrees of transformation of the m o n o mer up to 5 0 ~ (Fig. 2). There has been an a t t e m p t (3) to explain the increase in molecular weight during the polymerization of styrene in the presence of t e r t i a r y but yl perbenzoate and t e r t i a r y butyl peroxides, by a chain transfer reaction to the polymer, involving th e formation of polymer radicals b y capture of t e r t i a r y hydrogen * The analysis of the polymer for chlorine content was carried out by V. A. Balandina, .4.. P. Nikolayeva and G. F. Komarova, to whom the authors wish to give their sincere thanks.

..........

C0--

BrC~CO--

CH30

~f--

Br

N/~--~/CO -

C~/CH~CH~CO

~.=j

-

--

61-15

85-10

88"12

72-50

85.35

48.35

64.28

48"35

70"27

70.91

~

48.12

64.48

48"15

70'13

70.00

~o

4'76

7.14

4"76

8"10

7-27

~

~0~

5-68

6-62 8-11 11.76 12.35

H

4.50

7.19

4"73

8"46

7.50

~o

~

5"70

6.68 8.4I 11.45 12.20

found

-

29-30

--

29'30

-

--

1~

15-55

21.32 ---

~

--

15"55

21-41 ---

found

halide

calculated

-

29.30

--

29"30

-

279

224

273

222

220

~,o

~

228"5

166.5 148.0 272.0 356.0

caleulated

274

226.2

271

223

212.2

_,~

~,~

228-2

164 145 275 352

found

Mol. w t .

-

-

-

1.1081 1.0102 0.8903

d2 o

--

1.5094

1"5268

1-4907

1-5361

_

--

1.0685

1-3227

1'1005

1.0355

, ~ , 0 0 ~

--

-

1.4366 1.4014 1.4398

n~

~

40

---15

°C

M.p.

43

--

--

--

--

o

\--/ NO~

~o,~

~o

57-75

43.14 47.96 69-85 74.50

calculated

°/o

,~'~oo

C

found

composition,

5'

~0

57"76

43.24 48.65 70.58 74.16

ealculated

Element

C1

oo_

8~

83'05

CI(

~/CO -

69.67 96.67 77.75 64.48

! Yield of iperester' °,/o

CH~C1CO-CH30CO-CHa(CH2h0C0-CH3(CHa)laCO--

Acyl radicM (1R)

I

PROPERTIES OF PERESTERS I~OO-TERT. C4H 9

2270

G.A. NosAYI~V and T. V. REIZVlKlt

atoms in the polystyrene chain b y tertiary b u t o x y radicals according to the equation: H

~ C--CH2 ~ + (CH3)3CO'-+ ~ C--CHs ~ + (CH3)3COH.

I

(1)

I

Cell5

C~H5

The experimental data of Smets [5] does not confirm equation (1). He established t h a t methylmethacrylate is not grafted to polystyrene if a tertiary butyl peroxide is used as initiator. In connection with the data obtained b y us on the change in the molecular weight of the polymer, it was of interest to study the change in initiation efficiency in the process of the polymerization of styrene. For this purpose, the concentration of chlorine, joined to the ends of the polymer chains in the form of chlorbenzoate groups (because of the decomposition of the perester) was determined. The results obtained are shown in Fig. 3. As m a y be seen from the Figure, the chlorine concentration of the purified polymers being formed falls during the entire polymerization process, in a reverse way to the increase in polymer molecular weight.

Mo/.wt.

40,000 1

~ 0.3

S I 2

~,~

~0.2

I I 4 G Time, hours

F~G. 2

I 8

I 0

[ 2

] 4

] 6

I. 8

E m e , hours

Fie. 3

FIG. 2. Dependence of polystyrene molecular weight on the percentage polymerization FIG. 3. Change in the chlorine concentration in polystyrene in the process of polymerization

Attention should be paid to the fact that the reduction in chlorine concentration b y a factor of 2 (from an initial value in the reaction mixture of 0"32%) is observed just at a degree of transformation of 2 0 ~ . On the completion of polymerization, the chlorine concentration in the polymer is three times less than in the initial mixture. In this way, the results obtained are evidence of the fact that the initiation efficiency (the number of benzoate radicals joined to the polymer chains) decreases within an increase in the degree of transformation of the styrene. Thus, the ratio of the quantity of chlorine joined to the polymer to that in the initial

Polymerization of styren(,

2271

reaction mixture, amounts to 0.8 in the initial period, to 0.5 with a 50~o degree of conversion and to 0.3 in the final stage (Fig. 3). The following explanation of the results obtained seems to us to be the most probable. The primary peroxide radicals react with styrene principally in the initial period of polymerization (up to 4 0 ~ conversion). Later on, at a greater degree of conversion and a considerably higher viscosity of the medium, because of the intensification of the influence if the cellular effect, the peroxide radicals being formed begin to recombine to a greater extent than in the initial period, so that they begin to escape from the sphere of the polymerization reaction. The main role in growth of the polymer chain begins to be played by the polymer radicals. The doubling of the molecular weight of the polymer takes place at this stage in polymerization (Fig. 2). The trend of the polymerization curve (Fig. 1)--a certain acceleration in polymerization after 5 0 ~ transformation of the styrene has been achieved--corresl)onds to the increase in the molecular weight of the polymer. These features of the polymerization of styrene in the presence of tertiary butyl peresters may be explained b y the special nature and behaviour of the polymer radicals being formed, especially at high degrees of transformation. ])uring polymerization in an aqueous suspension at a comparatively high teml)erature (90°C), together with b u t o x y radicals, tertiary butyl hydroperoxide is also formed by hydrolysis of the perester: O I[ (CH3)aCOOCR+HOH-+(CHa)3COOH ~RCOOH .

(2)

In the presence of an iron salt (traces of iron are found in distilled water) tertiary butyl hydroperoxide is decomposed in the following way [6]: F(}2+

2(CH3)aCOOH ------~ (CH3):~CO" ~ (CHa).~COO"-~H20 •

(3)

The radicals being formed during the polymerization1 of styrene enter into the reaction according to the scheme: (CH3)aCO0" ÷ CH 2- CI-I-> (CH3)3COOCH~H I t

(~6H~

,

C6H5

(4)

(CH3)3COO"-~ "CH2CH~->(CHa)aCOOCH2CH~ . I

C6H5

t

C~H5

(5)

In this way, the polymer being formed contains peroxide alkyl groups on the ends of the chain. Their presence in carefully reprecipitated polystyrene, obtained in the presence of tertiary butyl hydroperoxide, has been convincingly demonstrafed b y Kern and coworkers [7], and also b y Smets [8]. Such polymeric mixed dialkyl peroxides decompose in their turn to the corresponding radicals according to the equation:

2272

G.A. NOSAYEVand T. V. REIZVIKlt (CHs)aCOOCHsCH~-+(CH3)aCO" + " O C H ~ C H ~ .

I

CsI-I5

I

Cell5 (ii)

(i)

(6)

The m a c r o - o x y radicals being formed, II, prolong t h e g r o w t h of t h e p o l y m e r chain, increasing the p o l y m e r ' s molecular weight, a n d the m i c r o - b u t o x y radicals I s t a r t a new chain f r o m the remaining m o n o m e r . I n t h e ease of r e c o m b i n a t i o n of the p e r o x i d e macro-radicals with the f o r m a t i o n o f chains with peroxide groups a t the ends: (CHa)aCOOCH~CH--[--CH~CH--].v--CHCH~O OC(CI-Ia)3

I C8H5

I Cell5

I

C6H5

(7)

a n d w i t h t h e s u b s e q u e n t decomposition of the latter, a biradical m e c h a n i s m takes place, giving rise to chaill g r o w t h a t b o t h ends a n d c o n s e q u e n t l y to a considerable increase in the molecular weight of the polymer. I n this way, one m a y consider t h a t in the initiation of the p o l y m e r i z a t i o n of s t y r e n e b y t e r t i a r y b u t y l peresters, a p a r t i c u l a r t y p e of block p o l y m e r i z a t i o n takes place a n d is a c c o m p a n i e d b y a continuous increase in t h e molecular weight of t h e p o l y m e r a t m e d i u m a n d large degrees of t r a n s f o r m a t i o n . CONCLUSIONS

(l) The p o l y m e r i z a t i o n of styrelle has b e e r studied in the presence of tert i a r y b u t y l peresters as initiators. (2) An e x p l a n a t i o n has been given for the special features of the polymerization kinetics and of the increase in the molecular weight of the p o l y m e r in the course of the reaction. Translated by G. MODLEI~ REFERENCES 1. A. V. GOLUBEVA and G. A. NOSAYEV, Plast. massy, No. 1, 3, 1961 2. G. A. NOSAYEV, R. N. STEPANOVA and O. P. SAMARINA, Plast. massy, No. 7, 8, 1961 3. S. S. IVANCHEV, A. I. YURZHENKO and N. I. 8OLOM]KO, Dokl. Akad. Nauk SSSR 140: 1079, 1961 4. G. A. NOSAYEV and R. N. STEPANOVA, Plast. massy, No. 3, 7, 1963 5. G. SMETS, Khimiya i tekhnol, polimerov, No. 7-8, 186, 1960 6. C. S. MARVEL and R. L. RANDS, J. Amer. Chem. Soc. 72: 2642, 1950; M. S. KHARASCH, B. PAUSON and W. NUDENBERG, J. Organ. Chem. 18: 322, 1953 7. W. KERN, M. A. ACHON, G. KHR(JDER and R. SCHULZ, Z. Elekbroehem. 66: 309, 1956 8. G. SMETS, Pure and Appl. Chem. 4: 287, 1962