Polymer International 45 (1998) 366È368

A Qualitative Criterion Proving theParticipation of Comonomer Complexes

in the Chain Propagation of RadicalCopolymerization

Georgi S. Georgiev, Latchezar K. Christov, Nely S. Koseva, Elena B. Kamenska*& Elena D. Vasileva

University of SoÐa, Department of Chemistry, 1 J. Bourchier Ave., 1126 SoÐa, Bulgaria

(Received 6 October 1997 ; accepted 30 October 1997)

Abstract : The juxtaposition of the equations for copolymer composition forchain propagation following the terminal (T), penultimate (P) and complex (C)mechanisms shows that the copolymer composition depends on the total co-monomer concentration only when a comonomer complex participates in the pro-pagation. This makes it possible to deÐne an easily applicable criterion provingcomonomer complex participation yet not excluding propagation according tothe T and P mechanisms. The criterion has been tested for the copolymerizationof 1-vinyl-2-pyrrolidone with acrylic and methacrylic acids, and of styrene withmaleic anhydride. It has been shown that such a dependence cannot be claimedfor styreneÈmethyl methacrylate copolymerization. 1998 SCI.(

Polym. Int. 45, 366È368 (1998)

Key words : copolymerization ; acrylic acid ; methacrylic acid, 1-vinyl-2-pyrroli-done ; styrene ; maleic anhydride

INTRODUCTION

The equations for copolymer composition according toterminal (T), penultimate (P) and complex (C) modelsare as follows.

Terminal model :

F\ r1 f ] 1r2f

] 1(1)

where : and and (i\ 1, 2)f \M1/M2 , F\ m1/m2 Mi

mi

are the mole fractions of the i-th comonomer in theinitial monomer feed and of the i-th monomer unit inthe copolymer.

* To whom all correspondence should be addressed.

Penultimate model :

F\1 ] r1@ f (r1 f] 1)

r1@ f ] 1

1 ] r2@ (r2] f )f (r2@ ] f )

(2)

where :

r1\ k11, 1k11, 2

r2\ k22, 2k22, 1

r1@ \ k21, 1k21, 2

r2@ \ k12, 2k12, 1

Complex model :

F\ f

(1] p2s2K[2])(1]r1 f ]2p1s1K[1]] s1K[1])[2]]s2K[2]2(p1s1K[1]]1)

(1] p1s1K[1])( f]r2]2p2s2K[1]] s2K[1])[2]]s1K[1]2(p2s2K[2]]1)

(3)

3661998 SCI. Polymer International 0959È8103/98/$17.50 Printed in Great Britain(

Comonomer complex participation in chain propagation 367

where :r1\ k11

k12r2\ k22

k21

s1\ k1, 21k12

s2\ k2, 12k21

p1\ k1, 12k1, 21

p2\ k2, 21k2, 12

K is the stability constant of the comonomer complex,[1] and [2] are the concentrations of the free monomers1 and 2.

It can be seen that in the case of P and T mechanismsthe composition F depends solely on the comonomerconcentration ratio f. However, if the C mechanism ispresent, F depends on both comonomer concentration(not just their ratio) and hence on the total monomerconcentration Therefore, at a Ðxed value of f, F(Ctot).will vary with the change of Such a peculiarityCtot .makes it easy to experimentally check the participationof comonomer complexes in the chain propagation.This, however, neither excludes the possibility for par-ticipation of free comonomers in the propagation, nordoes it rule out the e†ect of the penultimate unit.

In the present communication the efficiency of thiscriterion has been tested for the copolymerizations ofacrylic acid (1) with 1-vinyl-2-pyrrolidone (2), meth-acrylic acid (3) with 2, styrene (4) with maleic anhydride(5) and 4 with methyl methacrylate (6).

EXPERIMENTAL

The monomers 4 and 6 were puriÐed by distillationunder vacuum in an inert medium. The initiator 2,2@-azobisisobutyronitrile (AIBN) was twice recrystallizedfrom methanol. The puriÐcation procedure for the othermonomers has been described earlier.1h3

The experimental conditions for the 1È2, 2È3 and 4È5copolymerizations have also been described.1h3

Copolymerization of 4 with 6 was carried out at twodi†erent values of 1É2 mol l~1 and 7É2 mol l~1.Ctot :Toluene and AIBN (0É5% w/w) were used as solventand initiator, respectively. Copolymerization wascarried out in a glass tube after saturation with argon at60¡C. The copolymers were puriÐed by precipitationfrom acetone solutions in methanol and then driedunder vacuum at 30¡C to a constant weight. Conversionwas determined gravimetrically. Copolymer composi-tions were determined by elemental analysis of carbon.

RESULTS

Effect of on the 1–2 copolymerizationCtot

The experimental plots of 1È2 copolymer compositionversus monomer feed at three di†erent values of Ctot(0É87, 2É6 and 7É8 mol l~1) are presented in Fig. 1. They

provide convincing evidence that the copolymer com-position depends on It has been found1 that theCtot .acid dimer 11 and the comonomer complex 12 with sta-bility constants andKd \ (2É0 ^ 0É2) ] 103 l mol~1

respectively, take part in theK1\ 68É5 ^ 0É5 l mol~1,chain propagation when the copolymerization is carriedout in chloroform. Apparently the concentrations ofboth molecular complexes depend on whichCtot ,explains the substantial inÑuence of on the value ofCtotF at any Ðxed f.

Effect of on the 2–3 copolymerizationCtot

Although this comonomer pair has not been studied insuch detail as the 1È2 pair the functional similarity of 1and 3 raises the expectation that a complex between 2and 3 may participate in the chain propagation. In thepaper of Turaev et al.2 this has been proved, and it hasbeen shown that the copolymer composition dependssigniÐcantly on (1É0 ; 2É0 ; 4É0 and 6É0 mol l~1) at anyCtotmonomer feed composition, even when the copolymer-ization is carried out in methanol at 60¡C with AIBN(0É5% w/w) as initiator.

An important point for both systems 1È2 and 2È3 isthat by increasing the alternating tendency grows.CtotThis proves the dominating e†ect of the comonomercomplexes.

Effect of on the 4–5 copolymerizationCtot

This copolymerization has been studied in a number ofresearch centres.3h8 A variety of chain propagation

Fig. 1. Dependence of the monomer 2 units mole fraction (m2)in the 1È2 copolymer obtained by radical copolymerization onthe mole fraction of 2 in the monomer feed at 22¡C in S(M2)at three di†erent values for 0É87 mol l~1 ;Ctot : >, …,

2É6 mol l~1 ; 7É8 mol l~1.K,

POLYMER INTERNATIONAL VOL. 45, NO. 4, 1998

368 G. S. Georgiev et al.

TABLE 1. 4–5 copolymer compositions, obtained in

ethyl methyl ketone, at two different values.Ctot

(3·0 mol lÉ1 and 5·0 mol lÉ1) at 60ÄC

Mole fraction of 5 Mole fraction of 5 in copolymer

in monomer feed composition

Ctot

¼3·0a Ctot

¼5·0b

(mol lÉ1) (mol lÉ1)

0·1 0·460 0·376

0·2 0·492 0·400

0·4 0·508 0·439

0·5 0·516 0·441

0·6 0·530 0·454

0·8 0·570 0·473

0·9 0·578 0·481

a Initiator is benzoyl peroxide at a concentration of

1·0 Ã10É4 mol lÉ1 as used by Chen and Chang.5

b Initiator is benzoyl peroxide at a concentration of

4·12 Ã10É3 mol lÉ1 as used by Dodgson and Ebdon.3

mechanisms have been suggested, such as C, P andrecently the complex-dissociation (CD) mechanism. Thecompositions of 4È5 copolymers prepared under stan-dard polymerization conditions, varying only (3É05Ctotand 5É03mol l~1) are compared in Table 1. Here a sub-stantial variation of F at any Ðxed f with the change of

is demonstrated again. However, if the mole frac-Ctottion of 5 in the monomer feed is the copoly-M5¹ 0É6,mer composition is closer to the equimolar one for(m5)the lower (3É0 mol l~1) value of This is a result ofCtot .the proven combination of the C and P propagationmechanisms3,4,6 and of the fact that the reactivity ratios

andr45\ k44/k55 , r4, 54 \ k44/k4, 54 r4, 45 \ k44/k4, 45are considerably lower than 1É0, andr45[ r4, 45 B r4, 54

This result convincingly proves the par-k5, 45 [ k54 .3ticipation of the comonomer complex in the copolymerchain propagation. However, as mentioned above,neither the participation of free monomers, nor thee†ect of the penultimate unit on the reactivity of thepropagating ends should be excluded.

TABLE 2. 4–6 copolymer composition, obtained in

toluene at two different values (1·2 mol lÉ1 andCtot

7·2 mol lÉ1) at 60ÄC

Mole fraction of 4 Conversion Mole fraction of 4

in monomer (%) in copolymer

feed

1·2a 7·2a 1·2a 7·2a

0·10 3·67 2·06 0·16 0·15

0·20 3·99 3·99 0·28 0·27

0·30 3·83 3·17 0·36 0·33

0·40 2·73 4·15 0·46 0·44

0·50 3·99 0·38 0·55 0·53

0·90 3·19 0·83 0·82 0·81

in mol lÉ1.a Ctot

Effect of on the 4–6 copolymerizationCtot

The 4È6 copolymerization is interesting because theparticipation of a comonomer complex has never beensuspected in this process.9,10 Both the T11,12 andP13h15 mechanisms have been discussed as operative.The dependence of the 4È6 copolymer composition onthe monomer feed composition for two di†erent valuesof (1É2 and 7É2 mol l~1) is presented in Table 2. It isCtotobvious that the di†erences of the copolymer composi-tion at any comonomer ratio for these two valuesCtotare very slight. They fall within the limits of experimen-tal error.

In the paper of Madruga and San Roman16 the inde-pendence of copolymer composition on at di†erentCtotmonomer feed compositions has been proven indepen-dently. Therefore, the participation of a monomercomplex in the chain propagation should be excludedfor this monomer pair.

CONCLUSIONS

An easily applicable criterion, for identiÐcation ofmonomer complex participation in the propagationreaction is suggested. It is based on the dependence ofthe copolymer composition on the total monomer con-centration at a constant monomer concentration ratio.Its application helps to prove the participation of com-onomer complexes in the propagation reaction of 1È2,2È3 and 4È5 copolymerizations and to reject such par-ticipation for the 4È6 copolymerization.

REFERENCES

1 Georgiev G. S., Koseva N. & Christov L., Polym. Int., 37 (1995)277.

2 Turaev, A., Nadjimutdinov, Sh., Aripov, J., Bruevich, G.,Usmanov, H. & Mjagchenkov, V., Dokl. Akad. Nauk SSSR, 283(1985) 934.

3 Dodgson, K. & Ebdon, J., Eur. Polym. J., 13 (1977) 791.4 Hill, D., OÏDonnell, J. & OÏSullivan, P., Macromolecules, 18 (1985)

9.5 Chen, S.-A. & Chang, G.-Y., Makromol. Chem., 187 (1986) 1597.6 Brown, P. & Fujimori, K., Makromol. Chem., Rapid Commun., 15

(1994) 61.7 Brown, P. & Fujimori, K., J. Polym. Sci. : Part A: Polym. Chem.,

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17.10 Fukuda, T., Ma, Y-D. & Inagaki, H., Makromol. Chem., Suppl., 12

(1985) 125.11 Kuo, J. & Chem, C., Macromolecules, 14 (1981) 335.12 Kuo, J., Chem. C., Chen, C. & Pan, T., Polym. Eng. Sci., 24 (1984)

22.13 Fukuda, T., Ma, Y-D., Kubo, K. & Inagaki, H., Macromolecules,

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