The reactivities of nuclear-substituted phenyl acrylates in radical copolymerization with methyl methacrylate

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Eur. Polym. J. Vol. 30, No. 2, pp. 185-188, 1994 Elsevier ScienceLtd Printed in Great Britain 0014-3057/94 $6.00+ 0.00

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THE REACTIVITIES OF N U C L E A R - S U B S T I T U T E D P H E N Y L A C R Y L A T E S IN R A D I C A L C O P O L Y M E R I Z A T I O N WITH M E T H Y L M E T H A C R Y L A T E A. MILLER Institute of Synthetic Fibres, Technical University of Lodz, Lodz, Poland (Received 30 March 1993; accepted 5 April 1993)

Abstract--The radical copolymerizations of p-cresyl acrylate, p-chlorophenyl acrylate, p-bromophenyl acrylate and m-nitrophenyl acrylate with methyl methacrylate have been studied. The reactivity ratios for these systems have been determined for copolymerization at 60° in benzene; they were calculated by the linear method of Kelen and Tiid6s. Parameters Q and e for phenyl acrylates have been determined.

lates with styrene; San R o m a n [5] discussed the copolymerizations of three aromatic esters of acrylic acid with methyl methacrylate. The present study refers to four aromatic acrylates substituted in the ring; it should provide additional information about the reactivities of monomers of this group, and allow for some generalization concerning the effect of a substituent (--CH3) at the ~t position on the reactivities of aromatic acrylates and methacrylates. It can be expected that e parameters for the present series of acrylates will be higher than those of the similarly substituted methacrylates. Lack of the electron-donor group - - C H 3 at the ct position at C-------C should, however, cause a decrease in the Q values for substituted acrylates, similar to that for the Q values for or-substituted aliphatic vinyl monomers of the acrylate and methacrylate groups (acrylyl chloride, methacrylyl chloride, acrylic and methacrylic acids, etc.).

INTRODUCTION

It follows from numerous studies on the correlation between the reactivity of monomers and their chemical composition that reactivities of monomers and macroradicals depend to a great extent on resonance stabilization, polarization and steric hindrance [1]. The type, n u m b e r and arrangement of substituents at the carbon atoms attached to a double bond govern which of these three factors is dominant. The m o n o m e r reactivity has been mostly considered in terms of the relative reactivity as indicated by the reactivity ratios r~ and r 2. One of the attempts to relate structural parameters with reactivity ratios is the Q - e scheme proposed by Alfrey and Price [2]. The Q and e values, being characteristic for a given monomer, can be calculated from experimental data from the copolymerization process. The Q value, associated with the electron mobility in a monomer, determines the possibility of resonance stability dependent on the monomer reactivity (high Q values in monomers with a conjugated system of bonds). The value e characterizes the monomer polarity and that of the resultant radical. It follows from the corrected Q and e values collected by Greenley [3] that:

EXPERIMENTAL PROCEDURES

Materials Benzene was purified by standard methods. 2,2' ct-azobisisobutyronitrile (AIBN) was dissolved in chloroform. The solution was filtered and AIBN was precipitated with diethyl ether. This procedure was repeated. Mp of product 102°C. Methyl methacrylate (MMA) was washed with 5 wt% aqueous NaOH, dried and distilled twice under reduced pressure. Esters of acrylic acid were synthesized by the Schotten-Baumann reaction of acrylyl chloride with the corresponding phenols in the presence of triethylamine as described earlier [6, 7]. The resulting monomers (X-PhA) were purified by fractional distillation under reduced pressure (for p-CH3, p-C1PhA, p-BrPhA) or by recrystallization from ethanol (for m-NO2). The physical constants and the elemental analyses of these acrylate monomers are shown in Table 1.

- - v i n y l monomers with electron-donor substituents are characterized by a high negative value of e (most derivatives of styrene, propylene or vinyl esters). - - m o n o m e r s with electron-acceptor substituents are characterized by a high positive value of e (derivatives of acrylic and methacrylic acids, acrylonitrile, etc.). The above mentioned list [3] does not include data for aromatic esters of acrylic and methacrylic acids except for information about the phenyl ester of methacrylic acid. Some information on the reactivities of monomers belonging to this group of esters has been reported by Otsu [4] and San R o m a n [5]. Otsu [4] dealt with the radical copolymerization of eight aromatic methacryEPJ 3o/2-D

Copolymerization procedure Copolymerizations were carried out in glass tubes filled on a vacuum line and sealed at a final pressure of <10-4mmHg. The copolymerization temperature was 60 __+0.1 °. The copolymers were precipitated with excess 185

A. MILLER

186

Table 1. Physical prope~ies and elemental analy~s of synthesized substituted acrylates Calcd

Substituent X in PhA p-CH 3 p-Cl p-Br m-NO 2

(~p)

Bp

d~

n~

~ • 103 (°C - I )

1.0488 1.2149 1.4816 --

1.5205 1.5385 1.5612 --

0.609 0.835 1.171 --

(°C/ram Hg) 77-78/4 95-96/5 110/105

---

-29-30

methanol, and purified by several precipitations in methanol from benzene solutions; they were dried at 70° at a pressure of 0.1 mm Hg. T h e c o m p o s i t i o n s o f the m o n o m e r s a n d c o p o l y m e r s w e r e d e t e r m i n e d b y e l e m e n t a l a n a l y s e s f o r C, H , N , CI o r B r ( M r S. B i n k o w s k i , T h e M o l e c u l a r R e s e a r c h C e n t r e , L 6 d z , Poland). RESULTS AND DISCUSSION

The results for copolymerizations of X-PhA (M2) with methyl methacrylate (ML) at 60 ° are shown in Table 2. The monomer reactivity ratios (r t and r2) and the Q2 and e2 values for X - P h A were calculated as given in Table 3. The reactivity ratios were calculated by the linear method of Kelen and Tfid6s (KETL) [9] as extended to systems with high conversions (KETH) [10].

%C 74.05 59.19 47.60 55.96

Found

%H

%C1 %Br or % N

%C

%H

%0 %Br or % N

6.21 3.86 3.11 3.65

-19.42 35.19 7.25

73.81 60.06 47.44 56.08

6.28 4.04 3.34 3.78

-19.61 35.27 7.15

The KETH transformation gives the best estimates of copolymerization parameters obtainable by linear least-squares calculations and it provides a valuable visual display of experimental points. The values of r~ and r 2 calculated by the method proposed [11] allow for determination of the quantitative intervals of Ar I and Ar2 [12], and also the quantitative confidence coefficient 6 [] and parameter Q, defined thus: Arl Ar2 Q

t~ o

= exp

-

In ~2t

rl r2

The obtained values of 6 [] and Q (Table 3) for the four systems under investigation allow, in terms of the Kelen-Tiid6s classification [11], for including the performed determinations to class I--strictly linear

Table 2. Copolymerizations of methyl methacrylate (M l) with phenyl acrylates (M 2) in C 6H 6 solution at 60° [AIBN] = 3 0 . 1 0 -3 tool/din 3, [M]0 = [Mi ] + [M2] = 4.0 tool/din 3 [Mt] in feed mole fraction

Time (rain)

Conversion (%)

C/H; CI; Br or N (%)

[ml] in copolymer mole fraction

p -CH 3

0.138 0.232 0.379 0.515 0.611 0.755

22 29 52 52 70 70

24.4 18.7 34.5 24.2 28.3 10.3

10.99 10.51 10.05 9.46 9.02 8.62

0.298 0.427 0.538 0.665 0.750 0.820

p -C1

0.140 0.238 0.372 0.508 0.625 0.763

13 17 27 24 31 37

11.8 16.5 16.2 I 1.9 13.7 12.3

15.50 14.00 12.40 10.50 8.40 6.00

0.317 0.415 0.509 0.608 0.705 0.803

p-Br

0.142 0.234 0.376 0.513 0.741 0.901

12 12 24 24 35 90

17.8 14.0 23.0 16.4 18.5 31.5

28.89 26.72 23.46 20.65 13.94 7.02

0.331 0.418 0.53 I 0.615 0.776 0.901

m -NO 2

0.150 0.249 0.380 0.592 0.759 0.890

60 60 60 60 60 60

5.0 6.9 8.3 7.6 15.6 I 1.9

6.72 6.25 5.54 3.86 2.88 1.57

0.132 0.236 0.373 0.629 0.745 0.875

X in X-PhA

Table 3. Monomer reactivity ratios for methyl methacrylate (M~) with X - P h A (M2) and Q2 and e2 values for X - P h A X in X-PhA

~ values of X

Ht p-CH3 p-CI p-Br m-NO 2

0.000 -0.170 0.266 0.230 0.710

E, values of X

rI

r2

~o

Q

Q ,

e*

I/r I

log l/r I

0.00 0.03 0.10 0.12 0.35

1.555 + 0.08 1.453 + 0.259 1.018 + 0.126 0.928 + 0.048 0.912 _+ 0.144

0.450 + 0.035 0.230 + 0.075 0.240 + 0.046 0.198 + 0.026 1.064 _+0.178

-0.058 0.024 0.007 0.026

-0.560 0.688 0.351 0.828

0.630 0.774 1.168 1.342 0.871

I. 110 1.446 1.587 1.702 0.575

0.643 0.688 0.982 1.078 1.096

- 0.192 -0.162 -0.008 0.033 0.040

*Calculated by assuming that Ql = 0.74, e~ = 0.40 [8]. ?Taken from Ref. [5].

Nuclear-substituted phenyl acrylates in radical copolymerization

187

0.15

1.2

p-Br 1.0

m-NO 2 o

/

0.10 p-CI

0.8 0.05 0.6

loo/

0.4

f 0.10

0.15

ER

o --

0.2

-0.05

y = 0.995

I

I

I

0.5

1.0

1.5

-0.10

9-CH 3

Q2 Fig.

1. C o r r e l a t i o n between relative reactivities m o n o m e r s X - P h A a n d the A l f r e y - P r i c e Q values.

of

-0.15

y = 0.999

systems describable by the two-parameter model and giving accurate parameters. Table 3 gives also the values of Q2 and e2 for X-PhA calculated from the Alfrey-Price equation [2] for which the values of Ql and el were taken for methyl methacrylate as: Qj---0.74 and e z = 0.40 [8]. It follows from the results that, as for the series of aromatic methacrylates copolymerized with styrene by Otsu [4], the simple equation of Hammett does not describe the copolymerization of the investigated aromatic acrylates with methyl methacrylate. The investigated systems do not satisfy the equation of Hammett modified for radical processes by Otsu and Yamamoto [13, 14].

0.05

/ B r

-0.20 # - H

Fig. 3. C o r r e l a t i o n between A l f r e y - P r i c e Q values of X - P h A and resonance substituent c o n s t a n t E a.

log(l/r1) = p6 + TEa where 6 is the Hammett substituent constant, E R is the resonance substituent constant and ? is a reaction constant. On the other hand, one can observe for the investigated system of comonomers a clear linear correlation for the three of the four investigated comonomers (p-CH3PhA, p-CIPhA, p-BrPhA) and PhA [5] in the systems: l/rl = al Q2 + bl (Fig. 1)

r

0

0.05

o' 7 _

log 1/r a = a2ER + b2 (Fig. 2)

I

/5 p-CI

0.15

log Q2 = a3 ER + b3 (Fig. 3)

ER

where: -0.05

-0.10

aj = 0.64 + 0.045

bj = 0.22 __+0.05

a 2 = 1.9 __+0.15

b: = - 0 . 2 + 0.012

a 3 = 2.7 + 0.06

b3 = - 0 . 2 + 0.005

o Table 4. Comparison of the Q and e values for the series of phenyl acrylates (PhA) and phenyl methacrylates (PhMA)

-0.15 y = 0.994 -0.2/0/

H

-0.25 -Fig. 2. C o r r e l a t i o n between relative reactivities o f X - P h A and resonance substituent c o n s t a n t E a.

e

X in

Q

PhA and PhMA

PhA

PhMA

PhA

PhMA

H p-CHj p-CI p-Br m-NO2

1.11" 1.446 1.587 1.702 0.575

0.517 0.45? 0.72? -0.86?

0.63* 0.774 1.168 0.871 1.342

1.17? 1.237 1.35¢ -1.47¢

*Taken from Ref. [4]. ?Taken from Ref. [5].

188

A. MILLER

The correlation coefficients given in Figs 1-3 do not include the coordinates of m-NO2PhA. The special case of m-NO2PhA can be explained by the specific (inhibiting) effect of the N O 2 group on the radical polymerization and copolymerization processes. The calculated values of Q and e for the series of phenyl acrylates under investigation (Table 3) allow comparison with those obtained by Otsu [4] for the series of phenyl methacrylates (Table 4). It follows from the above list of the Q and e values that the electron-donor substituent - - C H 3 at the position of C-----C clearly decreases the polarity of monomers from the group which characterizes the resonance stabilization of the reacting monomers. Acknowledgements--The author thanks Mrs A. Biasinska, for working out the computer program and Mrs I. Chmieleeka for technical assistance. REFERENCES

1. T. Otsu. Progress in Polymer Science, Vol. 1, p. 4. Wiley, New York (1971),

2. T. Alfrey Jr and C. C. Price. J. Polym. Sci. 2, (11) 101 (1947). 3. R. Z. Greenley. J. Macromolec. Sci.-Chem. A14, 427 (1980). 4. T. Otsu, T. Ito, Y. Fuji and M. Imoto. Bull. Chem. Soc. Japan 41, 204 (1968). 5. J. San Roman, E. L. Madruga and M. A. Del Puerto. J. Polym. Sci.; Polym. Chem. Edn 21, 3303 (1983). 6. A. Miller and J. Szafko. J. Polym. Sci. 15, 1595 (1977). 7. A. Miller and J. Szafko. J. Polym. Sci. 18, 1177 (1980). 8. J. Brandrup and E. H. Immergut. Polymer Handbook, p. II-393, 2nd edn. Wiley, New York (1975). 9. T. Kelen and F. Tiidfs. J. macromolec. Sci.-Chem. A9, 1 (1975). 10. F. Tiid6s, T. Kelen, T. Ffldes-Berezsnich and B. Turcsanyi. J. macromolec. Sci.-Chem. A10, 1513 (1976). 11. F. Tiidrs, T. Kelen and B. Turcsanyi. J. Polym. Sci. Chem. Edn 19, 1119 (1981). 12. T. Kelen, F. Tiidrs and B. Turcsanyi. Polym. Bull. 2, 71 (1980). 13. T. Yamamoto and T. Otsu. Chem. Ind. 787 (1967). 14. T. Otsu and T. Yamamoto. J. Soc. Org. Synth. Chem., Japan 23, 643 (1965).