Radiation Induced Polymerization of Some Vinyl Monomers in

4

Radiation Induced Polymerization of Some Vinyl Monomers in Emulsion Systems DIETER HUMMEL, GREGOR LEY, and CHRISTEL SCHNEIDER

Downloaded by EAST CAROLINA UNIV on December 22, 2017 | http://pubs.acs.org Publication Date: January 1, 1962 | doi: 10.1021/ba-1962-0034.ch004

Institut für physikalische Chemie und Kolloidchemie an der Universität Köln, Germany

Aqueous emulsions of styrene, methyl methacrylate, methyl acrylate, and ethyl acrylate were polymerized with γ-radiation from a Co

source in

60

the presence of sodium dodecyl sulfate or sodium laurate.

The continuous measurement of conver

sion and reaction rate was carried out dilato metrically.

The acrylates polymerized fastest and

the over-all polymerization rate increased as fol lows:

styrene on the initiation rate i n the period of zero order, w h i c h was observed b y us, agrees well w i t h classical conceptions: The period of particle formation is over and the radicals formed now affect initiation and termination likewise. Therefore the initiation rate can not influence the reac tion rate. (Actually the reaction rate increases somewhat, on strongly increasing the dose rate. This shows that the mean radical concentration, n, i n the particles is slightly higher than 0.5. T h e termination reaction is already retarded. ) Br

Br

PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

HUMMEL ET AL.

71

Radiation Induced Polymerization

F i n a l l y , we polymerized four standard charges, two each w i t h dose rates of 50 and 200 rad per hour respectively. T h e maximum over-all reaction rate rose by a factor of 2 w i t h quadruple dose rate, from about 0.2 to about 0.4 m g . of polymer per minute per gram of emulsion. This corresponds to the "square root l a w " (termination w i t h two radicals) : v ~ /o.s Br

where I = radiation intensity or dose rate (4). It cannot be decided from our ex perimental results, whether the exponent amounts to 0.5 or 0.4 according to Smith and Ε wart ( 3 3 ) . M M A . Figure 6 shows the over-all reaction rate plotted logarithmically vs. time i n case of the γ-emulsion polymerization of M M A . After the sharp rise of t ) , a period of zero order of v seems to follow. B u t then u increases further and reaches a maximum at about 5 0 % conversion. Soon afterwards, the curve drops sharply, and v decreases almost as fast as if the radiation source were removed at this point. This decrease does not follow, or follows for only a short time, a first-order law w i t h respect to monomer concentration. There also is no reaction of the second order w i t h respect to [ M ] . T h e first part of the log v /t function up to the maximum may be interpreted as follows. A t the beginning, the reaction proceeds according to the conception of Harkins. Dispersed P M M A takes up 3 to 4 times its monomer (by w e i g h t ) ; contrary to P M M A , dispersed polystyrene dissolves only 1 to 1.5 times its own weight of monomer (Table I ) . In the case of the emulsion polymerization of M M A , the pure monomer phase therefore disappears at about 3 0 % conversion. F r o m here on, the TrommsdorfF (38) or gel effect acts to increase the over-all reaction rate until the maximum is reached. D u r i n g this period, the bulk of the monomer i n monomer-polymer particles is consumed. T h e following sharp drop of v may probably be explained by the assump tion that because of high concentration of polymers of h i g h molecular weight in monomer-polymer particles, diffusion of not only polymer molecules but also monomer molecules is retarded. Therefore further polymerization takes place more slowly, despite the high mean radical concentration (gel effect) ! Trommsdorff et al. (38) and Baxendale et al. (7,8) observed a similar be havior i n the catalytic emulsion polymerization of M M A ; the reaction was not studied dilatometrically, however. T h e conversion-time functions of Baxendale and coworkers do not show the acceleration effect as obviously as the curves of Trommsdorff or ours, probably because of long intervals between sampling. E t h y l Acrylate ( E A ) . Figure 7 shows the over-all reaction rate plotted logarithmically vs. time i n case of the γ-emulsion polymerization of E A . T h e function shows a very simple form: from the beginning ν increases rather fast ( i n 6.5 minutes at 200 rad per hour) u p to a maximum, and then decreases slowly without a period of zero order, following w i t h considerable accuracy the first-order l a w w i t h respect to [ M ]. A t high conversions and very low reaction rates (about 0.05 m g . per minute per gram of emulsion), the curve falls less steeply. Other authors observed that acrylic esters showed smaller gel effects, the larger the alkyl groups linked. A c c o r d i n g to M e l v i l l e (25, 2 6 ) , butyl acrylate polymerized i n bulk shows no gel effect. If one assumes that E A shows no gel effect (at least under our conditions of γ-emulsion polymerization), and that the pure monomer phase disappears at the maximum of v then the behavior of our system harmonizes w e l l w i t h theory: after the maximum, the over-all reaction rate must decrease following first order w i t h respect to [Af ]. Br


Br

B r

Br

Br

Br

Βτ

Bry


ADVANCES IN CHEMISTRY SERIES

72

EP

disappearance of pure monomer phase

MA)

of

MA

\3 moles/ kg emulsion

SD$ 4,58 W~ molesjkg solution l

dose rate 50rjhr


ft nal con vers io η δ 1,3 */.

disappearance of pure monomer phase

$ZA) 1,23moles/kg emulsion [SDS] 4,5-IO' moles/kg solution dose rate 200r/hr final conversion 78,5% 2

7. conversion 5 10 20 30

» 40 /5

50 20

60 25

30

Figure 7.

70 35

40 t minutes

50

75

60

60

Over-all reaction rate vs. time

M e t h y l Acrylate ( M A ) . T h e γ-emulsion polymerization of M A was studied most intensively i n our investigations. T h e dependence of the reaction rate/time function, and the maximum reaction rate, on composition of the mixture, dose rate, and temperature was studied. I N F L U E N C E OF DOSE R A T E . Figure 8 shows the reaction rate/time functions for the γ-emulsion polymerization of M A at three different dose rates. T h e "stand ard function" at 200 rad per hour very rapidly passes u p to a maximum (period I ) ; this is reached after 5 to 7 minutes. The reaction rate then falls off i n two periods (II and I I I ) , first slowly, and then faster. Both periods are linear i n the first approximation. A t high conversions, the reaction rate decreases somewhat more slowly (similar to E A , period I V ) . A t lower dose rates period II becomes longer, and the maximum value of t> decreases. Br

plotted vs. dose rate i n double logarithmic presentation ( F i g u r e 9) produces a straight line w i t h the slope 0.55. T h e same diagram shows the slope of periods II and III, plotted vs. dose rate. T h e resulting straight lines show similar slopes. Table I V shows the measured values. I N F L U E N C E O F T E M P E R A T U R E . W e determined reaction rate/time functions for reaction temperatures of 15°, 25°, and 50°C. (Table I V ) . None of the parameters showed a remarkable temperature influence. PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

HUMMEL ET AL

Radiation Induced Polymerization Influence of Dose Rate and Temperature on y-Emulsion Polymerization

Table IV. Br *x>

v

m

Dose Μξ. Polymer/ Rate, G. rad/Hour X Min. E m u l 8 i o D

TV, Slop* Particles/ML Per. II Per. Ill X 70 14

DOSE R A T E


73

200

4 4

1 16

50

2 2

0 51

22.2

1 2

0 25

3 3 1 1 0 0

M, Dl./G.

Mol. Wi. Χ 70

6

6

16 36 54 84 77 90

1 .85 1 .85 1 .55 1 .55 1 27 1 27

3.85

1.38

4.4 5.0

1.62 1.88 —

— —

—

— —

TEMPERATURE*

Temp., °C. 15

2.1 0 45 1 .46 1.95 4.4 1.62 2.2 0 45 1 .55 — — — 25 2.2 0 51 1 .54 1.55 — — 2.2 0 51 1 .84 4.4 1 .62 — 50 2.0 0 46 1 .24 1.55 4.3 1.58 1.8 0 46 1 28 — — — ° Arbitrary units. Temp. 25 °C. Emulsifier 0.045 to 0.046 mole sodium dodecyl sulfate/kg. soin. 1.29 to 1.32 moles MA/kg. emulsion. Dose rate 50 r/hour. Monomer 1.30 to 1.34 moles MA/kg. emulsion. Emulsifier 0.0451 to 0.046 mole sodium dodecyl sulfate/kg. soin. 6

c

I N F L U E N C E O F M O N O M E R C O N C E N T R A T I O N IN ORIGINAL M I X T U R E .

V

BT

A >

* max

increases w i t h [ Μ ] · (Figure 1 0 ) ; at the same time, the maximum values are reached earlier. A t the highest monomer concentrations investigated by us, v seems to become independent of monomer concentration. This is shown i n Figure 0

8

BTmA%

Figure 8.

Influence of dose rate on v /t curve 25° C. Br



74

4,4 mg 2,2mg 1,2mg • EPofMA

0,15mg

• V^max. versus dose rale

•3,40

• slope period U versus dose rale - slope period JUversus dose rale

•V6 •05/


•025 50

0J5

200

r/hr

Figure 9.

Effect of dose rate on maximum reaction rate and slope of periods II and III

10, where ϋ is plotted vs. monomer concentration i n a double logarithmic scale. Period II becomes shorter with decreasing monomer concentrations, and finally it cannot be distinguished from period III (Figure 11). Period III be comes steeper w i t h decreasing monomer concentration. T h e number of particles per milliliter of dispersion seems to increase w i t h monomer concentration; the values from the highest monomer concentrations studied by us are not uniform, however. T h e viscosity number of the polymers increases w i t h monomer concentration, but seems to fall again at the highest monomer concentrations. In this case also the values were not uniform. Table V shows the measured values. Β Γ | η Μ

INFLUENCE OF EMULSIFIER CONCENTRATION.

M o s t experiments on the

in

fluence of emulsifier concentration were carried out at a dose rate of 50 rad per hour, with a monomer concentration of 1.2 to 1.4 moles per k g . of emulsion

30 20

ε ^

05

Οι

° 0,2

Q)

01

Y-EP of MAfSOr/hr^SmMol SDS/kg solution) max. overall reaction rate versus monomer cone η. Q2

Q3 Of OA

ΐβ

2P

30

φ 50

log [MA] mol/kg

Figure 10.

Effect of monomer concentration on maximum over-all rate 25° C.



HUMMEL if AL.

10

20

75


30

40

SO

60

70

80

90

100

110

120

130

1*0

150

ISO 170

t minutes

Figure 11. Effect of monomer concentration on ν j t curve 25° C. Br

(volume ratio 1 to 7 ) , and at a temperature of 25°C. T h e concentrations of sodium dodecyl sulfate were varied between 0.77 X 10~ and 11.9 X 10~ mole per kg. of solution. Table V shows the results of our measurements. T h e reaction rate/time functions of three emulsions with lowest, medium, and highest emulsifier concen tration are shown i n Figure 12. Periods II and III become indistinguishable at the lowest emulsifier concentrations (about 2 grams of S D S per k g . of solution) studied b y us: After rapidly rising to a maximum, log t ; decreases linearly w i t h time. A t higher emulsifier concentrations, a break appears between periods I I and III. Simultaneously, period II becomes longer, until a long period of constant reaction rate has formed at the highest emulsifier concentrations. M a x i m u m over-all reaction rate is always reached after about 5 to 7 minutes. It is highest at the lowest emulsifier concentrations, and decreases continuously with rising emulsifier concentrations (Figure 1 3 ) . T h e number of particles per milliliter of dispersion increases w i t h increasing emulsifier concentration; the diameter of the particles decreases simultaneously. A t the highest emulsifier concentrations used, the particle sizes fell below the resolving power of the ultramicroscope, and w e could not count them. Intrinsic viscosity and molecular weight of the polymers increase w i t h increas ing emulsifier concentrations. 2

2

B r

E F F E C T O F I N T E R M I T T E N T RADIATION.

If d u r i n g the γ-emulsion p o l y m e r i z a

tion of M A , the irradiation is stopped once or repeatedly, the reaction rate/time function always rises again to the value w h i c h would have been reached w i t h continuous irradiation and at the same conversion (Figure 1 4 ) . Neither υ nor other figures measured b y us change with intermittent irradiation, except the falling and rising of the log v /t function at stopping and starting of irradiation. Β Γ ι η χ

Br


76

ADVANCES IN CHEMISTRY SERIES Table V. Influence of Original Monomer and Emulsifier Concentrations on y-Emulsion Polymerization of Methyl Acrylate (Dose rate: 50 rad/Hour. Temp. 25 °C.)

[MA], Moles/Kg. Emulsion

^Brmax..

[SDS], Mg. Polymer/ Ν, Slope" Mmoles/ G. M, Particles/ Kg. Soin. X Min. Per. II Per. Ill ML X 70 *Dl/G. Kmulsion

l

Mol. Wt.

X 70*


ORIGINAL MONOMER GONCN.

0 .485

41 .2

0 .88 0 .88 1.16 1.16 1.1 1.2 1.6 1.7 2 .2 2.2 2 .4 2 .72 2 .8 3.0 2 .9 3.0 3.0 3 .0 3..0 3..1 2. 8 2 .9

0 .680

42 .8

0 .836

44 .3

0 .870

45 .5

1.30

45 .8

1.72

45 .5

2 .10

51 .4

2 .24

51 .3

2 .64

52 .0

3 .0

55 .4

3,.57

58,.5

1. 25

22. 9

2. 88

0. 68

1..20

23..0

1. 33

23. 0

2. 6 2. 8 3. 2 3. 2 2. 2 2. 2 2. 2 2..2 1. 6 1. 8 1. 26 1. 2 1. 2 1. 0 1. 5

0. 62 0. 62 0. 91 0. 91 0. 51 0. 51 0. 45 0. 45 0. 3 0. 3 0. 1 0 0 0 0

0 .51 0 .51 0 .52 0 .52 0 .44 0 .44 0 .48 0 .48 0 .395 0,.395 0. 29 0..365 0. 2 0 .2

1.58 1.58 1.73 1.73 1.6 1.7 1.75 1.75

— —. 1.05 — — — — — 1.55 — 2.6 — 3.2 — — — — — 3.1 — — —

4.1 — 4.65 — 5.0 — 5.1 — — 4.4 6.0 — 3.6 — 3.7 — 3.5 — 4.3» —. 2.55 —

1.49 — 1.73 — 1.88 — 1.92 — — 1.62 2.36 — 1.28 — 1.32 — 1.24 — 1.58» — 0.83 0.83

1..68

2.0

4.4

1.62

1.76 1.76 1 .76 1.76 1.54 1 .64 1 .28 1 .32 1 .08 1 .4 1.,12 1..04 1. 25 1. 07 1. 34

2.0 — 2.1 — 1.55 —. 2.25 — 2.8 — 3.3

5.3 — 3.6 — 4.4 — 4.8 — 5.6 — 5.8 5.3 —. 6.0 —

2.0 — 1.36 — 1.62 — 1.8 — 2.15 — 2.25 2.02 — 2.36 —

1.54 1.84 1.04 1.46

1.7 1.38 1.38 1.19 1.25 0 .92 0 .92

EMULSIFIER CONCENTRATION

1. 30

45. 8

1. 49

60. 0

1. 37

74. 3

1. 42

90. 2 90. 2

1. 32 1. 39

119

° Arbitrary units. Soluble fraction. Invisible with Zsigmondy microscope.

c c

6

c

T h e pre- and after-effects are characteristic; they are discussed below. E F F E C T O F INTENSITY C H A N G E S DURING P O L Y M E R I Z A T I O N .

I n three experi

ments, the irradiation was stopped after having reached different stages of poly merization. Hereafter, the reaction was continued w i t h fourfold dose rate. I n a l l cases t ) increased to twice the value w h i c h w o u l d have been obtained w i t h the lower dose rate. Discussion of y-Emulsion Polymerization of MA. Period I of increased reaction rate is caused by the growing of the stationary radical concentration i n the system. T h e interpretation of this part of the curve is like the interpretation of the same period i n the emulsion polymerization of styrene. B r


HUMMEL ET AL.

77


ίο : 4

Effect of Emulsifier Concentration on EP of MA -— [SDS] 774 • !0~3 moles 1 kg solution — [SOS] 4.58 · W" moles I kg solution [SOS] 902 · W" molesj kg solution 2

2


^4 - [3 molesj kg emulsion dose rale - 50ή hr

toi

~JÔ

20

To 50

30

60

To 80

S

WO ï/0

W

140 150 160 170

180

t minutes

Figure 12.

Effect of emulsifier concentration on v /t curve Br

25° C. ΤΈΡ of MA (50r/hr;l2...1,5 Mol M A/kg Emuls.) max overall reaction rate versus SDS-concn. &2

4 5 6 [SDSj mol/kg

-r

Figure 13.

Ίο

7

Γι Wlb'
thus calculated are some decimal powers lower than those determined b y different methods i n homogeneous systems. This fact demonstrates—if our interpretation is right—the effective hindrance of the termina tion reaction i n the emulsion polymerization system. It must be caused b y the heterogeneity of the system, w h i c h is divided into numerous isolated reaction phases. T h e retardation of the termination reaction, postulated b y a l l workers on the subject, is thus demonstrated experimentally b y the values of k . p

p

t

after

ρ Γ β

h

2

2

p

-1

p

1

p

1

-1

t

h

p

t

Conclusion Styrene, methyl methacrylate, ethyl acrylate, and methyl acrylate are easily polymerized in aqueous emulsion under the action of C o γ-radiation. T h e maxi m u m over-all reaction rate increases i n the sequence given above. U s i n g a dose rate of 200 rad per hour, the doses required to obtain a conversion of 80 to 9 0 % amount to about 1 0 rad. This dose is far lower than the doses required for a measurable degradation or cross linking of the polymers formed. T h e G value of formation of polymer molecules was found to be orders of magnitude higher than the G ( H 0 ) values referred to in the literature. T h e course of the γ-induced' emulsion polymerization was followed w i t h a highly sensitive self-recording dilatometer. T h e variation of the over-all reaction rate w i t h time i n the emulsion polymerization of Μ ΜΑ, ΕA , a n d M A deviated 6 0

3

R

2


HUMMEL ET AL.

85


from the classical behavior of styrene. D u r i n g the γ-emulsion polymerization of M A , the Trommsdorff or gel effect controls t> from the very beginning of the reaction. Variation of the temperature between 15° and 50° C . had no detectable effect on the polymerization. D u r i n g the γ-emulsion polymerization of M M A a strong gel effect seems to occur. B y γ-ray initiation of the emulsion polymerization, the initiation rate c a n be altered instantaneously without interfering with the system. T h e termination constants of the emulsion polymerization systems are orders of magnitude lower than the corresponding values of k determined i n homogeneous systems. Thus the hindrance of the termination reaction i n the emulsion polymerization system is demonstrated b y the values of k . Polymers obtained at small dose rates h a d rather high molecular weights ( > 1 0 ) . T h e number of particles of polymer dispersions were i n the magnitude range of 1 0 particles per m l . Br

h


t

6

1 4

Acknowledgment T h e authors thank G . Schmid, director of the Institut fur physikalische Chemie und Kolloidchemie, University of Cologne, E . Trommsdorff, R o h m & Haas G . m . b . H . , for many helpful discussions, and E . Zehender, Robert Bosch G . m . b . H . , for the electron micrographs. This work was supported b y the Bundesminister fur Atomkernenergie u n d Wasserwirtschaft. O n e of us ( G . L e y ) thanks the American Research Foundation for a stipendium. Literature Cited

(1) Allen, P. Ε. M., Downer, J. M., Hastings, G. W., Melville, H. W., Molyneux, H. P., Urwin, J. R., Nature 177, 910 (1956). (2) Bagdasaryan, K. S., J. Phys. Chem. (Moscow) 22, 1181 (1948). (3) Baker, C. A., Williams. R. J. P., J. Chem. Soc. 1956, 2352. (4) Ballantine, D. S., Rept. BrookhavenNatl.Lab. T-50 No. 294, p. 18; T-53 No.317, 7 (1954).

(5)

B a m f o r d , C. H., "Kinetics o f V i n y l P o l y m e r i z a t i o n ,"

Butterworths, L o n d o n ,

Eng

land, 1958. (6)

Bartholomé, Ε., Gerrens, H., Herbeck, R., Weitz, H. M., Ζ. Elektrochem.

60, 334

(1956).

(7)Baxendale,J.H.,Bywater,S.,Evans, M. G., J. Polymer Sci.1,237,466(1946). (8) Baxendale, J. H., Evans, M. G., Kilham, J. K., Trans. Faraday Soc. 42, 668-75 (1946). (9) Bovey, F. Α., Kolthoff, I. M., Medalia, A. I., Meehan, Ε. J., "Emulsion Polymeriza tion," Interscience, New York, 1955. (10)Burnett,G.M.,"Mechanism of Polymer Reactions," Interscience,NewYork,1954. (11) Burnett, G. M., Trans.FaradaySoc. 46, 772-82 (1950). (12) Chapiro, A., Ind. plastiques mod. (Paris) 8 (9) 67 (1956); 9 (1), 41; 9 (2) 34 (1957). (13) Chapiro, Α., Maeda, N., J. chim.phys.56(2),230(1957). (14) Charlesby, Α., "Atomic Radiation and Polymers," Pergamon Press, New York, 1960. (15)Fuhrmann,N.,Mesrobian,R.B.,J.Am.Chem.Soc.76,3281(1954). (16) Gerrens, H., "Fortschritte der Hochpolymeren-Forschung," Vol. I, No.2,Springer Verlag, Berlin, 1959. (17) Hachihama, Y., Sumitomo, H., Tech. Repts., Osaka Ind. Tech Research Inst. 3, 91, 385 (1953). (18)Harkins,W.D.,J.Am. Cham. Soc. 69, 1428 (1947). (19)Harkins,W.D.J.Polymer Sci. 5, 217 (1950). (20) Haward, R. N., Ibid., 4, 273 (1949). (21) Heller, W., J. Colloid Sci. 9, 547 (1954). (22) Marzolph, Η., Schulz, G. V., Makromol. Chem. 13, 120 (1954). (23) Matheson, M. S., J. Am. Chem. Soc. 73, 5395 (1951). PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.



86

(24) Matheson, M. S., Auer, E . E., Bevilacqua, Ε. B., Hart, E . J., Ibid., 73, 1700 ( 1951 ). (25) Melville, H. W., Trans. Faraday Soc. 45, 1049 ( 1949 ). (26) Melville, H. W., etal.,Proc.Roy Soc. 207 A, 285 ( 1951 ). (27) Meyer, F. W., Ronge, G., Angew. Chem. 52, 637 ( 1939 ). (28) Mezhirova, A. P., etal.,Vysokomolekulyarnye Soedineniya ( Moscow ) 1, 68 ( 1959 ). (29) Okamura, S., etal.,Intern. Conf. on "Application of Large Radiation Sources in In dustry and Especially to Chemical Processes," Warsaw Poland, Sept. 8 to 12, 1959. (30) Okamura, S., Motoyama, T., Chem. High Polymers ( Tokyo ) 12, 102 ( 1955 ). (31) Prevost-Bernas, Α., et al., Discussions Faraday Soc. 12, 98 ( 1952 ). (32) Smith, W. V.,J.Am. Chem. Soc. 70, 3695 ( 1948 ). (33) Smith, W. V., Ewart, R. H.,J.Chem. Phys. 16, 592 ( 1948 ). (34) Starkweather, H. W., Taylor, R. H.,J.Am. Chem. Soc. 52, 4708 ( 1930 ). (35) Staudinger, H., J. prakt. Chem. 155, 261 ( 1940 ). (36) Swallow, A. J., "Radiation Chemistry of Organic Compounds," Pergamon Press, New York, 1960. (37) Treloar, F. E., Polymer 1 ( 4 ) 513 ( 1960 ). (38) Trommsdorff, E., Kohle, H., Lagally, P., Makromol. Chem. 1, 169 ( 1947 ). (39) Vanderhoff, J. W., etal.,J. Polymer Sci. 50, 265 ( 1961 ). (40) Walling, C., J. Am. Chem. Soc. 70, 2561 ( 1948 ). RECEIVED September 5,1961.


Radiation Induced Polymerization of Some Vinyl Monomers in

Recommend Documents