Addition and Condensation Polymerization Processes

10 Emulsion Copolymerization of Vinyl Esters of Branched Carboxylic Acids with Vinyl Acetate

Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0091.ch010

G. C. VEGTER Koninklijke/Shell-Laboratorium, Amsterdam, The Netherlands

Vinyl esters of trialkylacetic acids copolymerize with vinyl acetate.

Such copolymers

randomly

show excellent per-

formance in paint latices. A variant of the monomer emulsion addition procedure for preparing latices yielded stable, coagulum-free

products with very low residual monomer

content. In this technique the initial reactor charge, consisting of part of the water, anionic emulsifier, initiator, and neutralizing agent, is heated to the reaction

temperature.

A monomer emulsion, containing all the monomers and nonionic emulsifier as well as the balance of the other ingredients is then added gradually.

The reproducibility

of the

process is, irrespective of the scale of operation, very good when a relatively large proportion of the anionic emulsifier is present in the initial reactor charge.

'"phe A

use of Versatic acids as the base material to manufacture alkyd

resins was described a few years ago (2, 4, 5, 6, 7, 12, 15, 16, 17).

These acids are prepared b y the acid-catalyzed reaction between olefins, carbon monoxide, and water. O w i n g to rearrangements i n the intermediate carbonium ion, they are nearly a l l trialkylacetic acids, of w h i c h one alkyl group is invariably methyl.

Ri—C—COOH

I CH3 178 Platzer; Addition and Condensation Polymerization Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1969.


10.

VEGTER

Emulsion

Copolymerization

179

It appeared that the incorporation of these branched acids into saturated alkyds contributed to the chemical resistance and outdoor durability —especially color and glass retention—of the final stoved films. More recent investigations revealed that the vinyl esters of these branched acids are excellent base materials for preparing paint latices (3, 8, 9, 10, 11, 13, 14). Their use as comonomer in vinyl acetate copolymer latices imparts improved alkali resistance and weatherability to the paint films. These investigations were concentrated on the vinyl ester of Versatic 911, the acid derived from C 8 - C i 0 olefins. This product w i l l be referred to further as W 911. The copolymerization of V V 911 with vinyl acetate, especially the emulsion copolymerization, was studied extensively. This paper describes the copolymerization characteristics of V V 911, a process developed for latex manufacture, and the reasons for its excellent reproducibility. Relative

Reactivity

Ratios

According to literature data vinyl esters of saturated aliphatic carboxy fie acid copolymerize randomly with each other ( I ) , the monomers being incorporated into the copolymer in about the same ratio at which they are present in the monomer mixture. This means that for practical purposes the relative reactivity ratios f i and r 2 can be taken to be equal and unity. To check whether vinyl esters of strongly branched acids behave differently, mixtures of vinyl acetate and V V 911 in molar ratios of 1/3, 1/1, and 3/1 were polymerized in bulk to a conversion of about 10%, using benzoyl peroxide as initiator at 5 0 ° C . The reaction mixtures were then diluted with benzene, and the polymers were precipitated with methanol. After five further dissolutions in benzene and precipitation with methanol the polymers were freeze dried from their solutions in benzene and analyzed for carbon content. The results given in Figure 1 show that, at least for practical purposes, the assumption that rx = r2 = 1 is valid, and at any time during the polymerization random copolymers are formed at any vinyl acetate-VV 911 ratio. Emulsion

Polymerization

Procedure

Many polymerizations are performed by the emulsion technique to prepare a polymeric substance. The latex obtained is then coagulated, and the polymer is isolated. A paint latex, however, is used as such in the paint formulation, which leads to some special requirements for its stability, such as storage, mechanical, electrolyte, and freeze/thaw stability.

Platzer; Addition and Condensation Polymerization Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1969.

180

ADDITION

A N D CONDENSATION

POLYMERIZATION

PROCESSES

CARBON CONTENT 74r 72 \

70-

\

\

\

68 -

\ \

66

\

64

\

\ \

62


\

• THEORETICAL CURVE (r, » r = 1) EXPERIMENTAL RESULTS g

X

\

\

\ \

60

\ \ \

58

\ \

56,

\

-J 10

I 20

I I I 100 90 80 VINYL ESTER OF

I 30

I 40

I 50

I I I 70 60 50 VERSATIC 911, %m

1 60

L_ 70

1 40

VINYL ACETATE, %m 1 L 1 1 30 20 10 0

80

90

100

Figure 1. Carbon content (wt. %) as a function of the composition (moles) of vinyl acetate-VV 911 copolymers. Asterisk (*) denotes 72.88% carbon found for poly(W 911)

Another important aspect of the entire latex's being applied i n the paint is that the ingredients used for latex preparation cannot be removed and w i l l influence the performance of the ultimate paint film. Emulsifiers especially can have an adverse effect i n this respect, and it is therefore desirable to use as small an amount as possible to obtain the desired stability. For vinyl acetate-VV 911 copolymer latexes a suitable recipe was developed and is given i n Table I. These latexes have excellent stability and impart superior performance to paints. The small amount of acrylic acid is required to ensure freeze/thaw stability of the latex at a p H of 7 or higher and contributes to its mechanical stability. The anionic emulsifier (Fenopon S F 78) regulates the particle size and contributes to the stability of the system during latex preparation. The nonionic emulsifier (Tergitol N P 40) is required to obtain sufficient electrolyte stability and contributes to the mechanical and the freeze/thaw stability of the latex. Borax is used as a neutralizing agent. Of the various methods of latex preparation known and practiced, a variant of the emulsion-addition method was chosen for further investigation because the reaction temperature is easy to control and coagulum


10.

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VEGTER

181

Copolymerization

formation is easier to prevent than in the monomer-addition technique. Redox recipes were not considered i n connection with the desirability to keep the amount of ingredients as low as possible and because of the observed difficulties to obtain conversions above 99.5%. Table I.

Ingredients Used in Preparing Vinyl Acetate-VV911 Latexes


Ingredient

Parts by Weight

Vinyl acetate V V 911 Acrylic acid Water (deionized) Fenopon FS 78 (85% active material) 0 Tergitol N P 40 6 Potassium persulfate Borax

52.5 46.5 1.0 85 1.0 2.5 0.5 0.5

Sodium alkylbenzene sulfonate from Antara Chemicals. Nonylphenol condensed with on an average 20 moles of ethylene oxide per mole, from Union Carbide Chemical Co. a

6

A n initial reactor charge was prepared by dissolving 0.1 part by weight ( p b w ) of potassium persulfate, 0.05 pbw of borax, and 0.6 pbw of Fenopon FS 78 i n 25 pbw of denioized water. The rest of the ingredients were used as follows for preparing a monomer feed emulsion. In the 60 pbw of water left were dissolved 2.5 pbw of Tergitol N P 40, 0.4 pbw of Fenopon SF 78, 0.4 pbw of potassium persulfate, and 0.45 pbw of borax. To this solution 100 pbw of the monomer mixture were added with stirring. The monomer feed emulsion thus obtained was stable for about one day. The reactor, a 750-ml. conical glass flask provided with a stainless steel anchor-type stirrer, which contained the initial charge, was then heated to 8 0 ° C , and the monomer feed emulsion was added gradually with stirring i n about 2^ hours. The temperature was kept at 80 ° C . After addition of the emulsion, stirring was continued for another 2 hours, the temperature being kept at 8 0 ° C . The latex then was cooled with stirring to room temperature. Monomer conversion was 99.8%, the p H 4-4.5. Variation

in Emulsifier

Emulsion

and

Initial

Distribution Reactor

Ratio

between

Monomer

Peed

Charge

A n important variable for paint latexes is their particle size, which influences properties such as their stability, viscosity, and pigment-binding properties. Since emulsifiers determine the particle size of the latex, we studied the influence of the distribution ratio of the emulsifiers between monomer feed emulsion and initial reactor charge on the latex properties. W e found that small amounts of the nonionic emulsifier in the initial reactor charge caused coagulation during latex preparation. Hence, the total


ADDITION AND CONDENSATION

182

POLYMERIZATION

PROCESSES

amount of nonionic emulsifier required had to be added with the mono mer feed emulsion. Variation in the amount d i d not affect the particle size.

The distribution ratio of the anionic emulsifier, however, greatly affected the particle size, as illustrated i n Figure 2. It was practically unaffected as long as more than about 15% of the anionic emulsifier was i n the initial reactor charge. A further reduction of this amount, however, led to a steep increase i n particle size.


AVERAGE PARTICLE SIZE, A. 3600ρ 3400 3200 3000 2800 |ϊ 2600 2400 2200 2000| 1800 1600 1400 100/0

60/40 40/60 80/20 , ΛΓ DISTRIBUTION OF ANIONIC EMULSIFIER ( |

Figure

,-r,^,,, .

2.

r-..,^,r-,^r^

0/100 20/80 MONOMER EMULSION . L REACTOR CHARGE

NmA

Influence of distribution of anionic on average particle size

emulsifier

Since the total recipe is the same for all distribution ratios and the differences are introduced mainly at the beginning of the latex prepara tion, the initial conditions are very important for particle size. To gain a better understanding of this phenomenon we followed the number of particles i n the reactor with time during the monomer emulsion addition for three different distribution ratios of the anionic emulsifier. The ratios 40/60, 97/3, and 100/0 were chosen because they gave dif ferent particle sizes of the ultimate latex: the first on the flat part of the curve i n Figure 2, the second just i n the bend, and the third on the



10.

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Figure

Emulsion

Copolymerization

183

3. Number of particles during the addition period for different partitions of the anionic emulsifier

extreme left. The number of particles was derived from the known amount of monomer mixture added at any stage, and the average particle size determined via turbidity measurements. The results of these experiments are depicted in Figure 3. They show that the number of particles formed i n the initial stages of the latex preparation depends on the amount of anionic emulsifier present. W h e n this amount was small, few particles were formed, and their number remained constant during further latex preparation. Thus, after initial particle formation, only a growth of existing particles took place. W h e n a large amount of anionic emulsifier was initially present i n the reactor, many particles were formed. This number decreased during the latex preparation because not enough emulsifier was added with the monomer feed emulsion to keep the surface of the particles covered. Controlled agglomeration of polymer particles occurred to a stage where



184

ADDITION

AND CONDENSATION

POLYMERIZATION

PROCESSES

the total surface area of the particles had become so small that the amount of anionic emulsifier present just provided the stability required under the conditions of the experiment. Thus, when more particles are initially formed than can be stabilized by the amount of anionic emulsifier added later, the ultimate average particle size is determined by the total amount of anionic emulsifier used i n the latex formulation. W h e n fewer particles are initially formed, the final average particle size is determined by the number of these particles. Figure 2 shows that when, under our conditions, more than about 15% of the anionic emulsifier was present i n the initial reactor charge, the average particle size was independent of the distribution ratio, indicating that it was determined only by the total amount of anionic emulsifier present. In actual fact, under these conditions the average particle size of the latexes was readily reproducible, but poorly so when less than 15% of the anionic emulsifier was present i n the initial reactor charge. This can be understood by realizing that the number of particles formed initially cannot be very reproducible. Small variations i n the induction period, for instance, w i l l affect this number considerably because anionic emulsifier is added with the monomer feed emulsion. AVERAGE PARTICLE SIZE, A.

TOTAL ANIONIC, pbw

Figure 4. Influence of total amount of anionic emulsifier on average particle size at a constant 40/60 distribution over monomer feed emulsion and initial reactor charge Variation

in the Amount

of Anionic

Emulsifier

The above-mentioned influence of the total amount of anionic emulsifier on the particle size of the latex was checked by varying this total amount, the 40/60 distribution between monomer feed emulsion and initial reactor charge being kept constant. The results of these experi-



10.

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185

Copolymerization

ments are given in Figure 4. In Figure 5 they are compared with those obtained by changing the distribution ratio of anionic emulsifier at con stant total concentration. The essential difference between the two series of experiments is the amount of anionic emulsifier on the monomer feed emulsion, indicated by the figures near the curve. Points of the two curves on any vertical line drawn through the graph relate to two experi ments in which only the amount of anionic emulsifier in the monomer feed emulsion differs. Variation in this amount influences the average particle size considerably, which agrees with our previous statement that in the region of controlled agglomeration the average particle size is governed by the total amount of anionic emulsifier and is thus very reproducible. In fact, identical results were obtained when working on a 750-ml., a 20-liter, or a 250-liter scale. AVERAGE PARTICLE SIZE, A. 4400y-0 -RESULTS OBTAINED BY CHANGING THE DISTRIBUTION OF ANIONIC EMULSIFIER AT CONSTANT TOTAL CONCENTRATION

4000

-RESULTS OBTAINED BY CHANGING THE TOTAL AMOUNT OF ANIONIC EMULSIFIER AT CONSTANT DISTRIBUTION (40/60) (FIGURES NEAR CURVE INDICATE THE CORRESPONDING AMOUNT IN pbw OF ANIONIC EMULSIFIER IN MONOMER EMULSION)

3600 1.0'

3200

2800 H-

^•0.066 2400

\

\ \0.13 \ ^20 VO.27

2000

\

v0.9 1600'

0.1

0.8

07

0.6

vp.33 \ 0.5

Τ 0.5

X0.4 0,3

Τ Q6

1 0.7

02

ζ0.8 η

0.1

QO

• 1.0

0.2 0.3 0.4 0.9 ANIONIC EMULSIFIER IN INITIAL REACTOR CHARGE, pbw

Figure 5. Influence of distnbution ratio and total amount of anionic emulsifier on average particle size


186

ADDITION

Particle

Size

A N D CONDENSATION

POLYMERIZATION

PROCESSES

Distribution

The particle size distribution of various latices, prepared via the above monomer emulsion addition technique, was determined with the aid of an ultracentrifuge. It was found to be invariably of the log-normal type, as shown i n Figure 6, independent of the way the particles are formed. This illustrates that the agglomeration of particles during latex preparation, when the initial reactor charge contained more than 15% of the anionic emulsifier, is a random and not a selective process. W.FR., %


100 ρ 90-

/

80-

/

70 -

/

60-

/

50 -

/

40 -

/

30 -

/

20 -

/

10-

o'

1000

/ /

^

1

1400

Figure 6.

1

1

1800

1

I

2200

I

I

2600

Particle size distribution

I

ι

'

3000 3200

PARTICLE SIZE, Δ ,

of a latex

Conclusions

V i n y l esters of trialkylacetic acid copolymerize randomly with vinyl acetate. Paint latices with a very low residual monomer content, based on vinyl acetate-VV 911 copolymers, can be prepared reproducibly via a variant of the monomer emulsion addition technique, when a relatively large part of the anionic emulsifier is present i n the initial reactor charge.

Literature

Cited

(1) Adicoff, Α., Buselli, Α., J. Polymer Sci. 21, 340 (1956). (2) Brockman, A. L. S., Moore, W. V., Paint Mfg. 32, 423 (1962).



10.

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Emulsion Copolymerization

187

(3) Bruin, P., Oosterhof, H. Α., Vegter, G. C., Vogelzang, E. J. W., F.A.T.I.P.E.C. Congr., 7th, 1964, 49. (4) Goppel, J. M., Bruin, P., Zonsveld, J.J.,F.A.T.I.P.E.C. Congr., 6th, 1962, 31. (5) Herzberg, S., F.A.T.I.P.E.C. Congr., 6th, 1962, 319. (6) Herzberg, S., F.A.T.I.P.E.C. Congr., 7th, 1964, 387. (7) Kreps, R. W. F., Fette, Seifen, Anstrichmittel 66, 1072 (1964). (8) Oosterhof, H. Α., J. Oil ColorChemists'Assoc. 48, 256 (1965). (9) Reader, C. Ε. L., Oosterhof, H. Α., F.A.T.I.P.E.C. Congr., 8th, 1966, 440. (10) Reader, C. E. L.,Gastineau, G., Double Liaison 125, 642 (1966). (11) Tsatsos, W. T., Illman, J. C., Tess, R. W., Paint Varnish Prod. 55, 46 (1965). (12) Vegter, G. C., Oosterhof, H. Α., Fette, Seifen, Anstrichmittel 68, 283 (1966). (13) Ibid., 69, 79 (1967). (14) Vegter, G. C., Grommers, E . P., J. Oil Color Chemists' Assoc. 50, 72 (1967). (15) Vogelzang, E. J. W., J. Oil Color Chemists' Assoc. 46, 89 (1963). (16) Vogelzang, E. J. W., Oosterhof, Η. Α., F.A.T.I.P.E.C. Congr., 7th, 1964, 381. (17) Vogelzang, E. J. W., Farbe Lack 71, 455 (1965). RECEIVED April 1, 1968.


Addition and Condensation Polymerization Processes

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