Thaw Stability of Polymer Emulsions - ACS Publications

11 Freeze/Thaw Stability of Polymer Emulsions

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HAROLD NAIDUS and ROGER HANZES Northeastern University, Boston, Mass. 02115

The freeze/thaw (F/T) stability of a polymer emulsion serves as a macroscopic probe for investigating the proper ties of the average particle in a polymer emulsion. A review of the factors which contribute to this stability is included. A study of styrene-ethyl acrylate-methacrylic acid poly mers shows the existence of a minimum in the plot of minimum weight percent acid required for F/T stability vs. the minimum film formation temperature (MFT) of the polymer. This is considered to be a function of both the amount of associated surfactant and the minimum acid content. Thus, both the type of surfactant and the copolymer ratio—i.e., MFT—play major roles. Chain transfer between radicals and polyether surfactant resulting in covalently bonded surfactant-polymer combinations is important in interpreting the results.

Τ η the past 20 years a fragmented literature has grown around the phenomena related to freezing and thawing of polymer emulsions. A l though much of the patent literature, by far the major source of informa tion, focuses primarily upon specific methods for preparing freeze thaw ( F / T ) stable polymer emulsions, it has been possible to classify arbi trarily the various methods used. The major factors contributing to the stability of emulsions to freezing and thawing appear to fall into three classes: (a) copolymerization with vinyl carboxylic acids, (b) grafting of monomer to surface-active agents, and (c) postadditions of glycols, salts, surfactants, etc. to the emulsion. A

Classes a and b imply the requirement of a covalently bonded, nondiffusible protective layer to achieve F / T stability, whereas Class c involves either a freezing-point lowering (glycols, salts) or additional stabilization (surfactants), presumably i n emulsions already moderately stable to freezing and thawing. 188

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

11.

NAiDUs

AND HANZES

Freeze/Thaw

Stability

189

These three factors do not appear to be independent of one another a polymer emulsion containing insufficient carboxylate ions to be F / T stable may frequently be made stable to the particular set of F / T tests by incorporating one of the addends of Class c.

—i.e.,


Factors

Affecting

F/T

Stability

Copolymerization with Vinyl Carboxylic Acids. The acids usually suggested for this method include maleic and fumaric acids and their half esters, crotonic, itaconic, methacrylic, and acrylic acid. The latter three appear to be most generally preferred. O n occasion, the amides of these acids are suggested for achieving the same end result (24). Suggested specifically for butadiene-styrene latexes are these acids at about 0.05-10 wt. % based on total monomer. The latex should be adjusted to p H 8-11 (28, 29). F o r copolymerization with vinyl acetate (2) and acrylic monomers (18) identical acid monomers are suggested. Use of such latexes is claimed to give F / T stable emulsion floor polishes (25) and paints (16). A closely related patent (17) describes a method i n which very high concentrations of K 2 S 2 0 8 are used to initiate styrene-butadiene emulsion polymerizations, and F / T stability is claimed. In view of the well-known sulfate end group formation resulting from the use of persulfates, it would appear plausible that such end groups have been linked to the unsaturated polymer by radical transfer as well as by normal initiation and termination and thus function as non-diffusible anions to protect the particles during freezing and thawing. Grafting of Monomer to Surface-Active Agents. A recent patent claims the preparation of a F / T stable poly(vinylacetate-vinylbenzoate) copolymer emulsion i n the presence of a graft polymer of vinylacetate on a polyalkylene glycol (21). A publication of the Celanese Chemical C o . (18) describes the preparation of a highly crosslinked vinyl acetate homopolymer prepared with poly (vinyl alcohol) stabilizer i n which the poly (vinyl alcohol) contains about 12% residual acetyl groups, and a very reactive redoxinitiator system is used: H 2 0 2 and zinc formaldehyde sulfoxylate. It has been shown (21) that this emulsion exhibits improved F / T stability compared with similar emulsions made with other colloids and less reactive initiating systems. In view of the work of Wheeler (31, 32), i n which he points out the relative ease with which the hydrogens of the acetyl group undergo chain transfer, one may visualize the partially acetylated polyvinyl alcohol) as a multifunctional chain transfer agent participating i n the polymerization reaction so as to create a highly branched or crosslinked polymer (Figure 1). The product therefore would contain dis-



190

ADDITION

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PROCESSES

persed particles of poly (vinyl acetate) of higher glass temperature (Tg) than linear poly (vinyl acetate) and would have associated w i t h it a closely adhering layer of covalently bonded, non-diffusible colloid. Both are likely to contribute to improved F / T stability. Experimentally, this polymer is not 100% soluble. There are several patents on F / T stable poly (vinyl acetate) polymer emulsions which may be interpreted i n a similar light (6, 11). F o r example, in Ref. 6 the following statement appears: These advantages (wet rub and gloss) may be attributed to the fact that during the polymerization process, there are formed grafted copolymers of vinyl acetate and the water soluble colloids present i n the polymerizing medium. These graft copolymers possess marked surface activity and contribute to the stabilization of the emulsion i n which they are formed. . . . ter Particle

Figure

1.

Postulated participation of polyvinyl emulsion polymerization (schematic)

alcohol) in

The emulsion polymerization of styrene with shellac salt stabilizer yields a highly crosslinked, F / T stable emulsion from which it is not possible to extract all the shellac by conventional means (21). This may be interpreted in a similar manner although it has not, as yet, been possible to determine the sites on the shellac which undergo chain transfer. Both the poly (vinyl acetate)-poly (vinyl alcohol) and styrene-shellac examples of colloid participation i n the polymerization require much investigation especially with respect to whether grafting to the colloid occurs i n aqueous solutions or at the particle surface. The former would appear more likely for the relatively water soluble vinyl acetate monomer, while the latter should be favored for the less soluble styrene. In any case, both would result i n identical particle stabilization. Postadditions. Although definitive experiments have yet to be carried out, present information leads us to assume that emulsion polymers that



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A N D HANZES

Freeze/Thaw

191

Stability

are particularly unstable to freezing and thawing cannot be made stable by postadditions i n a F / T test which requires that the emulsion be frozen solid. That is, the suggested addition of glycols and the other freezing-point depressants often enhances F / T stability simply by preventing complete freezing under the test conditions. O n the other hand, it is equally reasonable to assume that polymer emulsions that are borderline with respect to F / T stability may be nudged over the border by adding compounds which either modify the crystal form of the continuous phase, prevent complete freezing at the test temperatures, or furnish additional stabilization by adsorption on the polymer particles. It has been suggested, for example, that the addition of glycol and polyethylene glycols enhances the F / T stability of emulsions (2). Further, the addition of electrolytes has been to achieve the same goal (5). A l l are freezing-point depressants influence the other factors as well.

ethylene polymer proposed and may

The addition to poly (vinyl acetate) emulsions of poly (oxy ethylene) poly(oxypropylene) glycols is claimed to improve F / T stability (JO) as are nitrogen-containing polyalkylene glycols (13). A general treatment of the improvement i n F / T stability by adding surfactants is given by Digioia and Nelson (4) and Leonard (14). Both papers indicate that improvement i n F / T stability is obtained by adding surfactants. F/T

Stability

and

Mechanical

Stability

W h e n polymer emulsions are subjected to freezing and thawing or to mechanical shear, the stabilizing layer of each particle (whether ionic or nonionic) is subjected to deformation which permits easier particle-toparticle approach (8,15,19, 26, 27) and frequently results in coagulation. Since F / T and mechanical stability appear to be mechanistically related, several authors have undertaken work to elucidate at least one of the stability relationships (8, 15, 19, 26). The first paper measures mechanical stability by subjecting the emulsion to shear at 1100-1400 r.p.m. i n a Couette viscometer and records the time required for the onset of coagulation. The author evaluates acrylic copolymers containing methacrylic acid and demonstrates that mechanical stability improves with increasing emulsion particle charge (Figure 2). This is completely consistent with F / T results on similar emulsions (22). The author notes that his results are consistent with those of Stamberger (27) who worked with a styrene—ethyl hexyl acrylate—acrylic acid emulsion terpolymer. A t p H 8, the emulsion was stable to liquid shear, whereas at p H 3, it was unstable. There was little difference i n zeta potential of the latex at the two p H values.



192

ADDITION

ni

I

0

Figure

4

2.

I

I

8

12

I

16

POLYMERIZATION

I

20

-4 (Electron Charges / Particle) χ 10

Effect of particle

Coagulation

AND CONDENSATION

by Freezing

charge on mechanical (after Ref. 8)

and

stability

I

24

(MAA

PROCESSES

1

1

28

32

terpolymer)

Thawing

The freezing and thawing of polymer emulsions has been a wellknown method for latex coagulation for many years. In 1959, Barb and M i k u c k i ( J ) investigated the particle size of the coagulate. The systems chosen were polystyrene copolymer emulsions stabilized with cationic surfactants. B y evaluating the coagulate through a three-sieve system having spacings of approximately 178, 104, and 66/A, it was possible to correlate the distribution of coagulate particle sizes with the rate of freez ing, the rate of thawing, the time interval between freezing and thawing, the concentration of the emulsion, the emulsifier concentration and type, latex particle diameter, and polvmer type. Of all these variables, only the freezing rate, the emulsion concentra tion, and the polymer type appeared to have a significant effect upon the appearance and particle size distribution of the polymer coagulate. In a styrene-acrylonitrite (S—AN) copolymer series, those of higher softening point give finer, less agglomerated coagulate (see Table I ) .


11.

NAiDUS

Table I.

AND

Freeze/Thaw

193

Stability

Coagulate Particle Size and Polymer Softening Point (1)

Polymer

Styrène (S) 75/25 S - A N 10/90 S - A N Downloaded by UNIV OF CALIFORNIA SANTA CRUZ on October 31, 2014 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0091.ch011

HANZES

Softening Point

Coagulate Retained by 178μ Sieve (wt. %)

102 110 200

56 33 negligible

Our results differ significantly from these observations. Emulsifier and monomer types appear to play a much more complex role than implied above. Experimental

Minimum Film Formation Temperature (MFT). Equipment described by Protzman and Brown (24) was built, calibrated, and used for all measurements. A series of 25% emulsions, adjusted to p H 9.5 with N H 3 , was used throughout unless otherwise indicated. Polymerization. The procedure described in Ref. 22 was followed, except that the redox-initiated system involving styrene required a 100% increase in redox initiators and a 50% increase in Triton X-405. The polymerization formula used in all the styrene systems was: Weight, grams

Monomers Triton X-405 H 2 0 (distilled) Glacial acetic acid ( N H 4 ) 2 S 2 O s (4% aq.) N a 2 S 2 0 5 (10% aq.)

288.9 39.6 368.0 (topH2.5) 60.4 26.0

[In those experiments with sodium lauryl sulfate (SLS), the same dry weight as for Triton X-405 was used for emulsion stability. The appropriate adjustment in H 2 0 was made as well. Triton X-405 is a poly(ethoxylated) octyl phenol containing about 40 moles ethylene oxide per mole and used as supplied by Rohm & Haas Co. at 70% solids.] All the emulsions appeared to have similar particle sizes, estimated to be in the range of 0.1-0.5/A. The monomers were all polymerization grade and polymerized without purification since no significant difference in induction period or rate was observed with distilled monomer. Methacrylic Acid Content in Polymer. One gram of methanol-precipitated, water-washed, dried polymer was dissolved in 100 ml. tetrahydrofuran ( T H F ) and titrated to a faint pink phenolphthalein end point with 0.055 n-benzyltrimethylammonium hydroxide in T H F . The base was standardized by potentiometric titration against 0.01N acetic acid in methanol. The value for a non-acid containing polymer of the same series was used as a blank. All analyses were within 5% of the theoretical value. Other Procedures. Residual monomer content, solids content, viscosities, F / T stability, and surface tension were determined as described


194

ADDITION AND CONDENSATION

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PROCESSES

i n Ref. 22. A l l infrared data were obtained w i t h a Beckman I R 5 A infrared spectrophotometer.


Results

and

Discussion

Methyl Methacrylate-Ethyl Aerylate-Methacrylie A c i d ( M M A - E A M A A ) Terpolymers. In an earlier paper (22, 23) values for the M F T of each of a series of acrylic copolymer emulsions were obtained by calcu lating Τ g values using the equation of W o o d (34), ignoring the presence of methacrylic acid. These were then converted to M F T values using available literature data (20, 24) and by extrapolating and interpolating the straight line obtained. The M F T values for these identical emulsions at p H 9.5 have now been determined experimentally, and these data are compared i n Table II. Values for M F T s below 0 ° C . could not be obtained experimentally. Table II.

M F T Values for M M A / E A / M A A Emulsion Polymers MFT,

MMA-EA

100/0 80/20 50/50

°C.

MAA, wt. %

(calc.)

(exp.)

0.4 0.86 1.13

109 78 32

108.1 78.6 30.0

It appears that use of the W o o d formula for calculating Tg values combined with the use of literature data relating M F T and Tg was reliable for obtaining previously unknown M F T values despite the pres ence of small amounts of acid i n the polymer and a likely difference i n polymerization method. Styrene-Ethyl Acrylate (S-EA) Copolymers. A t the inception of the research on F / T stability, it was evident that more than one polymer system would require investigation before adequate conclusions could be drawn regarding the various pertinent parameters. These include, i n addition to the previous considerations, surfactant type and amount as a function of polymer type. To this end, work has been initiated on a series of somewhat less polar styrene-ethyl acrylate-methacrylic acid emulsion polymers. The first major difference encountered i n changing from the M M A - E A - M A A to the S - E A - M A A polymers was the need for at least a 50% increase i n surfactant to obtain a coagulate-free emulsion for the 100% styrene vs. 100% methyl methacrylate. The determination of the minimum weight percent of M A A required to yield a F / T stable emulsion for various copolymers gave the results listed i n Table III.


11.

NAiDUs

Freeze/Thaw

AND HANZES

Table III.

195

Stability

F / T and MFT Data for S / E A / M A A Copolymers Stabilized with Triton X-405


MFT,

°C.

S-EA Ratio

MAA, wt. %

F/T Stable

pH Unadjusted41

pH 9.5 with NHS

pH 9.5 with NaOH

100/0 100/0 75/25 75/25 50/50 50/50

0 0.834 6 0 0.34 6 0 0.82 b

no yes no yes no yes

101.4 — 77.1 74.6 — —

— 102.2 76.4 74.5 — 35.5

— — — 74.3 — —

The pH of unadjusted emulsions ranged from 2 to 2.5. These values for wt. % MAA are the minimum required for F/T stability using N H 3 to pH 9.5.

a

h

These data show that for the low levels of acid in the p H range considered, M F T values are relatively insensitive to methacrylic acid content. O n the other hand, i n the SLS system, the 100% S polymer requires 4.4% M A A for F / T stability, and the M F T becomes 1 1 3 ° C . To see more clearly the marked differences i n M F T relationships between these polymers and the M M A - E A - M A A polymers (22), Figure 3 has been constructed to compare the data of the two series. Among the questions which become apparent from Figure 3 and which require explanation are: (a) Since the M F T s of 100% M M A and 100% S emulsions are not too different ( 3 8 2 ° and 3 7 5 ° K . ) , w h y does the latter require appreciably more M A A to achieve F / T stability? In emulsion systems, an equilibrium between surfactant associated with the particles and free surfactant is considered to exist—i.e., S (assoc.) ^ S (free)

(1)

where S (assoc.) may include both adsorbed and chemically combined surfactant. If one makes the reasonable assumption, consistent with colloid stability theory, that F / T stability is a direct function of the total thickness of the minimum hydration layer required for F / T stability, (H)m, which is i n turn a function of both the minimum carboxylate ion content, wm, and the associated surfactant, then F / T stability =

(H)m = awm + b S(assoc. )

(2)

Since it was observed that a 50% increase in surfactant was required to prepare a coagulate-free polystyrene emulsion compared with poly( methyl methacrylate) emulsion, it appears clear that for poly-S emulsion Equation 1 is shifted to the right compared with p o l y - M M A emulsion.


196

ADDITION

AND

CONDENSATION

\

25Downloaded by UNIV OF CALIFORNIA SANTA CRUZ on October 31, 2014 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0091.ch011

PROCESSES

\o\ \

W

POLYMERIZATION

\

\ \

2.0 15

• Ο

O

\\

30/70 MMA/EA w. S o dx-405 i u m L a u r y l S u l f a t eΟ ( S L S ) MMA/EA/MAA w. Triton

\

>

\ S/EA/MAA

1.0 •

0.5

100 %

0

w. T r i t o n x - 4 0 5

w.

S

* _ \

100

200 Temperature

Figure

3.

Minimum

Ο

SLS

weight

percent MFT

300

400

( Κ)

acid required (°K.)

β

for F/T

stability

vs.

Under F / T conditions, desorption of surfactant presumably occurs more readily w i t h the poly-S emulsion as a new equilibrium is established (a slight surface-tension lowering was observed after each F / T cycle throughout the series.) This conclusion is further substantiated by the exceptional increase i n minimum weight percent acid required for poly-S in SLS (black square) compared with the 80/20 M M A - E A i n SLS (black dot) despite the fact that less than one-half as much SLS was used i n the latter case. Thus, it appears that poly-S is a less favorable surface for surfactant adsorption and as predicted by Equation 2 more carboxylate ions are required to obtain F / T stability. (b) W h y does the 75/25 S - E A polymer require even less acid than 100% p o l y - M M A which has a higher M F T (347.5° vs. 3 8 2 ° K . ) ? Since the styrene series contains more surfactant than the methyl methacrylate series and since the ethyl acrylate has afforded increased surfactant adsorptivity to the styrene by a mechanism to be proposed under Question d, the equilibrium suggested by Equation 1 is shifted markedly to the left, resulting i n lower requirements for carboxylate ions to achieve F / T stability. (c) W h e n replacing Triton X-405 by SLS weight for weight, why is the minimum weight percent acid necessary for F / T stability increased



11.

NAiDUS

A N D HANZES

Freeze/Thaw

Stability

197

so markedly despite the fact that the Triton X-405 represents many fewer moles? By virtue of the chemical structure of the two surfactants, it would appear reasonable that many more moles of water per mole surfactant would be associated with the Triton X-405 than the SLS and thus effec tively increase the hydration layer thickness. O n the other hand, this would not necessarily maintain the equilibrium represented by Equation 1 shifted sufficiently far to the left following multiple F / T cycles. Main tenance of an equilibrium shifted to the left can only be assured if the surfactant is covalently bonded to the polymer particle by some means. B y invoking certain well-known chemical phenomena and by analogy with the poly (vinyl alcohol)-poly (vinyl acetate) system (Figure 1), it becomes possible to recognize that a polyether, like Triton X-405, would tend to undergo chain transfer during an emulsion polymerization reac tion, whereas it is much less likely with SLS. It has been shown (31) that the chain transfer constants of alcohols at the — O H group is low, about equal to that of aliphatic hydrocarbons, i n agreement with the high dissociation energies of the bonds involved. W h e n transfer does take place, it occurs at the α-hydrogen. W i t h ethers, both the autoxidation to form hydroperoxides (9, 29) and transfer with radicals (3) occur at the α-hydrogen. Radical transfer reactions involving poly ethers of the poly (ethylene oxide) type are well known (7). Heating polyethylene glycols of various molecular weights at 140 ° C . with dicumyl peroxide for 2.5 hours has resulted i n a gel fraction explained by transfer at the α-carbon followed by combination of the polymer radicals. Further, poly (ethylene oxide) dissolved i n M M A and heated i n the presence of benzoyl peroxide results in grafted copolymer. In a highly favorable medium, containing a reactive redox-initiating pair, transfer is likely to occur either i n the aqueous phase or at the particle surface. In either case, the surfactant w i l l reside at a particle surface bound to the polymer by one or more covalent bonds (see Figure 4 ) . To follow up this reasoning, we subjected reprecipitated polystyrene to spectrographic analysis. Emulsion polymer at its unadjusted p H was precipitated in 10-fold excess of methanol (a solvent for Triton X-405), dried, dissolved in toluene (a nonsolvent for the Triton), filtered, and the toluene solution was added to a 10-fold excess of methanol. About 1.5% of the polymer remained as a fine dispersion which could not be precipi tated or separated by the addition of water or by centrifugation, thus exhibiting characteristics to be expected of a polystyrene graft to Triton X-405. [The value of 1.5% is completely consistent with the calculated value of about 18% by weight of Triton X-405 which could be associated



198

ADDITION

AND CONDENSATION

POLYMERIZATION

PROCESSES

with a polystyrene particle of Ο.ΐμ diameter assuming complete surface coverage by the Triton X-405. F r o m the Rohm and Haas literature, Triton X-405 has an area per molecule of 88 sq. A . and a molecular weight of about 1900 grams per mole.] The infrared spectrum of the precipitated polystyrene at this stage exhibited no absorption using thermally polymerized polystyrene i n the reference beam. A 3.5% solution of dried Triton X-405 i n chloroform showed intense adsorption at about 1100 cm." 1 , characteristic of the ether linkage.

Reviews in Macromolecular Chemistry

Figure

4.

Chain

transfer with polyethoxylated (schematic) (7)

octylphenol

The dispersed polymer was evaporated to dryness to yield a low softening point residue exhibiting complete solubility i n C C 1 4 and no water solubility. The spectrum of this material ( 3 % i n C C 1 4 ) was taken using a solution of the precipitated polymer of the same sample i n the reference beam. Strong absorption was observed at about —1110 cm." 1 , and the rest of the spectrum was essentially identical to that of Triton X-405. It has also been observed consistently that frozen and thawed samples of n o n - F / T stable emulsions prepared with Triton X-405 and SLS exhibit significantly different characteristics. In the frozen and thawed samples of SLS-stabilized emulsions, the psuedo-crystalline coagulate separates cleanly leaving a relatively clear supernatant liquid. In the Triton X-405 samples, a white, swollen amorphous coagulate is obtained with an opaque supernatant liquid. These combined observations lend credence to the conclusion that Triton X-405 molecules are bound chemically to the polymer particles. ( d ) W h y does the styrene series exhibit a marked minimum? There appear to be several factors playing simultaneous roles i n the S - E A polymer series. A n increase i n minimum weight percent acid



11.

NAiDUs

AND HANZES

Freeze/Thaw

199

Stability

required for F / T stability would be predicted for increased E A content on purely M F T considerations by analogy with the M M A - E A series (22). O n the other hand, aery late radicals have a transfer constant for toluene about 310 times that of styrene (30) which, by analogy, would increase its capability of transfer with the polyether, Triton X-405. Moreover, the greater solubility of E A i n water compared with S would increase the probability of transfer in the favorable aqueous environment. Both these influences would increase the quantity of surfactant associated with the polymer particle. Thus, at relatively low E A contents, it appears that the increase i n hydration layer thickness associated with the increase i n bonded surfactant far outweighs the influence of the decrease i n M F T . A t higher E A levels, it appears that the relative influence of the two factors is reversed. (e) Are the data of Figure 3 and Table III valid for alkalies other than N H 3 or at different surfactant levels? In an earlier paper (22) studies on a commercial latex as a model system indicated clearly no difference in F / T results when N H 3 or N a O H was used to adjust p H . It is now observed that at the minimum acid levels, the quantity of alkali and not p H is the controlling factor. Thus, Table I V shows that less N a O H than N H 3 is required to obtain p H 9.5, but an equal number of equivalents is necessary to achieve F / T stability. Moreover, as might have been expected, if more than the minimum acid content is present, F / T stability can be obtained at a lower p H so long as an equivalent amount of alkali is added—i.e., as long as the same concentration of carboxylic acids are converted to carboxylate ions. Table IV. Alkali and p H Requirements for F / T Stability in Triton X-405 Stabilized Styrene Copolymer Emulsions Polymer

Acid, %

100% S

0.834" 1.2 0.834 a

0.158 ( N H 3 ) 0.158 ( N H 3 ) (NH3)

0.34 a

0.158 ( N H 3 ) 0.048 (NaOH) 0.158 (NaOH)

75/25 S-EA

a

Base, meq.

pH

9.5 9.15 9.15 9.5 9.5 11.8

F/T

Stability

stable stable unstable stable unstable stable

Minimum wt. % acid for F / T stability.

In the 100% S emulsion stabilized by SLS, a sample containing 3% M M A was not F / T stable but became stable following addition of an amount of Triton X-405 equal to the SLS originally used. This was expected on the basis of the previous arguments and is consistent with the


ADDITION AND CONDENSATION

200

POLYMERIZATION

PROCESSES

literature which recommends postaddition of surfactants to improve F / T stability.


Conclusions

(1) The W o o d equation (33) is suitable for calculating Tg values for emulsion copolymers. (2) A t low M A A levels ( < 1% ) neither the acid content, the p H , nor the type of alkali affect the measured value of the M F T . (3) Nonionic polyethoxylated surfactants exemplified b y Triton X 405, tend to chain transfer i n redox-initiated emulsion polymerizations and become chemically bound to the polymer. (4) S L S tends to be less associated with emulsion polymer particles than does a polyethoxylated octylphenol. (5) Polystyrene has a lower affinity for surfactant than acrylic polymer. (6) The results confirm that transfer agents ( i n this case Triton X 405) have higher transfer constants with acrylate radicals than with styrene radicals. (7) It is possible to convert a carboxyl-containing emulsion polymer which is not F / T stable to one which is stable by the addition of surfactant. (8) It is the absolute amount of alkali used i n neutralization which controls F / T stability and not the p H . (9) F / T stability is controlled b y the carboxylate i o n content and not the carboxylic acid content, although with sufficient alkali these are probably synonymous.

Literature

Cited

(1) (2) (3) (4) (5)

Barb, W. G., Mikucki, W., J. Polymer Sci. 37, 499 (1959). Belgian Patent 644,919 (1964). Cass, W. E., J. Am. Chem. Soc. 69, 500 (1947). Digioia, F. Α., Nelson, R. Α., Ind. Eng. Chem. 45, 745 (1953). Fikentscher, H., Berkert, H., Newfeld, E., Plötz, German Patent 1,055,239 (1959). (6) Guest, D. V., Lord, F. W., Peace, W., British Patent 854,346 (1960). (7) Gurgiolo, A. E., Rev. Macromol. Chem. 1(1), 136, 160 (1966). (8)

Hatala, R. J., Am. Chem. Soc., Div. Org. Coatings Plastics Chem., Pre-

(14)

Leonard, F. J., Offic. Dig. Federation Paint Varnish Prod. Clubs 28, 441

prints 24(1), 257 (1964). (9) Hawkins, E. G. E., "Organic Peroxides," van Nostrand, Princeton, N. J., 1961. (10) Holdsworth, R. S., German Patent 1,093,558 (1960). (11) Kahrs, Κ. H., Koch, G., Jeckel, P., Bork, S., German Patent 1,071,954 (1959). (12) Kahrs, Κ. H., Staller, Α., Wolfgang, J., U. S. Patent 3,301,805 (1967). (13) Kahrs, K. H., Starck, W., German Patent 1,123,470 (1962). (1956).


11.

NAIDUS

Freeze/Thaw Stability

201

(15) (16) (17) (18) (19) (20) (21)

Mast, W. E., Fisher, C. H., Ind. Eng. Chem. 41, 790 (1949). McDowell, M. J., Hill, T. B., U. S. Patent 3,309,331 (1967). Miller, V. Α., Bebb, R. L., Masch, J. H., U. S. Patent 2,822,341 (1958). "Monomer References," Celanese Chemical Co., pp. 102, 652A. Muroi, S., Nomura, J., Kogyo Kagaku Zasshi 68, 1800 (1965). Myers, R., Schulz, R., J. Appl. Polymer Sci. 4, 81 (1960). Naidus, Η., unpublished work.

(23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34)

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AND HANZES

Naidus, H., King, A. P., Am. Chem. Soc., Div. Polymer Chem., Preprints

RECEIVED

March 14, 1968.


Thaw Stability of Polymer Emulsions - ACS Publications

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