New Fluorocarbon-Containing Hydrophobically Associating

Chapter 10

New Fluorocarbon-Containing Hydrophobically Associating Polyacrylamide Copolymer Y.-X. Zhang , A.-H. Da , Thieo E. Hogen-Esch , and George B. Butler 1

1

1,2

2

Department of Chemistry, Loker Hydrocarbon Research Institute, University of Southern California, Los Angeles, CA 90089-1661 Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, Gainesville, F L 32611-2046 1

2

The synthesis of polyacrylamide copolymers containing fluorine-containing acrylates 1, 2, 4 or 5 or silicone-containing methacrylate 6 was carried out by emulsion polymerization using persulfate as initiators and ionic perfluoro surfactants. The Brookfield viscosities of these copolymers, especially those containing 1 or 2, were much higher than the laurylacrylate (3) containing co polymer. The comonomer content of the 1 or 2 containing copoly mers that were most strongly viscosifying was only .07-.28 mole percent, well below that of the corresponding copolymers contain ing 3. Viscosity increases of the 1 and 2 copolymers, observed upon increases in temperature or NaCl concentration were consis tent with association of these copolymers through intermolecular hydrophobic binding. Reduced viscosity or dynamic light scattering studies are consistent with the existence of polymer assemblies above polymer concentrations of about 100 pm. Addition of surfac tants water miscible organic solvents or increasing shear rate was shown to lead to sharp viscosity decreases consistent with the proposed model.

The replacement of hydrocarbon- by perfluoroalkyl groups in hydrophobically associating polymers is of potential interest since the hydrophobic character of perfluoroalkyl groups is more pronounced compared to their hydrocarbon analogs. Thus, the critical micelle concentrations of fluorocarbon surfactants generally are significantly lower than the hydrocarbon analogs of the same chain length and surface tensions of fluorocarbon surfactant solutions are also much lower. 1

2

2

3

Also hydrophobic bonding of fluorocarbon surfactants to β-cyclodextrines is much stronger (about 300 times) compared to similar hydrocarbon containing surfactants. Significantly, the latter process is enthalpy driven (ΔΗ = -9.0 kcal/mole, A S = -12 eu) whereas the bonding of the fluorocarbon 4

0097-6156/91/0467-0159$06.00/0 © 1991 American Chemical Society

160

WATER-SOLUBLE

POLYMERS

surfactant is mostly favored by entropy (AS = +15 eu, ΔΗ = -1.7 kcal/mole). These results suggest, at least in this case, that the binding of fluorocarbons is qualitatively different from that of hydrocarbons and is not merely due to the larger surface of the perfluorocarbon chain compared with the hydro carbon chain of the same carbon number. As a result of these considerations, we have started a research program aimed at investigating the synthesis of copolymers of polyacryl amide and other water-soluble polymers containing perfluorocarbon groups (Scheme 1 ). Included in the group of comonomers investigated was also a silicone containing methacrylate. This monomer was of interest because of the pronounced hydrophobic character of silicones. ' 5 6

/

S0 (CF )7CF , 2

2

3

y

^

O ^ v

Ki/

^CH (CF )6CF

3

2

2 (FX-14)

^ \ (

3

3 (RF-8)

C

H

2

(

C

F

2

)

2

C

F

3

4 (RF-4)

yO / K /

2

2

ο

1 (FX-13)

2

S0 (CF )7CF

y ° V ^ \ ^ [SiMe O] SiMe 2

NCH )iiCH 2

Ο

3

10

3

/ / ^ / Ο

5 (LA) Scheme 1

6 (ASi) Structures of Hydrophobic Comonomers

Experimental Section The copolymers were prepared by an emulsion type polymerization under argon in deionized H 0 (20 ml) containing various amounts of acetone (0-5 ml) and a perfluoroalkyl containing surfactant supplied by the 3 M Company (FC-129) at a concentration between .05 - 0.15 %. Acrylamide (2 gr) (Poly2

10. ZHANG ET AL.

Fluorocarbon-Containing Polyacrylamide Copolymer

161

sciences, "ultrapure") was dissolved in the mixture and the comonomer was usually added as an acetone solution. Comonomers FX-13 (1) and FX-14 (2) were kindly supplied by the 3 M Company. The comonomers 3,4 and 5 were supplied by Polysciences and comonomer 6 was purchased from Petrarch Systems, Inc. The polymerization was initiated by (NH4)2S20s (.0228 gr) and Na2S2Û5 (.0190 gr) added as aqueous solutions. The mixture was stirred at temperatures varying from 25° to 50° for periods between 6 24 hrs. After polymerization, the gel-like product was dissolved in deionized H2O and dialyzed against deionized water. The dissolution process varied between several hours and several months. The resulting solutions were then diluted to the proper concentrations for rheological studies. In this case, the polymer concentrations were determined by precipitation in excess acetone and weighing of the dried polymer. Alternatively, the concentrated solutions were precipitated in acetone followed by drying in a vacuum oven at 40° for 24 hrs. The solid polymer was then redissolved in a known volume of H2O or NaCI solutions. The viscosity of the polymer solutions was measured using a Brookfield viscometer (LTV model) with appropriate sample adaptor. Reduced viscosities were determined at 30.0° using a Cannon-Ubbelode viscometer.

Results

A series of copolymers of acrylamide and comonomers 1, 2 and 5 were prepared initially. The Brookfield viscosity results are shown in Tables I - III and in Figures 1 - 2. Table I shows the Brookfield viscosities of 0.5 % solutions of the FX-13 copolymers. It is interesting to see that the viscosities of the 0.5 % solutions are very high and that the comonomer content of the most strongly viscosifying solutions is very low. For instance, the solution of the copolymer containing only .006 mole % (or .05 weight %) of 1 still has a viscosity (at .40 sec ) that is about 10 times larger than that of the homopolymer prepared under identical conditions. Figure 1 shows the viscosity versus concentration profiles for several of the copolymers as well as the homopolymer prepared under identical conditions. The viscosity differences are especially pronounced at higher concentrations consistent with the pattern expected for associating polymers. A copolymer (AL-3) containing laurylacrylate (5) is shown for comparison. This polymer, as expected, shows a viscosity increase compared to the homopolymer (PAM) at polymer concentrations above 0.5 %. However, the laurylacrylate copolymer seems far less effective as a viscosifier compared to the FX-13 containing samples AF-10 and AF-12. Sample AFT was a terpolymer containing 16 mole % of Na AMPS along with .14 mole % of FX-13. This terpolymer, although less strongly viscosifying than copolymer AF-10, at the higher concentrations gave more viscous solutions at low polymer concentrations (< 0.1 wt %) presumably as a result of polyanion expansion (Fig. 1). _1

1

162

WATER-SOLUBLE POLYMERS

Table I Synthesis of FX-13 containing polyacrylamide Sample

Mole % Comonomer

Weight % Comonomer

Conversion (%)

PAM AF-22 21 18 17 12 10 9 8 7 AFT-13

0 .006 .012 .023 .045 .070 .14 .28 .56 1.12 .14

0 .05 .10 .20 .40 .62 1.25 2.40 4.80 9.10 1.25

99.9 90.3 90.7 88.5 95.2 95.0 96.3 96.1 101.4 100.0 78.9

s

d

a

Brookfield Viscosity iCenterpoisei 50 480 1760 7000 10800 12000 6200 300 50 50 2500

b c

a. See Experimental Section for details of synthesis. Emulsifier was CF (CF )6COOK at .12 wt %. b. Polymer concentration = 0.50gr/dl. c. Shear rate is 0.40 sec , d. Refers to conversion of total monomer; determined gravimetrically. e. Terpolymer containing 16% AMPS (see text). 3

2

-1

Table II Synthesis of FX-14 containing polyacrylamide Sample AF-24 23 15 16 19 20 32 33

Mole % Comonomer .022 .044 .069 .14 .28 .55 1.11 1.66

Weight % Comonomer .20 .40 .62 1.25 2.40 4.80 9.10 13.00

Conversion %

101.0 100.0 100.7 83.1 74.3 75.9 71.8 67.8

a

Brookfield Viscositv (Cn) 120 2220 6000 6800 10,800 9000 200 120 b c

Footnotes a-d see Table I. Figure 2 shows a plot of the viscosity of 0.5 wt % solutions of a series of FX-13 containing copolymers as a function of comonomer content (mole %). The plot shows a clear maximum at about .07 mole %. Significantly, the decrease in viscosity with increasing comonomer content above .07 mole % is more pronounced than the viscosity decrease observed in the low comonomer content part of the curve (Discussion). The pronounced viscosifying tendency of the polyacrylamide copolymers containing FX-13 was also observed for the corresponding copolymers containing the methacrylate (FX-14) (Table II, Figure 2). In this case, the maximum viscosity as a function of comonomer content is observed at slightly higher content of FX-14 (.014%). The asymmetry in the viscositycomonomer content plot is observed in this case also.

10. ZHANG ET AL.


163

Table III Synthesis and Properties of Laurylacrylate Containing Polyacrylamides 3

Sample .d -3d -d 2

4

Al-7e -5β -6e -8e PAM

Comonomer mole % wt % .74 2.44 1.64 4.80 2.99 9.13 4.52 13.20 .75 1.50 3.00 4.50 0

2.40 4.80 9.10 13.00 0

Conversion

13

%

100.4 99.5 100.4 92.3

Brookfield Viscosity Î1.0wt%) i0.5wt%) 84 10 120 30 170 40 44 10 0

86.4 86.7 83.4 76.6

400 420 760 250

99,9

450

50 100 120 40 50

a. Polymerization Conditions: 2gr AM in 20 ml deionized water, b. Based on weight of precipitated polymer, c. Shear rate is 0.40 sec , d. Sodium lauryl acrylate (.25 wt %). e. Emulsifier was CF3(CF2)6COOK (obtained from 3M Company) at .12 wt %. -1

In contrast, the 5 containing copolymers are less strongly viscosifying by at least a two order of magnitude (Table III). Furthermore, the molar content of 5 in these copolymers is almost two orders of magnitude higher than that of the FX-13 series. Thus, the hydrocarbon containing polyacryl amides are both less effective and less efficient than the FX-13 and FX-14 containing copolymers. Table IV shows the Brookfield viscosities of 0.5 weight percent polyacrylamide copolymers containing comonomers 3 (RF-8) and 4 (RF-4) containing C7 and C3 perfluoroalkyl groups respectively. Apparently both comonomers lead to more effectively viscosifying copolymers compared with the laurylacrylate copolymers although the RF-4 and laurylacrylate copoly mers are not that different. Again the comonomer content corresponding to the most strongly viscosifying copolymers is lower for the RF-4 and RF-8 series compared to the hydrocarbon analogs both on a mole and weight % basis. However, the RF-4 and RF-8 containing comonomers are less effectively and efficiently viscosifying compared to the FX-13 and FX-14 series. Although it is possible that the differences between the FX-13/FX-14 type and the RF-8 type copolymers are due to the slightly greater degree of fluorine substitution of the octyl groups in FX-13/FX-4, it appears plausible that the different "spacer" group in the FX-type comonomers plays a role. The polar nature of the sulfonamide group makes it plausible that the hydro philic spacer in this case may act to decouple the motions of the polymer and the hydrophobic aggregate. Such an effect of spacer groups was recently demonstrated by Schulz et al for hydrocarbon acrylate comonomers contain ing poly-ethyleneoxide spacers of various lengths. 7

164


Q. Ο

CO Ο Ο CO

0.00

1.00

0.50

1.50

2.00

2.50

3.00

Concentration (%)

Figure 1. Brookfield Viscosities of Samples PAM, AL-3, AF-10, AF-12 and AFT-13 Measured at 0.40 sec . 1

5.0-

Concentration 0.5% Shear rate 0.4(1/s)

• A X

A F series MF series AL series

υ CO

ο ο

3.0 Η

CO

ο ο

2.0-

1.0-1

-3.00

1

-2.00

r -1.00

0.00

1.00

Log mole(%)

Figure 2. Dependence of Brookfield Viscosities Against Mole % Comono mer for the Copolymers Containing FX-13 (AF Series) and FX-14 (MF Series).

10. ZHANG ET AL.


165

Table IV Synthesis and Properties of RF-4 and RF-8 Containing Polyacrylamides e

Comonomer RF

Sample AF-25 AF-26 AF-27

4

Conversion Comonomer Mole% wL%^ % 70.7 .625 .18 .88 3.03 87.6 3.50 11.11 89.3

0

.11 .51 .98 1.96

AF-28 -29 -30 -31

RF-8

88.1 86.7 94.6 90.3

.67 3.03 5.88 11.11

Brookfield> Viseositv icpi 450 1000 400 a

d

24b 3000b 2960 120 b

b

a. Polymer concentration is 1.0 wt %. b. Polymer concentration is 0.50 wt %. c. Based on weight of precipitated polymer, d. Shear rate is 0.40 sec , e. CF (CF )COOK was emulsifier at .12 wt %. 1

3

2

A comparison of the RF-4 and RF-8 copolymers points up the expected greater viscosifying power of the RF-8 copolymers. Such increases are not unexpected in view of the well documented decreases in CMC of a series of surfactants with increasing hydrocarbon length. Similar trends in fluorocarbon surfactants have also been documented. 3

3

Table V Synthesis and Properties of ASi Containing Polyacrylamides

3

Sample Comonomer Mole % ASi-8 .005 -7 .009 -5 .018 -4 .036 -3 .089 -2 .446 -1 .890 a-c

Comonomer Wt% .06 .12 .23 .46 1.13 5.70 11.40

Monomer Brookfield -° Conversion Viscosity (cp) 250 420 75.8 750 77.3 780 82.8 600 85.7 400 74.7 350 b

See footnotes, Table I

Table V shows the Brookfield viscosities of a series of silicone methacrylate 6 containing polyacrylamide copolymers (ASi series). These copolymers are less strongly viscosifying compared with the fluorocarbon containing copolymers but appear to be somewhat more effective than the laurylacrylate copolymers. Thus, the viscosities of 0.5 wt % solutions of sample ASi-4 are from 6.5 to about 20 times more viscous compared with the laurylacrylate copolymers solutions of the same polymer concentration (0.5 wt %). However, since the number average number of -SiMe20- units is about 10, the hydrophobe, in this case, is essentially almost twice as long as the lauryl group. Interestingly, the optimal molar- and weight-comonomer content for the ASi-series is quite low compared with the laurylacrylate and

166


RF4/RF8 series and comparable with the FX-13/FX-14 series. Thus in comparison, the ASi-comonomers are less effective than the FX-13/FX-14 comonomers but about as efficient.

Characterization Characterization of these associating polymers was attempted by reduced viscosity measurements and by dynamic light scattering. The reduced viscosity vs concentration of sample 12-65 in water is shown in Figure 3. The apparent intrinsic viscosity ([η]) is about 23 dl/gr. However, in H 0-DMF mixtures of 25/75, 40/60 and 50/50 (V/V), the intrinsic viscosities decrease rapidly to about 18 dl/gr, 10 dl/gr and about 3 dl/gr respectively. In contrast, the [η] of homopolyacrylamides typically decrease by about a factor of 1.5-2.0 depending on molecular weight in going from water to 60/40 water DMF. It is therefore plausible that the intrinsic visco sities reported (Table VI) are apparent values and that molecular weights are much lower than predicted from reduced viscosity measurements in water. The association of these new fluorocarbon containing copolymers is also demonstrated by dynamic light scattering measurements. Figure 4 shows the diffusion constant D as a function of polymer concentration for sample M-23 prepared with .07 mole % of FX-13. Starting at about 100 ppm, D shows a sharp decrease indicating perhaps the onset of aggregation at that concentration. Using scattering techniques of this type aggregate sizes between 1000-5000 nm have been detected. It is not clear yet whether the scattering species below 100 ppm represents the unassociated macromole cules. Studies aimed at this are continuing. 2

8

Table VI Intrinsic Viscosities and Huggins Constants of Polyacrylamides Containing Comonomers 1, 2 and 5 Copolymer

Comonomer

PAM AL-3 AF-17 AF-12 AF-10 AF-19 AFT-13

none 5 1 1 1 2

1/AMPS

Mole % Comonomer 3.0 .045 .070 .14 .28 .14C

[η]3 iDI/grt 5.22 4.37 10.13

.81 1.08 2.12

9.71 11.07 4.8ld

.91 2.34 3.47

-

-

a. Measured in H 0 at 30° *0.1°. b. Huggins constant, c. Refers to content of 1 ; AMPS content is 16 %. d. Measured in 2.0 % NaCI solution. 2


10. ZHANG ET AL.

167

Figure 3. Plots of Reduced Viscosity vs Concentration For Polymer 12-65 in Various H2O/DMF Mixtures.

10"

: -

ο

ΙΟ"

θ

8

Μ-23 0.07 mole % FX-13

8

0

8

: Ο

fx,

ο

-

ω ο υ

ο ΙΟ" Η—1

β 9

θ

m !=> fx,

ο

-

10"

1 0

I 1

..I 10

ι

ι

. . . .1 100

I

I

I

I 1 I I

I

103

I

I

I

I

I I I I

10

CONCENTRATION, P P M

Figure 4. Dependence of Diffusion Coefficient D of Polymer M-23 on Polymer Concentration.

4

168


Rheology

Since the FX-13/FX-14 copolymers appeared to be most promising as viscosifiers, they were studied in somewhat greater detail. Figures 5-7 show the effects of shear, addition of NaCI and temperatures on the Brookfield viscosities of AF-12 (FX-13 series). The pronounced pseudoplastic behavior of this and similar samples (Fig. 5) is not unexpected. The application of even moderate shear apparently efficiently degrades the large macromolecular assemblies into smaller units. However, the viscosity recovers rapidly upon removal of shear. Again, this appears consistent with the occurrence of a "network" of hydrophilic polymers held together by small hydrophobic assemblies. Hydrophobic aggregation of these polymers is also consistent with the effects of NaCI addition and heating. The salting-out effect of NaCI is well known and clearly leads to enhanced hydrophobic bonding. - However, the enhancement in viscosity upon addition of NaCI is relatively small (Fig. 6). The viscosity changes with temperature are more complex and show both minima and maxima, especially at low shear rates (Fig. 7). The increased hydrophobic association between 40° and 60° is consistent with hydrophobic bonding, an entropy driven process. Above 60° and below 40°, viscosity decreases with increasing temperature. Apparently above 60°, enhanced hydrophobic bonding is outweighed by a general decrease in viscosity at higher temperature (see Discussion). The effects of addition of ionic surfactants is also consistent with the existence of hydrophobically driven aggregation of macromolecules. Figure 8 shows a decrease in viscosity of a sample AF-90 (.05 - .15 wt %) with increasing concentration of a fluorine containing ionic surfactant FC-149 (CF3[CF2]7COOK). Apparently the surfactant competes effectively for the perfluoro chains of the polymer at very low surfactant concentrations. The pattern for non ionic surfactants such as Triton-X-100 and FC-171 (CF (CF2)nCH2[OCH2CH2] OH) is quite different (Fig. 9). In the case of FC-171, there is a viscosity maximum as well as a minimum upon addition of surfactant. Increases as well as decreases in viscosity are also observed for Triton-X-100. Increases in viscosity in these cases may be rationalized by micellar bridging in which intermolecular polymer association occurs via a micelle. However, the patterns are complex and further experimentation is needed to better understand these effects. Further research into this interesting new class of associating watersoluble polymers is continuing. 5 6

3

m

Discussion

The maxima in the Brookfield viscosity-comonomer content profiles for the FX-13/FX-14 and similar hydrophobic comonomer-containing polymers are of interest (Fig. 2, Tables l-V). The maxima for the fluorocarbon copolymers are especially pronounced. It is plausible that this behavior correlates with the very high efficiency of the fluorocarbon moieties in hydrophobic association. Since hydrophobic association is pronounced for fluorocarbons, the comonomer content in the chain can apparently be decreased without

10. ZHANG ET AL.

-1.0


0.0

1.0

169

2.0

Log shear rate(1/s)

Figure 5. Dependence of Brookfield Viscosity of Polymer AF-12 on Shear Rate at Various Polymer Concentrations.

170


35000 Comonomer:0.14 mol%

30000 -

Concentration :0.5 wt%

• •

0.084(1/s) 0.168(1/s) 0.42(1/s)

25000 -

1.68(1/S) 8.40(1/S)

20000 15000 10000 5000 0 0.0

20.0

40.0 T(°C)

60.0

80.0

100.0

Effect of temperature on the viscosity of MF-25 Figure 7. Effect of Temperature on Brookfield Viscosity of Sample MF-25 at Various Shear Rates.

Figure 8. Effect of Concentration (wt %) of Surfactant FC-129 on Brookfield Viscosity of Polymer AF-90 at Various Polymer Concentrations, Shear Rate is 0.40 sec . 1

10. ZHANG ET AL.


4.0

171

FC-171 Triton-X-100

AF-19(0.25%)

g> 2.0 O

Ί "1———•——ι——~~~~——ι—————ι————*" 0.0 1.0 2.0 3.0 4.0 1

1

1

1

r

l

1

1

1

1

1

1

1

1

Surfactant(%) Figure 9. Brookfield Viscosities as a Function of Added Non-Ionic Surfac tants FC-171 and Triton-X-100.

172

WATER-SOLUBLE

POLYMERS

decreasing intermolecular association. This decrease in comonomer concentration lowers the degree of intramolecular hydrophobic association and this in turn tends to diminish chain contraction. Effectively associating hydrophobic groups thus would tend to favor intermolecular association even further. Even at .006 mole % of FX-13 intermolecular association appears to be marked (Table I). As the comonomer concentration increases intermole cular association also increases. Eventually increased FX-13 content tends to favor intramolecular association even more and the resulting chain contraction lowers the size and thus the viscosity contribution of the polymer. This viscosity decrease is quite dramatic. A four fold increase in FX-13 content lowers the Brookfield viscosity by a factor of more than a hundred. It is of course, not clear whether the magnitude of the viscosity changes is solely attributable to changes in hydrophobic association patterns. For instance, molecular weight effects may also be present. However, the over all pattern most likely is due to a balance between inter- and intramolecular association that is affected by the hydrophobic character of the side chain. This tendency of the hydrophobic groups to promote association is strongly influenced by their chain length as a comparison between the RF4 and RF8 copolymers shows (Table IV). The results also indicate that the presence of a water-soluble flexible spacer such as the -CH2CH2N(C H5)S02- group enhances the ability of the hydrophobic group to associate. This effect appears to have first been documented by Schulz et al who showed that increasing the oligo ethyleneoxide spacer length in a series of acrylates with the same hydrocarbon group increased the association of the corresponding polyacrylamide copolymers. It may be argued that this effect is due to the decoupling of the motions of the chain and of the hydro phobic moiety in the aggregate. In this sense, the spacer would play a role similar to that of the spacers in liquid crystalline forming polymers. Also, increasing the distance between the chain and the hydrophobe may lessen the importance of excluded volume effects operating between associating polymers in the polymer assembly. Finally, the spacer may lessen unpro ductive intramolecular associations between the hydrophobe and the hydro phobic carbon chain of the polymer or between the hydrophobic groups of the same chain. The behavior of the silicone hydrophobe is unusual in that it resembles the hydrocarbon chains in its ability to promote association (Tables III and V). It is not surprising that fluorocarbons are more effective than silicones in pro moting association since their hydrophobic character is more pronounced. However, the silicones are similar to the fluorocarbons in that they are quite effective at very low comonomer levels. Perhaps this is due to the much longer chain-length and perhaps to the greater surface area of the silicone chain. Further studies with comonomers with varying silicone chain lengths should clarify this point. Although the nature of the polymer association appears reasonably clear, the degree of polymer association is not. From the very high value of the reduced viscosity of about 23 dl/gr of sample 12-65 in water at a concen tration of about .015 wt % (-150 ppm) (Fig. 3) it would appear that this still represents an associated polymer assembly. Further evidence for this comes from the much lower value of η οΐ in a 50% mixture of H2O-DMF. However, 1

2

7

3b

Γθ

10. ZIIANG ET AL.


the dynamic light scattering data on similar polymers are consistent with association beginning around 100 ppm (Fig. 4). It is of course, possible that there is residual association below 100 ppm but there is no evidence so far. It seems probable that this can be clarified by more extensive light scattering and viscosity studies of copolymers with varying comonomer content and in various water-DMF systems. We have studied the effects of cosolvent addition on the viscosity of aqueous solutions of these copolymers including DMF, DMSO acetone, etc. The addition invariably leads to viscosity decreases presumably as a result of a less hydrophobic environment and thus a lesser driving force toward hydrophobic association. Also, competitive interactions may occur between the hydrophobic groups and the cosolvent similar to the effects caused by the addition of surfactants. Unfortunately, precipitation occurs at 30-50% cosolvent so that the range of solvent compositions is limited. Although the addition of ionic surfactants results in a simple decrease of viscosity, the addition of non ionic surfactants leads to more complex changes (Fig. 9). These effects are rather puzzling and it is likely that there are several effects operating simultaneously. These effects are expected to include, a) competition of the surfactant molecule for the polymer hydrophobe, b) micellar bridging that would lead to crosslinking by intermolecular association of two or more polymers with a single micelle and c) intramolecular micellar bridging in which several hydrophobic groups of a single polymer associate with a micelle. An unknown quantity in all of these considerations is the size of the hydrophobic domains in the polymer assemblies specifically the number of hydrophobic groups/ hydrocarbon aggregate. In view of the associating ability of the copolymers with extremely low comonomer content (Tables l-ll) it is not probable that this number is large for the FX-13/FX-14 copolymers. A large number would entail unacceptably large excluded volume effects for intermolecular association. Moreover, such a case would be expected to lead to predominant intramolecular micellization at low comonomer content and this is not observed. It is more likely that the number of hydrophobic groups/aggregate is rather small, perhaps as low as two. Therefore, the hydrophobic aggregates themselves would not resemble micelles but much smaller entities. Studies aimed at this are in progress. 9

Acknowledgments This research was supported by the Department of Energy, office of Basic Energy Sciences. We wish to thank Professor Eric Amis and Thomas Seery for carrying out the dynamic light scattering measurements. Literature Cited 1. Evani, S.; Rose, G.D., Polym. Mat. Sci. Eng. Preprs., 1987, 57, 477 ; Landoll, L.M., J. Polym. Sci. Chem., 1982, 20, 443 ; Schulz, D.N.; Kaladas, J.J.; Maurer, T.T.; Bock, J.; Pace, S.J.; Schulz, W.W., Polymer,

173

174

2.

3.

4. 5. 6. 7. 8. 9.


1987, 28, 2110; Turner, S.R.; Schulz, D.N.; Siano, D.B.; Bock, J., Polym. Mat. Sci. Eng. Preprs., 1986, 55(2), 355 ; Middleton, J . C . ; Cummins, D.; McCormick, C.L., Polym. Preprs., 1989, 30(2), 348. a. Zhang, Y-X; Da, A - H ; Hogen-Esch, T . E . ; Butler, G.B., Polym. Preprs., 1989, 30(2), 338. b. Ibid., J. Polym. Sci. (Polym. Lett.), 1990, 00, 000. a. Schwartz, E . G . ; Reid, W . G . , Ind. Eng. Chem., 1964, 56, 26. b. Myers, D., Surfactant Science and Technology; V C H Publishers, Inc., New York, NY, 1988. Jiang, X-K: Acc. Chem. Res., 1988, ? ? , 362. Tanford, C . , The Hydrophobic Effect; Second E d . , Wiley, New York, 1980. Ben-Naim, Α., Hydrophobic Interactions; Plenum Press, New York, 1980. Schulz, D.N. et al, Polymer, 1987, 28, 2110. Amis, E.; Seery, T . J . , Unpublished results. Zhang, Y-X; Da, A - H ; Hogen-Esch, T . E . , Unpublished Results.

RECEIVED July 2, 1990

New Fluorocarbon-Containing Hydrophobically Associating

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