A Review of Block Polymer Surfactants

A Review of Block Polymer Surfactants IRVING R. SCHMOLKA, BASF Wyandotte Corp., Wyandotte, MI 48192 ABSTRACT AND SUMMARY addition first o f p r o p y l e n e oxide and then ethylene oxide to a low molecular weight water-soluble organic c o m p o u n d , propylene glycol. The h y d r o p h o b e is the inner p o l y o x y propylene glycol which changes from a water soluble- to a water insoluble- p o l y m e r as the molecular weight goes above 750. The a d d i t i o n o f ethylene oxide in the final step provides water solubility to the molecule. In this-series, as in all other syntheses to be presented, the o x y a l k y l a t i o n steps are carried o u t in the presence of an alkaline catalyst, generally sodium or potassium hydroxide. The alkaline catalyst is then neutralized and usually removed from the final product. The equations representing this synthesis are shown in Figure 1. When the o r d e r of a d d i t i o n o f the alkylene oxides is reversed, the m e r o x a p o l series is produced (3), as shown by the equations in Figure 2. In this series, e t h y l e n e glycol is the initiator. It is informative to n o t e the essential important differences between the p o l o x a m e r and the m e r o x a p o l structures. This should be kept in m i n d when physical properties o f the two series are c o m p a r e d with each other. The p o l o x a m e r structure is terminated b y two p r i m a r y h y d r o x y l groups, while the meroxapol series has secondary h y d r o x y l groups at the ends. In the p o l o x a m e r series the h y d r o p h o b e is on the inside, while the corresponding m e r o x a p o l has the hydrophobe split in two, each half o f which is on the outside of the surfactant. This is illustrated in Figure 3. A slightly different structure is exhibited b y the 'poloxamines, which are p r e p a r e d (4) from an ethylenediamine initiator. These resemble the poloxamers in having the same sequential order o f a d d i t i o n o f alkylene oxides. Their synthesis is shown in Figure 4. Structurally, the p o l o x a m i n e s differ from the other polymers in that t h e y have four alkylene oxide chains, rather than two, since four active hydrogens are present in the initiator. These surfactants also differ from the other polymers in that t h e y contain two tertiary nitrogen atoms, at least one of which is capable o f forming a quaternary salt (5). These p o l y m e r s are also terminated by primary hydroxyl groups. The fourth series o f surfactants to be discussed are the PLURADOT polyols. Currently there is no n o n p r o p r i e t a r y name assigned to this family of polymers. These surface active agents can be p r e p a r e d (6) from a low molecular weight trifunctional alcohol, such as glycerine or trimethyl- A brief historical review of four series o f c o m m e r cially available b l o c k p o l y m e r surface-active a g e n t s the P L U R O N I C R, T E T R O N I C R, P L U R A D O T R, and P L U R O N I C R R p o l y o l s - i s presented. A comparison is made o f the physical properties within each series, in the form o f trend lines. These parameters encompass solubility, rate of solubility, wetting, foaming, defoaming, emulsification, thickening, cleansing, and t o x i c i t y . The physical p r o p e r t y relationships which depend u p o n variation in the h y d r o p h o b e molecular weight and variation in the hydrophile h y d r o p h o b e balance are shown to be similar in each series o f surf a c t a n t s . Differences among the four series of polymers, where t h e y exist, are seen to vary from little to significant. The m a n y controversial articles on the micellar nature of the block p o l y m e r s and their critical micelle concentrations are examined. Considerations o f the i m p o r t a n t physical properties which lead to practical applications are discussed. S o m e o f the more i m p o r t a n t newly developed p o t e n t i a l uses o f these p o l y m e r i c surfactants are then described in various application areas, including the cosmetic, medical, paper, pharmaceutical, and textile industries. INTRODUCTION A b l o c k p o l y m e r nonionic surfactant is a surface active agent prepared by the sequential addition o f two or more alkylene oxides t o a low molecular weight water-soluble organic c o m p o u n d containing one or more active hydrogen atoms. It is the p u r p o s e of this review to c o m p a r e the physical p r o p e r t i e s of four different groups o f commercially available b l o c k p o l y m e r surfactants and to discuss some of their most recent industrial applications. The block p o l y m e r surfactants t o be reviewed include the PLUR O N I C R, P L U R O N I C R R, TETRONIC R, and the P L U R A D O T R polyols. The corresponding n o n p r o p r i e t a r y names o f the first three are p o l o x a m e r , m e r o x a p o l , and p o l o x a m i n e , ( 1 ) respectively. SYNTHESIS The p o l o x a m e r s are synthesized (2) b y the sequential CIH3 C-H3 (OH-) CIH3 HOCHCH2OH + (b-l) CHCH2 >HO(CHCH20)bH \/ O CH3 HO(CHCH20)bH + (2a) CH2CH 2 x / O > HO(CH2CH20)a(CHCH20)b(CH2CH20)aH FIG. 1. Poloxamer Synthesis HO-CH2CH2-OH + (n-l) CH2--CH2 (OH-) >HO-(CH2CH2-O)nH -o' CH 3 I HO-(CH2CH2-O)nH + 2b CH--CH 2 %, J O > H(O-CH-CH2)b-(OCH2CH2)n-(CH2-CHO)bH FIG. 2. Meroxapol Synthesis 110 MARCH, 1977 SCHMOLKA: BLOCK POLYMER SURFACTANT Meroxapol I 1 Poloxamer IF o l o ol FIG. 3. /0~ (OH-) H2N-CH2CH2-NH 2 + 4b CH 2 - C H - C H 3 > OH I (CH 3CHCH2)b~ OH I / (CH 2CHCH3)b NCH2CH2N~ (CH37HCH2)b / (CH27HCH3)b OH OH ~0 (OH-) HYDROPHOBE + 4a CH2-CH 2 > H(C2H40)a(CaH60)b /(C3H60)b(C2H40)aH ~NCH2CH2N H(C2H40)a(C3H60)b / ~(C3H60)b(C2H40)aH explained. As seen in Table I, which illustrates the p o l o x a m e r series, the first two digits of a p o l o x a m e r , when multiplied by 100, indicate the a p p r o x i m a t e h y d r o p h o b e molecular weight. The last digit, when m u l t i p l i e d b y 10, gives the percent of ethylene oxide in the molecule, the balance being p r o p y l e n e oxide. The m e r o x a p o l series is shown in Table II. The first two digits, when m u l t i p l i e d by I 0 0 , give the t o t a l m o l e c u l a r weight o f the t w o p o l y o x p r o p y l e n e glycol h y d r o p h o b e s . The last digit, multiplied by 10, gives the percent ethylene oxide in each polymer. In this respect the m e r o x a p o l n o m e n c l a t u r e system resembles the p o l o x a m e r system. The p o l o x a m i n e series is described in Table III. The same system is used with the poloxamines as with the previous two series. The last digit, multiplied b y 10, gives the percent e t h y l e n e oxide in the final molecule, while the first t w o digits are indicative of the h y d r o p h o b e m o l e c u l a r weight. The zero was included so as to minimize confusion with the p o l o x a m e r numbering system. The last series, the P L U R A D O T polymers, is shown in Table IV. The exact relative percentages of ethylene and p r o p y l e n e oxides in the h y d r o p h o b e and the h y d r o p h i l e in this series a r e p r o p r i e t a r y information. However, f r o m physical p r o p e r t y data, specifically cloud points, it can be seen that the larger the s e c o n d digit, the greater is the t o t a l percent of e t h y l e n e oxide in the molecule. As seen in the table, the larger the first digit, the greater is the h y d r o p h o b e molecular weight. PHYSICAL PROPERTI ES FIG. 4. Poloxamine Synthesis ~C3H60. ~ R(OH)3+3n ~C2--~-~40~ (>I) 111 (OH-) > R[O(C3H60/C2H40)nH] 3 ~ C2H40 .~ (OH-) R[O(C3H60/C2H40)nH] 3 + 3m \C3-C--~-~} (>1) > R [O( C 3H 60/C 2 H40 )n-( C2 H40/C 3H60 )mH ] 3 FIG. 5. Pluradot Polyol Synthesis olpropane, which is o x y a l k y l a t e d initially with a blend of p r o p y l e n e and ethylene oxides, but mostly with propylene oxide, to form the h y d r o p h o b e . This is followed b y oxyalkylating with a blend of ethylene and propylene oxides, but mostly with ethylene oxide, to form a hydrophile. This synthesis scheme is shown in Figure 5. This group o f surfactants has three chains, one more than the p o l o x a m e r and m e r o x a p o l series, b u t one less than the p o l o x a m i n e polymers. Because o f the slower rate of reaction o f p r o p y l e n e oxide, c o m p a r e d to ethylene oxide, it is suggested that the terminal h y d r o x y l group is composed primarily o f secondary h y d r o x y l groups rather than of primary h y d r o x y l groups. Obviously there are no chemical differences within any one series of p o l y m e r i c surfactants. A m o n g the four series, there are two differences. (1) The presence of the two tertiary nitrogen a t o m s in the poloxamines and their absence in the o t h e r polymers, and (2) the terminal secondary or primary h y d r o x y l groups, as mentioned previously. NOMENCLATURE Since there are more than seventy-five different polymeric surfactants, the nomenclature of each system will be Cloud Point Major differences in physical properties are seen to exist within any one series. In addition, when one c o m p a r e s one series with another, some differences and some similarities are readily apparent. All four nonionic series are alike in that t h e y derive their solubility in water from h y d r o g e n b o n d f o r m a t i o n between the m a n y ether o x y g e n atoms present and p r o t o n s in the water. When the t e m p e r a t u r e of a solution of a nonionic surfactant is raised, the h y d r o g e n b o n d is b r o k e n and the nonionic clouds out o f solution. This is k n o w n as the cloud point. F o r p o l o x a m e r s , the 1% cloud p o i n t ranges from a low of 14 C t o a high of 100 C. This latter figure is for the most h y d r o p h i l i c p o l y m e r s containing 80% e t h y l e n e oxide. In contrast, the m e r o x a p o l s have a n a r r o w e r cloud p o i n t range. The i m p o r t a n t difference w o u l d be the lowered cloud p o i n t with the most h y d r o p h i l i c members, those that contain 80% ethylene oxide. The p o l o x a m i n e s resemble the p o l o x a m e r s in this property, s i n c e t h e y are structurally similar. The P L U R A D O T p o l y m e r s have the lowest m a x i m u m cloud p o i n t p r i m a r i l y because the m o s t h y d r o p h i l i c m e m b e r s have a l o w e r e t h y l e n e oxide c o n t e n t t h a n the 80% e x h i b i t e d b y the o t h e r series, and perhaps, p a r t l y due to the presence of some p r o p y l e n e oxide in the terminal h y d r o p h i l e . These data are shown in Table V. Water Solubility Within any one series, as the percent o f e t h y l e n e oxide increases, or the molecular weight of the h y d r o p h o b e decreases, the solubility in water increases. This is true for all f o u r series. Within any one series, the rate o f solubility o f a p o l y m e r in water decreases as the h y d r o p h o b e m o l e c u l a r weight increases. In a comparison of the rate o f solubility in water of t w o similar polymers, one with the h y d r o p h i l e on the outside, p o l o x a m e r 188, and the o t h e r with the h y d r o p h i l e on the inside, mero~/apol 17R8, the latter h a d a faster rate of solubility t h a n the former. In a n o t h e r comparison b e t w e e n t w o p o l y m e r s with a 112 J O U R N A L O F T H E A M E R I C A N O IL C H EMIS TS ' S O C I E T Y VOL. 54 TABLE I P o l o x a m e r Series Hydrophobe molecular weight 4000 3250 2750 2250 2050 1750 1200 950 401 331 402 403 333 407 334 284 234 282 231 181 212 182 122 183 123 184 124 20 30 40 101 10 335 235 215 185 338 288 238 237 217 188 105 108 50 60 70 80 % Ethylene oxide TA B LE II Meroxapol Series Hydrophobe molecular weight 31RI 25R1 17R1 31R2 25R2 17R2 10 3100 2500 1700 1000 20 31R 4 25R4 17R4 25R5 25R8 17R8 10R8 10R5 30 40 50 60 70 80 % Ethylene oxide TABLE 111 P o l o x a m i n e Series Hydrophobe molecular weight 1501 1301 1101 901 701 1502 1302 1102 10 6750 5750 4750 3750 2750 1750 750 20 1504 1304 1104 904 704 504 304 702 30 40 1508 1307 1107 908 707 50 60 70 80 % Ethylene oxide similar molecular weight and the same ethylene oxide/ p r o p y l e n e oxide ratio, the t e t r a f u n c t i o n a l p o l y m e r , poloxamine 707, was f o u n d to dissolve more rapidly than the difunctional p o l y m e r , p o l o x a m e r 407. This suggests that the length of the p o l y m e r chain has an effect on the rate of solubility. This is substantiated when one compares the rate of solubility, within any one series, of a group of polymers with the same ethylene o x i d e / p r o p y l e n e oxide ratio, but of varying molecular weight. It has been f o u n d that the larger the molecular weight of the h y d r o p h o b e , the slower is the rate of solubility. No solubility rate comparisons have been carried out with the P L U R A D O T polymers. Oil Solubility None of the poloxamers is soluble is mineral oil. However, b y placing the p o l y p r o p y l e n e glycol h y d r o p h o b e on the outside o f the molecule, it is o f interest t o note that m a n y of the m e r o x a p o l p o l y m e r s do exhibit m o d e r a t e solubility in this lipophilic solvent. The p o l o x a m i n e and P L U R A D O T p o l y m e r s are also insoluble in mineral oil. This is t o be e x p e c t e d , since they m o r e closely resemble the p o l o x a m e r than the m e r o x a p o l structure. The solubility characteristics of the four series of p o l y m e r s in an organic solvent, such as p r o p y l e n e glycol, are quite similar. The higher the h y d r o p h o b e molecular T A B L E IV P l u r a d o t H A Series Increasing hydrophobe molecular w e i ght l 510 520 530 540 550 410 420 430 440 450 Low High % Ethylene oxide TABLE V 1% Cloud Point, ~ Surfactant Minimum Maximum A Poloxamer Meroxapol Poloxamine Pluradot 14 25 15 25 100 99 100 77 86 74 85 52 weight, the less soluble is the polymer. Also, those polymers with a high percentage of ethylene oxide or a high percentage of p r o p y l e n e oxide, everything else being equal, are less soluble in p r o p y l e n e glycol than those p o l y m e r s which have an ethylene oxide c o n t e n t o f between 40 and 60%. MARCH, 1977 113 SCHMOLKA: BLOCK POLYMER SURFACTANT T A B L E VI P o l o x a m i n e W e t t i n g Times, a Sec. Hydrophobe molecular weight 6750 5750 4750 3750 2750 1750 51 30 15 84 48 37 88 185 >360 38 10 20 30 40 >360 >360 50 60 70 80 % Ethylene oxide a D r a v e s t e s t , 3 g H o o k , 0 . 1 % s o l u t i o n , 2 5 C. T A B L E VII M e r o x a p o l D y n a m i c F o a m H e i g h t s , 25 C a Hydrophobe molecular weight 3100 2500 1700 1000 15 40 115 40 45 195 10 20 215 260 300 125 110 145 125 260 30 40 S0 60 70 80 % Ethylene oxide a F o r 0 . 1 % s o l u t i o n at 4 0 0 m l / m i n f l o w r a t e . Wetting In each of the p o l y m e r series, the same wetting trend is observed in that wetting time, as measured by the Draves test for a 0.1% solution at 25 C, decreases as the percent hydrophile decreases. Also as the molecular weight of the hydrophobe increases, the wetting time decreases. However, above a certain limit, which varies with each series, there is no decrease in the wetting time as the hydrophobe molecular weight increases. This is exemplified in Table VI, by the poloxamine series, which shows that wetting time reaches a m i n i m u m as the hydrophobe molecular weight increases from 750 to 4750 but then rises slightly as the molecular weight increases further to 6750. Foaming Within each series, the foam property reaches a maximum at a different ethylene oxide/propylene oxide ratio. With the meroxapols, m a x i m u m foam height, at 25 C, is at a 40:60 ethylene oxide/propylene oxide ratio, but at 49 C, the m a x i m u m shifts to a 50:50 ratio. The poloxamers exhibit m a x i m u m foam at a slightly higher ethylene oxide/ propylene oxide ratio, namely 60:40, at 49 C. From data on the limited n u m b e r of polymers prepared in the poloxamine series, it appears that foam is maximized between the 40:60 and 7 0 : 3 0 ethylene oxide/propylene oxide ratios. Foam values in the P L U R A D O T series increase as the cloud point of the p o l y m e r increases. However, the limited n u m b e r of polymers makes it impossible to draw any valid conclusions. F o a m properties of each surfactant series increase and t h e n decrease slightly, as the hydrophobe molecular weight increases. This is exemplified in Table VII where the n u m b e r s represent millimeters of foam generated at a 400 m l / m i n flow rate in the dynamic foam machine for the meroxapols. However, the biggest difference in foam properties is found in a comparison of the foam properties of the two series which have terminal hydrophile groups, the poloxamers and the poloxamines, with the meroxapols, where the h y d r o p h o b e groups are on the outside. The latter series exhibits little or n o foam, even by its most hydrophilic members. As an example, a 0.1% solution of p o l o x a m e r 188 has a foam value of 600 m m at 40 C at a 400 m l / m i n dynamic flow rate, while its meroxapol counterpart, 17R8, has a foam height of only 44 mm, u n d e r the same conditions. Poloxamer and poloxamine foam heights appear comparable for comparable polymers. Thus, for example, poloxamer 407 has a foam value of 160 m m at a 200 ml flow rate, while poloxamine 707 has a foam value of 180 mm, u n d e r identical test conditions. For defoaming properties, all four series resemble each other in that the highest propylene oxide/ethylene oxide ratio surfactants are very effective defoamers and n o t r e n d lines can be drawn or large differences noted. If any generalization can be drawn, it might be that the meroxapols appear to be better defoamers than their corresponding poloxamers. EMULSIFICATION Attempts to correlate emulsification properties with ethylene oxide/propylene oxide ratios and h y d r o p h o b e molecular weights have n o t been very successful. Within any one series, the higher molecular weight h y d r o p h o b e s are generally better emulsifiers than their lower molecular weight homologs. Some of the poloxamers appear to be better emulsifying agents for mineral oil or f l u o r o c a r b o n s in aqueous systems than the meroxapol or p o l o x a m i n e polymers, while several of the latter appear superior for preparing stable emulsions of glyceryl trioleate in water. However, no trend lines can be presented. Thickening The thickening power of each series of surfactants in w a t e r increases as the h y d r o p h o b e molecule weight increases and as the ethylene oxide/propylene oxide ratio increases. The available data, b u t n o t shown here, indicate that the meroxapol and P L U R A D O T series do n o t form gels at a n y concentrations in water, whereas only 20% o f either poloxamer 407 or p o l o x a m i n e 1508 is needed to form a 114 JOURNAL OF THE AMERICAN OIL CHEMISTS' SOCIETY VOL. 54 strong gel. In comparison, a 20% solution of p o l o x a m e r 403, p o l o x a m e r 188, p o l o x a m i n e 1504, or p o l o x a m i n e 908 is a fluid liquid at r o o m temperature. Cleansing Because of the varying nature o f substrates, soils, cleaning conditions, and t y p e s of e q u i p m e n t used, n o one trend line can be drawn which would best describe the cleaning properties of the four series o f b l o c k p o l y m e r surfactants. Toxicity Within any one series the t o x i c i t y o f a b l o c k p o l y m e r surfactant decreases as the ethylene o x i d e / p r o p y l e n e oxide ratio increases and as the molecular weight of the hydrop h o b e increases. This has been shown by the acute oral L D s 0 values for the p o l o x a m i n e and m e r a x o p o l series. Most values are very high, generally =>5 g/kg, which is at the lower limit of the slightly toxic class in the classification s c h e m e given in Clinical T o x i c o l o g y of Commercial Products (I 2). It is n o t valid to c o m p a r e the t o x i c i t y of any one series with another. FIG. 6. Suggested poloxamer micelle configuration. Critical Micelle Concentrations (CMC) The early published reports (13-15) on the s t u d y of micelle f o r m a t i o n o f b l o c k c o p o l y m e r s of ethylene and p r o p y l e n e oxides claimed that these surfactants did not form micelles, in contrast to the o x y e t h y l a t e d f a t t y alcohols or alkylphenols. However, Becher (16) r e p o r t e d that the CMC for p o l o x a m e r 182 was 2.4 wt % while Ross and Olivier (17) r e p o r t e d the CMC for p o l o x a m e r 184 to be 0.026 wt %. Subsequently, Williams and Graham (private c o m m u n i c a t i o n ) d e t e r m i n e d critical micelie concentrations for several o f the p o l o x a m e r s , using surface tension depression methods. This c o n t r o v e r s y as to whether or n o t the p o l o x a m e r s form micelies was e x a m i n e d once again when Schmolka and R a y m o n d used a differential dye absorption technique (18) and verified the existence of micelles. The values t h e y obtained, n a m e l y t h a t the poloxamers had critical micelle c o n c e n t r a t i o n s in the range o f 3.0 to 11.0 #tool per liter, agreed closely with the data previously f o u n d by Williams and Graham. At a b o u t this time, Saski and Shah (19), using three different techniques, r e p o r t e d considerably higher critical micelle concentration values for the poloxamers. These were 2.4, 2.2, and 0.1 wt % respectively, for p o l o x a m e r s 182, 184, and 188. On the o t h e r hand, Sheth (20) r e p o r t e d a critical micelle c o n c e n t r a t i o n value for p o l o x a m e r 188 of 0.2 wt %, by means o f surface tension depression. This confusion on CMC values has been c o m p o u n d e d even further. Thus, A n d e r s o n (21) has reported, using the same surface tension depression m e t h o d , that the critical micelle concentration values for p o l o x a m e r s 181, 182, and 1 8 8 w e r e significantly lower t h a n those previously r e p o r t e d . Anderson also used the differential dye absorption technique with b e n z o p u r p u r i n 4B and iodine m e t h o d s t o s t u d y this problem, b u t claimed that, due to interaction o f the iodine and dye with the polymers, resulting in increases in absorbance, these m e t h o d s would not p e r m i t a satisfactory d e t e r m i n a t i o n o f the critical micelle concent r a t i o n values of the b l o c k c o p o l y m e r surfactants. Nuclear magnetic resonance has been used (22) to s t u d y the interaction o f p o l o x a m e r 188 and phenol. Starting with l o w phenol concentrations, up t o 2%, in a I0% aqueous p o l o x a m e r 188 solution, the authors r e p o r t e d that the p h e n o l was associated mainly with the p o l o x y p r o p y l e n e chain. However, as the ratio o f p h e n o l to p o l o x a m e r increased, it a p p e a r e d that the p o l y o x y p r o p y l e n e chain b e c a m e saturated with p h e n o l and relatively more phenol e n t e r e d the p o l y o x y e t h y l e n e chain. The authors c o n c l u d e d t h a t this indicated the presence o f micelles in the p o l o x a m e r phenol water system. However, t h e y suggested t h a t FIG. 7. Suggested poloxamer micelle configuration. the micelle would not necessarily be aggregates of cop o l y m e r molecules as is f o u n d with other types of surfactants, but consisted o f one molecule with the poloxyethylene chains rolled a r o u n d the p o l o x y p r o p y l e n e region. This is illustrated in Figure 6. The solution properties o f several of the poloxamers were studied in water as well as in a nonaqueous solvent, such as benzene, dioxane, and b u t y l chloride. Considerable difference was found (23) b e t w e e n the weight and numberaverage molecular weight o f the p o l o x a m e r micelles, as determined by light scattering and t w o methods of measuring vapor pressure lowering. The n u m b e r of molecules per miceile found by light scattering varied, for example, for p o l o x a m e r 188, from 1.5 to 8 in the various solvents and less widely for p o l o x a m e r s 108 and 338. The authors coneluded that the poloxamers with a molecular weight below 2000, such as 101 and 105, failed to associate in benzene whereas higher molecular weight homologs, such as poloxamers 108 and 188, did. In order to meet the r e q u i r e m e n t s of 2-8 molecules per micelle, it is suggested t h a t each surfactant molecule is shaped like a horseshoe, and t h a t 2-8 interlocking horseshoe-shaped molecules form a micelle, as illustrated in Figure 7. The solid lines represent the molecules which lie in the plane o f the paper, while those represented b y a d o t t e d line are below and above the plane o f the paper. On the other hand, the micellar molecular weight o f p o l o x a m e r 188, as determined by light scattering, has been reported (24) to be l0 s . Two of the poloxamines have been reported to exhibit micelles. Poloxamine 707 was f o u n d (18) to exhibit a critical micelle concentration o f 0.005 wt % at 25 C, using the differential dye a b s o r p t i o n technique. On the other MARCH, 1977 SCHMOLKA: BLOCK POLYMER SURFACTANT hand, the CMC value for p o l o x a m i n e 908 was found to be 0.06 w t % , using b o t h surface tension depression and solubility methods. Previous measurements were carried out at 25 C. Most recently, the effects of t e m p e r a t u r e on the micellar properties of p o l o x a m e r 184 have been studied (25) over a range of temperatures by surface tension and light scattering techniques. The authors r e p o r t e d t h a t at 25 C the micellar molecular weight is 2656, which is close to the molecular weight of 2900. However, at 30 C and 35 C, the authors r e p o r t e d aggregation numbers of 5.9 and 29.9, respectively. These results suggested to the authors that poloxamers behave differently from o t h e r nonionic surfactants. First, whereas other nonionic surfactant micellar sizes increase with temperature, with the poloxamers there may be temperature ranges within which no micelles form at all. Secondly, the authors believed that the growth of aggregates to a stable size takes place over much wider concentration ranges than for o t h e r nonionic surfactants, and lastly, the authors thought that the normal methods for determining CMC values of the poloxamers were inaccurate. Thus, one is led to conclude t h a t the micellar nature of the block p o l y m e r surfactants and their critical micelle concentrations is a very c o m p l e x and confused subject. APPLICATION AREAS Many new and interesting industrial applications for the block p o l y m e r nonionic surfactants have been developed, just in the past five or six years alone. Most o f these uses have been r e p o r t e d in publications such as magazine articles or patents and are not proprietary information. In reviewing these new applications, consideration will be given to the i m p o r t a n t physical p r o p e r t y or properties which led to the selection of the block polymer. No a t t e m p t will be made to present a complete application picture, b u t rather only selected cases in just a few industries will be described. The first application area to be reviewed will be cosmetics. Obviously, the p r i m a r y reason for using block p o l y m e r surfactants here is their absence of toxicity, but in addition, o t h e r very specific physical properties are required. A new dentifrice, designed for sensitive teeth, called PROTECT, uses p o l o x a m e r 407 because it is a gelling agent. The p o l o x a m e r / s o d i u m citrate combination was reported (26) t o have a highly significant desensitizing effect, in comparison with a control formulation of unknown composition. A n o t h e r desirable p r o p e r t y of the poloxamer in this application is its absence o f any bitter taste. This is a new p r o d u c t currently being m a r k e t e d in several locations in the United States. An alcohol-based m o u t h w a s h was reported stabilized (27) by the addition of a p o l o x a m e r with an ethylene oxide content of :>40%. The a d d i t i o n of the p o l o x a m e r prevents the f o r m a t i o n of a cloudy appearance which would otherwise develop on standing. In this application, the lack of taste of the p o l o x a m e r , plus its ability to solubilize water insoluble aromatic flavors, are i m p o r t a n t considerations for its use. In the field of aerosol antiperspirants, it has been r e p o r t e d (28) that the use of certain polyalkylene oxides, including certain poloxamers, would prevent the staining of clothing after repeated use o f the antiperspirant formulation. The nonirritating properties, plus the solubilizing action, would be responsible for selecting the block p o l y m e r surfactants in this application. In the same type of aerosol p r o d u c t , the a d d i t i o n o f a p o l o x a m e r to the formulation was r e p o r t e d (29) to prevent formation of lumps in storage. The dispersing p r o p e r t i e s of the poloxamer are believed to be the reasons for its selection in this application. 115 Many new applications in the medical field have been r e p o r t e d , and only a small n u m b e r can be described here. The use of poloxamers with at least 50% e t h y l e n e oxide c o n t e n t has been reported (30) in a new process for the p r e p a r a t i o n of a stable and c o n c e n t r a t e d antiserum from h u m a n or animal plasma and serum, b y fractional precipitation. At b e l o w r o o m t e m p e r a t u r e conditions, the p o l o x a m e r selectively precipitates the p r o t e i n fractions in various molecular weights. This p r e c i p i t a t i o n is due to the ability o f the two macromolecules, the p o l y m e r i c poloxamer and the b l o o d proteins, to form insoluble complexes at low temperatures. The c o m p l e x e s are then readily separated and purified. Several p o l o x a m i n e s and their tetraesters have been f o u n d (31) to be useful as h y p o c h o l e s t e r o l a e m i c agents in animals and man. The starting p o l o x a m i n e s have a maxim u m e t h y l e n e oxide c o n t e n t of 30% and the h y d r o p h o b e molecular weight lies between 2250 and 3250. A dramatic r e d u c t i o n in b l o o d serum cholesterol levels was r e p o r t e d when the p o l y m e r s were regularly i n c o r p o r a t e d in the diet. It is suggested that the ability of the p o l o x a m i n e or its esters to solubilize the sterol is the reason for this useful application. The clinical use o f p o l o x a m e r 188 as an emulsifying agent for a p e r f l u o r o o c t y l b r o m i d e emulsion, useful as a r a d i o p a q u e m e d i u m for contrast studies in medicine, is a relatively new development (32). The radiographs are equally as effective as, or more effective than, those o b t a i n e d with organic i o d i d e c o m p o u n d s and b a r i u m sulfate. The p o l o x a m e r was selected because o f its a b i h t y to function as an emulsifying agent, and due to its lack of t o x i c i t y , including its n o n t h r o m b o g e n i c properties. In a similar application, p o l o x a m e r 188 has been the emulsifying agent o f choice in the artificial b l o o d program, for preparing stable emulsions o f f l u o r o c a r b o n in physiological saline (33). An antiseptic skin cleaning f o r m u l a t i o n based u p o n chlorhexidine gluconate has been developed (34) containing 25% p o l o x a m e r 187. A p r o b l e m is o f t e n e n c o u n t e r e d in h a n d wash formulations, n a m e l y t h a t the cationic or antiseptic is inactivated in the micelles o f the surfactant being used. This was eliminated b y using a p o l o x a m e r as the wetting agent because, of all the nonionics tested, it e x h i b i t e d the least inactivation of the chiorhexidine. The 187 grade was selected because it e x h i b i t e d the highest foam. The 25% concentration was used in o r d e r to provide suitable f o a m viscosity and washing p r o p e r t i e s in the final product. A m e t h o d for enhancing drug or antibiotic levels in the b l o o d has been r e p o r t e d (35) b y oral administration of a capsule containing the drug and a p o l o x a m e r . Gastrointestinal h y p o m o t i l i t y is i n d u c e d and as a result o f the delayed gastrointestinal transport, dwell time in the u p p e r p o r t i o n of the gastrointestinal tract is increased. This is desirable since drugs are preferentially a b s o r b e d in the u p p e r G.I. tract. The properties associated with the selection o f a p o l o x a m e r , which contains from 5-80% ethylene oxide, no d o u b t include absence of b i t t e r taste, lack of t o x i c i t y , and its rate of solubility. The effective c o n t r o l o f bloat in b e e f cattle during feeding lot fattening, was r e p o r t e d (36) to be c o n t r o l l e d when the cattle were fed a high c o n c e n t r a t i o n of a feed lot bloat inducing ration for an e x t e n d e d p e r i o d of t i m e and concurrently fed a bloat controlling c o m p o u n d , such as p o l o x amine 1501 or P L U R A D O T H A 520, t o g e t h e r with a water soluble salt of a d i m e t h y l d i a l k y l q u a t e r n a r y a m m o n i u m compound. P o l o x a m e r 188 has been used (37) to s t u d y the developm e n t o f t u m o r metastasis in rats. T r e a t m e n t o f rats, which had been intravenously administered t u m o r cells, with the p o l o x a m e r decreased the incidence o f p u l m o n a r y metastasis 1 16 JOURNAL OF THE AMERICAN OIL CHEMISTS' SOCIETY f r o m 85.3% in the control to only 16.1%. The p01oxamer p r o p e r t y believed responsible for this application is its ability to prevent microvascular sludging of red cells, as well as its lack o f toxicity. This is but one of a few hundred articles in various medical and pharmaceutical journals which describe the use of a p o l o x a m e r being studied in a research project. In the paper industry, the preparation o f a single transfer coating for paper utilized a p o l o x a m e r on a production scale (38). P o l o x a m e r 182 was used as the wetting and dispersing agent to apply a coating on a backing surface of the paper sheet. Afte r drying, the coating is tested for transfer properties by typing the front surface o f the sheet with a second u n t re a te d sheet in facial c o n t a c t with the coating. The second sheet was f o u n d to apply a transferred copy which had a sharp blue image and offered good smudge resistance. It has been reported (39) that the moisture level in.a sheet of cellulose, such as paper, can be stabilized by using a polyalkylene oxide as a stabilizing agent and a p o l o x a m e r to enhance the rate o f absorption of the polyglycol by the sheet material. Using p o l y o x y e t h y l e n e glycols of molecular weights varying from 400 to 4000, a dramatic decrease occurred in the time needed to saturate the sheet, from more than 2 min t o less than 5 ser u p o n addition o f the block polymer. The wetting properties o f the poloxamers proved useful in this application. The textile industry has recognized the antistatic properties of the p o l o x am i n e s and their derivatives. This is due to the following: (a) the presence o f the t w o pairs of unshared electrons on the tertiary nitrogen atoms provides a slight cationic effect; (b) the p o l o x a m i n e branched structure more readily lends itself to crossllnking and increased viscosity, and (c) the superior p o l o x a m i n e th e r m a l stability is believed to be due to the ability to form amine oxides u p o n oxidation. H y d r o p h o b i c fibers having antistatic properties were made (40) by incorporating an ester of a dibasic acid with a p o l o x a m i n e having up to 30% propylene oxide at a mol wt of 2 0 0 - I 0 0 0 0 into the spin bath prior to spinning the n y l o n fiber. A p o l o x a m i n e having a mol wt b e t w e e n 4000-135,000 has been r e p o r t e d (41) to give excellent antistatic action in n y l o n 6 when used at 1-12%, based on the weight o f the nylon. The fibers showed excellent antistatic activity through 25 washes. An effective antistatic agent giving improved performance to nylon was obtained (42) by chain e x t e n d i n g a p o l o x a m i n e with a diepoxide or a diisocyanate. Even better antistatic effectiveness was reported achieved by further reaction with a sulfuric acid derivatives, such as sodium paratoluene sulfonate. This increased the viscosity of the polymer, thus making it more compatible with the high viscosity n y l o n melt prior to spinning. A novel m e t h o d for softening laundry was reported (43) by t u m b l i n g it in a damp state with coated polystyrene foam spheres. By dip-coating the spheres in a blend o f a p o l o x a m e r 407, sodium tallow alcohol sulphate slurry, and ethyl alcohol, the softener was readily transferred to the laundry while tumbling in a dryer. I m p r o v e d lubricating oil compositions containing lubricating viscosity and conventional gear oil and hydraulic oil additives m a y be obtained (44) by i n c o r p o r a ti n g relatively small amounts, as little as 0.01%, of a p o l o x a m i n e with a VOL. 54 molecular weight range o f 1650-15000 and an ethylene oxide co n t en t of about 10-50%. The poloxamine addition serves to improve the oil compositions by giving improved rust protection, by a standardized test, by improving rate of demulsibility in a standard demulsification test, and by giving less emulsion sludge in a standard engine test. The surfactant properties reponsible for this i m p r o v e m e n t i n c l u d e its wetting, interracial tension lowering, a n d dispersing abilities. REFERENCES 1. CTFA Cosmetic Ingredient Dictionary, 1st Ed., Bull. No. 9, CTFA Inc., Washington, DC (March 1975). 2. Vaughn, T.H., H.P. Suter, L.G. Lundsted, and M.G. Kramer, JAOCS 28:294 (1951). 3. Jackson, D.R., and L.G. 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