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Silicones—Basic Chemistry and Selected Applications Anthony J. O’Lenick, Jr. Siltech Inc., Dacula, Georgia 30019

ABSTRACT: The objective of this review is to provide a working knowledge of the chemistry of silicone compounds to the practicing chemist. Although silicone compounds have been known for over 50 yr, the chemistry of these materials remains elusive to the average formulating chemist. This is indeed unfortunate, since the chemistry of the silicon atom and resulting silicone compounds is every bit as wide in scope and rich in content as the chemistry of the carbon atom and the resulting surfactant chemistry upon which it is based. Only in the past decade has the use of silicone as a hydrophobic building block for the preparation of surfactants become common. The recent trend to combine silicone, fatty and polyoxyalkylene moieties in the same molecule has resulted in a plethora of new compounds with new properties. Paper no. S1175 in JSD 3, 229–236 (April 2000). KEY WORDS: Antifoam, chlorosilane, cyclomethicone, emulsions, fluids, polysiloxane, Rochow, silicon, silcone.

ration at interfaces, leading to surface tension values substantially lower than those of organic polymers. One of the most basic technical errors made by people referring to materials is confusing silicon with silicone. The former, silicon, is used to refer to the elemental material, Si; the latter, to refer to materials in which silicon is bonded to oxygen. Because it is not found free in nature, the first step in silicone chemistry is to produce silicon from quartz (SiO2). The term silicone is actually a misnomer. It was incorrectly thought that the early silicone polymers were silicon-based ketones, hence the contraction silicone. Despite this error, the term is still widely used and accepted. Silicon is obtained by the thermal reduction of quartz with carbon. The reaction is conducted at very high temperatures and therefore is commonly carried out where there is abundant inexpensive power. The reaction is as follows: 1700°C

SiO 2 + C  → Si + CO 2

Silicon is the 14th element in the periodic table. Although it does not occur in nature in its elemental state, in its combined form it accounts for about 25% of the earth’s crust. Silicone compounds are unique materials both in terms of the chemistry and in the wide range of their useful applications. In combination with organic moieties, silicon provides unique properties that function over a wide temperature range, making silicone-based products less temperature sensitive than most organic surfactants. These properties can be attributed to the strength and flexibility of the Si–O bond, its partial ionic character, and the low interactive forces between the nonpolar methyl groups, characteristics that are directly related to the comparatively long Si–O and Si–C bonds. The length of the Si–O and Si–C bonds also allows an unusual freedom of rotation, which enables the molecules to adopt the lowest energy configuE-mail: [email protected] Copyright © 2000 by AOCS Press

[1]

The resulting silicon is generally at least 99% pure. In addition, certain trace contaminants must also be controlled to obtain a material that is suitable for the preparation of silicone compounds. Because the silicon produced in Equation 1 is a solid metallic material, it must then be crushed into powder with particle sizes of 100–350 nm for reaction in the Rochow process. This process which produces chlorosilanes from ground-up silicon metal, is named after Eugene G. Rochow, the father of silicone chemistry (1). The process technology is complicated and requires high capital requirements for the construction of plants suitable to practice the chemistry. As a result, few companies actually carry out the Rochow process. Because silicon is crushed prior to reaction in a fluidized bed, the companies practicing this technology are referred to as “silicon crushers.” This is an elite group of companies, and being referred to as a silicon crusher is considered an honor in the silicone world.

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The next step in the preparation of silicone compounds is the reaction of suitable silicon to make products from which silicones may be derived. Commercially, the Rochow process is the most important route for the preparation of silicone compounds. In this process, methyl chloride is reacted with solid silicon metal, in the presence of copper catalysts and certain promoters, to produce a mixture of chlorosilanes. Simplistically, the overall reaction is as follows: 2 CH 3 Cl + Si   → CH 3 ) 2 SiCl 2 Catalyst ( 300°C

[2]

In fact, a complex mixture of products is actually obtained (Scheme 1). The predominant material obtained is dimethyldichlorosilane (approximately 80% by weight). In order of decreasing concentration, the most abundant compounds are methyltrichlorosilane (approximately 12%), followed by trimethylchlorosilane (approximately 4%) and methylhydrogendichlorosilane (approximately 3%). This composition information is very important since it drives the economics of the silicone business. Every pound of chlorosilanes produced results in the distribution of products described. The cost of each must be allocated in proportion to the amount produced and to the commercial demand for it. To operate this business profitably, one must sell every pound of product produced. This by definition makes this a commodity business. Specialty producers, on the other hand, make what they can sell and do not have to balance by-product and co-product streams. Since many silicone surfactants are based upon methylhydrogendichlorosilane, a relatively minor component of the silane stream, the cost of these materials is high, relative to silicone fluids based upon dimethyldichlorosilane. The reaction to make chlorosilanes is quite complex and is carried out at about 300°C, under pressures typically of 3 bars. The mass of starting material must be heated to initiate reaction. Once the reaction temperature is reached, the reaction becomes exothermic, and consequently requires very stringent temperature control. It is a solid/gas reaction carried out in a fluidized bed reactor. To maximize the reaction efficiency, the solid silicon must be low in other metallic components. The fine residue that is extracted from the process is dependent upon the quality of

the silicon going into the process but is generally made up of Cu, Fe, Al, and Ca. Consequently, silicon with low concentrations of these elements is desired for the process.

SILICONE FROM CHLOROSILANES Hydrolyzate. The preparation of silicone compounds from chlorosilanes is an important synthetic pathway. The most important process to achieve this transformation is the socalled hydrolysis process. In this process the chlorosilane compounds produced in the Rochow process are reacted with water, converting them into a mixture of linear and cyclic compounds. The exact composition of the Rochow products, the conditions of pH, concentration of water, and temperature of hydrolysis determine the exact composition of the hydrolysis produced (Scheme 3). Since the Rochow process produces primarily dimethyldichlorosilane, the reaction of that component with water is shown in Equation 3.

( CH 3 ) 2 SiCl 2 + 2H 2 O → HCl + ( CH 3 ) 2 Si( OH ) 2

This step results in the formation of hydrochloric acid and a siloxanediol. By-product HCl must be handled with care to avoid corrosion of the equipment. In a dehydration reaction siloxanediol is subsequently converted to cyclomethicone and silanols (Eq. 4). n( CH 3 ) 2 Si ( OH ) 2  →

(

(CH3)2–Si–Cl2 (predominant) (CH3)3–Si–Cl CH3–Si–Cl3 Si–Cl4 CH3HSiCl2 (CH3)2HSiCl Others

[4]

This process results in two types of compounds that are used by the industrial chemist, silanol (dimethiconol) and cyclomethicone. The former is used in hair gloss compounds and the latter is commonly used in antiperspirant compositions. Cyclomethicone. Cyclomethicone, which refers to a series of cyclic silicone compounds, is distilled from the mixture (Eq. 4). The predominant cyclomethicone produced is D4, with lesser amounts of D5 and D3. (D refers to the number of silicon atoms within the cyclized compound; structures of D4 and D5 are presented in Scheme 2.)

CH3

O

Si O

(CH3)2–Si

O

Si–(CH3)2

O

(CH3)2–Si

O

O

Si H 3C

CH3

H 3C

Si

Rochow Process

Si + 2 CH3Cl

)n

H 2 O + HO - Si ( CH 3 ) 2 - O H + cyclomethione

H3C

(SYNTHESIS OF CHLOROSILANES)

[3]

O Si–(CH3)2 O

H3C–Si-----Si–CH3 CH3

CH3 CH3

D4

SCHEME 1

D5 SCHEME 2

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The ratio of D4 to D5 in the reaction (Eq. 4) is generally 85% D4 to 15% D5. The cyclomethicone mixture distills off the hydrolysis process as an azeotrope. This common azeotrope is the least expensive cyclomethicone composition produced. Since separation of the two from each other requires distillation, pure D4 is more expensive than the azeotrope, and D5 is still more expensive. Pure D3 is also available. The terms “volatile silicone” and “cyclomethicone” are sometimes confused, because lower cyclomethicone compounds are volatile compounds used in applications like antiperspirants and as cleaning solvents for electronic parts like circuit boards. It is important to realize that all cyclomethicone compounds are not volatile (for example, when there are 30 silicon atoms in the compound), and similarly all volatile silicones are not cyclic (for example MM, see below). The term cyclomethicone refers to a structure; the term volatile refers to a physical property. Silanol compounds. Silanol compounds are also called dimethiconols (2). These compounds carry Si-OH groups that can enter many organic reactions and are in many respects analogous to the carbanol group, –CH2OH with one major exception. Silanol groups can homopolymerize under many conditions to produce water and a higher molecular weight silanol. An example appears in Equation 5. CH3

CH3

2 HO-Si–O-(--Si–O)10H CH3

CH3

CH3

CH3

HO-Si–O-(--Si–O)20H + H2O CH3

CH3

[5]

Despite the fact that these materials can homopolymerize under certain conditions, they find utilization in a variety of applications, most notably waxes, textiles, and personalcare products. Silanols are available in a range of viscosities from 5,000 to 50,000 cSt. By virtue of their hydroxyl reactive groups, these materials are raw materials for sealants, paints, and, more recently, a series of silanol-based esters.

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SILICONE TERMINOLOGY In most applications, silicone compounds used are polymeric rather than monomeric products. A chemical shorthand has been developed which is more enlightening to the chemist than the name dimethicone copolyol. Developed by Alfred Stock (3) in 1916, the nomenclature is based upon the type of groups present in the molecule (Table 1).

SILICONE STRUCTURE There are three types of construction of silicone polymers, as illustrated in Scheme 4. Among the functional differences between the comb and the terminal structures shown in Scheme 4, one of the most important is the difference in the number of possible substituents. This number is limited to two in the terminal number of (*) substituents (one at each end), while in the comb polymer the number can be much larger. The reason is that the number of substituents in the terminal compounds can be no more than two (one at each end). The number of functionalized groups in a comb compound can be much larger than two. The other major difference is one of economics. Terminal compounds are more expensive than comb compounds having the same molecular weight. This is a direct consequence of the fact that the raw material for making the terminal products M*M* is not abundant in the Rochow process and is therefore expensive. There has been an interest in developing a terminal polymer with a methyl group on one end and an organoComb CH3

Organofunctionals Gums

Hydrolyzate

Cyclics (D4/D5 D4 D5) Dimethicone Dimethiconol "Silicone surfactants"

CH3

CH3

CH3--Si–O----(----Si---O)50--(--Si----O)10----Si---CH3 CH3

CH3

R

M

D50

D*10

CH3 M

Terminal CH3

SILICONE DERIVATIVES FROM HYDROLYZATE

CH3

CH3

CH3

R--Si----O--(---Si---O)50------Si---R CH3

CH3

CH3

M*

D50

M*

Multifunctional CH3

CH3

CH3

CH3

R----Si-O----(--Si---O)50--(---Si----O)5--------Si---R CH3

CH3

M*

D50

R

CH3

D*5

M*

SCHEME 4

SCHEME 3

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TABLE 1 Silicone Backbone Nomenclature CH3 “M unit” is monosubstituted

(one oxygen atom on silicon)

–O–Si–CH3 CH3

“D unit” is disubstituted

(two oxygen atoms on silicon)

CH3 –O–Si–O– CH3

“T unit” is trisubstituted

(three oxygen atoms on silicon)

O –O–Si–O– CH3 O

“Q unit” is tetrasubstituted

(four oxygen atoms on silicon)

–O–Si–O– O

If organofunctional groups other than carbon are introduced, an “°” is added to its designation.

“M* unit” is monosubstituted

(one oxygen atom on silicon)

CH3 –O–Si–CH3 R CH3

“D* unit” is disubstituted with organofunctionality

(two oxygen atoms on silicon)

–O–Si–O– R

O “T* unit” is trisubstituted with organofunctionality

(three oxygen atoms on silicon) –O–Si–O– CH3

There is no “Q* unit” since there is no possibility of functional groups.

functional group on the other. In fact MM* is available. However, since the preparation of the silicone polymer is based on equilibration chemistry, even though MM* is used as a raw material, the resulting polymer is a mixture of 2 parts monosubstituted monomethyl-terminal polymer, 1 part fluid (dimethyl terminated), and 1 part difunctional compound having no methyl terminal group. The fluid is not water soluble and is therefore always present in the reaction mixture. To avoid forming a fluid in a polymer equilibration reaction, there must be a certain number of water-soluble functional groups D* in a comb structure relative to D units. The smallest ratio of D*/D can be established experimentally (5). It is that ratio which leads to a water-soluble product, substantially free of fluid. We have evaluated the minimum number of D units to D* units needed to make a

product that is substantially free of fluid. The formula for determining the amount of D* units to D units is #D* units = (0.17)(#D units) + 1

[6]

Therefore, if 5 D units are present a minimum of 1.9 D* units needs to be present to get a water-soluble product. If 10 D units are present, then at least 2.7 D* units need to be present.This observation explains why only a limited number of products in this class are offered commercially.

SILICONE FLUIDS (4) Synthesis. Silicone fluids are synthesized by the equilibration reaction of MM and cyclomethicone. Typical of the synthesis of fluids is the following reaction (Eq. 7) in which

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CH3

CH3

CH3

CH3-Si---O---Si-CH3 + -(-Si-O)4 CH3

CH3

CH3 D4

MM

CH3

Catalyst

CH3

CH3

CH3-Si–(-O–Si---)4–O–Si-CH3 CH3

[7]

CH3

CH3 MD4M

one MM is reacted with one D4 compound to make MD4M, a simple silicone fluid. The reaction may be run with either an acid or base catalyst. Typically, the reaction is conducted at room temperature for 12 h, with sulfuric acid at 2% by weight as catalyst resulting in a mixture of about 10% free cyclic product and 90% linear fluid. It the catalyst is neutralized and the cyclic product is stripped off, a stable fluid results. If the catalyst is not neutralized during stripping, the fluid will degrade back to MM and D4. The equilibration process is critical not only to produce stable silicone fluids but also as a means of introducing functional groups into the polymer. This will be discussed in more detail in the section on hydrosilylation, a process used to make organofunctional silicone compounds. A “finished silicone fluid” may be placed in contact with D4 and catalyst and re-equilibrated to make a higherviscosity fluid. Conversely, a “finished silicone fluid” may be re-equilibrated with MM and catalyst to make a lowerviscosity fluid. Finally, silicone rubber may be decomposed into MM and D4 via stripping of the product in the presence of catalyst. This property of silicone polymers makes them decidedly different from organic compounds. Properties. Silicone fluids, also called silicone oils or simple silicone, are sold by their viscosity and range from 0.65 to 1,000,000 cSt. If the product is not made by blending two different viscosity fluids the viscosity is related to molecu-

TABLE 2 Viscosity of Silicone Fluids Viscosity 25°C (centistokes)

Approximate molecular weight

Approximate number of D units

5 50 100 200 350 500 1,000 10,000 60,000 100,000

800 3,780 6,000 9,430 13,650 17,350 28,000 67,700 116,500 139,050

9 53 85 127 185 230 375 910 1,570 1,875

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lar weight. The viscosity allows for an approximate calculation of the value of n in Table 2 (5). Silicone can adhere to a substrate, including fiber, fabric, metal surface, hair and skin by virtue of one or more of the following mechanisms. (i) Hydrophobicity. Oil introduced into water disrupts the hydrogen bonding between the water molecules. This disruption is accomplished only when the energy of mixing is sufficient to break the hydrogen bonds. When the mixing is stopped the oil is forced out of the water by the re-formation of the hydrogen bonds between water molecules. This phenomenon can be used to deliver oil to a surface. Silicone fluids are delivered this way. (ii) Ionic interactions. The charge on the molecule will also have an effect upon the delivery of the oil to the substrate. An oil carrying a cationic charge will form ionic bonds with substrates that carry negative surface charges. The two opposite charges together form a so-called ion pair bond. Since ionic charges commonly exist on textile fabrics, fibers, glass, hair, and skin this type of bonding is quite important. (iii) General adhesion. If an oil delivered to a substrate penetrates and then polymerizes, an interlocking network of polymer will develop. Although not bonded directly to the substrate, this polymer network will adhere to the substrate. (iv) Specific adhesion. If an oil is delivered to a substrate penetrates and then reacts with groups on these substrates, a chemical bond will be formed. This is the strongest and most permanent of the adhesion mechanisms. Silicone fluids react almost exclusively by hydrophobicity, or (i). To the extent the other mechanisms may be introduced, the conditioner can be delivered more strongly and efficiently to the substrate. Organofunctional silicones depend in large part on these additional mechanisms (ii–iv) to provide thorough and efficient conditioning, lubrication, and softness to the substrate.

SILICONE EMULSIONS Silicone emulsions are used in both hair and skin care products. The preparation of stable emulsions results in a silicone oil in a micelle, having a fine particle size. The preparation of a stable emulsion requires the selection of the proper emulsifier pair and, commonly, the use of a homogenizer. All must be optimized for best performance of the emulsion in the formulation. Many of the complications of using emulsions for the delivery of silicone to substrates relate to the fact that the silicone is delivered out of a surfactant micelle. When an emulsion is applied to the skin or hair, the silicone oil is delivered to a substrate that has been wetted by the surfactant at the air-water interface (Fig. 1). The emulsion breaks, and the oil is deposited. However, the surfactant, having emulsification properties of its own, re-emulsifies some of the oil. The net result is that silicone ends up

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FIG. 1. Micellar delivery of silicone.

both on the substrate and in the wash water. This complex equilibrium results in inefficiency in the use of emulsions. In addition, emulsions are subject to some inherent shear instability, and freeze-thaw instability. Finally, there are limitations as to the type of surfactant that can be added to an emulsion-containing system. If the hydrophilic-lipophilic balance of the formulation is shifted too much, the emulsion will break. However, with a properly selected emulsion and proper formulation techniques, silicone emulsions can be used in the creation of many emulsions useful in a plethora of applications. These applications include mold release agents, automotive tire gloss compounds, textile softeners, overspread in web offset printing, and antifoam compounds. Dimethicone and dimethiconol emulsions are used commonly in industrial applications. All emulsion products comprise (i) water, typically at least 40%, (ii) silicone, typically 55%, and the remainder. The fact that silicone is contained in an emulsion by necessity requires that the delivery be from a micelle. Since an equilibrium exists between the silicone on the substrate—like fabric, fiber, metal, rubber, hair or skin—and the silicone in the emulsion, much of the silicone ends up in the wash water. Not only is this a very costly and inefficient use of expensive raw materials, but also there are real environmental concerns since the wash water ends up in the sewer. In order to overcome this limitation, silicone surfactants have been developed that provide nonmicellar delivery to the substrate. These surfactants will be covered in a subsequent review article.

SILICONE ANTIFOAM COMPOUNDS Background (6). By virtue of their structure, surfactants perform many useful functions in aqueous solution including the generation of foam. In some situations, however, foam generation interferes with the other surfactant functions. When modification of the surfactant molecule offers minimal relief, antifoam compounds are added to many processes. Antifoam agents are divided into three classes: (i) those compounds used in industrial applications, (ii) those compounds used in applications sanctioned under U.S. Code of Federal Regulations Title 21 sections 173.105, 173.340, or 173.300, and (iii) those compounds that have been modified to meet specific performance requirements. Since most silicone compounds are water insoluble, they simple float on water as oily liquids. This behavior makes them useful in destroying or inhibiting foam. The term “antifoam” is generally used to denote a compound with the ability to prevent foam formation. In contrast, the term “defoamer” generally denotes a material that will knock down existing foam. Although some types of compounds are more effective in antifoaming applications and some compounds are more effective in defoaming, most compounds have properties that make them useful in both applications. Mechanism of antifoam. Regardless of the process, there are two mechanisms by which antifoam compounds work. By the first, they destroy interfacial films, and by the second they impair foam stability. The former is more com-

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mon and more effective in most applications. A layer of antifoam, by virtue of its insolubility, ends up in between the bubble and its contact points with the water. This dislodges the bubble and breaks it. Silicone fluids per se have both antifoam and defoaming attributes. They can be modified by reaction with silica to make significantly more efficient antifoam compounds. Silicone-based antifoam compounds for use in detergents are composed of two major components: silicone fluid and hydrophobic silica. The fluid polymer acts as a carrier to deliver the silica particles to the foam air–water interface, where film rupture then occurs. Very efficient antifoam compounds can be prepared by the reaction of silanol compounds with silica to form so-called in-situ hydrophobized silica. The performance of silicone-based antifoam compounds is independent of water hardness. They are effective at very low addition levels in all types of surfactant systems normally present in detergent formulations and are effective across a wide range of use conditions. Furthermore, silicones cause no yellowing of fabric. Thus siliconebased antifoam compounds have a number of benefits over soap-based foam control systems. A 100% active silicone-based antifoam compound is normally referred to as a silicone antifoam compound. If the silicone antifoam is in water it is referred to as an antifoam emulsion. Mixtures of silicone antifoam compounds with nonaqueous dispersion or delivery systems also exist, which aid their dispersion in aqueous media. The term emulsion applied to aqueous silicone antifoam is a misnomer. The compositions are actually thickened dispersions. Addition of water will cause them to separate into two layers. The dispersion can be re-thickened with polyacrylate or a similar thickener. Industrial processes. Many industrial processes utilize aqueous solutions and suspensions with surfactants that can produce foam that is detrimental to the efficient conduct of the process. If simple antifoam agents are employed to control foam, they may lead to deposition of insoluble material upon process equipment, requiring costly and inconvenient clean up and down time. Many specially formulated products, designed for specific processes, have been developed and are used commercially. In fact, the vast majority of antifoam applications do not use simple antifoam compounds. They rely upon formulated products, sold by companies that supervise the use of the product and in many instances guarantee results. The following processes specifically employ formulated antifoam compounds. (i) Paper manufacture. In the paper industry, the Kraft process is one of the most frequently used alkaline pulping processes. It is valuable in that spent chemicals may be recycled and reused thus decreasing processing costs. A large disadvantage of this process is the occurrence of foam during the pulp screening and washing procedures. Water-dispersible antifoam compounds used during the

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screening operation control foam and entrapped air and contribute to the washing efficiency of the pulp. (ii) Paper de-inking. Paper de-inking processes use detergents that can cause considerable undesirable foam while they effect the desired removal of ink (7). De-inking agents are used in solution in substantially aqueous media at temperatures from 40–70°F (4.5–21.1°C), up to about 200°F (93.3°C) and at a pH range of about 7.0 to 11.5. Undesirable foam is encountered most commonly under conditions of high temperature and high agitation, when maximum detergency is needed to remove ink from the paper. Standard antifoam compounds are based upon hydrophobic silica, ethylene bis-stearamide, silicone oils, or mineral oils; although they are effective, they are insoluble and deposit on process equipment, causing what is commonly referred to as pitch. Control of foam and pitch is critical to efficient operation of a de-inking operation. (iii) Antifoam formulations for textiles. Antifoam formulations are employed in textile wet processing during scouring, desizing, bleaching, and dyeing operations. The scouring, desizing, and bleaching operations remove foreign materials such as warp size, processing oil, dirt and natural waxes from the fabric. This is done prior to dyeing in order to ensure a well-prepared substrate that will accept dye evenly. The processes employ surfactants for wetting and detergency. Surfactant foaming must be controlled in order to maintain a proper liquor to goods ratio that ensures adequate fabric preparation. Antifoam formulations employed for these processes are composed of emulsified hydrophobic silica, silicone oil, mineral oils, and emulsified bis-stearamide waxes in mineral oil. Foaming surfactants are also used as wetting agents and post-scouring agents to remove loose dyestuff. Foam must be controlled during the dyeing process with materials that do not redeposit on the fabrics. (iv) Detergent systems. Foam in laundry processes must be controlled to avoid overfoaming during washing and persistent foam, particularly in the rinse step. Antifoam compounds desired for detergent applications must have these properties: •Remain effective over a wide range of temperatures; •Be stable over a wide range of pH; •Be easily and completely rinsable to avoid spotting on laundry items. Antifoam compounds can be found in many type of formulated products including dishwashing detergents and rinse aids, home laundry formulations, home laundry softeners, window cleaners, alkaline metal degreasers, hard surface cleaners, acidic metal cleaners, and bottle cleaning formulations. One major application for antifoam compounds is in processing aqueous detergent and softener formulations, specifically in filling bottles. Here, low concentrations of antifoam compounds prevent foam formation and over-

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flow which can shut down the bottling operation. Antifoam compounds are also used during the washout and clean up operations in detergent plants. The turbulent washing action of domestic horizontalaxis automatic washing machines, combined with low water levels used during wash and rinse cycles, generates considerable foam levels. For good cleaning power, excessive foaming must be avoided. For these machines, heavyduty detergent formulation have been developed that include foam control agents. The unique properties of silicone-based antifoam compounds have led to their wide use by the detergent industry. They are active at low use levels in all types of surfactant systems present in detergent formulations. Many custom-formulated antifoam compounds have been developed for use in detergents. U.S. Patent 5,589,449 to Dow Corning discloses a particulate foam control agent on a zeolite carrier designed to facilitate incorporation of antifoam into a powdered detergent. These processes selected here illustrate the complications of effectively using antifoam compounds. There are many other processes that offer equally challenging application and synthesis opportunities.

FUTURE TRENDS Utilization of silicone compounds in industrial applications will increasingly be determined by (i) the synthesis skills of the organosilicone chemist, and more importantly (ii) the formulating and engineering skills of the chemists and engineers that design formulations and processes using these materials. Most of the applications that can utilize simple silicone compounds without customization have been exploited. New markets will be developed by

the specialty applications. The technology of producing silicone compounds, although immense and interesting, is still in its infancy relative to surfactant chemistry. There is good reason to feel that the best is still to come.

REFERENCES 1. U.S. Patent 2,371,068, Rochow, E.G. April 30, 1940, assigned to General Electric. 2. Schueller, R., and P. Romanowski, Conditioning Agents for Hair and Skin, Marcel Dekker, New York, 1999, p. 205. 3. Stock, A., Ber. Deutsch. Chem. Ges. 49:108 (1916). 4. U.S. Patent 2,384,284 issued September 1945, to McGregor, assigned to Dow Corning Corporation. 5. Goddard, E.D., and J. Gruber, Principles of Polymer Science and Technology in Personal Care Products, Marcel Dekker, New York, 1999, p. 295. 6. Siltech Inc. Bulletin, Silicone Fluids, Emulsions Antifoam and Specialties, Siltech, Dacula, GA, p. 28, 1989. [Received August 10, 1999; accepted February 11, 2000]

Anthony J. O’Lenick, Jr. is President of Siltech Inc. in Dacula, Georgia. Siltech Inc. is a silicone and surfactant specialty company he founded in 1989. Prior to that he held technical and executive positions at Alkaril Chemicals Inc., Henkel Corporation and Mona Industries. He has been involved in the personal-care market for over 25 yr. O’Lenick has published over 25 technical articles in trade journals, contributed chapters to three books, and is the inventor on 150 patents. In addition, he received the 1996 Samuel Rosen Award given by the American Oil Chemists’ Society, the 1997 Innovative Use of Fatty Acids Award given by The Soap and Detergents Association, and the Partnership to the Personal-Care Award given by the Advanced Technology Group. O’Lenick is also a member of the Committee on Scientific Affairs of the Society of Cosmetic Chemists.

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