7
`Polymers and Polymer Chemistry in
`Hair Products
`
`Polymers have become increasingly important components of cosmetics
`over the past few decades. Their more important uses are as primary in(cid:173)
`gredients or adjuncts in shampoos, conditioning products, styling products
`(lotions and gels), mousses, and hair sprays. They have been used to con(cid:173)
`dition hair [1,2] and to improve the substantivity of other ingredients to
`hair [3,4], to improve combing [I], manageability [1.2], body [5], and curl
`retention [2,6,7]; to thicken formulations [8,9]; and to improve emulsion
`stability [8].
`Of special relevance to applications of polymers in hair products are:
`
`-The binding interactions of polymers to hair,
`-The chemical nature of polymers used in hair products,
`-In situ polymerization reaction mechanisms,
`-Rheological or flow properties of polymer solutions, and
`-Film formation and adhesional properties of polymers.
`
`The major emphasis in this section is on the first three of these subjects(cid:173)
`the chemical and/or binding interactions of polymers to hair; the chemical
`nature of hair sprays, setting products, and mousses; and in situ poly(cid:173)
`merization reactions in hair. Although the rheological properties of polymer
`solutions are especially important to formula viscosity, and to the sensory
`perceptions of cosmetics, they will not be emphasized here. It suffices to
`say that cellulosic ethers [8,9] are probably the most important thickening
`agents in hair products, and ethoxylated esters and carboxy vinyl polymers
`are also important.
`For hair sprays, polymer setting products, and polymeric conditioners,
`film properties as well as the ability of the polymer solution to spread
`over the fiber surface are important to product performance. The spreading
`characteristics of the polymer are governed by its solution viscosity and
`the wettability of the fiber surface against the polymer solution. For op(cid:173)
`timum spreading, low solution viscosity is important, and both polar and
`dispersion interactions have been shown to be important to the ease of
`spreading over hair fiber surfaces [10]. The surface of cosmetically un-
`
`C. R. Robbins, Chemical and Physical Behavior of Human Hair
`© Springer Science+Business Media New York 1988
`
`

`
`The Binding of Preformed Polymers to Hair
`
`197
`
`altered hair is generally considered to be hydrophobic, whereas the cortex
`is more hydrophilic. Kamath et al. [10] have shown that both bleaching
`and reduction of hair increase the wettability of hair, making its surface
`more hydrophilic. For a more thorough treatment of wettability and the
`spreading of liquids on solids, see the references for this chapter [10-13].
`
`The Binding of Preformed Polymers to Hair
`
`Chapter 5 describes the work of Steinhardt and Harris and the affinities
`of organic acids [14] and quaternary ammonium hydroxide compounds
`[15] to keratin. It illustrates the importance of increasing molecular size
`and even nonprimary bonds to the substantivity of ingredients to hair. In
`the case of polymeric ingredients, these same principles are operative,
`and even more important.
`
`CHEMICAL BONDING AND SUBSTANTIVITY
`
`It is convenient to consider three extreme types of bonds between polymer
`and hair.
`
`I. Primary valence bonds (ionic and covalent bonds).
`2. Polar interactions (primarily hydrogen bonds).
`3. Dispersion forces (Van der Waals attractions).
`
`It should be noted that bond classifications of this type are not rigorous,
`and the transition from one type to another is gradual. Therefore, inter(cid:173)
`mediate bond types do exist [16], although for simplicity in the following
`discussion a rigorous classification of bond type is presented.
`Primary valence bonds include ionic and covalent bonds and are the
`strongest binding forces. They generally have bond energies of approxi(cid:173)
`mately 50 to 200 kcal/mole [17]. Ionic bonds are extremely important to
`the interactions of polymeric cationic ingredients and hair, whereas co(cid:173)
`valent bonds are probably involved between polymer and hair in certain
`in situ polymerization reactions or in the reaction of oxidation dyes with
`hair.
`Hydrogen bonds are the most important polar interactions and are the
`next strongest binding forces, with bond energies generally of the order
`of 4 to 10 kcal/mole [17]. These bonds are important to the binding of
`polymers containing polyalcohol or polyamide units, including polypep(cid:173)
`tides and proteins.
`Dispersion forces or Van der Waals attractions have bond energies gen(cid:173)
`erally of the order of I kcal/mole [18]. Van der Waals attractions are rel(cid:173)
`atively weak and are dipolar in nature. Since electrons are in constant
`motion, at any instant in time, the electron distribution is probably dis(cid:173)
`torted, creating a small dipole. This momentary dipole can affect the elec-
`
`

`
`198
`
`7. Polymers and Polymer Chemistry in Hair Products
`
`tron distribution in an adjacent molecule, and if contact is just right, at(cid:173)
`traction is induced [19]. These attractive forces are short-range and act
`only between the surfaces of molecules. Therefore, the total strength of
`Van der Waals bonding increases with molecular surface area (i.e., with
`increasing molecular size), and in polymers it can approach the strength
`of primary valence bonds.
`
`MOLECULAR SIZE AND SUBST ANTIVITY
`
`Mark [20,21] has described the forces involved in multiple polar and dis(cid:173)
`persion binding in polymers by means of molar cohesions (see Table 7-
`I). These data show that in polymers of even low molecular weight, 10,000
`daltons, the cohesive energy approaches that of primary chemical bonds.
`Therefore, by analogy, one may predict the importance of molecular size
`to substantivity of ingredients to hair.
`Obviously, multiple sites for attachment of even stronger bonds (i.e.,
`
`TABLE 7-1. Polar and dispersion forces in polymers.
`Approximate molar cohesions
`for structural units shown*
`(kcal/molel
`
`Structural unit
`
`Polymer
`
`Polyethylene
`
`Poly isobutylene
`
`Polystyrene
`
`Polyvinly
`alcohol
`
`Polyamides
`
`(- CH2CH- CH2CH-)
`I
`I
`C=O C=O
`I
`I
`NH2
`NH2
`
`1.0
`
`1.2
`
`4.0
`
`4.8
`
`5.8
`
`*Molar cohesions listed are actually for a chain length of 5 angstrom
`units. The structural units shown above are approximately 4.6 ang(cid:173)
`stroms long, assuming a constant carbon-carbon bond length of 1.54
`angstroms [21).
`
`

`
`The Binding of Preformed Polymers to Hair
`
`199
`
`polar and especially primary valence bonds) are even more important to
`substantivity. Multiple covalent attachment sites could conceivably occur
`via in situ polymerization reactions and with bifunctional cross linking
`agents (see Chapter 3). However for pragmatic reasons, this is not nearly
`as important as multiple ionic attachments to hair-e.g., with cationic
`polymers.
`The appropriate spacing of groups in the polymer so that maximum
`bonding can occur, especially to ionic and polar groups on the keratin
`structure, is also important to substantivity. As a first approximation,
`maximum frequency of primary bonds and maximum molecular size will
`provide maximum substantivity.
`
`Iso ELECTRIC POINT OF HAIR AND POLYMER
`SUBSTANTIVITY
`
`Although polymers may penetrate to a limited extent into human hair [23],
`the key interactions between hair and most polymers occur at or near the
`fiber surface. Since ionic bonds are the most important primary valence
`bonds for binding to hair under low temperature conditions in an aqueous
`or aqueous alcohol system, the net charge at the fiber surface is critical
`to polymer hair interactions.
`Wilkerson has shown that unaltered human hair has an isoelectric point
`near pH 3.67 [24]; therefore the surface of hair bears a net negative charge
`at all pH values above this. Since most cosmetic hair treatments are above
`this pH, cationics are attracted to hair more readily than anionics, and
`polycationics are far more substantive to hair than polyanionics.
`
`DESORPTION AND BREAKING OF MULTIPLE BONDS
`
`Faucher et al. [25] have shown that the desorption of a polymeric cationic
`cellulose (polymer JR) (see Table 7-2) from hair is slower than would be
`expected from a simple diffusional release predicted by the square root
`of time law [26]. They suggest that desorption of a polymer occurs only
`after all sites of attachment are broken. Statistically, the process of break(cid:173)
`ing all attachments simultaneously is of low probability. Therefore, one
`would expect high substantivity and a slow rate of release with increasing
`molecular size and increasing primary valence binding sites.
`
`PENETRATION OF POLYMERS INTO HAIR
`Low-molecular-weight polypeptides [27] (M)fi = 1000) and polyethylene(cid:173)
`imine (Mn = 600) [28] have been shown to diffuse into hair. Somewhat
`larger polypeptides (Mn = 10,000) [27] and polymer JR, with an average
`molecular weight of 250,000 [23], have also been reported to penetrate
`into hair. The polymer JR study involved bleached hair. These data suggest
`
`

`
`200
`
`7. Polymers and Polymer Chemistry in Hair Products
`
`TABLE 7-2. Approximate structural formulas for three cationic polymers used
`in hair care products.
`
`Polyethyleneimine (PEl) with a charge density of 176, assuming 25%
`protonation at pH=8 [41]
`
`H
`
`O--r-",,","
`I
`N :c u
`I
`N :c
`u
`I
`~
`
`H
`
`N
`
`N :c
`u
`I
`:c
`u
`I
`0
`:c
`
`N :c
`u
`I
`N :c
`u
`I
`0 :c
`
`Quaternized hydroxyethyl cellulose with a charge density of 689 (polymer JR)
`(polyquaternium-lO)
`
`Quaternized copolymer of PVP and dimethyl aminoethyl methacrylate with a
`charge density of 616 (polyquaternium-ll)
`
`

`
`Cationic Polymers and Their Interactions with Hair
`
`20 I
`
`that penetration is limited to about 10% of the hair after 7 days and about
`an order of magnitude less in unaltered hair [25]. Sorption of a higher(cid:173)
`molecular-weight JR polymer (average molecular weight of 600,000) by
`bleached hair is similar to the smaller polymer by unaltered hair.
`It appears that some limited penetration into human hair can occur by
`the lower-molecular-weight species of low molecular weight polymers (less
`than 10,000 daltons). Larger polymers, up to 500,000 daltons, may even
`contain species that can diffuse into the cuticle and perhaps further. In(cid:173)
`tercellular diffusion or diffusion via the low-sulfur regions is probably the
`preferred route for these large molecules (see Chapter 5, Figure 5-3). If
`the hair is degraded sufficiently or if the degree of polymerization for the
`polymer provides a very broad distribution, transcellular diffusion is also
`likely. However, it is highly unlikely that large polymers penetrate to a
`significant extent into human hair. Neutral or anionic polymers have not
`been studied for penetration effects; however, as a first approximation,
`one might draw similar conclusions with regard to the size and extent of
`penetration of these polymers also.
`
`Cationic Polymers and Their Interactions with Hair
`
`Cationic polymers as a group are one of the more important types of poly(cid:173)
`mers used in hair products. Because of their high degree of substantivity
`to hair, they are useful in shampoos and conditioners. Their major asset,
`high substantivity, is also a potential problem, because they can be so
`substantive that they are difficult to remove from hair with ordinary
`shampoos.
`Cationic ingredients in general are highly substantive to hair because
`of hair's low isoelectric point, which is approximately pH 3.67 [24] in
`cosmetically unaltered hair, and even lower in bleached hair. Therefore,
`at any pH above the isoelectric, the surface of hair bears a net negative
`charge, and positively charged (cationic) ingredients are attracted to it.
`Even monofunctional cationics are substantive to hair; i.e., they resist
`removal by water rinsing. For example, stearyl benzyl dimethyl ammonium
`chloride and cetyl trimethyl ammonium chloride are major active ingre(cid:173)
`dients in creme rinse products because they are substantive to water rinsing
`of hair, and they condition the hair fiber surface.
`Dye staining tests [29,30] show that substantivity of monofunctional
`cationics to water rinsing does not occur unless the hydrocarbon portion
`is approximately 8 to to carbon atoms-that is, unless there are sufficient
`Van der Waals attractive forces in addition to the electrostatic bond to
`bind the molecule to the keratin in the presence of the aqueous phase.
`As the molecular size of the cationic structure is increased, even greater
`sorption and substantivity result [30]. This enhanced substantivity is partly
`
`

`
`202
`
`7. Polymers and Polymer Chemistry in Hair Products
`
`due to an increase in dispersion binding and partly due to the fact that
`the structure becomes less hydrophilic and partitions from the aqueous
`phase to the keratin phase.
`Approximate structural formulas for three cationic polymers that have
`been used in hair care applications are described in Table 7-2.
`
`INTERACTIONS OF QUATERNIZED CELLULOSIC POLYMERS
`WITH HUMAN HAIR: POLYMER JR (POLYQUATERNIUM-IO,
`FORMERLY QUATERNIUM-I9)
`
`Polymer JR has been used in several different commercial hair products
`as a conditioning ingredient, including many different conditioning sham(cid:173)
`poos. Polymer JR has a relatively low charge density 670 [31], and a high
`density of polar groups. Charge density is the residue molecular weight
`per unit of positive charge. This type of polymer has been studied in three
`different molecular weight versions-250,000, 400,000, and 600,000--in
`several excellent publications by Faucher, Goddard, and Hannah
`[23,25,31-33].
`The formula in Table 7-2 approximates the structure of this polymer
`and is based on information in the CTF A cosmetic ingredient dictionary
`[34] and the charge density value of approximately 670 [33]. Note that
`the positions and numbers of ethoxamer units may vary for this structure,
`as does the position of the hydroxypropyl quaternary grouping. Polymer
`JR has been used in several different commercial hair products as a con(cid:173)
`ditioning ingredient, including several different conditioning shampoos.
`
`Adsorption and Absorption to Hair
`
`Faucher and Goddard [23] have studied the uptake of polymer JR onto
`bleached and unaltered hair. Their data suggest limited penetration into
`bleached hair and possibly some penetration into unaltered hair, too, for
`the lower-molecular-weight versions. At 0.1 % polymer concentration, ap(cid:173)
`proximately 35 mg polymer per gram hair was sorbed onto bleached hair
`after 8 days, and 8 mg polymer per gram hair after about I hour (polymer
`molecular weight: 250,000).
`
`Effect of Molecular Weight
`
`Three different molecular weight versions (250,000, 400,000, 600,000) were
`studied with respect to sorption onto bleached hair [23]. The lowest-mo(cid:173)
`lecular-weight species was sorbed fastest and to the greatest extent. The
`sorption curve for the highest-molecular-weight species shows a rapid up(cid:173)
`take followed by leveling, indicating saturation of the hair fiber surface
`and limited penetration, if any.
`
`

`
`Cationic Polymers and Their Interactions with Hair
`
`203
`
`Effect of Charge
`
`Polymer JR uptake was compared to an analogous uncharged hydroxyethyl
`cellulose polymer. The uptake of the charged polymer was 50 times that
`of the uncharged polymer [23].
`
`Effect of Concentration
`
`The uptake of polymer JR increased six-fold with concentration, from
`0.01% to 1.0% [23]. However, apparent diffusion coefficients from initial
`slopes indicate a slower diffusion rate with increasing concentration.
`Faucher and Goddard [23] explain this anomaly by suggesting that a more
`compact polymer deposits on the hair at the higher concentrations. This
`may be somewhat analogous to the effects of pH on the activation energy
`for diffusion of orange II dye into keratin fibers [35]. In this latter situation,
`the activation energy for diffusion of dye into the fibers increases with
`decreasing pH where a higher concentration of dye enters the fibers. Ap(cid:173)
`parently, the steeper concentration gradient with decreasing pH increases
`the energy required for each dye molecule to enter the fibers.
`
`Effect of pH
`
`The influence of pH on polymer JR sorption was studied in unbuffered
`media [23], starting at pH 4, 7, and 10. The largest uptake was at pH 7,
`with about 15% less polymer sorbed at pH 4 (which can be attributed to
`a decreasing net negative charge on the fiber surface). However, there is
`about 30% less polymer pickup at pH 10 than at pH 7, which would not
`be predicted on the basis of electrostatics or swelling of the hair. Drifting
`pH caused complications, and the observed differences, although small,
`await a satisfactory explanation.
`
`Effect of Salt
`
`Added salt produces a larger effect on the uptake of polymer JR than does
`pH [25] and may in fact help to explain the pH effect. The addition of
`0.1% sodium chloride decreased pickup by almost two-thirds. This may
`be attributed to shielding of sorption sites on the hair; i.e., competitive
`inhibition. Although the affinity of sodium ion for hair should be much
`less than for polymer JR, at this concentration sodium ion has more than
`20 times the cationic charge concentration of polymer JR.
`Other salts, such as lanthanum and calcium, had an even greater effect
`in decreasing polymer pickup. Trivalent ions (lanthanum, aluminum, and
`iron) had the largest effect, followed by divalent ions (calcium and ferrous
`iron). Monovalent ions showed the least effect. Faucher et al. [25] sug(cid:173)
`gested the analogy to hair of a strong acid ion exchange resin and postulated
`that the decrease in polymer uptake by inorganic cations is due to com(cid:173)
`petitive inhibition.
`
`

`
`204
`
`7. Polymers and Polymer Chemistry in Hair Products
`
`Effect of Hair Damage
`
`Most of the studies with polymer JR employed bleached hair. Bleached
`hair has a higher .concentration of negative sites at and near the fiber sur(cid:173)
`face to attract and bind cations, and is more porous than chemically un(cid:173)
`altered hair. As one might predict, uptake of polymer JR onto unaltered
`hair was an order of magnitude lower than for bleached hair [25].
`
`Desorption of Polymer JR from Hair
`
`Desorption of polymer JR from hair by distilled water is very slow, and
`less than 15% was removed in a time period of 30 min [25,32]. Sodium
`dodecyl sulfate (SDS at 0.1 M) solution, analogous to a shampoo, was
`much more effective, removing more than 50% of the polymer in 1 min
`and nearly 70% in 30 min. However, a small amount of strongly bound
`polymer was still attached to the hair after SDS treatment [32]. Attempts
`to remove this strongly bound polymer by multiple treatments with SDS
`were not examined.
`Salts were also found to be effective in removing a portion of the poly(cid:173)
`mer, and trivalent salts were more effective than divalent, which were
`more effective than monovalent. However, even after I week in 0.1 M
`lanthanum nitrate solution (La + + + ), approximately 40% of the polymer
`was still bound to the hair [25]. Most of these results were on bleached
`hair, but desorption experiments on chemically unaltered hair indicate
`similar behavior.
`
`Effect of Surfactants on the Sorption of Polymer JR
`
`All surfactants that have been examined, whether neutral, anionic, or cat(cid:173)
`ionic, decrease the uptake of polymer JR onto hair [23,33]. Pareth-15-9,
`a non ionic surfactant, exhibited the smallest effect in decreasing the uptake
`of Polymer JR. Faucher and Goddard [23] attribute this to the relatively
`low affinity of this surfactant for both keratin and the polymer.
`
`R-O-(CH2-CH,-O)9-H
`Pareth-15-9 (R = CII to CIS)
`
`Cocoamphoglycinate had a slightly greater effect in decreasing the uptake
`of JR.
`
`~
`/CH2-CH2-OH
`R-C-NH-CH2-CH2-N
`\
`CH2-C02H
`Cocoamphoglycinate
`
`Pickup was greater in the presence of potassium laurate than cocoam(cid:173)
`phoglycinate. Goddard et al. [33] found a relatively thick, nonuniform
`deposit in the presence of laurate which they attributed to precipitated
`calcium laurate (soap) with polymer.
`
`

`
`Cationic Polymers and Their Interactions with Hair
`
`205
`
`Anionic and cationic surfactants show the largest effect in decreasing
`polymer JR uptake onto hair. The cationic myristyl benzyl dimethyl am(cid:173)
`monium chloride probably functions via competitive inhibition. Anionic
`surfactants probablY function by forming association complexes that neu(cid:173)
`tralize the cationic charge of the polymer. Nevertheless, small amounts
`of polymer JR were still detected on the hair even in the presence of
`excessive amounts of anionic surfactant [33].
`
`Cationic Polymer-Surfactant Complexes
`
`Polymers have been shown to form association complexes with surfactants
`in solution [36--40], and the interaction of polymer JR with anionic sur(cid:173)
`factants such as sodium dodecyl sulfate (SDS) has been studied by God(cid:173)
`dard and Hannan [31]. These authors conclude that this interaction occurs
`in two stages with increasing concentration of anionic detergent relative
`to polymer. The first stage involves adsorption of surfactant to the poly(cid:173)
`mer, forming a primary layer which neutralizes the cationic charge of the
`polymer. A decrease in solubility occurs at this stage, and the new polymer
`complex is highly surface-active. As the ratio of anionic surfactant to cat(cid:173)
`ionic polymer increases, adsorption of a secondary layer results, accom(cid:173)
`panied by reversal of the net charge of the total polymer complex species.
`Increased solubility also occurs.
`Hannan et al. [32] have shown that this type of polymer complex, formed
`from 0.1 % polymer JR and 1 % SDS does indeed sorb to the hair. Water
`can remove only some 30% of this JR-SDS complex, and SDS and salts
`are no more effective, leaving some 60% (approximately 0.1 mg complex
`per gram hair) strongly bound to the hair. Analogous complexes with other
`cationic polymers have been used for binding or for increasing the sub(cid:173)
`stantivity of ingredients to the hair [3,4].
`
`Polyethyleneimine
`
`Polyethyleneimine (PEl) is no longer used in commercial hair products.
`However, several interesting scientific studies have been conducted with
`this polymer, and these studies illustrate some useful principles relevant
`to the adsorption of cationic polymers to keratin fibers. There are two
`significant structural differences between PEl and polymer JR:
`
`1. PEl has a much higher charge density than polymer JR.
`2. PEl is not quaternized, but is a polyamine.
`
`Polyethyleneimine is formed from the aziridine ethyleneimine, and its
`chemistry has been reviewed by Woodard [41]. Although PEl is not qua(cid:173)
`ternized, it is highly cationic, since a large number of its amine groups
`
`CH,-CH,
`\fu
`
`Ethyleneimine
`
`Polyethyleneimine
`
`

`
`206
`
`7. Polymers and Polymer Chemistry in Hair Products
`
`are protonated even near neutral pH. Woodard [41] indicates that at pH
`10.5,4% of the amine nitrogens are protonated; at pH 8, 25%; and at pH
`4, 50%. Therefore, PEL would have a charge density of approximately
`176 at pH 8, or nearly four times the frequency of cationic sites as polymer
`JR.
`Three different polyethyIeneimines have been described with regard to
`their interactions with human hair; PEI-6 (molecular weight 600); PEI-
`600 (molecular weight 60,000); and PEI-600E, which is PEI-600 reacted
`with an almost equivalent amount of ethylene oxide. This reaction with
`ethylene oxide forms quaternary nitrogen groups and increases the mo(cid:173)
`lecular weight to approximately 100,000 [28,41].
`Chow [28] has provided evidence for penetration of the lower-molecular(cid:173)
`weight PEl-6 into hair, and Woodard [41] has shown that sorption increases
`with concentration and with bleaching of hair similar to polymer JR.
`Sorption ofPEl-6 was also slightly greater at neutral pH compared with
`acidic or alkaline pH. However, since the charge density of PEL decreases
`with increasing pH, this result is not unexpected. This PEL study was
`conducted in an unbuffered medium.
`Although a direct comparison has not been made, PEL appears to be
`even more substantive to hair than polymer JR, probably because of its
`higher charge density. PEI-600 was sorbed onto hair and tested for de(cid:173)
`sorption toward a 10% shampoo system. After 30 min, less than 20% of
`the PEL was removed, and only approximately 30% after 6 hours [41].
`The rate of PEl desorption has also been examined with radiolabeled
`PEL on the hair, desorbing with unlabeled PEL Most of the polymer,
`>60%, could not be removed in 24 hours by this procedure [28,41]. This
`result is consistent with a slow degree of release of PEL due to multiple
`ionic binding sites to the hair.
`PEL polymers, like polymer JR, also interact with anionic ingredients,
`and they have been used for increasing the substantivity of other molecules
`to hair [3,4]. PEL was formerly used in one commercial shampoo but is
`no longer being used, presumably because ethyleneimine monomer has
`been found to be a carcinogen.
`
`POLYQUATERNIUM-6 AND -7, FORMERLY QUATERNIUM-40
`AND -41 (MERQUATS)
`
`Merquat polymers are another type of cationic polymer finding use in hair
`care products [42]. There are two different Merquat polymers. One of
`these is a homopolymer of dimethyldiallylammonium chloride (DMDAAC)
`and the second a copolymer of DMDAAC and acrylamide. The homo(cid:173)
`polymer is Merquat 100 (polyquaternium-6) with an average molecular
`weight of approximately 100,000, and the copolymer is Merquat 550
`(polyquaternium-7) with an average molecular weight of approximately
`500,000. Polyquatemium-7 has been used commercially in several different
`conditioning shampoos.
`
`

`
`C~JfHJ
`N<±l
`I
`(CH,-CH = CH,),
`Dimethyldiallylammonium chloride
`
`CIEl
`
`Other Polymers
`
`207
`
`CH,=CH
`\
`-
`CO-NH,
`
`Aerylamide
`
`The homopolymer has a charge density of approximately 126, and the
`copolymer 197. Thus, both of these polymers have a relatively high charge
`density compared with polymer JR or many other cationic polymers avail(cid:173)
`able for use in hair care today.
`Sykes and Hammes [42] have described the adsorption of both of these
`cationic polymers onto hair from solutions of different amphoteric and
`anionic surfactants. Analogous to the adsorption of polymer JR, uptake
`values were greater onto bleached hair than onto unbleached hair, and
`greater from amphoteric systems like cocobetaine or cocoamphyglycinate
`than from anionic surfactants like sodium lauryl sulfate or triethanolam(cid:173)
`monium lauryl sulfate.
`The following rationale accounts for these experimental findings. Sodium
`lauryl sulfate interacts with polymer primarily through an electrostatic
`interaction, and the net result is to neutralize the charge of the polymer
`and thereby reduce its affinity for keratin. Amphoterics do not neutralize
`the charge of the cationic polymer as effectively as do anionics. Therefore,
`cationic polymers demonstrate a greater affinity for keratins in an am(cid:173)
`photeric surfactant system than in an anionic surfactant system.
`
`OTHER CATIONIC POLYMERS
`
`A large number of other cationic polymers have been made available over
`the past few years by chemical suppliers for use in hair care products.
`Some of these polymers are polyquaternium-4 ( a grafted copolymer with
`a cellulosic backbone and quaternary ammonium groups attached through
`the allyl dimethyl ammonium chloride moiety; see the section on mousses);
`cationic guar gums such as Guar hydroxypropyl trimonium chloride(cid:173)
`e.g., Jaguar C-I3-S or Guar C-261; Ucare polymer LR, a lower-charge(cid:173)
`density cationic cellulose derivative of polymer JR; copolymer 845 (PVP/
`dimethyl aminoethyl methacrylate copolymer derivative of polyquater(cid:173)
`nium-ll, but of lower charge density); copolymers of vinyl imidazole and
`vinyl pyrrolidone of varying charge density; and even quaternized and
`amino silicone polymers and copolymers of varying charge density. For
`additional details on some of these cationic polymers, see the article by
`Idson and Lee [78].
`
`Other Polymers
`
`POL YPEPTIDES AND PROTEINS
`
`Polymeric collagen peptides should be somewhat substantive to hair, since
`they contain multiple ionic and polar sites for bonding, in addition to of-
`
`

`
`208
`
`7. Polymers and Polymer Chemistry in Hair Products
`
`fering large molecular surfaces with many sites for Van der Waals bonding.
`Methionine, tyrosine [43], and tryptophan [44] are monomeric species of
`proteins, and they have been shown to sorb onto hair from aqueous so(cid:173)
`lution. Collagen-derived polypeptides, or polymers of amino acids, have
`also been shown to have an affinity for hair [45-47], and one would predict
`that they should be more substantive to hair than their monomers.
`Uptake of this type of species by hair has been shown to increase with
`either increasing hair damage or increasing polypeptide concentration. An
`average molecular weight (Mn) of about 1,000 provides optimum pickup,
`which decreases with higher molecular weight [48]. Bleaching produces
`an increase in uptake at neutral pH, whereas thioglycolate-treated hair
`sorbs more polypeptide at alkaline pH, as does unaltered hair [44].
`Bleaching should lower the isoionic point of hair more than thioglycolate
`treatment, producing more swelling at neutral pH and additional anionic
`sites to bind the polypeptides. Penetration of polypeptide mixtures into
`hair has been shown by Cooperman and Johnson [47] and is described
`earlier in this chapter.
`The desorptive action of surfactants and salts on polypeptides already
`sorbed to hair has not been examined as fully as for polymer JR. On the
`basis of theory, one would not expect collagen-derived polypeptides to
`be as substantive to hair as a high-charge-density cationic polymer.
`
`NEUTRAL AND ANIONIC POLYMERS
`
`The low isoelectric point of hair, near pH 3.6 [24], suggests that the net
`charge on the hair fiber surface is negative in the presence of most hair
`care products (at any pH above the isoelectric point). Table 7-3 describes
`structural formulas for some of the neutral and anionic polymers that have
`been used in hair products. These structures and the isoelectric point of
`hair suggest that the primary binding of these molecules to hair is by polar
`and Van der Waals interactions, Since shampooing is in an aqueous sys(cid:173)
`tem, and water is a good hydrogen bond breaking agent, the principal
`binding to resist shampooing for this kind of structure comes from Van
`der Waals attractive forces. Therefore, anionic and neutral polymers are
`not highly substantive to hair and they have been used in applications
`where their ease of removal by shampoos is almost as important as their
`adhesional and film properties.
`
`Hair Fixatives
`
`HAIR SPRAYS
`
`Aerosol hair sprays were introduced into the marketplace by the Liquinet
`Corporation in Chicago in 1949 [49], and they have enjoyed considerable
`commercial success for more than two decades. However, hair spray sales
`
`

`
`TABLE 7-3. Some neutral and anionic polymers used in
`hair products.
`
`Hair Fixatives
`
`209
`
`-CHl-CH-
`I
`N
`/ \
`HlC C=O
`I
`I
`HlC-CHl
`
`Polyvinylpyrrolidone
`
`o
`II
`0-C-CH3
`I
`-CH2-CH-CH-CH2
`I
`N
`/ \
`HlC c=o
`I
`I
`HlC-CHl
`Copolymer of
`polyvinylpyrrolidone
`and vinyl acetate
`
`0-CH3
`I
`-CH2-CH-CH-CH(cid:173)
`I
`I
`O=C c=o
`I
`I
`o
`0-CHl -CH3
`I
`H
`Copolymer of methyl vinyl
`ether and ethyl ester of
`maleic anhydride
`
`An ethoxylated ester
`polymer
`
`peaked during 1969 and began to decline owing to public acceptance of
`more natural hair styles not requiring hair fixatives.
`In the early to mid 1970's, hair spray sales declined even further because
`of environmental pressures to restrict the use of fluorocarbons in aerosol
`products. The large drop in hair spray sales occurred in 1975, after Roland
`and Molina theorized how fluorocarbons deplete the ozone layer in the
`stratosphere. For additional details on the rise and the decline in hair
`spray sales, see the article by Root [50].
`Three types of hair sprays are being produced today: pump hair sprays,
`hydrocarbon aerosols, and carbon dioxide aerosols. The first two ofthese
`products account for the major sales for this type of product.
`Hydrocarbon aerosol hair sprays contain an alcohol-hydrocarbon sol(cid:173)
`vent-propellant system, a synthetic polymeric resin, a base to neutralize
`the resin if it is a carboxylic acid-containing resin, plasticizer(s), fragrance
`and, in some cases, surfactant(s) to improve the spreading characteristics
`of the polymer.
`Pump sprays are ve