I have reported in previous articles that several polymeric systems have been introduced that enable restyling of hair after the initial application. L’Oréal researchers invented such a system based on polymers with a glass transition temperature less than 10°C and a minimum defined separation force. One such system was based on branched sulfonic polyesters, and in this disclosure Eastman’s AQ resin 1350 (INCI Polyester-5) was particularly preferred.1 Recently, it has been disclosed that when these polymers are applied from alcohol solutions, they are not homogeneously distributed over the hair and the hair feels dry after brushing. It has been demonstrated that these drawbacks can be overcome by including a polysaccharide thickener in the composition.2 The polysaccharides can be chosen from cellulose derivatives or Gellan gums. An example of the improved compositions that confer natural, long-lasting hold is shown in Table 1.

It may be expected that the interaction of anionic polyester-5 and nonionic polysaccharides may be minimal and this would favor their miscibility. However, the interaction between cationic polysaccharides and anionic polyester-5 commonly results in precipitated complexes rather than gels. In this instance it is interesting that Eastman Chemical can make compatible gels containing both Polyquaternium-10 and Polyester-5.3 These clear gels offer the prospect of styling conditioners or conditioning styling agents.

Table 1: Examples of a composition for natural hold from U.S. Patent Application 2010/0236569

AB
Branched sulfonic polyester52
Hydroxypropyl methyl cellulose2.2—
Gellan gum—1
Glycerol31
Propylene glycol1—
Sorbitol—2.7
Sodium chloride—0.25
PEG-40 hydrogenated castor oil0.50.5
Fragrance0.20.2
Preservativesq.s.q.s
Waterto 100to 100

Soft hold can be achieved by combining special polyurethane with PVP homopolymers or copolymers.4

Chitosan derivatives are being applied to enhance long-term hold. Thus, compositions containing chitosan derivatives and elastomeric silicones improve the fullness and long-term hold of hair.5 Long–lasting hold is also achieved by combining chitosan derivatives with a polymer comprising an amino-substituted vinyl unit, a hydrophobic nonionic vinyl unit, an associative vinyl unit, and a semi-hydrophobic vinyl surfactant unit.6

Thornsten Knapp of Henkel took inspiration from the proteins that allow mussels to adhere tenaciously to surfaces even when they are underwater. Blue marine mussel (Mytilus edulis) secretes adhesive proteins containing the amino acid, L-3,4-dihydroxy-L-phenylalanine (DOPA). There is an ample supply of these proteins at the interface between adhesive pads of the mussels and the surfaces to which they adhere.7,8 The o-dihydroxyphenyl (catechol) functional group of DOPA has strong affinity for many surfaces.9 Under oxidizing conditions, the catechol group transforms its chemical structure into a quinone; aqueous gelling agents have been produced by reacting DOPA with thiol end-capped Poloxamer.10 Knapp used copolymers that contained a group shown in Fig. 1.


Fig. 1 : Monomeric unit similar to catechol,
that was used to synthesize adhesive copolymers.

This group is similar to catechol and the copolymers adhere tenaciously to surfaces. However, the mussel proteins and these copolymers do not confer styling on hair. Fortunately, the copolymer readily coats polysilicic acids and this forms a particulate material that adheres to hair and allows recovery of style even when it has been altered by wind or water.11

Permanent waving involves a first step of reducing the cystine bonds within the hair fiber, shaping the hair into the desired style, then re-oxidizing it to restore the S-S bonds in their new configuration. This process is known to damage the hair and the damage is exacerbated by the common practice of heating the hair with perming irons. Many treatments have been applied to mitigate the damage. The application of cationic polymers to the hair surface during the perming process can reduce the damage.12 This is exemplified by a reducing treatment with cysteine and protection from an amodimethicone (Wacker- Belsil ADM).

Thickeners
Frederic Blondel reports that he is surprised that he can thicken aqueous cosmetic formulations with a copolymer of acrylamide and acrylamidomethylsulfonate (INCI Acryloyldimethyltaurate) crosslinked with an amine-based crosslinking agent that includes three allyl groups.13 Polymeric thickeners based on acryloyldimethytaurine and its salts were introduced into the market in the 1990s14 (Aristoflex AVC from Clariant) and they were found to offer better thickening efficiencies than conventional carbomers in acid and salt-containing compositions. The Blondel patent application indicates that the triallylamine crosslinkers resist hydrolysis whereas the more common dimethylacrylamide crosslinker can be hydrolyzed on acid solutions.

Fig. 2. The structure of Acryloyldimethyltaurate
from WO 98/00094


It is reported that in end-product compositions, the concentration of residual acrylamide monomer in such acrylamide copolymers can rise during storage. An inverse emulsion polymerization process has been devised to produce acrylamide/acryloyldimethyltaurate copolymers that maintain acrylamide concentrations below 2ppm upon storage of the final product.15 This was demonstrated by thickening water with the copolymers and heating the resulting gel to 80°C for 48 hours while monitoring the acrylamide monomer concen- tration by high performance liquid chromatography using an ultra-violet detector.

Crosslinked polyelectrolyte thickeners such as carbomers are inherently sensitive to the presence of salt in solution. This property is used to advantage in carbomer delivery systems that collapse upon application to the salt on the surface of skin, to effectively deliver benefit agents. During the 1990s hydrophobically modified versions of carbomers (acrylates/C10-30 alkyl acrylate crosspolymer) were introduced with both emulsifying and rheology-modifying properties.16 These polymeric emulsifiers offered a route to surfactant-free emulsions with triggered oil release upon application to the skin. These new emulsifiers also overcame the tendency of conventionally emulsified products to re-emulsify after the emulsion broke. This led to products such as sports sunscreen that resisted sweat. Now, (meth)acrylic acid/alkyl (meth)acrylate copolymers, crosslinked with allyl ethers of pentaerythritol have been disclosed as thickening systems that maintain aqueous solution viscosity even in the presence of electrolyte.17

Stimuli-responsive systems have piqued our interest for approximately 20 years. Most commonly, these are systems that are soluble at low temperatures and they show gelling or phase separation when the temperature is raised above a critical temperature (the lower critical solution temperature) that is usually called the cloud point. The very name “cloud point” conveys the impression that these systems become translucent or opaque above the critical temperature. In some cosmetic compositions it is desirable to form clear gels when the critical temperature is reached and Florence L’Alloret of L’Oréal announced that she has achieved this goal by grafting random PEG/PPG copolymers to a poly(meth)acrylic acid backbone.18This was achieved by the reaction of amine end-capped random PEG/PPG copolymers (Jeffamine from Huntsman) with sodium poly(meth)acrylate. The polymers could be tailored to gel within a few degrees over a desired temperature range and the transition temperature could be tailored within the limits of about 20°C to about 60°C.

Hydrophobins are small proteins formed by filamentous fungi such as Schizophyllum commune. The purpose of these proteins seems to be to adjust the free energy of multifarious surfaces to the optimum surface free energy for invasion by the fungus. For example, some hydrophobins spontaneously raise the surface free energy of poly(tetrafluoroethylene) and lower the surface free energy of glass to an optimal range for the benefit of the fungus. Hydrophobins form relatively non-viscous aqueous solutions at low concentrations (less than 3%) but gel at higher concentrations.Surfaces coated with hydrophobins have been suggested for use as demulsifiers, evaporation retardants and soiling inhibitors (U.S. Patent Publication 2009/ 0305930). Their use as thickeners and emulsifiers has also been proposed. Apparently, hydrophobins interact synergistically with a wide range of water-soluble polymers to confer synergistic thickening and this could be used to advantage in cosmetic gels, and conditioners and in cleansing compositions such as shampoos.

Superhydrophobicity
The ability of the lotus leaf to repel water and soil from its surface is well known. The lotus leaf achieves this feat by having a regular periodic hydrophobic nanostructure on its surface. In recent years, there has been a fairly large effort to mimic the lotus leaf and to produce regular nanostructured superhydrophobic surfaces that could be self-cleaning. Avon researchers have proclaimed the ability to render hair and skin superhydrophobic by applying a water-in-silicone emulsion that contained a hydrophobic film-forming polymer and hydrophobic particles.19 As shown in Fig. 3 (next page), water contact angles of greater than 140° were realized. In this instance, the hydrophobic film-forming polymer is acrylates/dimethicone copolymer and the hydrophobic particles are hydrophobic fumed silica and iron oxide and triethoxycaprylsilane.

Fig. 3: A water drop on a superhydrophobic surface prepared by treating a glass slide with a water-in-silicone emulsion that contained a hydrophobic film-forming polymer and hydrophobic particles. (Reproduced from U.S. Patent Application 20100266648.)

The patent specification describes that such films could possibly shield the hair from sweat, rain and dirt. Moreover, the researchers suggest that treatment with such a composition could possibly allow the wearer to go swimming and then to spontaneously dry her hair with a mere shake of the head.

BASF researchers have pronounced that they have created ampholytic terpolymers for 2-in-1 shampoos that have a strong affinity for keratin substrates even in the presence of anionic surfactants, can provide conditioning on their own due to the presence of a hydrophobic monomer, form complexes with anionic, fatty amines and cationic surfactants for stimuli-responsive deposition for hair conditioning,andthey form complex coacervates that can act as deposition aids for silicones beneficial agents. An example terpolymer is synthesized from acryloylaminopropyl-N,N,N-trimethylammonium chloride, acrylic acid and diallylamine. These polymers were shown to enhance deposition of silicone from a conditioning shampoo, and reduce the“squeakiness” of hair and lowered the wet and dry combing friction of hair.20

An alternative approach to the use of shampoo is to treat the hair with a leave-in product that makes the hair feel clean and smell fresh. Such an approach is espoused by Unilever researchers who claim that compositions based on clays and cationic polymers do provide hair sprays that both style the hair and leave it feeling and smelling clean.21

Summary
In this short article, we have highlighted some trends that are apparent from an examination of recent published patent applications. In hair styling, the trends are toward restylability and long-lasting soft fixation of style. There is also a continuing improvement in deposition systems exemplified by conditioning shampoos. Sophisticated surface modification is arising as a result of advances in nanoscience. Two of the most notable trends are the move toward natural and biomimetic systems and the trend toward polymer blends.

Polymers are not usually incompatible and this move is interesting insofar as it will require definitive understanding of the systems to achieve goals of compatibility and synergy.

References
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3. Clear conditioning gels with Eastman AQTM 48 polymer and UCARE polymers JR;Eastman Technical Bulletin.
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