Advances in Polymers for Hair Styling - Allured Books

Chapter 9
Advances in Polymers for
Hair Styling
Robert Y. Lochhead and Lisa R. Huisinga
The School of Polymers & High Performance Materials, The University of Southern
Mississippi, Hattiesburg, Mississippi USA
KeY woRdS: Polymers, fixative, hair spray, styling, straightening,
conditioning
AbStRAct: Block and graft copolymers, including some produced by
living free-radical polymerization, are among the new
hair fixative polymers surveyed in this chapter. Other
new polymers offer advantages in hair styling gels, hair
straightening and hair conditioning.
Hair spray consists of more than polymer. All components
must be considered and these comprise fixative polymer,
solvent, propellant, adjuvant and the valve system of the aerosol.
Hair styling also has numerous components. In this chapter
we’ll discuss the hair styling components that depend on
polymers. They include hair fixatives, styling gels, straighteners
and conditioners. (For a brush up on the classes of polymer
architecture discussed in this chapter, see Figure 1.)
Hair Fixatives
The desired attributes of hair fixatives include hair style
hold improvement, ease of application on wet hair, ease of
combing, no sticky feel, quick drying, not powdery or flaky
during grooming, assurance of hair body and bounce, increased
hair volume, no clumping of the hair, formation of a nonhygroscopic
binding film that is removable by shampoo, good
hair gloss, and no excessive stiffness.

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homopolymers
consist of long
molecular chains
in which each link
is an identical
monomer.
random copolymers
consist of long
molecular chains
in which there
are two different
monomers and
these are arranged
randomly along the
chain.
In Block
copolymers the
monomers are
homopolymer
blocks joined
together. the figure
depicts an aBa
block copolymer.
Figure 1. Contact angle greater than 90° causes the fibers to be pushed apart
In Graft or ‘comb’
copolymers
branches consisting
of one type of
monomer are
“hung” from a main
chain consisting
of another type of
monomer.
Hair style hold improvement must be achieved with a minimal
amount of fixative polymer applied easily from an aerosol spray, a
pump spray, a gel or a mousse. For ease of application on wet hair,
the solvent must be compatible with water and the polymer must not
phase-separate as water permeates the system. The fixative system
must also be safe; especially upon ocular exposure or inhalation. 1 For
ease of combing, the cohesive strength of the polymer film must be
less than the tensile strength and shear strength of the hair; and the
adhesive bond of the film to the hair must be weaker than the shear
strength of the hair. For conventional systems, sticky feel is avoided if
the polymer in the dried film is immobile during the time of “touch”
and has insufficient time to interact with the stratum corneum of the
fingertips. Quick drying can be achieved either by judicious choice of
solvent and propellant or by causing the system to gel. The mechanical
property aesthetics of hair body and bounce, increased hair volume
non-clumping and lack of extreme stiffness depend upon the hair
matrix being lightly crosslinked rather than being coated by the
applied polymer film. The film must be non-hygroscopic; otherwise it
will be plasticized by absorbed water vapor under humid conditions.
Such uncontrolled plasticization leads to loss of hold.

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Random copolymers: During the last two decades the U.S.
aerosol hair spray industry has been driven to develop low volatile
organic compound (VOC) systems to comply with the Clean Air
Act. In most cases this has meant the development of “aqueous”
systems in which a significant portion of the solvent is replaced by
water. This has posed two main challenges. First, the kinetics and
thermodynamics of fiber wetting is less favorable for “aqueous”
systems than the original solvent-based systems (see sidebar). This
results in a reduction of capillarity and a concomitant loss of holding
power due to the inter-fiber effects discussed above. The second
challenge arises form the fact that the water rapidly penetrates into
the hair cortex, plasticizing the hair and causing “droop” of the style.
Random copolymers have a solubility parameter that is
intermediate between homopolymers made from the same monomers.
Twenty years ago, conventional hair spray resins were designed to
be soluble in a propellant mixture of ethanol solvent and propane/
isobutane. As water was added to the polymer solution, the solvent
mixture’s solubility parameter could move out of range of that of the
polymer and if this happened the polymer would phase separate.
The configurational entropy of mixing increases as the polymer
molecular weight decreases and this is manifested by solubility of the
lower molecular-weight polymer in a wider range of solvents than a
higher molecular-weight polymer. Therefore the polymer suppliers
initially responded to the need for “aqueous-compatible” polymer by
merely lowering the molecular weights of their polymer products.
However, the lowering of molecular weight also resulted in poorer
film properties and the consequent loss of holding properties imposed
limitations on the extent to which this approach could be adopted.
Block and graft copolymers: Compared to random copolymers,
block and graft copolymers can show dual solubility zones, with
each zone corresponding to the solubility parameter of the respective
homopolymers. Homopolymer mixtures do not, in general, form
compatible blends because the large molecules have low entropies
of mixing, and in the absence of large enthalpies of mixing, the free
energies of mixing favor segregation of the polymer mixture into two
phases – one rich in one of the homopolymers and the other phase
that is rich in the other homopolymer.

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Each of the component “molecular blocks” of block and graft
copolymers also display such segregative phase separation. However,
in this case because the molecular blocks are constituent parts of
the same molecule, the segregation is limited to microdomain or
nanodomain dimensions. This limited segregation leads to polymer
alloys in which glassy microdomains confer mechanical rigidity and
rubbery microdomains confer rubbery and shock-absorbing properties.
These materials are thermoplastic elastomers and they often display
enhanced mechanical properties. Thermoplastic elastomers comprise
block copolymers containing rigid glassy blocks and soft rubbery blocks
incorporated within each molecule and precise control of molecular
weight of the blocks produces separation into exact micro- and nanostructures
that can be “tuned” to display exact mechanical properties.
Moreover, if the block copolymer is amphipathic (that is it comprises at
least one hydrophilic polymeric segment and at least one hydrophobic
polymer segment) it may form films that exhibit the desired resistance
to humidity but susceptibility to shampoo.
wetting of the Hair
Wetting of the hair by an applied polymer solution is extremely
important because capillary forces are necessary to pull adjacent fibers
together in order to form inter-fiber seam-welds and to cause migration
of the solution to inter-fiber cross-points where the solution will be
captured owing to a balance of Laplace pressure between the curvature
at the hair-liquid interface
and opposite curvature at
the air-liquid interface. this
phenomenon is commonly
observed as the adhesion
between the bristles when a
paint-brush is loaded with
paint. Dewetting of the hair
can cause the fibers to be
driven apart (Figure 2) and
this would inhibit migration
Figure 2. Contact angle greater than 90° causes the
fibers to be pushed apart
of the fixative solution to crosspoints of the hair matrix and prevent the
formation of seam welds between fibers.

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In this context, it is interesting that Dubief et al 2 have reported
that the inclusion of a non-thickening amphiphilic block copolymer
in a fixative formulation with a conventional hair fixative polymer
enhances the cosmetic and styling properties of the conventional
polymer fixatives. The improvements are manifested by an increase
in conditioning or styling power without increasing the total
polymer concentration in the formula, or the same conditioning
and styling benefits at reduced polymer concentration. The nonthickening
polymer in this case is defined as a copolymer which
when dispersed or dissolved in water leads to dynamic viscosities
that are less than 0.1 Pa.s measured at a shear rate of 200 sec -1 .
Examples of such amphiphilic block copolymer/ fixative polymer
blends are demonstrated in Table 1.
table 1
examples of amphilic block copolymer/fixative polymer
blends from dubief 2
Fixative Polymer Amphiphilic block copolymer
Vinylpyrrolidone/vinylcaprolactam copolymer poly(styrene-b-2-hydroxyethyl methacrylate) having
(Luvitec VpC 55K65W, BaSF) block molecular weights: pS = 1500; pheMa =
44,000
Vinylpyrrolidone/dimethylaminoethylmethacrylate poly(styrene-b-acrylic acid) having block molecular
copolymer (Copolymer 845, ISp) weights: pS = 1500; paa = 44,000
polyurethane (Luviset pUr,BaSF)
ppG-1/IpDI/DMpa copolymer
poly(methylmethacrylate-b-acrylic acid) having
block molecular weights: pMMa = 1200;
paa = 38,000
(avalure Ur 450, Noveon) —
acrylic copolymer (avalure aC115, Noveon) —
The influence of the block copolymer on the morphology of the
bulk material and/or on the adhesion of the fixatives to the hair
surface could be speculated to follow the following scheme:
• Block copolymers tend to exhibit morphology of separated
microdomains, each of which is rich in one of the blocks.
• Separation of discontinuous glassy domains in rubbery matrix
would confer the properties of an elastomer