Conditioning Agents for Hair and Skin

Polymers as Conditioning Agents 259
A. Polyvinylpyrrolidone (PVP)
The growth of cationic polymers as hair conditioners was initiated by the introduction
of PVP (poly-N-vinyl-2-pyrrolidone) in 1950 by then-GAF [now
International Specialty Products, ISP (18)] and then by BASF (19). A homopolymer
is a molecule with repeating units of the same molecular structure.
Originally developed for incorporating into hairsprays, PVP has been found
to have conditioning properties if applied via a shampoo. The transparent film
on hair imparts smoothness and luster, as well as substantivity, to skin and hair.
The films have good holding power and do not flake under moderate climate
conditions. PVP has other properties which are used in shampoos and hair
conditioners—it improves foam stabilization, increases viscosity and, in certain
formulations, can reduce eye irritation (8). Today, PVP is occasionally
used as a conditioning agent in shampoos. However, PVP and its copolymers
are used primarily as styling resins.
As hair styles continued to progress, some of the deficiencies of PVP homopolymer
began to be noticed. PVP is hygroscopic. It tends to become sticky,
dull, and tacky as atmospheric moisture is adsorbed, and, of more significance,
the adsorbed moisture plasticizes the film and causes ductile fracture of the
bond. A further drawback of PVP homopolymer was its tendency to become
brittle and flaky in dry weather (20).
B. Copolymers of PVP
Many of the objectionable properties of PVP homopolymer were overcome
by the introduction of PVP random copolymers. A random copolymer tends
to have properties which are intermediate between the properties of the
homopolymers which would be formed by polymerizing the monomers separately.
Thus, a polar hygroscopic homopolymer can be rendered more moisture
resistant by introduction of a nonpolar comonomer (20).
1. PVP/Vinyl Acetate (VA) Copolymers
PVPA^A copolymer (Figure 1) was offered as an improved hairspray-conditioner
(18). Four compositional ratios were offered: 70/30, 60/40, 50/50, and
30/70. The higher the ratio of VA, the less susceptible to atmospheric humidity
and the harder the film, but consequently it is less easily shampooed off. The
copolymers used have less moisture sensitivity than PVP, with good hold and
good conditioning. The polymer will also coat the skin, leaving a conditioned,
less oily feel (1).
2. PVP-a-olefin Copolymers
GANEX series (ISP 10) are linear copolymers of PVP and long-chain aolefins.
There are four varieties, differing in the olefin copolymer: P-904 (buty-