Enantioselective aza-Diels-Alder reaction catalyzed by a chiral Br?nsted acid: Effect of the additive on the enantioselectivity

Article abstract of DOI:10.1016/j.jcis.2006.03.066

Danishefsky's diene and aldimine underwent aza Diels-Alder reaction under the influence of chiral phosphoric acid derived from (A)-BINOL as a chiral Br?nsted acid to afford piperidinone derivatives in good to high enantioselectivity. Addition of CH_3<

Full text of DOI:10.1016/j.jcis.2006.03.066

Journal of Colloid and Interface Science 300 (2006) 141–148
www.elsevier.com/locate/jcis
Mechanism of oil-in-water emulsification using a water-soluble amphiphilic
polymer and lipophilic surfactant
Eri Akiyama a,∗, Akio Kashimoto a, Hajime Hotta a, Tomohito Kitsuki b
a
Kao Corporation, Tokyo Research Lab, 2-1-3, Bunka, Sumidaku, Tokyo 131-8501, Japan
Kao Corporation, Wakayama Research Lab, 1334, Minato, Wakayama 640-8580, Japan
b
Received 11 October 2005; accepted 23 March 2006
Available online 3 April 2006
Abstract
A new O/W (oil-in-water) emulsification system was developed using the amphiphilic polymer HHM-HEC (hydrophobically–hydrophilically
modified hydroxyethylcellulose) and a lipophilic surfactant. HHM-HEC was used as a thickener and polymeric surfactant, and the addition of
small quantities of various types of nonionic lipophilic surfactant (hydrophilic–lipophilic balance <5) decreased the droplet size of several types of
oil due to a lowering of the tension at the water/oil interface. The oil droplets were held by the strong network structure of the aqueous HHM-HEC
solution, preserving the O/W phase without inversion. These stable O/W emulsions were prepared without the addition of hydrophilic surfactants
and thus show improved water repellency.
© 2006 Elsevier Inc. All rights reserved.
Keywords: HHM-HEC; Water-soluble polymer; Oil-in-water emulsion; Lipophilic surfactant
1. Introduction
bilize the emulsions. However, the performance of conventional
water-soluble polymers is limited. There have been several re-
ports of O/W-type emulsification systems that contained con-
ventional water-soluble amphiphilic polymers and hydrophilic
surfactants [7,8], as well as polysaccharides and polar organic
compounds [9]. However, the O/W-emulsions composed of
water-soluble polymers and various kinds of oil without hy-
drophilic surfactant have been little investigated.
We prepared amphiphilic polymer HHM-HEC (sodium hy-
droxyethylcellulose hydroxypropyl stearylether hydroxypropyl
sulfonate), a good thickening and emulsifying agent [10,11].
It is a strong acidic polyelectrolyte with a high molecular
weight. It has a good solubility in water, high electrolyte toler-
ance [12], and high physical stability. Intermolecular aggrega-
tion occurs above 0.2 wt% and three-dimensional networks [13]
are formed in water through the aggregation of hydrophobic
alkyl chains in HHM-HEC. It forms thixotropic and elastic gel
above 0.6 wt% [11]. These properties enable O/W emulsions
containing various kinds of oil to be stabilized in the absence
of surfactants. However, the diameters of the oil particles in
the reported HHM-HEC/water/oil emulsions were much larger
than those of conventional O/W emulsions (with values rang-
Water based emulsions (oil-in-water (O/W)-type emulsions)
have been widely applied to cosmetics and toiletries. Actually
they have a good watery feeling when applied to skin. How-
ever, conventional O/W emulsions contain a large amount of
hydrophilic surfactant that is used to obtain fine emulsified par-
ticle. Therefore, these cause uncomfortable feeling and skin
irritation and lower water repellency. In order to improve cos-
metic formulations, such as lotions, creams, sunscreens, and
base make-up liquid foundations, it is important to obtain fine
O/W emulsions with minimum amount of hydrophilic surfac-
tant. Furthermore, the best is to obtain fine O/W emulsion with-
out hydrophilic surfactant.
Recently, functional water-soluble amphiphilic polymers be-
came highly developed [1–3]. Some of these polymers have
thickening and emulsifying abilities and have been used in
O/W-type emulsions [4–6]. They can reduce the required quan-
tities of low-molecular-weight hydrophilic surfactants and sta-
*
Corresponding author. Fax: +81 3 5630 9342.
E-mail address: akiyama.eri@kao.co.jp (E. Akiyama).
0021-9797/$ – see front matter © 2006 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcis.2006.03.066

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E. Akiyama et al. / Journal of Colloid and Interface Science 300 (2006) 141–148
ing from 5 to 50 µm and a mean diameter of 23.6 µm.) Such
a coarse emulsion does not have smoothness and it becomes
disadvantage when applied to cosmetics and toiletries. It was
difficult to combine “fine O/W emulsion” and “no hydrophilic
surfactant” with conventional method.
2.1.2. Oils
The oil materials used in this work are listed:
(1) Squalane (NIKKOL squalane, NIKKO Chemicals Co.,
Ltd.).
(2) Dimethyl polysiloxane (silicone KF-96A (6cs), Shin-Etsu
Chemical Co., Ltd.).
(3) Perfluoropolymethylisopropyl ether (FOMBLIN HC/04
Ausimont).
In this study, we achieved the creation of the fine O/W emul-
sion without hydrophilic surfactant. We have succeeded in re-
ducing the size of the oil particles by adding of small quantities
of lipophilic surfactant (hydrophilic–lipophilic balance (HLB)
<5) in HHM-HEC/water/oil emulsions. This system is unique
in that lipophilic surfactants promote the formation of an O/W
emulsion without phase inversion. In this paper we describe the
emulsification mechanisms of this system.
2.1.3. Surfactants
The surfactants used in this work are listed:
(1) Isostearyl glyceryl ether, GE-IS (HLB 2.5 calculated by the
Davies method, HLB 5.0 calculated by the Griffin method,
PENETOL GE-IS, Kao Corporation).
2. Materials and methods
(2) Dimethicone copolyol (polyoxyethylene methylpolysilox-
ane copolymer, HLB 2, supplied by Toray Dow Corning
Silicone).
(3) Polyoxyethylene(20) sorbitan monostearate (HLB 14.9,
RHEODOL TW-S120, Kao Corporation).
2.1. Materials
2.1.1. Water-soluble polymers
The water-soluble polymers used in this work are listed:
(1) Hydrophilically–hydrophobically modified hydroxyethyl-
cellulose (HHM-HEC).
The structures of surfactants (1)–(3) are shown in Fig. 2.
(2) Alkyl chain-bearing HEC (R-HEC).
(3) HEC (HEC QP-100MH, Union Carbide Corporation).
2.2. Preparation of emulsions
To prepare the O/W emulsions, HHM-HEC was thoroughly
suspended and swollen in water. A mixture of oil and surfactant
was then added to the aqueous polymer solution while stirring
with a propeller mixer at 400 rpm for 5 min. After this pre-
mixing, the emulsions were stirred for 10 min at 25 ◦C with a
laboratory homomixer operating at 5000 rpm.
The structures of compounds (1)–(3) are shown in Fig. 1.
Compounds (1) and (2) were prepared by the method reported
in [10]. The compound (3) was a raw material for the com-
pounds (1) and (2), and the number of glucose unit (7300)
was the same for all compounds (1)–(3). HHM-HEC has both
alkyl chain moieties and sulfonic acid moieties. The molecu-
lar weights and the substitution degrees of the alkyl chains and
the sulfonic acid moieties per one HEC unit are listed in Ta-
ble 1. We prepared two types of HHM-HEC (A) and (B), but
they have no significant differences in substitution degrees and
properties.
2.3. Viscosity measurements
Viscosity of emulsion was measured using a Toki-Sangyo
Model B viscometer (B8L, Rotor No. 4, 6 rpm), which gave
measurement errors of <5%.
Table 1
HEC derivatives employed in this work
Sample name
M
Number of alkyl chain moieties
(per monosaccharide unit)
Number of sulfonic acid moieties
(per monosaccharide unit)
w
6
6
6
6
HHM-HEC (A)
HHM-HEC (B)
R-HEC
1.8 × 10
1.8 × 10
1.5 × 10
1.5 × 10
0.0033
0.0048
0.0041
0
0.21
0.22
0
HEC
0
Fig. 1. Structures of HHM-HEC and HEC.

E. Akiyama et al. / Journal of Colloid and Interface Science 300 (2006) 141–148
143
Fig. 2. Structures of surfactant.
2.4. Particle size measurements
The distributions of droplet sizes in the emulsions were de-
termined using a laser scattering particle size distribution ana-
lyzer (HORIBA LA-920). Photomicrographs of the emulsions
were obtained using a Nikon OPTIPHOT-2 photomicroscope.
Measurements were carried out after appropriate dilution of the
sample with water. It was confirmed in advance that the dilu-
tion process did not significantly change the particle size. The
measurement errors were <0.7%.
(A)
2.5. Interfacial tension measurements
The tension of the aqueous polymer solution/oil (including
surfactant) interface was measured using a Wilhelmy-type auto-
mated surface tension meter (KRÜSS Processor tension meter
K122) with a platinum plate.
(B)
2.6. Rheological measurements
Fig. 3. (A) Photomicrographs of HHM-HEC/water/squalane emulsions:
(a) without surfactant, (b) with GE-IS (HLB 2.5). (B) Photomicrographs
of HHM-HEC/water/dimethyl polysiloxane emulsions: (a) without surfactant,
(b) with dimethicone copolyol (HLB 2).
Oscillatory measurements of each aqueous solution of
polymer and emulsion were taken with a Modular Com-
pact Rheometer MCR300 (PHYSICA Messtechnik GmbH),
which has cone-plate geometry (CP50-1: angle 1.0◦, diame-
ter 50 mm). All date were collected from a linear viscoelastic
region (strain amplitude γ = 1%). The sample was covered by
a reservoir filled with water during the measurements to prevent
the evaporation of water.
oil. Lipophilic surfactants caused a decrease in size of oil
droplets. The smallest oil droplets were obtained with the
combination of GE-IS and squalane, or the combination of
dimethicone copolyol and dimethyl polysiloxane. High vis-
cosity was also obtained at these combinations. No viscosity-
decrease was observed and the O/W phase was preserved at
high lipophilic surfactant concentrations. Therefore, precise ra-
tios of oil to surfactant are unnecessary in this emulsification
system. However, high-HLB hydrophilic surfactants caused a
decrease in viscosity and segregation of the emulsion. The vis-
cosity of the HHM-HEC/water/squalane/polyoxyethylene sor-
bitan monostearate (HLB 14.5) emulsion was 600 mPa s and
HHM-HEC/water/dimethyl polysiloxane/polyoxyethylene sor-
bitan monostearate emulsion was 580 mPa s. (0.4 wt% HHM-
HEC (A), 19.5 wt% oil, 0.5 wt% polyoxyethylene sorbitan
monostearate). Creaming was immediately observed for the
both emulsions.
3. Results
3.1. Decrease in particle size induced by lipophilic surfactants
The addition of low-HLB surfactants to the HHM-HEC/
water/oil systems caused a large decrease in particle size.
Figs. 3A and 3B show optical photomicrograph images of the
emulsions with and without surfactants. The distribution of par-
ticle size in the emulsions is shown in Figs. 4A and 4B. These
emulsions contained 0.5 wt% HHM-HEC (A), 19.5 wt% oil,
and 0.5 wt% surfactant.
Figs. 5A and 5B show the relationship between the quan-
tity of lipophilic surfactant added and (a) the size of the oil
droplets (squalane, dimethyl polysiloxane, and perfluoropoly-
methylisopropyl ether) and (b) viscosity of the emulsions.
These emulsions contain 0.4 wt% HHM-HEC (A) and 20 wt%
3.2. Interfacial tension
Figs. 6A and 6B show the interfacial tension at the aque-
ous HHM-HEC (A) or HEC solution/oil phase as a function

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E. Akiyama et al. / Journal of Colloid and Interface Science 300 (2006) 141–148
Table 2
Effect of type of polymer on state of emulsion (0.5 wt% HEC derivatives,
19.5 wt% squalane, 0.5 wt% GE-IS)
Sample name
State of emulsion Viscosity (mPa s) Particle size (µm)
HHM-HEC (A) O/W
HHM-HEC (B) O/W
22,000
23,000
–
–
4.0
3.4
5.8
4.4
R-HEC
HEC
Creaming
Creaming
Table 3
Effect of concentration of HHM-HEC on state of emulsion (19.5 wt% squalane,
0.5 wt% GE-IS)
HHM-HEC
concentration (wt%)
State of
emulsion
Viscosity
(mPa s)
Particle size
(µm)
(A)
0.1
0.2
0.4
0.5
0.8
1.0
Creaming
O/W
O/W
O/W
O/W
–
–
620
6.5
4.1
4.0
4.1
–
10,700
10,800
29,800
–
W/O
HEC derivatives, 19.5 wt% squalane, 0.5 wt% GE-IS) are
shown in Table 2. Small oil droplets (4–6 µm) were obtained
for all emulsions, but creaming was observed for R-HEC and
HEC emulsions. (Furthermore, stable emulsions with fine par-
ticles could not be obtained at any concentration (0.2–1.0 wt%)
for the HEC.) Both alkyl chain and sulfonic acid moieties has
an effect on state of emulsion containing lipophilic surfac-
tant.
As shown in Table 3, fine O/W emulsions were successfully
obtained for concentrations of HHM-HEC (A) between 0.4 and
0.8 wt%. These emulsions also contained 19.5 wt% squalane
and 0.5 wt% GE-IS. Creaming occurred for low HHM-HEC
concentrations (0.1 wt%) because the aqueous phase was too
dilute to hold the oil particles, and phase inversion occurred for
high HHM-HEC concentrations (1.0 wt%) because the aque-
ous phase became too viscous to contain the oil particles by
stirring.
(B)
Fig. 4. (A) Droplet diameter distribution by volume for HHM-HEC/water/
squalane emulsions. (B) Droplet diameter distribution by volume for HHM-
HEC/water/dimethyl polysiloxane emulsions.
of lipophilic surfactant concentration. In the absence of surfac-
tant the interfacial tension was large. When lipophilic surfactant
was added to the oil phase, a significant decrease in the inter-
facial tension (by approximately a factor of ten) was observed
regardless of the type of polymer.
3.3. Rheology
4. Discussion
Oscillatory measurements of the emulsion were carried out
to elucidate the relationship among aqueous solution of HHM-
HEC, the emulsion of the HHM-HEC/water/oil system and the
emulsion of the HHM-HEC/water/oil/lipophilic surfactant. The
concentration of HHM-HEC in water was constant. (HHM-
HEC (B) is 0.625 wt% in water.) The results are shown in
Figs. 7A and 7B. The aqueous solution of HHM-HEC was pre-
dominantly elastic. With regard to Figs. 7Aa and 7Ba, the shape
of rheological spectra of the emulsion containing 20 wt% oil
were similar to that of the aqueous solution but those of the
emulsion containing lipophilic surfactant were a little changed
(Figs. 7Ab and 7Bb)
Fine O/W emulsions were formed by lipophilic surfactant
and amphiphilic polymer HHM-HEC. Various kinds of oil
droplets were minimized by GE-IS or dimethicone copolyol.
This phenomenon is characteristic and two important mech-
anisms in the formation of the emulsification system could
be considered: a decrease in interfacial tension caused by
lipophilic surfactant and the formation of a three-dimensional
network structure by the HHM-HEC polymer in the continuous
phase, which holds the emulsified oil particles.
4.1. The role of lipophilic surfactants
Figs. 6A and 6B show the lowering of interfacial tension
by adding lipophilic surfactants to the oil phase. The size of
the oil particles in HHM-HEC/water/oil emulsions decreased
with the addition of lipophilic surfactants (Figs. 5Aa and 5Ba).
It indicates that lipophilic surfactants are able to decrease in-
3.4. Effect of polymer type and concentration on state
of emulsion
The effects of different types of HEC derivatives on the state
of O/W emulsions containing a lipophilic surfactant (19.5 wt%

E. Akiyama et al. / Journal of Colloid and Interface Science 300 (2006) 141–148
145
(A)
(B)
Fig. 5. (A) Effect of GE-IS concentration on (a) size of oil particles, (b) viscosity. (B) Effect of dimethicone copolyol concentration on (a) size of oil particles,
(b) viscosity.
(A)
(B)
Fig. 6. (A) Interfacial tensions at the aqueous solution of polymer/squalane as a function of GE-IS concentration. (B) Interfacial tensions at the aqueous solution of
polymer/dimethyl polysiloxane as a function of demethicone copolyol concentration.
terfacial tension as effectively as hydrophilic surfactants even
in O/W emulsions and the size of the oil particles decreases
with the lowering of interfacial tension. There was no signifi-
cant difference in the values of interfacial tension between the
HEC and HHM-HEC polymers, indicating that the alkyl chains
in HHM-HEC do not behave as surfactants [5,6]. Slight ad-
sorption of alkyl chains at oil/water interface can be possible,
however it does not have much effect on lowering interfacial
tension. The decrease of interfacial tension is simply caused
by the assembly of lipophilic surfactant molecules at the inter-
face.
Furthermore, it is preferable that the surfactants are highly
soluble in oil phase. When surfactants dissolve well in the oil
phase, the assembly of surfactants can be effective (because
mobility of surfactants is high) and fine emulsified particles can
be obtained. GE-IS dissolves well in squalane, while it does not
dissolve in dimethyl polysiloxane or perfluoropolymethyliso-
propyl ether. Likewise, dimethicone copolyol dissolves only in
dimethyl polysiloxane. As a result, the smallest oil droplets and
high viscosity of emulsion were obtained with the combina-
tion of GE-IS and squalane, or the combination of dimethicone
copolyol and dimethyl polysiloxane (Fig. 5A and 5B).

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E. Akiyama et al. / Journal of Colloid and Interface Science 300 (2006) 141–148
(A)
(B)
ꢀ
ꢀꢀ
Fig. 7. (A) The storage modulus, G (closed), and loss modulus, G (open), of (a) aqueous solution of HHM-HEC and HHM-HEC/water/squalane emulsion;
◦
ꢀ
ꢀꢀ
(b) aqueous solution of HHM-HEC and HHM-HEC/water/squalane/GE-IS emulsion at 25 C. (B) The storage modulus, G (closed), and loss modulus, G (open),
of (a) aqueous solution of HHM-HEC and HHM-HEC/water/dimethyl polysiloxane emulsion; (b) aqueous solution of HHM-HEC and HHM-HEC/water/dimethyl
◦
polysiloxane/dimethicone copolyol emulsion at 25 C.
The system described here takes advantage of the poor sol-
ubility of lipophilic surfactants in water. In general, the thick-
ening ability of self-assembly polymer is canceled by the ad-
dition of large quantities of hydrophilic surfactant. The hy-
drophobic domains, which are cross-linking point of three-
dimensional gel network, dissociate due to adhesion of the hy-
drophilic surfactant to the hydrophobic moiety [14–16]. The
decrease in viscosity of the HHM-HEC/water/oil emulsion on
addition of hydrophilic surfactants (polyoxyethylene(20) sorbi-
tan monostearate) is thought to be caused by the same effect.
Low-molecular-weight hydrophilic surfactants have a high mo-
bility in water and could therefore adhere to the hydrophobic
domains in the HHM-HEC network. Conversely, lipophilic sur-
factants are poorly soluble in water and the hydrophobic do-
mains of the HHM-HEC network are preserved. As a result, the
viscosity of the emulsion does not decrease.
4.2. The role of the HHM-HEC network structure in the
continuous phase
In general, low-HLB surfactants are used to make W/O-type
emulsions. Indeed, GE-IS (HLB 2.5) and dimethicone copolyol
(HLB 2) are known as W/O-type surfactants. However, in our
case the emulsions remain O/W-type without the occurrence of
phase inversion at high lipophilic surfactant concentrations and
thus differ from conventional emulsions that consist of only
low molecular weight media. The type of emulsion (O/W or
W/O) is not determined by the morphology of the surfactants
(the hydrophobic–hydrophilic balance), but by the rheological
properties of the polymers in the continuous phase. Ishihata
et al. reported that the thixotropy of the continuous phase had
an effect on the stability of O/W emulsions containing glyceryl
monostearate [9]. The aqueous solution of HHM-HEC shows

E. Akiyama et al. / Journal of Colloid and Interface Science 300 (2006) 141–148
147
Fig. 8. Schematic drawings of (a) aqueous solution of HHM-HEC, (b) HHM-HEC/water/oil emulsion, (c) HHM-HEC/water/oil emulsion with lipophilic surfactant.
non-Newtonian flow behavior, and has a high yield value (i.e.,
thixotropic). Oscillatory measurements reveal that the aqueous
solution of HHM-HEC is predominantly elastic (the value of
Gꢀ was larger than that of Gꢀꢀ) above 0.6 wt% [11]. Thixotropic
and elastic gel is formed by the aggregation of alkyl chains
in HHM-HEC structure. The gel structure of HHM-HEC in
the continuous phase has the ability to hold oil particles, in-
cluding lipophilic surfactants (Figs. 8a and 8c) [10,11]. Phase
inversion was avoided due to the low mobility of the HHM-
HEC polymers in the continuous phase, which is derived from a
high-molecular-weight, semi-rigid backbone [17] and strong in-
termolecular aggregates of HHM-HEC. Emulsions with highly
expanded networks in the continuous phase are not subject to
phase inversion.
When only oils were emulsified in aqueous solution of
HHM-HEC (0.625 wt% in water), the shape of rheological
spectrum of the emulsion was similar to that of the aqueous
solution of HHM-HEC (Figs. 7Aa and 7Ba). The viscoelastic
properties of HHM-HEC in disperse medium is overwhelming
and dominates the rheological properties of the emulsion. On
the other hand, when oils including lipophilic surfactant were
emulsified, the elastic properties became strong (Figs. 7Ab
and 7Bb). These rheological properties were based on both an
emulsification by surfactant and network structures of HHM-
HEC.
Using a preparative method in which oil and a lipophilic
surfactant are added to a HHM-HEC solution, emulsions of
the O/W-type are predominantly made. The aggregation of hy-
drophobic moieties of HHM-HEC in water takes place prior to
emulsification, and the C18 alkyl chain domains in HHM-HEC
are considered to exist solely as cross-linking point in water, not
to assemble at the oil/water interface like low-molecular-weight
surfactants [18]. The oil particles are emulsified in the HHM-
HEC network structure under the condition of low interfacial
tension promoted by the lipophilic surfactants.
In this system we conclude that several properties of the
polymer in aqueous solution are important. These are structure,
concentration, elasticity and thixotropy. This is explained by the
observations that both HEC and R-HEC were unable to form
stable O/W emulsions with lipophilic surfactants (Table 2). Sta-
ble emulsions with fine particles could not be obtained at 0.2–
1.0 wt% HEC. An aqueous solution of HEC is a viscous fluid
(not elastic) at 1.0 wt% and has no yield value [11]. 0.5 wt%
HEC emulsion showed apparent creaming even when it does
not contain lipophilic surfactant [11]. An aqueous solution of
R-HEC is thixotropic and elastic, but the solubility of R-HEC in
water is low and the expansion of network structure is not suffi-
cient. In fact, the aqueous solution of R-HEC was slightly turbid
[11]. The states of network of HEC and R-HEC in continuous
phase are not able to hold oil including lipophilic surfactants.
Similarly, the semi-dilute aqueous solution (0.1 wt%) of
HHM-HEC was also unable to form stable O/W emulsions (Ta-
ble 3). HHM-HEC was not thixotropic or elastic below 0.2 wt%
(in the region of intramacromolecular association of HHM-
HEC) [11]. On the other hand, between 0.4 and 0.8 wt%, fine
O/W emulsions were obtained. This concentration region is
corresponding to the region of intermolecular association of
HHM-HEC [11]. Therefore, in order to make stable O/W emul-
sions using water-soluble polymers and lipophilic surfactants, it
is necessary to choose a suitable type of polymer in an appropri-
ate quantity, otherwise phase inversion, creaming or segregation
easily occurs.
5. Summary
Fine O/W emulsions were obtained using a HHM-HEC/
water/oil/lipophilic surfactant system. It is supposed that the
three-dimensional networks formed by HHM-HEC play a vital
role in this system. The strong network structure of HHM-HEC
is able to hold oil particles, including the lipophilic surfac-
tant, without the occurrence of phase inversion. Conventional
polymers were unable to form O/W emulsions with lipophilic
surfactants because their network structures and viscoelastic
properties were not sufficient to hold oil particles in a stable
fashion.
This system utilizes the advantages of lipophilic surfactants:
their ability to lower interfacial tension and their poor solubil-
ity in water. Low interfacial tension decreases the diameter of
the oil droplets and poor solubility prevents dissociation of the
hydrophobic domains of HHM-HEC in water.
When this type of emulsion is applied to the skin, it has
a comfortable watery feeling and shows improved water re-
pellency because it does not contain hydrophilic surfactants.
(Re-emulsification is inhibited.) There are many potential ap-
plications of such systems for cosmetics and toiletries.
An investigation of the effects of the degree of alkyl chain
and sulfonic moiety substitution in HHM-HEC on the proper-
ties and stability of the emulsions are now in progress.

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E. Akiyama et al. / Journal of Colloid and Interface Science 300 (2006) 141–148
Acknowledgments
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We are very grateful to Dr. K. Kita, T. Nishioka, and Dr.
T. Ihara for their help with synthesis of the polymers. We also
thank K. Kawakami, a researcher in the Kao Corporation, for
useful advice on the preparation of emulsions.
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