Introduction
Description of water-soluble polymers is one of the main
research tasks of polymer chemistry and physics, since
for natural macromolecules, such as proteins and DNA,
water is the basic good solvent. Moreover, in last dec-
ades, synthetic water-soluble polymers found wide use in
various biomedical applications [1–3]. Understanding of
solution behavior of water-soluble polymers (both syn-
thetic and natural ones) is often important for knowing
their biological role. The properties of such macromol-
ecules in solutions depend on complicated interplay be-
tween hydrophobic, dipole–dipole, electrostatic
interactions and hydrogen bonding. Therefore, it is a
topical problem to propose some models that could
describe the complicated ensemble of forces in a sim-
plistic, yet correct, way. One of the initial attempts to
do that was undertaken by Lau and Dill [4, 5], who
proposed the subdivision of monomer units into two
classes: hydrophobic units (H) and polar units (P) (HP
model). The chains of amphiphilic polymers are modeled
as consisting of hydrophilic (polar) or hydrophobic
point sites (beads) distributed along the backbone in a
linear fashion (Fig. 1a). For aqueous systems, it is as-
sumed that the hydrophilic beads are in good solvent,
while hydrophobic beads are in poor solvent, so that H-
units attract each other, whereas, the interaction be-
tween P-units is repulsive.
Biological proteins are widely considered as HP co-
polymers and it is believed that the spatial structure of
globular proteins is of the core-shell type: the core is
mainly formed by H-units, whereas, the shell of a
globule consists of P-units interacting with the solvent
molecules and preventing them from contact with the H-
core. Thus, HP-model is widely used in protein-folding
concepts.
Ivan M. Okhapkin
Elena E. Makhaeva
Alexei R. Khokhlov
Two-dimensional classification of amphiphilic
monomers based on interfacial
and partitioning properties. 1. Monomers
of synthetic water-soluble polymers
Received: 9 February 2005
Accepted: 11 April 2005
Published online: 28 July 2005
Ó Springer-Verlag 2005
Abstract A classification of amphi-
philic monomers based on the
interfacial and partitioning proper-
ties has been proposed. Monomers
partitioned at equilibrium between
two immiscible phases were ascribed
with a pair of parameters: standard
free energy of adsorption at the
interface and standard free energy of
partition between the two phases.
These two parameters are repre-
sented in a form of two-dimensional
diagram (both of them being nor-
malized by kT factor). Comparison
of the parameters in question gives
information on energetic preferences
of the molecules to be located at the
interface or in the bulk phases. Four
monomers of synthetic water-soluble
polymers, namely, N-isopropyl-
acrylamide, 1-vinylimidazole,
N-vinylpyrrolidone and
N-vinylcaprolactam have been
classified according to the above
method at various temperatures.
The possibility to extend the
classification to arbitrary
chemicals is discussed.
Keywords Partition Æ Liquid/liquid
interfaces Æ Monomer units Æ
Interfacial activity Æ Amphiphilic
Colloid Polym Sci (2005) 284: 117–123
DOI 10.1007/s00396-005-1342-1
ORIGINAL CONTRIBUTION
I. M. Okhapkin Æ A. R. Khokhlov (&)
Department of Polymer Science,
University of Ulm,
Albert-Einstein-Allee 11
89069 Ulm, Germany
E-mail: khokhlov@polly.phys.msu.ru
Tel.: +7-095-9392959
Fax: +7-095-9392988
I. M. Okhapkin Æ A. R. Khokhlov
Nesmeyanov Institute of Organoelement
Compounds, Vavilov Street 28,
119991 Moscow, Russia
E. E. Makhaeva Æ A. R. Khokhlov
Physics Department,
Moscow State University,
119992 Moscow, Russia