Thermosensitive Hydrogels Made of N-alkylacrylamides and Their Applications
X. X. Zhu, M. Nichifor, H.Y. Liu, D. Avoce
Département de chimie, Université de Montréal,
C. P. 6128, succursale Centre-ville, Montréal, Québec, H3C 3J7, Canada
Some polymers in solutions can manifest a sharp solubility change at a certain temperature, known as the
lower critical solution temperature (LCST). This can be very useful because of its rheological and technological
implications and potential biomedical and industrial applications. The LCST of the thermosensitive polymers can be
varied by copolymerization, chemical modification of the polymer, or the addition of salts or surfactants in the
aqueous solutions. LCST have been observed various N-substituted alkylacrylamide polymers in aqueous systems,
but they have not drawn as much attention as poly(N-isopropylacrylamide), which has an LCST at ca. 32 C and has
been extensively studied. It is interesting and important to tune predictably the LCST of the polymers for the
different applications. The thermosensitivity of the polymers can be controlled by the relative hydrophilicity of the
copolymers, hence the chemical structure and composition of the constituent monomers. For the intended
applications, the following copolymers have been made and studied:
Copolymers of N-substituted acrylamide monomers: We have selected a number of N-substituted
acrylamide monomers in the preparation of several series of copolymers to vary the LCST of the polymers in a
systematic fashion. The LCSTs of the copolymers are quite sharp and can be varied between the LCST values of the
corresponding homopolymers. It was found that a small amount of styrene is capable of lowering significantly the
LCST of the copolymers. The thermosensitivity of such copolymers is clear, though the LCST is not as sharp as
that of the poly(N-alkylacrylamide)s. A stable emulsion can be formed for such polymers, providing the material
with interesting rheological properties. They have been tested for use as reversible flocculants and dispersants.
Functional thermosensitive copolymers as solid support in organic synthesis: N-substituted
acrylamides have been crosslinked and copolymerized with monomer with functional groups. Such polymers can be
used as solid support in organic synthesis. The thermosensitive behavior of the matrix has made the separation
process easier. Some crosslinked copolymers can be used as scavengers and absorbents.
Copolymers of N-alkylacrylamides with bile acid derivatives: Bile acids are natural amphiphilic
compounds with interesting properties. They can be potential used for biomedical applications such as drug delivery.
Methacrylic and acrylic derivatives of bile acids have been prepared by attaching a polymerizable double bond to
one of the functional groups of the bile acid molecules. Copolymers of N-substituted acrylamides have been made
with these derivatives and the aggregation behavior of the copolymers has been studied. In general, the LCST of the
acrylamide copolymers can be lowered by the presence of the bile acid residues in the copolymers, which can also
form micelles with added surfactants.
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