Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 4, pp. 724−726.
Pleiades Publishing, Ltd., 2011.
Original Russian Text © M.N. Grigor’eva, S.A. Stel’makh, L.U. Bazaron, D.M. Mognonov, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84,
No. 4, pp. 689−691.
Based on Polyhexamethyleneguanidine Hydrochloride
M. N. Grigor’eva, S. A. Stel’makh, L. U. Bazaron, and D. M. Mognonov
Baikal Institute of Nature Management, Siberian Division, Russian Academy of Sciences,
Buryat Republic, Ulan-Ude, Russia
Received December 6, 2010
Abstract—The possibility to prepare pH-sensitive hydrogels based on polyhexamethyleneguanidine hydrochloride
was explored. The equilibrium swelling rate of the hydrogels obtained at different monomer ratios was examined
in relation to pH of the medium.
Polymer hydrogels are hydrophilic network polymers
that swell upon contact with water and form a water-
insoluble three-dimensional network. Swelling of
polyelectrolyte gels is associated with repulsion between
the similarly charged units and the “swelling” osmotic
pressure of the free counter ions , and accordingly
a wide range of waters-soluble polymers are suitable
for their preparation. Many of hydrogels that comprise
charged groups, e.g., network systems based on
polyacrylic and methacrylic acids , exhibit pH-
sensitive behavior. This means that they can reversibly
change their volume in response to pH changes and hence
are promising, in particular, for preparation of swelling-
controlled release systems intended for directed transport
of medicinal drugs .
Polyguanidines are cationic polyelectrolytes
dissociating in aqueous media into a polycation and
a low-molecular-weight anion. The most widespread
polyguanidine is polyhexamethyleneguanidine
hydrochloride (PHMGHC) which can be synthesized
by melt polycondensation of hexamethylenediamine
(HMDA) and guanidine hydrochloride (GHC).
Owing to the three functional groups of GHC,
polyhexamethyleneguanidine hydrochloride is capable
of three-dimensional polycondensation forming a three-
dimensional polymer network , and positively charged
units of the polymer chain and a mobile low-molecular-
weight counter ion are responsible for the pH-sensitive
behavior exhibited by PHMGHC in aqueous media.
Polycondensation of HMDA and GHC leads to
a linear polymer if the monomers are taken in equimolar
amounts and to branched structures and a network
polymer under excess of bifunctional HMDA. However,
100% gelation cannot be achieved at any excess of the
bifunctional monomer, which fact contradicts the Flory’s
three-dimensional polycondensation theory , evidently
because of the equilibrium nature of polymer formation.
The hydrogels were synthesized using a two-stage
process by melt polycondensation in air at the GHC :
HMDA molar ratios of 1 : 1.15, 1 : 1.20, and 1 : 1.25.
The reaction mixture was initially kept at 165°C for
30 min, and subsequently the temperature was risen to
200°C. After the total synthesis time of 2.5 h the resulting
polymers were placed into water. The swollen hydrogels
were washed with distilled water to entirely remove
soluble fractions, as monitored with the refractive index of
the ﬁ ltrate. The puriﬁ ed swollen hydrogels with identical
weights were placed into distilled water, and pH was
adjusted with hydrochloric acid or sodium hydroxide.
The pH measurements were carried out with the use of an
I-160MI laboratory ion meter. The swelling rate Q