V. KONOVALOVA ET AL. 25
peratures lower and higher of Tp, such as for P(NIPA-co-
AlAm) (9:1) at temperature 23˚C and 38˚C and for hy-
drogel P(NIPA-co-AlAm) (3:2) at temperature 23˚C, 38˚C
and 53˚C, and results were summarized in Table 2.
The data in Table 2 show that for the P(NIPA-co-
AlAm) hydrogel (9:1) composition, the solvent quality
change is observed at elevated temperature. It is known
that the interaction parameter value χ smaller than ~0.5
indicates strong interactions between polymer macro-
molecules and solvent, high solvophility. On the contrary
χ values exceeding 0.5 indicate materials solvophobity.
Thus, in our work, P(NIPA-co-AlAm) hydrogel (9:1) with
90% content of thermo-sensitive monomer changes χ
from 0.5185 to 0.6916 when temperature increases from
23˚C to 38˚C. Moreover, c
decreases by 150 times!
And the c
value approximates average molecular
mass of copolymer chain at 38˚C. This effect can be ex-
plained by the increase of hydrophobic-hydrophobic in-
teractions between macromolecules and additional cross-
linking of the hydrogel due to H bonds.
With the decrease of content of hydrophobic NIPA
units up to 60%, solvent quality decreases insignificantly
even at temperature of 53˚C. At the same time, there is
20-fold decrease in c
values, which manifest as hy-
drogel transition to the collapsed state at the temperatures
higher than Tp.
4. Conclusion
In the present work thermo- and pH-responsive hy-
drogels were synthesized via copolymerization of N-
isopropylacrylamide and allylamine hydrochloride mono-
mers. It was shown that targeted control of the hydrogel
phase transition temperature can be realized by changing
their composition and pH of the environment. Thus rise
of hydrophilic allylamine mass fraction from 10% to
60% causes shift of phase transition temperature from
35˚C to 47˚C. Hydrogels of P(NIPA-co-AlAm) (3:2)
composition are the most pH-responsive. Values of av-
erage molecular mass between c
polymer cross-links
and Flory parameter χ were calculated using temperature
dependences of the synthesized hydrogel swelling. It was
found that the increase of hydrophilic component (AlAH)
in the copolymer results in the growth of c
, while
temperature rise causes decrease of the above-mentioned
Table 2. χ and c
M values for P(NIPA-co-AlAm) hy-
drogels.
Hydrogel Temperature, ˚C χ c
R2
23 0.5185 50 0000.99
P(NIPA-co-AlAm) (9:1) 38 0.6916 323 0.96
23 0.5096 143 0000.97
38 0.5117 100 0000.99P(NIPA-co-AlAm) (3:2)
53 0.5983 5000 0.87
parameter. Flory parameter χ grows both with tempera-
ture and NIPA content rise in copolymer hydrogels show-
ing intensification of hydrophilic interactions. The syn-
thesized “smart” hydrogel systems can be used to de-
velop novel medications, membranes, various sensors
and probes that are capable of radical change of their
working characteristics in response to the slightest envi-
ronmental changes.
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