Ternary interpenetrating polymer networks (T-IPN) hydrogels composed of poly(vinyl acohol) (PVA)

poly(acrylic acid)(PAA) and poly(2-acrylamido-2-methyl propyl sulfonic acid)(PAMPS) were synthesized by solution polymerization of acrylic acid (AA)

2-acrylamido-2-methyl propyl sulfonic acid (AMPS) and PVA.Fouriertransform infrared (FT-IR) was used to confirm the chemical structure of the T-IPN hydrogel.In FT-IR spectra

the peak of C—O stretching shifts to low wave numbers.This is attributed to the formation of strong hydrogen bond between PVA and PAA and PAMPS.The crystallinity properties of T-IPN hydrogels were investigated by X-ray diffraction spectrogram (XRD) and scanning electron microscope (SEM).The results show that the hydrogel forms perfect IPN networks when the content of PVA is low.However

when the content of PVA is high

the crystallization of PVA increases

and phase separation is formed.The swelling properties of the T-IPN hydrogels were studied

the results show that the equilibrium swelling ratio of the T-IPN hydrogels ranges from 200 to 340.The T-IPN hydrogel exhibits completely different deswelling properties in acid solutions and basic solutions

and this T-IPN hydrogel exhibits discontinuous volume phase transition when the pH of the solution is about 9.0. The compression strength of T-IPN hydrogels was also studied.The results show that T-IPN hydrogels composed of linear polymer

flexible polymer network and rigid polymer network exhibit both high swelling ratio and high compression strength.When the swelling ratio of the T-IPN hydrogels is 180

the maximum compression strength of the hydrogel is about 12.1 MPa.Further investigation shows that the compression strength and compression strain are influenced by the composition and the swelling ratio of the hydrogels.