Synthesis and Properties of PVA Enhanced P(AAEA-co-AA) Temperature Sensitive Hydrogels

Semi interpenetrating polymer networks (s-IPN) hydrogels composed of poly(vinyl acohol) (PVA), poly(4-acetyl acryloyl ethyl acetate-co-acrylic acid) [P(AAEA-co-AA)] were synthesized via solution polymerization using acrylic acid (AA), 4-acetyl acryloyl ethyl acetate (AAEA) and PVA. Fourier-transform infrared (FT-IR) was used to confirm the chemical structure of the s-IPN hydrogels. The results showed that the AAEA mainly existed as enol form, making the peak of C-O stretching in the IR spectra of PVA-P(AAEA-co-AA) flow to low wave numbers. This is attributed to the formation of strong hydrogen bonds between PVA, PAA and PAAEA. SEM macrographs revealed that PVA impenetrated into the P(AAEA-co-AA) ploymer networks homogeneously, and barricaded the phase separation of the hydrogels. XRD analyses showed that the hydrogels formed perfect s-IPN structure when the dosage of PVA was low. However, when the dosage of PVA was high, PVA could not impenetrate in P(AAEA-co-AA) ploymer networks homogeneously, making the crystallization of PVA increase significantly. The volume phase transition temperature (VPTT) of the s-IPN hydrogels was determined by their respective DSC thermograms of swollen hydrogel specimens. The results showed that the VPTT of the hydrogels ranged from 54.0 to 57.8 degrees C, and increased with the increasing dosage of PVA. The stress strength of s-IPN hydrogels was studied, the results showed that the s-IPN structure formed between PVA and P(AAEA-co-AA) improved the strength of the hydrogels significantly, and the maximum stress strength of the hydrogel was about 8.4 MPa. The temperature sensitivity of the s-IPN hydrogels was also investigated, the results showed that the hydrogels exhibited excellent temperature sensitivity. When the temperature was lower than VPTT, the hydrogels kept at a swelling state, but when the temperature was higher than VPTT, the hydrogels deswelled evidently.