To study the effect of adamantyl groups on the properties of temperature-sensitive hydrogels

hydrophobic monomer adamantyl methacrylate（AdMA）was synthesized and copolymerized with N-isopropylacrylamide (NIPAM).A series of temperature-sensitive P(NIPAM-co-AdMA) hydrogels with different content of AdMA were prepared.Fourier transform infrared (FTIR) spectroscopy was used to confirm the chemical structure of the resultant hydrogels.The peak of CO around 1714 cm-1 in FTIR spectra demonstrated that the AdMA units were successfully incorporated into the hydrogel network.The inner morphology of copolymer hydrogels was observed using an enviromental scanning electron microscope (ESEM).It is found that the morphology strongly depends on AdMA content.In a proper range(AdMA∶NIPAM≤3％)

with the increase of AdMA content

the copolymer hydrogels can form perfect porous structure

but when the AdMA content increases further

the porosity decreases

even the hydrogel surface becomes compact.The volume phase transition temperature (LCST) was characterized by differential scanning calorimetry (DSC).The results indicate that the LCSTs of the copolymer hydrogels decrease linearly with the increase of AdMA component

so it can be designed easily to obtain hydrogels with needed LCST.The equilibrium swelling ratios(SR) and the deswelling kinetics of the hydrogels were also measured gravimetrically.It is noteworthy that the swelling properties of the copolymer hydrogels can be optimized by the proportion of AdMA

with optimum AdMA content

the SR of the copolymer hydrogel can exhibt fast change with temperature

and the deswelling rate increase significantly.The hydrogel with 3% AdMA （AdMA∶NIPAM＝3％）can lose 92％ of water within 5 min and reach deswelling equilibrium within 10 min with a water retention below 4%.