Preparation and Characterization of Novel Temperature Sensitive Poly(N‐isopropylacrylamide‐co‐acryloyl beta‐cyclodextrin) Hydrogels with Fast Shrinking Kinetics

Abstract

Summary: Novel temperature sensitive poly(N‐isopropylacrylamide‐co‐acryloyl beta‐cyclodextrin) (P(NIPA‐co‐A‐CD)) hydrogels with fast shrinking rates were prepared by radical polymerization of NIPA, A‐CD and crosslinker in a mixture of water/1,4‐dioxane as solvent. Because the mixed solvent was a poor solvent for the copolymers, phase separation occurred during the polymerization, which resulted in a heterogeneous, porous structure of the hydrogels. In contrast to the normal PNIPA hydrogel and the homo P(NIPA‐co‐A‐CD) gel prepared in water, the P(NIPA‐co‐A‐CD) hydrogels synthesized in water/1,4‐dioxane as solvent exhibited higher swelling ratios at the temperature below the lower critical solution temperature (LCST) and shrunk rapidly to equilibrium within shorter time when the temperature was increased above LCST. Increasing the acryloyl beta‐cyclodextrin content in the gels led to a slight decrease of the swelling ratio at lower temperature and had no marked influence on the shrinking kinetics. The gels prepared in water/1,4‐dioxane, at different v/v ratios of 1.0/0.2, 0.8/0.4 and 0.6/0.6, showed similar properties.

Novel pH- and Temperature-Responsive Blend Hydrogel Microspheres of Sodium Alginate and PNIPAAm-g-GG for Controlled Release of Isoniazid

“…Water molecules take special orientations around the hydrophobic isopropyl groups to form "ice-berg" structures to decrease free energy of the system due to negative entropic contributions. When temperature is increased above the LCST, hydrogel structure gets disrupted, and hydrophobic groups of the polymer side chains become free (12,13). The resulting hydrophobic interactions between isopropyl groups of hydrogel lose a large amount of water and thereby change its volume dramatically.…”

Ultrafast Responsive Poly‐ (N‐isopropylacrylamide) Gel Produced by Cryostructuring of Self‐crosslinkable Polymer Microgels

“…Chemistry Diameter 8 mm and thickness 2 mm %5 min Grafting via co-polymerization with macromonomer [3] Rods 200 mm in diameter %10 min Poly(NIPAM-co-cholesteryl-and methacryloyl-substituted pullulan) [4] Diameter 20 mm and thickness %3-4 mm %1 min Copolymerization in water-dioxane mixture at 20 8C followed by ''freezing'' polymerization at À28 8C [6] Diameter 25 mm in and thickness 3 mm %1 min Polymerization in aqueous NaCl solutions [7] Diameter 2.3 cm %1 min Emulsion polymerization using polydimethylsiloxane [8] Diameter 25 mm and thickness 2 mm %5 min Poly(NIPAM-co-acryloyl b-cyclodextrin) crosslinked with BIS [5] Diameter 10 mm in and thickness 4 mm %3 min Polymerization in anhydrous DMSO at 0.5 8C, that is, below melting point of DMSO [9] Diameter 9 mm and thickness 3 mm <1 min Structuring of pNIPAM particles in a semi-frozen state (this study) a) Estimated from swelling degree versus time profiles as time needed to reach 90% of total response (shrinking).…”

“…Still, characteristic times give a clear indication that the strategies based on chemical modification, e.g., comb grafting [3] or copolymerization with another co-monomer [4,5] result in gels with characteristic times of 5 min and above (Table 1). The shortest response times of around 1 min were obtained for gels with clear porous structure produced either by emulsion polymerization [7] or phase separation polymerization [8] or polymerization in the semi-frozen system where crystals of frozen solvent perform as a porogen.…”

Temperature‐Sensitive Simultaneous Interpenetrating Polymeric Networks With Improved Mechanical Properties and Shrinking Kinetics

“…For the conventional PNIPAAm hydrogel, a thick and dense layer forms on the surface region, this prevents the inner water in the hydrogel from being further ejected out, so the process of reaching the new equilibrium state may be significantly delayed. [36][37][38] In our experiments, PNSi was incorporated into the conventional PNIPAAm networks by forming simultaneous IPN structures to improve the shrinking properties. As discussed above, there are two phase transition temperatures in IPN networks because copolymerization of MPTMS with NIPAAm lowers the LCST.…”