Temperature‐responsive characteristics of poly(N‐isopropylacrylamide) hydrogels with macroporous structure

Abstract

Macroporous poly(N‐isopropylacrylamide) (PNIPA) hydrogels were synthesized by free‐radical crosslinking polymerization in aqueous solution from N‐isopropylacrylamide monomer and N,N‐methylenebis (acrylamide) crosslinker using poly(ethylene glycol) (PEG) with three different number‐average molecular weights of 300, 600 and 1000 g mol−1 as the pore‐forming agent. The influence of the molecular weight and amount of PEG pore‐forming agent on the swelling ratio and network parameters such as polymer–solvent interaction parameter (χ) and crosslinking density (νE) of the hydrogels is reported and discussed. Scanning electron micrographs reveal that the macroporous network structure of the hydrogels can be adjusted by applying different molecular weights and compositions of PEG during polymerization. At a temperature below the volume phase transition temperature, the macroporous hydrogels absorbed larger amounts of water compared to that of conventional PNIPA hydrogels, and showed higher equilibrated swelling ratios in aqueous medium. Particularly, the unique macroporous structure provides numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to external temperature changes during the swelling and deswelling process. These macroporous PNIPA hydrogels may be useful for potential applications in controlled release of macromolecular active agents. Copyright © 2006 Society of Chemical Industry

A Novel Double‐Network, Self‐Healing Hydrogel Based on Hydrogen Bonding and Hydrophobic Effect

“…With the increase of PU monomer content, EWC is decreasing and ν c increases gradually. This is mainly because, with the increase of PU content, the rigidity of hydrogels and the “hydrophobic bonding” inside hydrogels are enhanced, which in turn leads to the physical crosslinking inside hydrogels, all of which are conducive to the improvement of tensile strength of hydrogels (as shown in Figure 5d).…”

Preparation and properties of fast temperature-responsive soy protein/PNIPAAm IPN hydrogels

“…Therefore, various strategies have been proposed to improve the response rate. These strategies include the introduction of comb-type grafted chains, 16,17 the fabrication of microgels 18 or nanogels, 19,20 and the formation of macroporous structures in hydrogel matrices using pore-forming agents, 21,22 foaming agents 23,24 and phase separation technologies. 25,26 In a previous work, the preparation and properties of soy protein/PNIPAAm IPN hydrogels were discussed.…”

Effect of hydrophobic comonomer content on assembling of poly (N‐isopropylacrylamide) and thermal properties

“…According to previous researches, LCST of PNIPAM could be influenced by conjugating the ionizable groups to PNIPAM chain 12, 13. Although many PNIPAM based hydrogels which showed temperature‐dependent drug release have been developed by chemically crosslinking,14–17 but the physically cross‐linked PNIPAM hydrogels are rare. Moreover, the researches on the effects of hydrophobic moiety on the properties of NIPAM have not been well investigated yet.…”