Introduction of pH‐sensitivity into mechanically strong nanoclay composite hydrogels based on N‐isopropylacrylamide

Abstract

AbstractpH-sensitive nanoclay composite hydrogels based on N-isopropylacrylamide (NIPA) were synthesized by copolymerization with cationic and anionic comonomers. Laponite nanoclay particles served as multifunctional crosslinkers, producing hydrogels with exceptionally high mechanical strengths, as measured by elongation at break. Cationic copolymer gels based on NIPA and dimethylaminoethylmethacrylate were prepared by aqueous free radical polymerization, adopting a procedure reported by Haraguchi (Adv Mater 2002, 14, 1120-1124. Without modification, this technique failed to produce anionic copolymer gels of NIPA and methacrylic acid due to flocculation of clay particles. Three methods were conceived to incorporate acidic MAA into nanoclay hydrogels. First, NIPA was copolymerized with acidic comonomer under dilute conditions, producing hydrogels with good pH-sensitivity but weak mechanical characteristics. Second, NIPA was copolymerized with methyl methacrylate, which was then hydrolyzed to generate acid sidegroups, yielding hydrogels that were much stronger but less pH sensitive. Third, NIPA was copolymerized with an acid comonomer following modification of the nanoclay surface with pyrophosphate ions. The resulting hydrogels exhibited both strong pHsensitivities at 37 °C and excellent tensile properties. Optical transparency changed during polymerization, depending on hydrophobicity of the components. This work increases the diversity and functionality of nanoclay hydrogels, which display certain mechanical advantages over conventionally crosslinked hydrogels.

Synthesis of thermoresponsive polysilsesquioxane with methoxyethylamide group and crown ether

“…In the IR spectrum of MCPSQ, as shown in Figure 2, the absorption of the hydroxyl group appears to be present besides the amide group. In our previous investigation on the formation of PSQ with a phenyl group, the 29 Si NMR spectrum showed signals corresponding to both the T 2 and T 3 structures. 45 Therefore, the structure of the polysiloxane main chain was speculated to consist of incomplete, but not randomly crosslinked, ladder and cage structures.…”

“…[27][28][29][30][31][32][33][34][35][36][37] The use of PSQ seems to be convenient for the introduction of such additional responsive functions. In particular, the silane coupling reagent with the low-molecular-weight organic group, which provides the thermoresponsive property, is expected to be a more useful material for the formation of the multi-functional PSQ.…”

High tensibility and pH-responsive swelling of nanocomposite hydrogels containing the positively chargeable 2-(dimethylamino)ethyl methacrylate monomer

“…All of the reported NC gels are anionic and swell at pH > 5, except for those described by Mujumdar that their NIPAm/DMAEMA NC gels started to shrink as the pH increased beyond eight; however, no details of the Laponite suspension stability with DMAEMA addition were provided [26]. In the present work, cationic NC gels containing the positively chargeable monomer DMAEMA were in situ copolymerized in a Laponite suspension.…”

“…In addition, Mujumdar and Siegel synthesized various pHresponsive NC gels by in situ copolymerization of NIPAm and some ionizible monomers, such as 2-(dimethylamino)ethyl methacrylate (DMAEMA), sodium methacrylate (SMA) and methacrylic acid. These gels showed elongation at break lower than 900% and a tensile strength lower than 100 kPa [26].…”

Solution Properties of Water-Soluble “Smart” Poly(N-acryloyl-N′-ethyl piperazine-co-methyl methacrylate)

“…In recent years, polymer systems that respond to more than one stimulus such as pH and temperature have received considerable research attention [11][12][13][14]. To prepare polymers that respond to more than one stimulus, monomers that are sensitive to certain stimuli have to be copolymerized.…”