Synthesis of Macroporous Thermosensitive Hydrogels: A Novel Method of Controlling Pore Size

Abstract

Macroporous thermosensitive poly(N-isopropylacrylamide) hydrogels were synthesized in the presence of dodecyl dimethyl benzyl ammonium bromide (DDBAB). Poly(vinyl alcohol) (PVA) was involved to control the pore size of the hydrogels. The morphology of the resulting hydrogels was studied by both an optical microscope and a scanning electron microscope. Moreover, the pore size and its distribution were examined by mercury intrusion porosimetry. The results indicated that size of the pores decreased with the increase of the amount of PVA added. The mechanism was explained after dynamic light scattering measurement of the size of hydrophobic initiator DDBAPS aggregates that were formed in situ in PVA aqueous solutions of various concentrations as the product of the reaction between DDBAB and the water soluble initiator ammonium persulfate. Swelling ratio and deswelling/reswelling kinetics of the hydrogels were also measured to investigate the response properties of the hydrogels. It would be a promising method of pore size control for synthesizing hydrogels of other vinyl monomers that could be initiated by persulfates.

Study of the properties of hydrolyzed polyacrylamide hydrogels with various pore structures and rapid pH-sensitivities

“…3, pores could be found after the freeze-drying process. It has been reported that the freezedrying process can result in porous structures for conventional hydrogels and that various structures may be obtained when different freezing conditions are adopted [13,14,[27][28][29]. Pores in the dried gel NG were found to be unconnected holes, whereas those in the dried gel HNG were found to be stria-like and arranged regularly.…”

“…For both conventional and modified cryogels, partially absorbed water could be extracted when a compressive stress was applied directly on the gels (similar to sponges) (The procedure has been shown elsewhere [29].). The added compressive stress was increased until no more water could be squeezed or until the sample was squeezed into breakage.…”

“…DDBAPS existed in the reaction medium in the form of aggregates with a size of several hundred nanometers. Pore structures were adjustable when mixed solvent or poly vinyl alcohol (PVA) was used [28,29]. Interconnected pores of hydrated samples could easily be observed by ESEM at a low vacuum (5.2 Torr, %700 Pa) [27].…”

A novel thermo-responsive hydrogel based on salecan and poly(N-isopropylacrylamide): Synthesis and characterization

“…From the figure it was also observed that salecan/PNIPAm hydrogels had an even faster deswelling rate than pure PNIPAm hydrogels. In general, a dense skin layer would be formed to blocks water runoff when PNIPAm hydrogels were placed into ambience above their T p [23]. However, the introduction of hydrophilic component into the network could restrain the layer formation and provide channels for water molecules release [25].…”

Preparation of macroporous poly(N-isopropylacrylamide) hydrogels using a suspension–gelation method

“…In our earlier studies, we developed macroporous hydrogels that entrapped enzymes in the macropores [1] and hydrogels containing oil microdroplets of an extractant used for metal adsorption [2,3]. Porous polymeric hydrogels have been prepared by polymerization in the presence of inert diluents as pore-forming agents (porogens), such as surfactants [4][5][6], polymers (polyethylene glycol [7,8], poly(L-lactide) [9], poly(dimethylsiloxane) [10], sucrose [11], and alginate [12]), silica particles [13,14], and oils [15,16].…”