Ultralow Self-Cross-Linked Poly(N-isopropylacrylamide) Microgels Prepared by Solvent Exchange

Abstract

We found that the poly(N-isopropylacrylamide) (PNIPAm) synthesized by free-radical polymerization in organic phase could also form stable microgels in water through solvent exchange without chemical cross-linkers. Dynamic light scattering and transmission electron microscopy showed the larger swelling ratio and higher deformability of these microgels. Nuclear magnetic resonance and infrared spectroscopy indicated that the self-cross-linking structures in these microgels were attributed to the hydrogen atom abstraction both from the isopropyl tert-carbon atoms and the vinyl tert-carbon atoms in PNIPAm chains and the organic solvents were important assistants in the hydrogen abstraction behavior. Our discovery revealed that the self-cross-linking of PNIPAm chains is a common phenomenon within their freeradical polymerization process, whether in aqueous phase or in organic phase. Besides, the addition of second monomers will not affect the cross-linkage of the PNIPAm portion, which may be of great significance for the synthesis of various functional ultralow cross-linking PNIPAm microgels.

Dual pH- and Thermo-Sensitive Poly(N-isopropylacrylamide-co-allylamine) Nanogels for Curcumin Delivery: Swelling–Deswelling Behavior and Phase Transition Mechanism

“…Protons (H + ions) are attracted to the amine, amide, and carbonyl groups of the p(NIPAm-co-Am) NG sample [30]. When the p(NIPAm-co-Am) NG sample is placed in an aqueous solution, the existing functional groups crosslink with water [31]. At low pH, the p(NIPAm-co-Am) NG system undergoes protonation, allowing the drug to be delivered into the tumor's low pH microenvironment.…”

Aggressive strategies for regenerating intervertebral discs: stimulus-responsive composite hydrogels from single to multiscale delivery systems

“…, CMCS-HA microgels, size 4 μm), 217 free radical synthesis after emulsion polymerization ( e.g. , PNIPAAM microgels, size 0.6 μm), 218 or in reverse-phase microemulsion and microemulsion polymerization ( e.g. , EDC-HCl modified with NHS for photosensitive ALG microgels, size of 15–40 μm 219 ).…”

“…A microgel is a micron-sized hydrogel. Microgels of different particle sizes are prepared in different ways, with smaller microgels typically prepared by dispersive precipitation (e.g., CMCS-HA microgels, size 4 mm), 217 free radical synthesis after emulsion polymerization (e.g., PNIPAAM microgels, size 0.6 mm), 218 or in reverse-phase microemulsion and microemulsion polymerization (e.g., EDC-HCl modified with NHS for photosensitive ALG microgels, size of 15-40 mm 219 ). Larger microgels were produced by soft photolithography (e.g., recombinant silk protein microgels), size 70-110 mm, 220 microfluidics (e.g., phytoglycerate cross-linked CS microgels), size 127 AE 16 mm 221 and stop-flow photolithography (e.g., MBA cross-linked PNIPAAM snowflakelike microgels, size 50-150 mm 222 ).…”

Adsorption of soft NIPAM nanogels at hydrophobic and hydrophilic interfaces: Conformation of the interfacial layers determined by neutron reflectivity

“…In this work we studied the self-assembly and interfacial behavior of NIPAM nanogels crosslinked with 5% methylenebisacrylamide (MBA) -as a function of concentration and temperature at both air-water and solid-water interfaces, the latter using hydrophilic and hydrophobic modified-silicon substrates. The choice of low crosslinked nanomaterials was driven by the wide range of applications currently reported for these matrices [29,[58][59][60][61]. The surface activities of the nanogels at the air-water interface were measured using a force tensiometer.…”