Preparation and thermal response behavior of poly(N‐isopropylacrylamide‐co‐a crylic acid) microgels via soap‐free emulsion polymerization based on AIBN initiator

Abstract

Poly(N-isopropylacrylamide-co-acrylic acid) (poly(NIPAM-co-AA)) microgels with different copolymer compositions were prepared through soap-free emulsion polymerization at 80 C, and 2, 2 0 -azobisisobutyronitrile (AIBN) was used as initiator. Scanning electron microscope (SEM) characterization shows that the prepared microgels are regular and smooth and not easy to distort. Result of1 H-NMR characterization shows that with increasing of the initial concentration of AA (AA in feed), the AA content in polymer chains increases. The thermal response of microgels latex was investigated by UV-3010 spectrophometer through detecting the transmittance of the latex at different temperature in the range of 190-900 nm. The thermal response of the poly(NIPAM-co-AA) microgels was tested by dynamic light scattering (DLS). The results show that with the increase of AA content in polymer chains, the low critical solution temperature (LCST) of microgels latex first decreases and then increases. Still, with increasing of AA in poly(NIPAM-co-AA) microgels, the LCST of microgels first increases and then decreases. The basic reasons causing the changes of LCST of microgels latex and microgels are interpreted clearly in this article from the perspective of hydrogen bonding interaction.

Creating a smart textile via the self‐assembly of responsive polymer particles on poly(ethylene terephthalate) fibers

“…Copolymer particles of P(NIPAM–AA) were selected to combine with the fibers because the polymer is not only a multiresponsive polymer but can also provide a reactive functional group, that is, a carboxyl group. A series of P(NIPAM–AA) particles were synthesized with different ratios of AA to NIPAM, that is, AA ratios, by a soap‐free precipitation polymerization . The resulting particles were characterized with SEM (Figure S1, Supporting Information) and FTIR spectroscopy (Figure S2, Supporting Information).…”

“…In addition, the molecular conformation of responsive polymers can be converted between collapsed and swollen states by external stimuli, depending on the conditions . For example, the molecular chains of poly( N ‐isopropyl acrylamide) (PNIPAM) are in the expanded coil state, such that the polymer is swollen and hydrophilic at temperatures below its lower critical solution temperature (LCST) because of hydrogen bonds between the amide groups and water molecules, whereas the molecular chains collapse and become hydrophobic when the temperature is above the LCST because of hydrogen‐bond cleavage . The introduction of a charged comonomer into PNIPAM provides the ability to tune the LCST.…”

In situ synthesis of magnetic poly(N-tert-butyl acrylamide-co-acrylic acid)/Fe3O4 nanogels for magnetic resonance imaging

“…The bands at 1651-1658 cm À1 and 1546-1560 cm À1 were regarded as amide I (C]O stretching) and amide II (N-H bending), respectively. 26,27 The characteristic bands at 1627-1636 cm À1 and 984-994 cm À1 assigned to C]C of AA and TBA, which could not be found in the spectra of the P(TBA-co-AA) and P(TBA-co-AA)/Fe 3 O 4 nanogels, indicating that the AA and TBA monomers totally formed the P(TBA-co-AA) and P(TBA-co-AA)/Fe 3 O 4 nanogels in the process of polymerization. 28,29 Two characteristic bands for Fe-O stretching observed at 587-593 cm À1 and 464-467 cm À1 were found in the Fe 3 O 4 spectra.…”

“…2a, the bands at 2964-2968 cm À1 could be attributed to stretching and bending vibrations of C-H groups. 26 The characteristic band at 1705 cm À1 was assigned to the C]O stretching of AA. The bands at 1651-1658 cm À1 and 1546-1560 cm À1 were regarded as amide I (C]O stretching) and amide II (N-H bending), respectively.…”

Effects of end groups on the thermal response of poly(N‐isopropylacrylamide) microgels

“…When the environmental temperature is below the LCST, PNIPAM adsorbs much water and exhibits a swollen and hydrophilic state, whereas above the LCST; it becomes hydrophobic because of expelling free water inside the polymer network and demonstrates abrupt volume shrinkage. 4,5 Because of their unique properties, PNIPAM microgels have numerous potential applications in various biomedical and biotechnological fields, including controlled drug delivery systems, [6][7][8][9][10] sensing, 11 catalysis, 12 optical devices, 13 artificial organs, 14 "on-off" switches, 15 and so on.…”