Papers by Keyword: Poly(N-isopropylacrylamide)

Abstract: A novel graded hydrogel based on poly(N-isopropylacrylamide) (PNIPAM), which is characterized with both ends of slightly cross-linked PNIPAM chains being grafted onto cross-linked PNIPAM chains, has been successfully prepared in a three-step process by a method of sequential synthesis for the first time in this paper. In the preparation of the graded hydrogels, with decreasing the crosslinker dosage, the swelling ratio of the hydrogel increased. The graded hydrogel displays faster and hydration/dehydration dynamic response to temperature cycling owing to slightly cross-linked PNIPAM chains to form big-hole structure. The proposed hydrogel structure provide a new mode of the phase transition behavior for thermo-sensitive "smart" or "intelligent" monodisperse micro-actuators, which is highly attractive for targeting drug delivery systems, chemical separations, sensors and so on.

Abstract: The thermo-responsive hydrogels poly(N-isopropylacrylamide) (PNIPAm) were synthesized by frontal polymerization (FP) in dimethylsulfoxide (DMSO) and ethanol mixture. The effects of composition of synthesis-solvent on FP feature and porous morphologies as well as their response behavior of the final products were studied. PNIPAm hydrogel synthesized in mixture exhibited a porous structure, which was responsible for its higher swelling ratio. Moreover, an improvement in swelling capability of the final PNIPAm hydrogel was found when the ethanol content in mixed media was elevated. The approach, frontal polymerization in mixed solvent, reported here provides a promising option to synthesize porous intelligent hydrogels PNIPAm.

Abstract: A temperature-sensitive N-isopropylacrylamide (NIPAAm) grafted cotton fabric was prepared by the plasma-induced graft polymerization technique. The surface morphology of the grafted fabric was observed from field scanning electron microscopy (FSEM). Fourier transform infrared spectroscopy (FTIR) and DSC were used to characterize the structure and thermal property of the grafted fabric. The results showed that the PNIPAAm was grafted onto cotton fabrics. The DSC analysis results indicated that LCST value of the grafted fabric was around 32 °C. The water permeation flux of the grafted fabric varied dramatically with a slight change at temperature around the LCST, which showed that the grafted PNIPAAm could act effectively as a chemical valve to control the on-off behavior of cotton fabrics.

Abstract: In this article, a novel structure poly(N-isopropylacrylamide) (PNIPAM) hydrogel, which is featured with both ends of linear PNIPAM chains being grafted onto semicircular and cross-linked PNIPAM chains, has been successfully prepared in a three-step process by a method of sequential synthesis for the first time. The proposed hydrogel displays faster and hydration/dehydration dynamic response to temperature cycling owing to linear PNIPAM chains to form big-hole structure. This work may be highly attractive for targeting drug delivery systems, polymeric machinery, and sensors and so on.

Abstract: The microgels with semi-interpenetrating polymer network (semi-IPN) structure based on cross-linked poly(N-isopropylacrylamide) (PNIPAM) and linear poly(acrylic acid) (PAA) were fabricated by one-step precipitation polymerization technique. The chemical composition of the microgels was determined by Fourier transformation infrared spectroscopy and elemental analysis. It was found that the PAA content inside the microgels decreased as the pH value of reaction media increased. The semi-IPN structure of the microgels was confirmed by transmission electron microscopy using uranyl acetate staining method. The pH dependent hydrodynamic diameters obtained by dynamic light scattering revealed that these microgels can reversibly shrink and swell in the pH range from 4.0 to 6.0. The semi-IPN microgels synthesized at pH 3.0 could undergo about 120 times volume change in the pH range.

Abstract: N-isopropylacrylamide was synthesized in a mixture of DMF and THF ( 7:3 in volume ratio) and characterized by FT-IR. The behavior of poly(N-isopropylacrylamide) chain was studied by spectrometer in mixtures of water with DMF and THF. Cononsolvency phenomena were found to be temperature-dependent, as demixing occurred upon increasing temperature. A significant shrinkage of polymer chains and deswelling of polymer gels, followed by phase separation, were observed for high water fractions.

Abstract: In this paper, temperature-sensitive PET fabrics were prepared by Ar-plasma-induced simultaneous grafting Ploy-N-isopropylacrylamide (PNIPAAm) onto PET fabric. Fourier transform infrared spectroscopy (FTIR) was used to identify the structure of the grafted fabric. Then the surface morphology of the grafted fabric was observed from scanning electron microscopy (SEM) and AFM. The results show that the PNIPAAm was grafted onto PET fabrics, respectively. The grafted PET fabrics are characterized by differential scanning calorimetric analysis (DSC). The DSC analysis results indicated that LCST value of the grafted fabric was around 32°C. And the water permeability of the grafted sample showed a sharp change around 32°C. It was proved that grafted fabric was sensitive to temperature.

Abstract: Submicron-sized monodisperse and spherical poly(N-isopropylacrylamide-co-glycidyl methacrylate)-β-cyclodextrin (PNG-CD) microgels with both thermo-responsive and molecular-recognition characteristics have been successfully fabricated via soap-free emulsion polymerization and subsequent chemical modification method. The thermo-responsivity of the microgels is based on the volume phase transition of poly(N-isopropylacrylamide) (PNIPAM) and the molecular-recognition property is based on the host-guest inclusion complexation of β-cyclodextrin (β-CD) units with specific guest molecules. The as-prepared microgels are characterized by Fourier transform infrared (FT-IR), scanning electron microscope (SEM), and dynamic light scattering (DLS) instrument. When β-CD is introduced onto the PNG-CD microgels, the volume phase transition temperature (VPTT) of resultant PNG-CD microgels shifts about 6 °C to a higher temperature in comparison with that of corresponding PNG microgels. When the β-CD units in PNG-CD microgels recognize 8-anilino-1-naphthal-enesulfonic acid ammonium salt (ANS) molecules in aqueous solution, the VPTT of PNG-CD microgels shifts around 3 °C negatively to a lower temperature. PNG-CD microgels present molecular-recognition induced swelling characteristics at fixed temperature. The results in this study provide valuable information for development of monodisperse and spherical dual thermo-responsive and molecular-recognition microgels which have potential applications in the fields of microscale molecular sensors and actuators and so on.

Abstract: The synthesis of thermo-responsive hydrogels poly(N-isopropylacrylamide )(PNIPAm) by frontal polymerization (FP) was carried out in four mixed solvents, i.e. dimethylsulfoxide (DMSO) mixing with water, ethanol, tetrahydrofuran (THF) and acetone, respectively. The influences of mixed solvent on frontal parameters, pore morphologies, swelling behavior of PNIPAm hydrogels were investigated. The pore of PNIPAm hydrogel synthesized in THF/DMSO was observed a big honeycomb cells, others were channel-like cells. Furthermore, the sample obtained in THF/DMSO had higher swelling ratio as compared to others, and the one synthesized in Water/DMSO showed the lowest. Above results indicated that fine-tuned poly(N-isopropylacrylamide) hydrogels can be prepared in short time and with easy protocol by adjusting mixed solvents in frontal polymerization process.

Abstract: Poly(N-isopropylacrylamide)(PNIPAM) with terminal aromatic groups were synthesized by atom transfer radical polymerization (ATRP), using N-isopropylacrylamide as monomer and phenyl 2-chloropropionate, (4’-phenyl)phenyl 2-chloropropionate and (2’,6’-diphenyl)phenyl 2-chloropropionate as initators. Then novel functional complexes of poly(N-isopropylacrylamide) and Eu(III) (PNIPAM-Eu(III)) with thermosensitive and fluorescent properties were synthesized and characterized by X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy. Eu(III) was bonded to nitrogen and oxygen atoms in the polymer chain of PNIPAM and formed the complexes of PNIPAM-Eu(III). The lower critical solution temperatures (LCSTs) of PNIPAM-Eu(III) were slightly greater compared with that of PNIPAM. Europium(III) complexes had excellent fluorescence performance, the fluorescence spectrum present characteristic emission of Europium(III) at 613 nm.