• Polymer(Korea)
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• v.32 no.4
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• pp.359-365
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• 2008

We have fabricated a novel thermo-responsive nanofibrous surfaces by grafting PIPAAm by electron beam irradiation onto poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) nanofibrous mats. The electrospun PHBV nanofiber structures revealed randomly aligned fibers with average diameter of 400 nm. Increased atomic percent of nitrogen was observed on the PIPAAm-grafted PHBV mats after electron beam irradiation determined by ESCA. The amounts of PIPAAm-grafted onto PHBV films were $6.49{\mu}g/cm^2$ determined by ATR-FTIR. The PIPAAm-grafted surfaces exhibited decreasing contact angles by lowering the temperature from 37 to $20^{\circ}C$, while ungrafted PHBV surfaces had negligible contact angle change. This result indicates that PIPAAm surfaces, which are hydrophobic at the higher temperature, became markedly more hydrophilic in response to a temperature reduction due to spontaneous hydration of the surface-grafted PIPAAm. Thermo-responsive nanofibers showed good tissue compatibility. Cultured cells were well detached and recovered from the surfaces by changing culture temperature from 37 to $20^{\circ}C$.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1994.04a
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• pp.145-152
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• 1994

• Clean Technology
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• v.24 no.2
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• pp.112-118
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• 2018

Thermo-responsive polymers that exhibit phase transition in response to temperature change can be used as materials for smart windows because they can control solar light transmission depending on the outside temperature. The development of thermo-responsive polymers for smart windows that can be used over a wide temperature range is desirable. To obtain high performance smart windows materials, three-dimensional thermo-responsive poly(N-isopropylacrylamide) (PNIPAm) gels were prepared by free radical polymerization from monomer N-isopropylacrylamide, N, N'-methylenebis acrylamide (MBAm) as a crosslinking agent, ammonium persulfate (APS) as a strong oxidizing agent/tetramethylene diamine as a catalyst, and a mixture of two solvents (water/glycerol). This study examined the effect of glycerol content on the lower critical solution temperature (LCST), freezing temperature and the solar light transmittance of crosslinked PNIPAm gel films. The LCST and freezing temperature of PNIPAm gel films were found to be significantly decreased from 34.3 and $6.3^{\circ}C$ to 28.2 and $-6.5^{\circ}C$ with increasing glycerol content from 0 wt% to 10 wt%, respectively. It was found that the transparent PNIPAm gel films at $25^{\circ}C$ (temperature < LCST) were converted to translucent gels at higher temperature ($45^{\circ}C$) (temperature > LCST). These results suggested that the crosslinked PNIPAm gel materials prepared in this study could have high potential for application in smart glass materials.

• Macromolecular Research
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• v.15 no.4
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• pp.363-369
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• 2007

Novel biodegradable elastic hydrogels, based on hydrophilic and hydrophobic polymer blocks, were synthesized via the radical crosslinking reaction of diacrylates of poly(ethylene glycol) (PEG) and poly(${\varepsilon}-caprolactone$) (PCL). PEG and PCL diols were diacrylated with acryloyl chloride in the presence of triethylamine, with the reaction confirmed by FT-IR and $^1H-NMR$ measurements. The diacrylate polymers were used as building-blocks for the syntheses of a series of hydro gels, with different block compositions, by simply varying the feed ratios and molecular weights of the block components. The swelling ratio of the hydrogels was controlled by the balance between the hydrophilic and hydrophobic polymer blocks. Usually, the swelling ratio increases with increasing PEG content and decreasing block length within the network structure. The hydrogels exhibited negative thermo-sensitive swelling behavior due to the coexistence of hydrophilic and hydrophobic polymer components in their network structure, and such thermo-responsive swelling/deswelling behavior could be repeated using a temperature cycle, without any significant change in the swelling ratio. In vitro degradation tests showed that degradation occurred over a 3 to 8 month period. Due to their biodegradability, biocompatibility, elasticity and functionality, these hydrogels could be utilized in various biomedical applications, such as tissue engineering and drug delivery systems.

• Polymer(Korea)
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• v.37 no.4
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• pp.539-546
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• 2013

Amino group-terminated poly(N-isopropylacrylamide) (PNIPAAm-$NH_2$) was synthesized via a radical polymerization of N-isopropylacrylamide (NIPAAm) using 2-aminoethanethiol hydrochloride (AESH) as a chain transfer agent. The molecular weight of the PNIPAAm-$NH_2$ was controlled by changing the concentration of AESH. The LCST of the aqueous solution of PNIPAAm-$NH_2$ increased slightly with increasing the AESH concentration. Alginate-g-PNIPAAm copolymer was synthesized by grafting PNIPAAm-$NH_2$ onto sodium alginate using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide and N-hydroxysuccinimide. The formation of the grafted copolymers was confirmed by FTIR spectroscopy, solubility in water, and SEM-EDS. Alginate-g-PNIPAAm also exhibited swelling-deswelling behavior. However, it showed a LCST at a slightly increased temperature compared to PNIPAAm. The swelling ratio of the alginate-g-PNIPAAm hydrogel increased with the increase of the grafted PNIPAAm content.

• Polymer(Korea)
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• v.37 no.6
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• pp.784-793
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• 2013

A two-step method for obtaining poly(N-isopropylacrylamide) (PNIPAAm) from poly(acrylonitrile) (PAN) was investigated in order to find a feasibility of imparting thermo-responsive property onto textile fiber materials. PAN was converted to poly(acrylic acid) (PAA) by hydrolysis at a first-step, and then PAA was converted to PNIPAAm at a second step via an amidation reaction of PAA with isopropylamine (IPA) in DMF medium using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) as catalysts. High content of carboxylic groups at the first step was obtained by the successive alkaline and acid hydrolysis of PAN. The degree of conversion of PAA to PNIPAAm at the second step was dependent on the amount of catalysts EDC and NHS. PNIPAAm converted from PAA through amidation reaction showed a lower critical solution temperature (LCST) behavior when the conversion was higher than about 53%.

• Polymer(Korea)
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• v.38 no.5
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• pp.626-631
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• 2014

Water purification requires a large amount of energy that can cause pollution problems. For this reason, forward osmosis (FO) has attracted intense interest that required a relatively low amount of energy for water purification. The forward osmosis has a serious problem that it needs drawing agents creating osmotic pressure to extract water from contaminated water. In this study, a copolymer of zwitterionic moiety and an interpenetrating polymer network (IPN) hydrogel based on thermo-responsive polymer hydrogel, poly(N-isopropylacrylamide) (PNIPAM) were prepared and attached on FO membranes, which successfully played the role of drawing agents. In the copolymer hydrogel, its swelling ratio was improved, but thermo-sensitivity was decreased. The swelling ratio and thermo-sensitivity of IPN hydrogel was lowered. We could confirm that swelling ratio is related to osmotic pressure.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3187-3190
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• 2007

Elastin-Like polypeptide (ELP) composed of elastin-based repeating units is an artificial biomaterial which is biocompatible and non-immunogenic. ELP shows a characteristic inverse phase transition between hydrophobic and hydrophilic phase by external stimuli such as salt, pH and temperature. In this study, ELP coated PS (polystyrene) beads are packed in tubing and the thermo -responsive flow characteristics of the packed bed are investigated. Preliminary test results show that the control of the fluid flow can be achieved by using the temperature driven phase transition effect of the ELP coated beads in a microchannel.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.1
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• pp.67-71
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• 2009

This research is a new structure of the semiconductor substrate heating apparatus in which the assembly and expansion are possible. The fast thermo-responsive according to the direct heating structure of the heating plate layer adhering closely to the floor side of a substrate and the fast heat loss minimization can be accomplished. Moreover, the contact area of the sheath heater, which is the heating plate layer built-in heating apparatus, is increased, so that it has more heating valid area. There is no problem with the deformation interpreted in the state where it assembles the block of a several of the simulation result structure, the safety, and the stress. In addition, it is confirmed that building a large-size heating block is possible since the temperature deflection of the manufactured plate is lower than the standard value.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2391-2399
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• 2014

Novel dual responsive pectin hydrogels composed from poly(acrylamidoglycolic acid-co-vinylcaprolactam)/Pectin (PAV-PC) and also PAV-PC hydrogels are used as templates for the production of silver nanoparticles. 5-Fluorouracil is an anticancer drug and has been loaded in situ into PAV-PC hydrogels. Structure and morphology characterization of PAV-PC hydrogels were investigated by fourier transform infrared spectroscopy, differential scanning calorimetry, thermo gravimetric analysis, X-ray diffraction studies, scanning electron microscopy and transmission electron microscopy. The results revealed a molecular level dispersion of the drug in PAV-PC hydrogels. In vitro release of 5-fluorouracil from the PAV-PC hydrogels has been carried out in GIT fluids as well as in various temperatures. 5-Fluorouracil released from PAV-PC hydrogels was 50% at pH 1.2, and 85% at pH 7.4 within 24 h. The release profile was characterized with PAV-PC hydrogels and initial burst effect was significantly reduced in two buffer media (1.2 and 7.4), followed by a continuous and controlled release phase, the drug release mechanism from polymer was due to Fickian diffusion. In situ fabrication of silver nanoparticles inside the hydrogel network via the reduction of sodium borohydrate by PAV-PC chains led to hydrogel nanocomposites. The diameter of the nanocomposites was about 50-100 nm, suitable for uptake within the gastrointestinal tract due to their nanosize range and mucoadhesive properties. These nanocomposite PAV-PC hydrogels showed strong antimicrobial activity towards Bacillus subtilis (G+ve) and Escherichia coli (G-ve).