• Polymer(Korea)
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• v.36 no.5
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• pp.617-621
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• 2012

PHEAs [${\alpha}$,${\beta}$-poly(2-hydroxyethyl-DL-aspartamides)], a class of poly(amino acid), have been widely studied as biodegradable and biocompatible polymers for potential biomedical and pharmaceutical applications. In this study, we investigated a homogeneous blend of PHEA with poly(N-vinyl pyrrolidone) (PNVP) and its semi-IPN (semi-interpenetrating polymer network) gels. Blend films were prepared by a solution casting method. The resulting blends were totally transparent over the whole composition ranges and the single $T_g$, changing monotonously with composition, was observed by DSC to confirm the miscibility between these two polymers. FTIR was used to discuss the possible hydrogen-bonding interaction between polymers. In addition, semi-IPN type gels were prepared by chemical crosslinking of PHEA/PNVP blend solution using hexamethylene diisocyanate (HMDI) as a crosslinking reagent. The prepared gel was characterized by their swelling property and morphology.

• Polymer(Korea)
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• v.37 no.2
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• pp.240-248
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• 2013

The curing behaviors of diglycidyl ether of bisphenol A (DGEBA) with mercaptan hardener were studied by the comparison with amine-adduct type hardener. Curing behaviors were evaluated by DSC at dynamic and isothermal conditions. In the DSC, the dynamic experiments were based on the method of Kissinger's equation, and the isothermal experiments were fitted to the Kamal's kinetic model. Activation energy of epoxy/amine-adduct type hardener was ca. 40 kcal/mol. As the functional group of mercaptan hardener, -SH increased, on epoxy/mercaptan hardeners, the activation energies decreased from 28 to 19 kcal/mol. Epoxy/amine-adduct type hardener was initiated at $90^{\circ}C$ or higher. However, epoxy/mercaptan hardeners reduced the initiation temperatures below $80^{\circ}C$ and shortened the durations of curing reaction within 10 min. We found out that the reaction kinetics of epoxy with mercaptan hardener followed the autocatalytic reaction models, and the maximum reaction rates were shown at the conversions of 20~40%.

• Polymer(Korea)
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• v.37 no.2
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• pp.218-224
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• 2013

Graphene oxide (GO) was prepared by the Hummers and Offeman method from graphite. Two different types of functionalized graphene sheets (FGSs) were synthesized by using GO. Hexamethylamine (HDA) substituted vertically to the graphene sheet (Ver-HDA-GS) was synthesized from HDA and epoxy group in GSs. Whereas, horizontally substituted hexadecanol (HDO) to the GS(Hor-HDO-GS) was synthesized from HDO and alcohol groups via reduced GO (RGO), respectively. The structures of the GO, RGO, Ver-HDA-GS, and Hor-HDO-GS were identified by Fourier transform infrared (FTIR). In addition, we examined the thermal stability and morphology. Atomic force microscope (AFM) disclosed that Ver-HDA-GS consisted of one- or two-layer graphene regions. However, the Ver-HDA-GS layers showed average thickness of 1.76 nm. The thermal stabilities of the FGSs were better than those of the GO and RGO. The Ver- HDA-GS was well dispersed in common solvents such as dimethyl sulfoxide (DMSO), toluene, chloroform, and decalin.

• Polymer(Korea)
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• v.38 no.5
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• pp.602-612
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• 2014

Polyurethanes containing poly(dimethyl siloxane) (PDMS) unit, PU-Si, were synthesized and their thermal and shape memory properties were investigated. Various amounts of PDMS units were incorporated via a solution polymerization method using mixed diols of poly(tetramethylene ether glycol) (PTMEG) and PDMS-diol as the soft segment (SS) and methylene diphenyl diisocyanate and 1,4-butanediol as the hard segment (HS). Two series of PU-Si samples with an HS content of 23% or 32% were prepared and analyzed. For PU-Si with an HS content of 23%, both the cold crystallization temperature ($T_{cc}$) and melt crystallization temperature of the SS domain moved higher temperature with increasing PDMS content, while the melting temperature ($T_m$) of the SS domain remained unaffected. The increase in HS content from 23% to 32% resulted in the increased $T_m$ and disappearance of $T_{cc}$. The shape recovery of PU-Si flim with an HS content of 32% increased while its shape retention decreased as PDMS content increased.

• Polymer(Korea)
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• v.38 no.5
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• pp.645-649
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• 2014

The causes of residual stress in an injection molded part are high temperature variation and shear stress during molding process. Chemical cracking test is one of the methods of measuring residual stress and cracks are developed according to the degree of residual stress. In this study, the relationship between chemical cracking and exerted stress have been investigated. Deformation jig was designed and used to give a stress through deformation in a specimen. Specimens were molded by a hot press using polycarbonate (PC) and annealed to remove residual stresses in the specimens. Specimens were fixed in the deformation jig and immersed into the solvent to create cracks in the specimens. Solvents were prepared by using tetrahydrofuran and methyl alcohol. As stress accordance with the deformation in the specimen increased, the frequency and density of cracks in the specimen also increased. The results of this study can be used for the measurement of residual stress quantitatively in an injection molded PC product using a chemical cracking method.

• Polymer(Korea)
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• v.37 no.5
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• pp.579-586
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• 2013

Poly(vinyl alcohol)(PVA) nanocomposite films containing various saponite (SPT) clay contents were synthesized using a solution intercalation method. The thermal property, morphology, optical transparency, and gas permeability of the PVA nanocomposite films with various SPT contents in the range of 0 to 10 wt% were examined. PVA nanocomposite film containing 5 wt% SPT showed excellent thermal and gas barrier property. The hybrid films containing 5 wt% SPT were equibiaxially stretched with stretching ratios ranging from 150 to 250%. The clay dispersion, optical transparency, and gas permeability were also examined as a function of equibiaxial stretching ratio. The PVA nanocomposite films with various equibiaxial stretching ratios showed excellent optical transparency and barrier to oxygen permeability.

• Polymer(Korea)
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• v.37 no.5
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• pp.649-655
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• 2013

In order to use as supporters for the reinforced composite fuel cell membrane, poly(acrylic acid)-grafted porous polytetrafluoroethylenes (PTFEs) were prepared via introduction of poly(acrylic acid) graft chains by a radiation grafting method. FTIR was utilized to confirm the successful introduction of poly(acrylic acid) graft polymer chains into the porous PTFEs. Contact angles were examined to observe the hydrophilicity of the surface of the prepared substrates. The result indicates that the hyrophilicity of the surface in the prepared substrates increases with an increase in the number of hydrophilic polymer chains. FE-SEM, gurley number, and tensile strength were also utilized to characterize the prepared substrates.

• Polymer(Korea)
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• v.36 no.2
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• pp.202-207
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• 2012

Biodegradable poly(${\varepsilon}$-caprolactone)(PCL) microcapsules containing pseudomonas were prepared by W/O/W emulsion system. The characteristics and release behaviors of the microcapsules were investigated as a function of manufacturing conditions. The morphology and particle distribution of the microcapsules were observed by a scanning electron microscope and a particle size analyzer. The release behaviors of the pseudomonas were determined using a cell culture method. It was found that smooth and spherical microcapsules were formed by W/O/W emulsion system and particle size was in the range of 10 to 60 ${\mu}m$. The release behaviors of the pseudomonas were influenced by the manufacturing conditions. It was indicated that the increase of the surfactant content and stirring rate led to an increased release rate, resulting from the high specific surface area of the smaller particle size, and the increase of the PCL content provided the sustained release behaviors by the delay effect of diffusion in the release medium.

• Polymer(Korea)
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• v.38 no.6
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• pp.809-814
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• 2014

An array structure of conducting polymer microtubule was fabricated for an amperometric biosensor. 3,4-Ethylenedioxythiophene (EDOT) was electropolymerized in the microporous template membrane with poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonic acid) (PEDOT/PSS) composite as a binder. The array structure can provide enhanced current collecting capability due to large active surface area compared to the macroscopic area of the electrode itself. For a biosensor application, the array electrode was tested for $H_2O_2$ detection and showed very sluggish electrochemical response to $H_2O_2$. To enhance the detection efficiency to the oxidation of $H_2O_2$, gold was treated on the electrode by two different approaches: sputtering and electrochemical deposition. Gold treatment with either method greatly enhanced the sensitivity of the electrode to $H_2O_2$. So, conducting polymer microtubule array with gold treatment was expected to be a sensitive amperometric biosensor system based on the detection of $H_2O_2$.

• Polymer(Korea)
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• v.38 no.6
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• pp.767-773
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• 2014

Rheological and electrical properties of polystyrene (PS)/carbon nanotube (CNT) nanocomposites via coagulated precipitation were investigated. Chemical modification and surfactant wrapping of CNT to improve the dispersion of CNTs may reduce the intrinsic properties of pristine CNT. To avoid this problem, PS and CNTs were dissolved and dispersed in dimethylformamide and then PS/CNT nanocomposites were prepared by the coagulated precipitation of CNT-dispersed PS solution in water. The coagulated precipitation method was highly effective enhancing the electrical conductivity of nanocomposites. Furthermore, the effect of adding poly(styrene-co-divinylbenzene) crosslinked particles to PS matrix on the rheological and electrical properties was investigated. With the addition of the crosslinked particles, the electrical percolation threshold of CNT reduced to 0.25 wt% and electrical conductivity increased further. It is speculated that CNTs in the volume occupied by crosslinked particles helped electrical pathway formation.