• Journal of the Korean Chemical Society
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• v.4 no.1
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• pp.44-50
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• 1957

Fibrous cellulose triacetate prepared from purified cotton under various temperatures was dissolved in the solution of 70%, monochloroacetic acid and it was fractionated using water as a precipitant. Eight fractions were obtained through the stepwise precipitation. Degree of polymerization and molecular weight of each fraction were measured viscometrically. Integral and differential molecular weight distribution curve were drawn for each sample prepared under various temperatures and were carefully observed. On this experimental study, following conclusions were obtained: Fractional precipitation can be carried out for fibrous cellulose triacetate in the solution of 70% monochloroacetic acid using water as a precipitant. The differences on the shapes of molecular weight distribution curve were occured on account of the various acetylation temperatures. At the relatively higher acetylation temperatures, the cellulose was randomly degraded and the portion of low degree of polymerization was increased. Commercial acetate, therefore, may not be prepared at above 40$^{\circ}C$ according to the molecular weight distribution curve regardless of higher viscosity and average degree of polymerization. It was concluded that the optimum acetylation temperature for commercial acetate was approximately 30$^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4122-4126
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• 2012

Cellulose-graft-poly (L-lactide) (cellulose-g-PLLA) was successfully prepared via ring-opening polymerization (ROP) by using 4-dimethylaminopyridine (DMAP) as an organic catalyst in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). The structure and morphology of the polymer was characterized by nuclear magnetic resonance (NMR) and transmission electron microscope (TEM). From wide-angle X-ray powder diffraction (WAXD) and degradation test (by acid, alkaline, PBS and enzyme solution), changes in the crystalline structure as a result of degradation was also investigated. The results indicated that materials which have low degree of crystallinity showing higher degradability, however, in acid liquor, enzyme solution, alkaline liquor and PBS system, the degradation rate of the polymer decreased by the above sequence. Moreover, with the further increase of graft degree of this material, its degradation degree decreased.

• Applied Chemistry for Engineering
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• v.8 no.6
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• pp.886-892
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• 1997

There are many methods to synthesize polystyrene latex. Emulsion polymerization technique is commonly used commercially, but it requires a new technology to replace a traditional polymerization method because of the disadvantage of chemical initiator for environmental pollution. Since free radicals can be produced by ultrasound energy effect, polystyrene latex was synthesized using ultrasound energy instead of chemical initiator. As the ultrasonic irradiation time was increased, average molecular weight was increased and polydispersity was decreased. The degree of polymerization was increased with the concentration of SDS and maximum degree of polymerization was shown at 2wt.% SDS concentration and the reaction temperature of $40^{\circ}C$. During the course of polymerization, molecular weight was repeatedly fluctuated because of occurrence of depolymerization. Narrow molecular weight distribution polystyrene latex having controlled molecular weight was synthesized by controlling ultrasonic irradiation time and the concentration of SDS.

• Fashion & Textile Research Journal
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• v.6 no.3
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• pp.384-392
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• 2004

The purpose of this study is in development of effective filter-type polymer adsorbent for removal of pollutants from wastewater by UV irradiation graft polymerization. Photografting of acrylic acid (AA) on polypropylene (PP) nonwoven fabric using benzophenone (BP) as a photosensitizer was investigated. Inhibition of homopolymerization was achieved by adding various concentrations of $FeSO_4{\cdot}7H_2O$, $CuSO_4{\cdot}5H_2O$ and Mohr's salt. As AA concentration was increased, the degree of grafting was increased as to a specific value and then decreased, and the effect of BP concentration showed the same tendency. It was also found that the degree of grafting increased with reaction time and reaction temperature. Addition of the polyfunctional monomers and $H_2SO_4$ to the grafting system accelerated the photografting. The melting temperature, molecular weight and breaking stress and breaking strain were decreased with the increase in the degree of grafting.

• Korean Journal of Human Ecology
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• v.2 no.1
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• pp.142-148
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• 1999

Tencel fabrics were treated with cellulase after mechanical prefibrillation treatment. SEM analysis was carried out to study morphological change of the treated fabric. The cellulase-treated Tencel fabrics were evaluated for weight loss and tensile strength. X-ray diffraction method, moisture regain, and K/S value were used to elucidate crystalline structural changes occurred by cellulase treatment. Degree of polymerization and copper number of the cellulase-treated fabrics were also measured to estimate effect of hydrolysis. SEM analysis indicated that with treatment of prefibrillation and cellulase, fibrils were produced and damage occurred deep into the fiber. Increases in concentration and time of cellulase treatment increased weight loss and decreased tensile strength retention of the treated fabrics. As cellulase hydrolysis progressed, degree of crystallinity, moisture regain and K/S value were not much changed. (Korean J Human Ecology 2(1) : 142∼148, 1999)

• Applied Chemistry for Engineering
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• v.17 no.3
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• pp.303-309
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• 2006

In this study, functional anion-exchange membranes have been prepared and characterized to improve the permeation fluxes of the anion and urea for peritoneum dialysis. They were prepared by UV and radiation graft polymerization methods. The separation-membrane prepared by UV graft polymerization showed the highest grafting degree when HEMA and VBTAC were mixed by 1:2 ratio. However, the grafting degree decreased slightly at compositions above the 1:2 ratio because of the disruption of UV penetration caused by build-up of homopolymer. In the case of photo-initiator, the grafting degree increased up to 0.2 wt%, above which it decreased to a small extent. For the two membranes prepared by radiation graft polymerization, the VBTAC/HEMA membrane showed 96% grafting degree for 6 h reaction time and the GMA membrane showed over 100% grafting degree for 2 h reaction time. Anion-exchange membranes were prepared with 113% grafting degree and with DEA and TEA exchange groups. The DEA membrane showed the conversion degree of 70% in 4 h reaction time while the TEA membrane showed 30% in 2 h reaction time. The prepared anion-exchange membranes were permeable to only anions and urea, but not cations.

• Applied Biological Chemistry
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• v.39 no.6
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• pp.477-481
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• 1996

It has been shown that tannins have adverse effects on growth of animals and feed utilization. Tannins are usually classified into hydrolyzable and condensed types but the adverse effects are more marked in condensed tannin in hydrolyzable tannin. Furthermore, the principle condensed tannins found in banana fruits are pro types by the polymerization of flavan-3, 4-diols either alone or in combination with other flavonoids such as catechins. Tannin of the investigated banana(Banana; Musa sapientum LINN)fruits was fractionated into four or five molecular forms, according to the degree of polymerization by chromatography on a column of Sephadex LH-20. The protein-precitating capacity of the fraction noted tannins increased in degree polymerzation. The inhibitory effect of tannins on trypsin(EC 3. 4. 21. 4), ${\alpha}-amylase$(EC 3. 2. 1. 1) and lipase(EC 3. 1. 1. 3) activities in vitro also increased with the incraesed in degree of polymerization.

• Current Optics and Photonics
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• v.6 no.4
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• pp.381-391
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• 2022

Two-photon-polymerization additive-manufacturing systems feature high resolution and precision. However, there are few reports on specific methods and possible problems concerning the use of small lasers to independently build such platforms. In this paper, a femtosecond-laser two-photon-polymerization additive-manufacturing system containing an optical unit, control unit, monitoring unit, and testing unit is built using a miniature femtosecond laser, with a detailed building process and corresponding control software that is developed independently. This system has integrated functions of light-spot detection, interface searching, micro-/nanomanufacturing, and performance testing. In addition, possible problems in the processes of platform establishment, resin preparation, and actual polymerization for two-photon-polymerization additive manufacturing are explained specifically, and the causes of these problems analyzed. Moreover, the impacts of different power levels and scanning speeds on the degree of polymerization are compared, and the influence of the magnification of the object lens on the linewidth is analyzed in detail. A qualitative analysis model is established, and the concepts of the threshold broadening and focus narrowing effects are proposed, with their influences and cooperative relation discussed. Besides, a linear structure with micrometer accuracy is manufactured at the millimeter scale.

• Fibers and Polymers
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• v.5 no.2
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• pp.89-94
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• 2004

N-Vinylcarbazole (VCZ) was solution-polymerized in tetrahydrofuran (THF) at 25, 35, and $45^{\circ}C$ using a room temperature initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (ADMVN); the effects of amount of solvent, polymerization temperature, and initiator concentration were investigated. On the whole, the experimental results corresponded to predicted ones. Room polymerization temperature using ADMVN proved to be successful in obtaining poly(N-vinylcarbazole) (PVCZ) of high molecular weight with small temperature rise during polymerization, nevertheless of free radical polymerization by azoinitiator. The polymerization rate of VCZ in THF was proportional to the 0.47 power of ADMVN concentration. The molecular weight was higher and the molecular weight distribution was narrower with PVCZ polymerized at lower temperatures. For PVCZ prepared in THF at $25^{\circ}C$ using ADMVN concentration of 0.00005 mol/mol of VCZ, weight-average molecular weight of 221,000 was obtained, with polydispersity index of 2.05, and degree of lightness converged to about 99%.

• Particle and aerosol research
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• v.11 no.4
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• pp.107-113
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• 2015

SBA-16 (Santa Barbara Amorphous) was synthesized over supported $TiCl_4/MgCl_2$. Due to its high surface area and excellent morphological performance, it was expected to form the bi-supported catalytic system and be used for ethylene polymerization. Polymerization of ethylene was carried out at atmospheric pressure using hexane as solvent and triethylaluminium as cocatalyst. ICP, FTIR, DSC, TG-DTA were used to characterize polyethylene and catalyst product. Optimum conditions for ethylene polymerization were found to be 100 mL hexane, Al/Ti molar ratio of 160 and 1 h polymerization at $60^{\circ}C$. The activity of 396.76 kg PE/mol Ti.h.atm was achieved. Melting point of the obtained polymer was in the range of $132-135^{\circ}C$ and the highest degree of crystallization was 46%.