• Carbon letters
• /
• v.11 no.1
• /
• pp.22-27
• /
• 2010

The precipitation polymerization of acrylonitrile (AN) was carried out in a mixture solution of dimethyl sulfoxide (DMSO) and water at $50{\sim}65^{\circ}C$ using ${\alpha},{\alpha}'$-azobisisobutyronitrile (AIBN) as an initiator. The increased molecular weight polyacrylonitrile (PAN) was prepared with increasing the $H_2O$/DMSO ratio from 10/90 to 80/20. The viscosity average molecular weight of $H_2O$/DMSO solvent was 4.4 times larger than that of $H_2O$/DMF solvent, and precipitation polymerization was accelerlated due to the far decreased chain transfer effect of DMSO. Based on the experimental results, the increased PAN molecular weight was regarded as the summation of two mechanisms: i) particle-particle aggregation and ii) particle-radical attachment. The theoretical equation derived from the mechanisms was well coincided with the experimental results showing the linear relationship between the viscosity average molecular weight and the H2O/DMSO ratio.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.25 no.5
• /
• pp.791-795
• /
• 1996

Toha-jeot(salt-fermented Toha shrimp) is a traditional fermented food in Korea. Toha-jeot is fermented for 90 days at $4\pm1^{\circ}C$ with 20%(w/w) salt per live Toha shrimp. We expect that the high polymer chitin of Toha shell will be hydrolyzed by chitinase during the fermentation of Toha-jeot and that the low molecular weight of chitin oligosaccharides will be produced. We experimented 7 samples which were taken at the interval of 15 days during the total 90 days of fermentation. We also measured molecular weight of Toha-chitin, viscosity and molecular weight distribution of chitin during fermentation of Toha-jeot, The decrease of viscosity and average molecular weight of chitin were observed as fermentation proceeds. Chitin oligosaccharide with $10^3molecular$ weight was low until 60 days fer-mentation. However, chitin oligosaccharide with $10^3molecular$ weight was high after 75 days fer-mentation. And chitin oligosaccharide with $10^2molecular$ weight were observed after fermenting Toha for 75 days and 90 days, but chitin oligosaccharide with 10'molecular weight did not appear up to 60 days of fermentation.ation.

• Korean Journal of Food Science and Technology
• /
• v.53 no.6
• /
• pp.695-700
• /
• 2021

The purpose of this study was to prepare low-molecular weight collagen using a commercial proteolytic enzyme (Protamex) from collagen extracted from feet of Korean native chicken and to investigate the quality characteristics of this collagen. The collagen content of Korean native chicken feet was 13.9 g/100 g, which was higher than the 6.21 g/100 g of general broilers. It was found that the content of low molecular weight collagen increased as the concentration of proteolytic enzymes and reaction time increased. In particular, reaction with 1% Protamex for 7 h resulted in 55.6% of low molecular weight (1,000-5,000 Da) collagen content, and the average molecular weight was 5,390 Da. Regarding the texture of the enzyme-treated collagen, the collagen with high molecular weight peptides decomposed into low molecular weight peptides, and the gel type could not be formed, whereas the sol type was maintained.

• Journal of the Korean Ceramic Society
• /
• v.25 no.5
• /
• pp.518-522
• /
• 1988

Polycarbosilane was synthesized from polydimethylsilane at 42$0^{\circ}C$, pyrolysis temperature with various times And IR, NMR, UV, and GPC were detected. Average molecular weight Mn was increased proportionally with the reaction time. Average molecular weight of polycarbosilane was about 700(n=20), which has chain structure and the product yield was 72%.

• Applied Chemistry for Engineering
• /
• v.33 no.6
• /
• pp.661-665
• /
• 2022

In this study, 2,5-dichlorobenzophenone was synthesized as a monomer using 1,4-dichlorbenzene, and subsequently, copolymers of benzoyl-p-phenylene and p-phenylene were prepared. The average molecular weight was improved using the low-molecular-weight polymer cutting method. The average molecular weight and glass transition temperature of the synthesized polymers were estimated. The as-prepared polymer was used as a hard coating material, and the coating was conducted on a poly(methyl methacrylate) plate. Furthermore, physical properties of the coatings, such as pencil hardness, adhesive strength, and abrasion resistance, were estimated. As the amount of p-phenylene in the copolymer increased, pencil hardness and abrasion resistance improved. The amount of p-phenylene in the copolymer can be increased to 30 mol% in order to increase the hardness of the coating, and the adhesive strength was insufficient for the copolymers with p-phenylene ratio greater than 35 mol%.

• Journal of the Korean Wood Science and Technology
• /
• v.49 no.1
• /
• pp.1-13
• /
• 2021

This study was conducted to investigate the effects of the synthesis method, melamine content, and GPC parameters (such as flow rate, column-detector temperature, and sample injection temperature) on the molecular weight of melamine-urea-formaldehyde (MUF) resins. Two different synthesis methods were employed. In the first method, MUF-A resins were synthesized by simultaneously reacting urea, formaldehyde, and melamine (5%, 10%, and 20%) using the reaction of alkaline-acid-alkaline steps under controlled temperature and viscosity. In the second method, MUF-B resins were synthesized by first reacting melamine at the same levels with formaldehyde and then by adding urea. The highest weight average molecular weight (Mw) of MUF-A resins was found at 10% melamine content when the flow rate was 0.3 and 0.8 ml/min; Mw decreased slightly at 20% melamine content. The results showed that Mw increased with an increase in the melamine content when the flow rate was 0.5 and 1.0 ml/min. In addition, Mw was the highest when the flow rate, column-detector temperature, and injection temperature were 0.3 ml/min, 50℃, and 25℃, respectively. On the contrary, MUF-B resins had greater Mw and number average molecular weight (Mn) than MUF-A resins. Overall, Mw and Mn increased as the melamine content increased. The optimal GPC parameter for MUF resins was determined as follows: a flow rate of 0.5 ml/min, a column-detector temperature of 50℃, and a sample injection temperature of 50℃.

• Journal of the Korean Chemical Society
• /
• v.4 no.1
• /
• pp.44-50
• /
• 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$^{\circ}C$.

• Journal of Environmental Health Sciences
• /
• v.27 no.2
• /
• pp.92-99
• /
• 2001

This present study was aimed to investigate the characteristics of dissoloved organic matter (DOC) in sewage. The results are summarized as follows ; The plateaux reached in 3~4 days by the biodegradability test on sewage samples based on DOC. 쏭 rations of BDOC to DOC were 48, 21, 13 and 11% for raw sewage, primary treatment effluent, secondary treatment effluent and final treatment effluent, respectively. As the SUVA values ranged less 3L/m.mg for the effluent of sewage treatment plant, the DOC is composed largely of non-humic materials, hydrophilic, less aromatic as compared to waters with higher SUVA values. Through the biodegradability test, Dissolved organics showed that the quantity of LMW(Low Molecular Weight) less than 1,000 daltons was decreased, HMW(High Molecular Weight) more than 30,000 daltons had a tendency to increase. Large portion of UV$^{254}$ in final treatment effluent was increased of MMW(Medium Molecular Weight). Also, average removal efficiency of DOC was 32% during sewage treatment.

• Polymer(Korea)
• /
• v.27 no.4
• /
• pp.358-363
• /
• 2003

Dispersion polymerization of acrylamide was carried out in the media of ethyl alcohol/water mixtures using hydroxypropyl cellulose and ammonium persulfate as steric stabilizer and initiator, respectively. The effects of concentrations of initiator and steric stabilizer, amount of monomer, polymerization temperature, ethyl alcohol/water ratio, and purification of monomer and nitrogen purge on the particle size of the latices and molecular weight of the polymers were investigated. The average particle diameter increased with increasing concentration of initiator, water content in ethyl alcohol/water media, and polymerization temperature, but decreased with monomer and stabilizer concentrations. The viscosity average molecular weight increased with increasing concentrations of monomer, steric stabilizer, and water content in dispersion media, but decreased with initiator concentration and polymerization temperature. The PAM polymers prepared with the purified monomer and the nitrogen purging before the reaction showed the highest molecular weight. In this study, PAM latices of 0.5∼2.4 $\mu\textrm{m}$ with 20000∼335000 in M$\_$v/ were prepared and the resulting PAM latices were all dissolved in water instantly.

• Bulletin of the Korean Chemical Society
• /
• v.13 no.1
• /
• pp.26-29
• /
• 1992

Copolymers with two different side groups, 2,2,2-trifluoroethoxy and p-chlorophenoxy groups, have been synthesized by reaction of poly(dichlorophosphazene) with their sodium salts, and characterized by elemental analysis, gel permeation chromatography, IR and NMR spectroscopies. The molecular weight measurement has shown that the weight average molecular weight, ${\bar{M}}_w$ of the copolymers are all above $10^6$ and their molecular weight distributions are monomodal and narrow (${\bar{M}}_w/{\bar{M}}_n<4$). Thermal properties of these copolymers measured by DSC and TGA exhibited to be intermediate between those of the two corresponding homopolymers.