• Journal of Sericultural and Entomological Science
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• v.34 no.1
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• pp.49-56
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• 1992

Treatment of vinyl monomers onto silk fiber modifies the properties of the original silk fiber considerably. This field has been the subject of investigation by many workers using chemical and radiation initiation. Many studies on the reaction conditions, polymerization mechanism, physical properties and practical performances of methacrylamide-treated silk fiber have been continued. However, the polymerization mechanism has not been clearly revealed yet and this remains ambiguously whether the grafting is formed on fiber or not. In general, it has been accepted that free radicals were formed and vinyl monomers were polymerized in silk fibroin by graft polymerization mechanism, while active sties were varied by the types of monomer and initiator as well as by the reaction conditions. On the other hand, there is another argument on polymerization mechanism, in which monomers are polymerized and impregnated in the internal side of the fiber by homopolymerization. Though a large number of analytical methods are used to examine the polymerization mechanism of methacrylamide-treated silk fiber, the results on the basis of thermal analysis are merely reported in this paper. In differential scanning calorimetry (DSC) analysis, the thermal decomposition behaviors of the methacrylamie-treated silk fibers were determined and compared to those of the controlled silk fibers. DSC curves obtained from the methacrylamide-treated silk fibers showed double peaks at around 290$^{\circ}C$ (A peak) and 320$^{\circ}C$ (B peak) which are attributed to the thermal decomposition of the methacrylamide polymer and silk fibroin fiber, respectively. The temperature of A and B peak shifted to higher value with the increase of add-on. Also, the moisture regain of the treated silk fibers increased with add-on.

• Polymer(Korea)
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• v.39 no.2
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• pp.235-239
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• 2015

In this work, we evaluated catalytic activity of LiOH, $Cu(acac)_2$ and n-butyltin hydroxide oxide hydrate in the early stage of the melt transesterification of isosorbide and bisphenol A as diol monomers and diphenylcarbonate for the melt polymerizaiton of polycarbonate. $Cu(acac)_2$ proved to be the most active catalyst for homopolymerization process, while the catalytic activity of LiOH was higher than the others in case of melt copolymerization depending on the catalytic mechanism and chemical structure of catalyst. We suggested that evaluation of catalytic activity can be used for selection of catalyst system in bio-based copolymerization of polycarbonate.

• Macromolecular Research
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• v.12 no.1
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• pp.100-106
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• 2004

We have prepared the polymethylene-bridged, dinuciear, half-sandwich constrained geometry catalysts (CGC)［Zr(η$\^$5/:η$^1$-C$\_$9/H$\_$5/SiMe$_2$NCMe$_3$)］$_2$［(CH$_2$)$\_$n/］［n=6(9), n=12(10)］by treating 2 equivalents of ZrCl$_4$with the corresponding tetralithium salts of the ligands in toluene. $^1$H and $\^$13/C NMR spectra of the synthesized complexes provide firm evidence for the anticipated dinuciear structure. In $^1$H NMR spectra, two singlets representing the methyl group protons bonded at the Si atom of the CGC are present at 0.88 and 0.64 ppm, which are considerably downfield positions relative to the shifts of 0.02 and 0.05 ppm of the corresponding ligands. To investigate the catalytic behavior of the prepared dinuciear catalysts, we conducted copolymerizations of ethylene and styrene in the presence of MMAO. The prime observation is that the two dinuclear CGCs 9 and 10 are not efficient for copo-lymerization, which definitely distinguishes them from the corresponding titanium-based dinuclear CGC. These species are active catalysts, however, for ethylene homopolymerization; the activity of catalyst 10, which contains a 12-methylene bridge, is larger than that of 9 (6-methylene bridge), which indicates that the presence of the longer bridge between the two active sites contributes more effectively to facilitate the polymerization activity of the dinuciear CGC. The activities increase as the polymerization temperature increases from 40 to 70$^{\circ}C$. On the other hand, the molecular weights of the polyethylenes are reduced when the polymerization temperature is increased. We observe that dinuciear metallocenes having different-length bridges give different polymerization results, which reconfirms the significant role that the nature of the bridging ligand has in controlling the polymerization properties of dinuclear catalysts.

• Journal of Sericultural and Entomological Science
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• v.34 no.2
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• pp.32-40
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• 1992

Many studies have been carried out on the graft finishing in order to improve the quality of silk fiber. Various vinyl monomers, for instance, styrene, methylmethacrylate, 2-hydroxyeth-ylmethacrylate and methacrylamide, have been used practically up to date. Among these monomers, methacrylamide has been applied as the most favourable monomer onto silk fibers in recent years. The polymerization mechanism about styrene- and methylmethacrylate-grafted silk fiber has been studied by many researchers. They proposed that free radicals were formed and vinyl monomers were polymerized in silk fibroin by graft polymerization mechanism, while active sites were varied by the types of monomer and initiator as well as by the reaction condition. In general. there is another Opinion that monomers are polymerized and impregnated in the internal side of the fiber by homopolymerization, which has not been proved experimentally yet More than 10 years have been passed since methacrylamide was applied on the silk fiber, and at the present time most finishings are being achieved by methacrylamide. However, no attention has been paid to the polymerization mechanism of the methacrylamide-treated silk fiber yeL In this paper, the treatments of methacrylamide on silk fibers were studied in aqueous solution using potassium persulfate as an initiator. The polymerization mechanism of the methacrylamide-treated silk fibers was investigated and analyzed on the basis of the results of infrared spectroscopy, amino acid analysis and scanning electron microscopy. From the results of these instrumental analyses, it can be suggested that polymerization mechanism about the methacrylamide-treated silk fibers is not performed by graft polymerization which has been accepted generally in styrene and methylmethacrylate-grafted silk fibers. The different mechanism is supposed to be due to the difference in monomer types, initiator types and treatment conditions.

• Applied Chemistry for Engineering
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• v.7 no.1
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• pp.75-82
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• 1996

Acrylic acid was graft-copolymerized on polyethylene film in the presence of additives such as acid and $FeSO_4(NH_4)_2SO_4{\cdot}6H_2O$ using peroxide grafting technique by ${\gamma}$-ray and electron beam, and the effect of $FeSO_4(NH_4)_2SO_4{\cdot}6H_2O$ and acid on the grafting yield was evaluated. The grafting mechanism and the physical property of grafted films were also examined. The results showed that the inclusion of $FeSO_4(NH_4)_2SO_4{\cdot}6H_2O$ in acidified acrylic acid grafting solution was extremely beneficial and led to a most unusual enhancement effect in the radiation grafting. In the other hand, inclusion of mineral acid in the grafting solution in the absence of $FeSO_4(NH_4)_2SO_4{\cdot}6H_2O$ could not lead to he suitable grafting reaction by the severe homopolymerization of acrylic acid. The addition of $H_2SO_4$, and HCl led to much higher grafting yield than $HNO_3$and $CH_3COOH$. It was shown that grafting yield of ${\gamma}$-ray irradiated-polyethylene was higher than that of electron beam irradiated polyethylene.

• Polymer(Korea)
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• v.36 no.1
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• pp.111-116
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• 2012

A functionalization of mesoporous materials with organosilane was carried out via a post-synthesis grafting method and $(n-BuCp)_2ZrCl_2$/methylaluminoxane (MAO) as subsequently immobilized on the functionalized mesoporous materials for ethylene polymerization. Organosilanes having amine, cyano or imidazoline group such as $N$-[(3-trimethoxysilyl)propyl]ethylenediamine (2NS), 4-(triethoxysilyl)butyronitrile (1NCy), 1-(3-triethoxysilylpropyl)-2-imidazoline (2NIm) were used for the surface functionalization of mesoporous materials. In the SBA-15/2NS/$(n-BuCp)_2ZrCl_2$ catalyst preparation, the amount of MAO in feed increased with an decrease in the Zr content of the supported catalyst, and Al content in the supported catalyst increased. The ethylene homopolymerization activity of SBA-15/2NS/$(n-BuCp)_2ZrCl_2$ dramatically increased as the amount of MAO in feed increased. Furthermore, when the immobilization time was 6 hrs, SBA-15/2NS/$(n-BuCp)_2ZrCl_2$ showed the highest activity. The activities of supported 2NS-, 1NCy-, 2NIm-functionalized catalysts decreased in the following order, SBA-15/2NS/ > SBA-15/2NIm/ > SBA-15/1NCy/$(n-BuCp)_2ZrCl_2$. 2NS and 2NIm which have two amine groups per silane molecule were shown to interact with $(n-BuCp)_2ZrCl_2$ strongly compared to 1NCy which has one amine group. Thus, the activities increased with an increase in the nitrogen and the Zr content of the supported catalysts.