Hydroxypropyl cellulose를 이용하여 제조한 cholestric gel의 액정특성 및 팽윤거동

마영대,김경희 단국대학교 1999 산업기술연구 Vol.1 No.-

The hydroxypropyl cellulose(HPC) with decree of substiturion DS ?? 2.7 and molar substitution MS = 4.9 was prepared by reaction of alkali cellulose with propylene oxide in an autoclave(10bar) at 70℃ for 16hr, and the HPC solid films crossliked with glyoxal, retaining cholestric liquid crystalline order, were prepared by casting the liquid crystalline solution in water. The liquid-crystalline properties of HPC itself and the crosslinked films and the anisotropic swelling behaviour of the corsslinked films in water were investigated. The HPC displays reflection colors in the temperature range about 30-150℃. The circular dicroism(CD) spectra of HPC show negative CD with the wavelength at the peak increasing with temperature, suggesting that the HPC has a right-handed helicoidal structure whose pitch increase with temperature. The crosslinked films display fingerprint patterns in the temperature range about 30-180℃, showing that the pitch of crosslinked films is longer than that of HPC itself. The pitch of crosslinked films increases with increasing temperature and concentration of crosslinking agent. The weight and volume swelling ratios for crosslinked films decrease with increasing of crosslinker concentration. The crosslinked films did not show preferred direction of swelling, suggesting that the three-dimensional crosslinking preferentially performs between HPC molecules under our experimental condition. The density of the crosslinked films increases with increasing crosslinking agent concentration.

폴리메틸렌 스페이서로 연결된 Cholesterol-twins의 합성과 이들의 열방성 액정의 특성

마영대,정승용,최정훈 단국대학교 2001 산업기술연구 Vol.2 No.-

Cholesterol-twins connected with central methylene chains (Cho-TW-n, where n, the number of methylene group, is 2, 4, 6, or 8) were prepared, and their thermal and mesomorphic properties were investigated. Among the samples, only Cho-TW-4 exhibited an enantiotropic cholesteric phase and the remainder a monotropic one. The monotropic isotropic-cholesteric and crystallization temperatures of the derivatives decreased irregularly with increasing n up to 6, after which they were virtually constant. All samples, which exhibit reflection colors over the full cholesteric range, formed left-handed helicoidal structures whose optical pitches (λ_ms) decrease with increasing temperature. It was also found that the temperature dependence of λ_m was virtually identical for all compounds. However, the magnitude of λ_m at the same temperature was sensitive to n.

N-hydroxypropy 1 chitosan과 N,O-hydroxypropy1 chitosan의 합성 및 액정성에 관한 연구

마영대,정종현 단국대학교 1999 論文集 Vol.34 No.-

N-hydroxypropyl chitosans(N-HPCTOs) were prepared by reaction of chitosan with propylene oxide in the solvent mixture of water and ethanol, The derivatives with different total degree of substitution(DS) and molar substitution(MS) were obtained by adjusting the molar ratio of propylene oxide to glucosamine unit, the reaction pressure, the reaction temperature, and the reaction time, N.O-hydroxypropyl chitosan(N.O-HPCTO) was prepared by reaction of alkali N-HPCTO with propylene oxide in an autoclave at 70℃. The MS value and the site of substitution were determined by the FT-IR and ^1H-NMR analysis. Both the DS and the MS values of N-HPCTOs were found to be less than 2, indicating that it is difficult to add propylene oxide to the hydroxy groups in the side chain or to the amino groups in the main chain under all the experimental conditions studied. On the other hand, the DS value of N,O-HPCTO is less than 4 but the MS is larger than 4, showing that the propylene oxide molecules became more and more difficult to reach the main chain as the side chain grew. By optical microscopic observation, N.O-HPCTO, which is soluble in water as well as common organic solvents, were found to form both thermotropic and lyotropic phases. However, all the N-HPCTOs, which are soluble in the specific solvents such as water, a alcohols and formic acid, do not form thermotropic liquid crystal phases but form lyotropic phases.

라디칼공중합의 속도론·성장반응속도정수와 단량체 반응성비의 재검토

馬永大 단국대학교 1988 論文集 Vol.22 No.-

The velocity of free-radical copolymerization is as yet not comprehensively understood in terms of the elementary processes of propagation and termination. A prevailinf view of this classical subject may be that the propagation process is, in most cases, correctly described by the simple mechanism embodyed by the "terminal model", wkereas, the termibnation process involves complexity, still remaining to be interpreted. One of the main reasons for this view may be attributed to the fact that the composition cuyves of most free-radical copolymerization are, at least to good approximations, represented by the terminal model equation, commonly termed the Mayo-Lewis equation. However, very recent experimental results show that the terminal fails to describe the propagation rate constants, and that a penultimate-unit (or higher-order effect) is responsible for the failure of the terminal model. On the other hand, the termination process is well described by simple model such as the North "diffusion model". In order to explain the origin of the penultimate-unit effect, a new model was introduced. The model is cconsistent with both of the two features exhibited by ST/MMA and pCS/MA systems, i.e., a marked penultimate-unit effect on the absolute rate constant of propagation but its apparent abses\nce on the composition curve. The validity of the proposed model was tested against available experimenta data for k_p, and found to be capable of reproducing the experimentally observed k_p vs. f_1 curves nearly quantitatively without introducing any adjustable parameters.

혼합용매중에서의 공중합체의 부분체적과 용액공중합계의 체적수축인자

馬永大,韓春暎 단국대학교 1986 論文集 Vol.20 No.-

On basis of the van Laar-Scachard type equation of mixing, formulas were developed for the partial molar volum of a copolymer (or a mixture of two polymers) in a mixture of three solvents and for the volume contraction factor in the solution-copolymerization of two monomers and one solvent. In order to test the validity of proposed formulas for the partial molar volume in the dilute limit of zero polymer concentration V~^o_p, density measurements were carried out on styreneethyl acrylate and methyl methacrylate-vinyl acetate copolymers dissolved in the relevant monomer(s) and solvent(s). The values of the ten parameters necessary to compute V~^o_p were determined for each system, and some comments have been made on the individual parameter values. The predicted values of V~^o_p were in good agreement with those directly measured. Based on the result, numerical expressions for the volume contraction factors for the incipient solution-copolymerizations of the two monomer pairs were derived as a function of concentration of the monomers.

Methyl Methacylate/Vinyl Acetate/Toluene 라디칼공중합계에 대한 속도론적 연구

마영대,원유찬 단국대학교 1997 論文集 Vol.31 No.-

The free-radical copolymerization of methy methacrylate and vinyl acetate at 40℃ in toluene was examined by the steady-state polymerization. The following results were obtained: The copolyemr composition confirms the terminal model. The reactivity ratios of this system agree with those of the bulk system within the experiment error, which means that the solvent had very little effect on the copolymer composition of this system. Velocity-of-copolymerization data were interpreted on the basis of the current notions that the penultimate unit effect with respect to absolute values of propagation rate constant (but not with respect to the monomer reactivity ratios) is a general rule and the termination step is well represented by the penultimate model with the geometric mean approximaton. By using these models, a new equation was derivied, which was found to describe experimental data well.

Styrene/Ethyl Acrylate/Toluene 라디칼 공중합계에 대한 속도론적 연구

馬永大,金判洙 단국대학교 1993 論文集 Vol.27 No.-

The free-radical copolymerization of styrene and ethyl acrylate at 40℃ in toluene was examined by the steady-state polymerization as a function of total monomer concentration. The following results were obtained : The coplymer composition confirms the terminal model(Mayo-Lewis equation). The monomer reactivity ratios of r_1 and r_2 at different monomer concentrations are constant within the limits of experimental error. Velocity-of-copolymerization data obtained in this work and reported in the literature for the St/EA/BZ/50℃ systems were reinterpreted on the basis of the current notions that the penultimate-effect with respect to absolute values of propagation rate constant (but not with respect to with the monomer reactivity ratios) is a general rule and that the termination step is well represented numerically by the chemical model with Ø=1 as well as by the North diffusion model. By making a few symplifying approximations, new two equations were derived, which were found to describe experimental data well. The single parameter s included in the equation, which measures the penultimate-unit effect, was found to have a positive correlation between r_1r_2 and S^2. This result is in support of the relation r_1r_2=s_1s_2 suggested by us.

라디칼공중합의 속도론. Acrylonitrile/Methyl Methacrylate/Dimethylformamide와 Styrene/Acrylonitrile/Dimethylformamide 공중합계의 체적수축인자

馬永大,鄭秉訓,南亨錫 단국대학교 1995 論文集 Vol.29 No.-

The volume contraction factors for the low-conversion copolymerizations of methylmethacrylate/acrylonitrile/dimethylformamide and styrene/acrylonitrile/dimethylformamide at 40℃ have been investigated by the previously developed formulas. The values of the ten parameters necessary to compute the volume contraction factors for each system were determined by measuring the densities of appropriate solutions, and some comments have been made on the individual parameter values. On the basis the results, numerical expressions for the volume contraction factors of the two systems were derived as a funtion of total monomer concentrations. The predicted values of the contraction factors were partially checked against those directly determined by measuring volume vs. conversion curve, and found satisfactory.

액정질서를 지닌 O-(1,2-dlhydroxypropy) cellulose 가교필름의 열 및 팽윤특성

마영대,김장훈 단국대학교 2000 論文集 Vol.35 No.-

O-(2,3-dihydroxypropyl) cellulose (DHPC) films crosslinked with glyoxal retaining liquid-crystalline order (DHPC-GN) were prepared by casting the liquid-crystalline solution in water, and their thermotropic properties were compared with those of uncrosslinked DHPC films cast from the same solution. The swelling behaviors for DHPC-GN in water and in methanol were also investigated. Both DHPC-GN and the uncrosslinked DHPC films did not show an isotropic phase and the briefringent textures of a mosaiclike texture were maintained up to about 250℃ corresponding to the degradation temperature, showing that the mesophases of both kinds of films are very stable to heat. The weight and volume swelling ratios for DHPC-GN in both solvents decreased with increasing concentration of the crosslinker. However, the swelling ratios in water were greater than those in methanol. DHPC-GN exhibited an anisotropic swelling in both solvents. The degree of anisotropy hardly depended on the solvent and the crosslinker concentration.

Hydroxypropyl cellulose의 acrylic acid 에스테르와 allyl 에테르를 이용하여 제조한 cholesteric겔의 열 및 팽윤특성

마영대,김경희 단국대학교 2000 論文集 Vol.35 No.-

The acrylic acid esters(ES-N) and allyl ethers(ET-N) of hydroxypropyl cellulose(HPC), which are heat- and light-sensitive polymers, were prepared from HPC and acryloyl chloride and allyl chloride, respectively. The cross-linked ES-N and ET-N films, retaining cholesteric liquid crystalline order, were also prepared by photo-cross- linking thermotropic mesophases of ES-N and ET-N, respectively. Both thermal properties of the uncross-linked and cross-linked films and the swelling behavior of the cross-linked films in both acetone and water were investigated. All uncross-linked films showed isotropization temperatures(T_is) that increase with increasing the degree of substitution(DS), showing that the Ti of ES-N is slightly higher than that of ET-N at the same DS. However, all cross-linked films did not show an isotropic phase and their birefringent textures of a polygonal focal conic organization, which are similar to those in the uncross-linked firms, were maintained up to about 230℃ corresponding to the degradation temperature. The weight and volume swelling ratios in both solvents for all cross-linked films decreased with increasing DS, depending on the solvent and cross-linking species. All cross-linked films exhibited an anisotropic swelling in acetone, but hardly in water.