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2001 Volume 19 Issue 4
2001, 19(4): 335-339
Abstract:
A novel method was established to investigate the gelation process of polymers. The change of refractive index ofa polymer system during gelation was determined in situ in a prismatic cell. It can give reliable information on the wholegelation process. The apparatus and the execution of this technique are illustrated and the error is also discussed.
A novel method was established to investigate the gelation process of polymers. The change of refractive index ofa polymer system during gelation was determined in situ in a prismatic cell. It can give reliable information on the wholegelation process. The apparatus and the execution of this technique are illustrated and the error is also discussed.
2001, 19(4): 341-350
Abstract:
Over 2×10*8 tons of polymers are produced every year, and a large portion of polymers faces the degradationproblem. There are many effective methods to protect polymers against degradation and the addition of stabilizers to polymerremains the most convenient and effective way of enhancing polymer life and performance. In this article, a series of effectivestabilizers with optimal molecular weight (MW), including common, monomeric and polymeric stabilizers (antioxidant andlight stabilizer) were synthesized using isocyanation,controlled isocyanation,hydrosilylation,epoxide addition,macroreaction of stabilizing functional compounds and polymerization stabilizers.The structure and performance of these new stabilizers were characterized by using IR,NMR,MS,UV-spectra,XPS and elemental analysis.The current development of stabilizer synthesis was also reviewed.
Over 2×10*8 tons of polymers are produced every year, and a large portion of polymers faces the degradationproblem. There are many effective methods to protect polymers against degradation and the addition of stabilizers to polymerremains the most convenient and effective way of enhancing polymer life and performance. In this article, a series of effectivestabilizers with optimal molecular weight (MW), including common, monomeric and polymeric stabilizers (antioxidant andlight stabilizer) were synthesized using isocyanation,controlled isocyanation,hydrosilylation,epoxide addition,macroreaction of stabilizing functional compounds and polymerization stabilizers.The structure and performance of these new stabilizers were characterized by using IR,NMR,MS,UV-spectra,XPS and elemental analysis.The current development of stabilizer synthesis was also reviewed.
2001, 19(4): 351-357
Abstract:
Starting with the L- and D,L-lactide copolymer (L:DL = 9: 1) [P(L-DL)LA] of Mw = 32.1×104, rods were obtainedthrough a two stage process: (1) melt-extrusion at 155℃, and (2) hot-drawing at 90℃ to various drawing ratios. Themolecular weight of P(L-DL)LA fell to 9.3×104 as a consequence of the production process. The crystallization andmolecular orientation of P(L-DL)LA developed as a result of the hot-drawing. The mechanical strengths of the rods increasewith the drawing ratio. The maximum for tensile strength,bending strength,bending modulus,and shear strngth are 329 MPa,237 MPa,8.8 GPa,and 157 MPa,respectively.
Starting with the L- and D,L-lactide copolymer (L:DL = 9: 1) [P(L-DL)LA] of Mw = 32.1×104, rods were obtainedthrough a two stage process: (1) melt-extrusion at 155℃, and (2) hot-drawing at 90℃ to various drawing ratios. Themolecular weight of P(L-DL)LA fell to 9.3×104 as a consequence of the production process. The crystallization andmolecular orientation of P(L-DL)LA developed as a result of the hot-drawing. The mechanical strengths of the rods increasewith the drawing ratio. The maximum for tensile strength,bending strength,bending modulus,and shear strngth are 329 MPa,237 MPa,8.8 GPa,and 157 MPa,respectively.
2001, 19(4): 359-370
Abstract:
A blue poly(azure B) film has been synthesized using repeated potential cycling between -0.25 and 1. 10 V (versusSCE). The electrolytic solution consisted of 2.5 mmol dm-3 azure B, 0.5 mol dm-3 NaCl and 0.2 mol dm-3 NaH2PO4 at the pHrange of 2.0 to 11.0. The in situ visible spectrum during electrolysis of azure B shows that the intensity at 740 nm peakincreases with increasing numbers of potential cycles, which is attributable to the formation of poly(azure B). The wavelength of its corresponding absorption peak is 98 nm longer than that of azure B.The polymerization rate is strongly affected by pH values.The anodic peak potential and cathodic peak potential of the poly(azure B)in a solution of pH 3.0 are not affected by increasing the scan rate from 25 to 600 mV s-1.Poly(azure B)has good electrochemical reversibility and fast charge transfer characteristic in the pH range of 2.0 and 11.0.The conductivity of poly(azure B) is 1.5×10-4 S cm-1.According to the differences between FTIR spectra of poly(azure B) and azure B,an electrochemical polymerization mechanism of azure B is proposed in this paper.
A blue poly(azure B) film has been synthesized using repeated potential cycling between -0.25 and 1. 10 V (versusSCE). The electrolytic solution consisted of 2.5 mmol dm-3 azure B, 0.5 mol dm-3 NaCl and 0.2 mol dm-3 NaH2PO4 at the pHrange of 2.0 to 11.0. The in situ visible spectrum during electrolysis of azure B shows that the intensity at 740 nm peakincreases with increasing numbers of potential cycles, which is attributable to the formation of poly(azure B). The wavelength of its corresponding absorption peak is 98 nm longer than that of azure B.The polymerization rate is strongly affected by pH values.The anodic peak potential and cathodic peak potential of the poly(azure B)in a solution of pH 3.0 are not affected by increasing the scan rate from 25 to 600 mV s-1.Poly(azure B)has good electrochemical reversibility and fast charge transfer characteristic in the pH range of 2.0 and 11.0.The conductivity of poly(azure B) is 1.5×10-4 S cm-1.According to the differences between FTIR spectra of poly(azure B) and azure B,an electrochemical polymerization mechanism of azure B is proposed in this paper.
2001, 19(4): 371-376
Abstract:
Polyurethane elastomers derived from 4,4'-methylene bis(phenyl isocyanate), butylene glycol and the lowoxyethylene moiety content copolyether of tetrahydrofuran and ethylene oxide, obtained by copolymerization usingheteropolyacid-ethylene oxide initiator system, were prepared. The polyurethanes exhibited an increased water absorptionand much better low temperature resilience, which remained high even at a temperature of -3℃, while that of polyurethanebased upon poly(tetramethylene ether) glycol of the same molecular weight,i.e. being 2000,and molecular weight distribution,i.e.in the range of 1.4-1.5,starts to decrease dramatically at 5℃.
Polyurethane elastomers derived from 4,4'-methylene bis(phenyl isocyanate), butylene glycol and the lowoxyethylene moiety content copolyether of tetrahydrofuran and ethylene oxide, obtained by copolymerization usingheteropolyacid-ethylene oxide initiator system, were prepared. The polyurethanes exhibited an increased water absorptionand much better low temperature resilience, which remained high even at a temperature of -3℃, while that of polyurethanebased upon poly(tetramethylene ether) glycol of the same molecular weight,i.e. being 2000,and molecular weight distribution,i.e.in the range of 1.4-1.5,starts to decrease dramatically at 5℃.
2001, 19(4): 377-384
Abstract:
This paper is concerned with the numerical simulation of the transient effect of an inertialess Boger flow past aconfined circular cylinder and the comparison of predictions with particle image velocimetry (PIV) measurements given byShiang et al., Dynamic simulation based on the Oldroyd-B constitutive model was carried out using a Lagrangian-Eulerianalgorithm. The evolution of velocity field was obtained for the flow at two Deborah (De) numbers, i.e. De = 1.2 and 3.0. Atlow De, the flow reached steady state rapidly,and showed a symmetric flow regime.However,at high De,the time required to reach steady flow behind the cylinder increased significantly,and the distribution of the velocity field appears to be asymmetric with respect to the stagnation line.Pairly good agreement between the numerical results and the experimental observations is reported.It can be concluded that both the experimental measurements and the present simulations indicate that the elasticity of the polymeric flow strongly affect the flow regime of viscoelastic flow around a confined cylinder.
This paper is concerned with the numerical simulation of the transient effect of an inertialess Boger flow past aconfined circular cylinder and the comparison of predictions with particle image velocimetry (PIV) measurements given byShiang et al., Dynamic simulation based on the Oldroyd-B constitutive model was carried out using a Lagrangian-Eulerianalgorithm. The evolution of velocity field was obtained for the flow at two Deborah (De) numbers, i.e. De = 1.2 and 3.0. Atlow De, the flow reached steady state rapidly,and showed a symmetric flow regime.However,at high De,the time required to reach steady flow behind the cylinder increased significantly,and the distribution of the velocity field appears to be asymmetric with respect to the stagnation line.Pairly good agreement between the numerical results and the experimental observations is reported.It can be concluded that both the experimental measurements and the present simulations indicate that the elasticity of the polymeric flow strongly affect the flow regime of viscoelastic flow around a confined cylinder.
2001, 19(4): 385-390
Abstract:
The oriented chitosan films obtained from pre-sheared liquid crystalline chitosan/dichloroacetic acid (DCA)solutions were studied by means of polarized optical microscopy (POM), scanning electron microscopy (SEM), infra-reddichroism technique and wide angle X-ray diffraction (WAXD). The shear induced band texture in the film was found tocorrespond to the sinusoidal fibrillar microstructure along the shearing direction on the basis of POM and SEM observations.The sinusoidal fibril was found to be lying within the film plane.The model of chitosan molecular orientation in the presheared film with band texture can be established assuming that the main chain orients in the shearing direction and the side group is perpendicular to the shearing direction.The WAXD azimuthal scanning at 2θ=20° indicates that the (002) plane orients perpendicular to the shearing direction.
The oriented chitosan films obtained from pre-sheared liquid crystalline chitosan/dichloroacetic acid (DCA)solutions were studied by means of polarized optical microscopy (POM), scanning electron microscopy (SEM), infra-reddichroism technique and wide angle X-ray diffraction (WAXD). The shear induced band texture in the film was found tocorrespond to the sinusoidal fibrillar microstructure along the shearing direction on the basis of POM and SEM observations.The sinusoidal fibril was found to be lying within the film plane.The model of chitosan molecular orientation in the presheared film with band texture can be established assuming that the main chain orients in the shearing direction and the side group is perpendicular to the shearing direction.The WAXD azimuthal scanning at 2θ=20° indicates that the (002) plane orients perpendicular to the shearing direction.
2001, 19(4): 391-397
Abstract:
The structural and morphological evolution of mono-domains in thin films has been investigated for a series ofliquid crystalline (LC) copolyethers. The copolyethers studied were synthesized by the reaction of 1-(4-hydroxy-4'-biphenylyl)-2 -(4-hydroxyl-phenyl)propane (TPP) with 1, 7-dibromoheptane and 1, 11-undecane at different compositions(coTPPs-7/11). In contrast to the solution-cast thin films without annealing, which exhibit the isotropic homogeneousmolecular orientation, mono-domains with a homeotropic alignment were found in coTPP-7/11(5/5) after the thin films were annealed in the high-temperature columnar phase(φ).Similar to the nucleation process in polymer crystallization,transmission electron microscopic observations show that small mono-domains appear in the initial stage of annealing,where molecules form a uniaxial in-plane chain orientation.With increasing annealing time,the molecular orientation gradually became tilted with respect to the substrate surface,and finally,a uniaxial homeotropic molecular orientation was achieved after a prolonged annealing time.The lateral size of mono-domains was found to increase continuously with annealing time and grew into a circular shape,indicating an isotropic lateral growth scheme which implies a hexagonal molecular packing proved by the electron diffraction experiments.
The structural and morphological evolution of mono-domains in thin films has been investigated for a series ofliquid crystalline (LC) copolyethers. The copolyethers studied were synthesized by the reaction of 1-(4-hydroxy-4'-biphenylyl)-2 -(4-hydroxyl-phenyl)propane (TPP) with 1, 7-dibromoheptane and 1, 11-undecane at different compositions(coTPPs-7/11). In contrast to the solution-cast thin films without annealing, which exhibit the isotropic homogeneousmolecular orientation, mono-domains with a homeotropic alignment were found in coTPP-7/11(5/5) after the thin films were annealed in the high-temperature columnar phase(φ).Similar to the nucleation process in polymer crystallization,transmission electron microscopic observations show that small mono-domains appear in the initial stage of annealing,where molecules form a uniaxial in-plane chain orientation.With increasing annealing time,the molecular orientation gradually became tilted with respect to the substrate surface,and finally,a uniaxial homeotropic molecular orientation was achieved after a prolonged annealing time.The lateral size of mono-domains was found to increase continuously with annealing time and grew into a circular shape,indicating an isotropic lateral growth scheme which implies a hexagonal molecular packing proved by the electron diffraction experiments.
2001, 19(4): 399-405
Abstract:
Viscoelastic behavior of the non-Hooke deformation of amorphous PET film before yield was investigated in thetemperature region 74--80.5℃ around the glass transition temperature. The film specimen was drawn to yield point followedby unloading to zero stress, then the residual deformation was held constant, while the subsequent evolution of the stress wasrecorded. An induction period was found in the course of stress evolution fol1owed by a stress step-increase. The induction period decreases with increasing drawing temperature with an activation energy of 1.10 MJ/mol·K,which is attributed to the time needed for the relaxation of rubbery deformation through cooperative internal rotations.At temperatures lower than 74℃,there is no stress increase or the induction period becomes too long to be observed.Thus the nature of anelasticity in the non-Hooke region before yielding is attributed to stress induced rubbery deformation.The experimental results are interpreted in terms of Perez'rheological model of a scries connected Hooke spring and a Voigt element consisting of a parallel connected elastic spring and a dashpot.
Viscoelastic behavior of the non-Hooke deformation of amorphous PET film before yield was investigated in thetemperature region 74--80.5℃ around the glass transition temperature. The film specimen was drawn to yield point followedby unloading to zero stress, then the residual deformation was held constant, while the subsequent evolution of the stress wasrecorded. An induction period was found in the course of stress evolution fol1owed by a stress step-increase. The induction period decreases with increasing drawing temperature with an activation energy of 1.10 MJ/mol·K,which is attributed to the time needed for the relaxation of rubbery deformation through cooperative internal rotations.At temperatures lower than 74℃,there is no stress increase or the induction period becomes too long to be observed.Thus the nature of anelasticity in the non-Hooke region before yielding is attributed to stress induced rubbery deformation.The experimental results are interpreted in terms of Perez'rheological model of a scries connected Hooke spring and a Voigt element consisting of a parallel connected elastic spring and a dashpot.
2001, 19(4): 407-413
Abstract:
Two unbridged metallocene catalysts, bis (2, 4, 7-trimethylindenyl)zirconium dichloride (met-I) and bis(2, 4, 6-trimethylindenyl) zirconium dichloride (met-II), which are different in the position o f substituents on the six-membered ringof the indenyl ligands were synthesized. The effect of substituents in the two metallocenes on the propylene polymerizationwas studied in the presence of methylaluminoxane (MAO) and triisobutylaluminium (TIBA). From the analysis ofmicrostructure determined by 13C-NMR, it was demonstrated that the polymers produced by met-II have higher [mmmm] isotactic sequences than that of met-I.Using a mechanism based on model statistical analysis,it was found that chain-end model was dominant for met-I.However,met-II obeys the concurrent two-sites model during polymerization,which can be attributed to the existence of "racemic-like"conformer in its system.
Two unbridged metallocene catalysts, bis (2, 4, 7-trimethylindenyl)zirconium dichloride (met-I) and bis(2, 4, 6-trimethylindenyl) zirconium dichloride (met-II), which are different in the position o f substituents on the six-membered ringof the indenyl ligands were synthesized. The effect of substituents in the two metallocenes on the propylene polymerizationwas studied in the presence of methylaluminoxane (MAO) and triisobutylaluminium (TIBA). From the analysis ofmicrostructure determined by 13C-NMR, it was demonstrated that the polymers produced by met-II have higher [mmmm] isotactic sequences than that of met-I.Using a mechanism based on model statistical analysis,it was found that chain-end model was dominant for met-I.However,met-II obeys the concurrent two-sites model during polymerization,which can be attributed to the existence of "racemic-like"conformer in its system.
2001, 19(4): 415-419
Abstract:
Microporous regenerated cellulose gel particles were prepared by mixing cellulose cuoxam with silk fibroin aspore former, and the mean pore size and pore volume of the pallicles were 525 nm and 7.27 mL g-1, respectively. Apreparative size-exclusion chromatography (SEC) column (550 mm×20 mm) packed with the cellulose gel particles wasused for the fractionation of two polysaccharides Dextran 07 (Mw = 7.14×104, d= 1.7) and Dextran 50(Mw = 50.5×104,d = 3.8) in water phase. The fractionation range of the stationary phase covered Mw from 3×103 to 1.1×106.The daily throughput was 2.9 g for Dextran 07(D07) and 4.3 g for Dextran 50(D50) with a flow-rate of 1.5 mL min-1.The fractions obtained by using the SEC were analyzed by an analytical SEC combined with laser light scattering(LLS),and the polydispersity indices of fractions for Dextran 07 and Dextran 50 were determined to be 1.34-1.57 and 4.53-3.36,respectively.The preparative SEC is a simple,rapid,and suitable means not only for the fractionation of polysaccharides in water but also for other polymers in organic solvents.
Microporous regenerated cellulose gel particles were prepared by mixing cellulose cuoxam with silk fibroin aspore former, and the mean pore size and pore volume of the pallicles were 525 nm and 7.27 mL g-1, respectively. Apreparative size-exclusion chromatography (SEC) column (550 mm×20 mm) packed with the cellulose gel particles wasused for the fractionation of two polysaccharides Dextran 07 (Mw = 7.14×104, d= 1.7) and Dextran 50(Mw = 50.5×104,d = 3.8) in water phase. The fractionation range of the stationary phase covered Mw from 3×103 to 1.1×106.The daily throughput was 2.9 g for Dextran 07(D07) and 4.3 g for Dextran 50(D50) with a flow-rate of 1.5 mL min-1.The fractions obtained by using the SEC were analyzed by an analytical SEC combined with laser light scattering(LLS),and the polydispersity indices of fractions for Dextran 07 and Dextran 50 were determined to be 1.34-1.57 and 4.53-3.36,respectively.The preparative SEC is a simple,rapid,and suitable means not only for the fractionation of polysaccharides in water but also for other polymers in organic solvents.
2001, 19(4): 421-427
Abstract:
A new organic/inorganic hybrid nonlinear optical (NLO) material was developed by the sol-gel process of analkoxysilane dye with tetraethoxysilane. A NLO moiety based on 4-nitro-4'-hydroxy azobenzene was covalently bonded tothe triethoxysilane derivative, i.e. γ-isocyanatopropyl triethoxysilane. The preparation process and properties of the sol-gelderived NLO polymer were studied and characterized by SEM, FTIR, 1H-NMR, UV-Vis, DSC and second harmonicgeneration (SHG) measurement. The results indicated that the chemical bonding of the chromophores to the inorganic SiO2 networks induces low dipole alignment relaxation and preferable orientational stability.The SHG measurements also showed that the bonded polymer film containing 75 wt% of the akoxysilane dye has a high electro-optic coefficient(r33) of 7.1 pm/V at 1.1 μm wavelength,and exhibit good SHG stability,the r33 values can maintain about 92.7% of its initial value at room temperature for 90 days,and can maintain about 59.3% at 100℃ for 300 min.
A new organic/inorganic hybrid nonlinear optical (NLO) material was developed by the sol-gel process of analkoxysilane dye with tetraethoxysilane. A NLO moiety based on 4-nitro-4'-hydroxy azobenzene was covalently bonded tothe triethoxysilane derivative, i.e. γ-isocyanatopropyl triethoxysilane. The preparation process and properties of the sol-gelderived NLO polymer were studied and characterized by SEM, FTIR, 1H-NMR, UV-Vis, DSC and second harmonicgeneration (SHG) measurement. The results indicated that the chemical bonding of the chromophores to the inorganic SiO2 networks induces low dipole alignment relaxation and preferable orientational stability.The SHG measurements also showed that the bonded polymer film containing 75 wt% of the akoxysilane dye has a high electro-optic coefficient(r33) of 7.1 pm/V at 1.1 μm wavelength,and exhibit good SHG stability,the r33 values can maintain about 92.7% of its initial value at room temperature for 90 days,and can maintain about 59.3% at 100℃ for 300 min.
