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1987 Volume 5 Issue 4
1987, 5(4): 269-284
Abstract:
This is a comprehensive survey of our work during the past thirteen years on the thermal analysis of acrylic fiber, including some recent, unpublished results.
This is a comprehensive survey of our work during the past thirteen years on the thermal analysis of acrylic fiber, including some recent, unpublished results.
1987, 5(4): 285-291
Abstract:
The Thermally Stimulated Current (TSC) spectra of a series of Sub-Tθ annealed polyethylene terephthalate (PET) specimens have been measured. It is found that there is only one peak at 80℃ above room temperature, which related to the thermo-relaxation of frozen-in dipoles. The activation energy of such dipole motion has been calculated. The relation between the maximum current and the storage time can be explained by the free volume theory and agrees with the results from the excess thermodynamic properties.Compared with Differential Scanning Calorimeter(DSC) and tensile stree-strain method,TSC is a simpler and more sensitive method in studying Sub-Tg annealed polymers.
The Thermally Stimulated Current (TSC) spectra of a series of Sub-Tθ annealed polyethylene terephthalate (PET) specimens have been measured. It is found that there is only one peak at 80℃ above room temperature, which related to the thermo-relaxation of frozen-in dipoles. The activation energy of such dipole motion has been calculated. The relation between the maximum current and the storage time can be explained by the free volume theory and agrees with the results from the excess thermodynamic properties.Compared with Differential Scanning Calorimeter(DSC) and tensile stree-strain method,TSC is a simpler and more sensitive method in studying Sub-Tg annealed polymers.
1987, 5(4): 292-297
Abstract:
In this paper, we have studied the piezoelectricity in the poled uniaxially drawn polyvinylidene fluoride. The piezoelectric constants d31, d32, d33α and Young's moduli 1/s11 and 1/s22 have been determined as a function of the remanent polarization Pr. The piezoelectric constants of the samples show a strong in-plane anisotropy. Such an anisotropy is mostly attributable to different Poisson's ratio. It is found that the piezoelectric activity mainly arises from macroscopic dimensional change.
In this paper, we have studied the piezoelectricity in the poled uniaxially drawn polyvinylidene fluoride. The piezoelectric constants d31, d32, d33α and Young's moduli 1/s11 and 1/s22 have been determined as a function of the remanent polarization Pr. The piezoelectric constants of the samples show a strong in-plane anisotropy. Such an anisotropy is mostly attributable to different Poisson's ratio. It is found that the piezoelectric activity mainly arises from macroscopic dimensional change.
1987, 5(4): 298-307
Abstract:
Copper(Ⅱ) complexes of sericin, chitosan, 6-and 2-aminodeoxystarch were used as catalysts in oxidative coupling of β-naphthol, the effects of conformation of the polymer ligands in these complexes on activities of the catalysts and mechanisms of the reaction were studied. It was found that if the catalysts react with the substrate by mechanism similar to the enzymic catalysis they must be composed of polymer ligands with highly coiled, especially with densely helicoidal, conformations. While catalysts composed of loosely coiled or helicoidal ligands react with the substrate through molecular collision and have relatively lower activities only.Under nitrogen,catalysts from sericin and chitosam reacting with β-naphthol give optically active β-binaphthol,rotating polarized light to right,but the stereiselectivities are rather low.
Copper(Ⅱ) complexes of sericin, chitosan, 6-and 2-aminodeoxystarch were used as catalysts in oxidative coupling of β-naphthol, the effects of conformation of the polymer ligands in these complexes on activities of the catalysts and mechanisms of the reaction were studied. It was found that if the catalysts react with the substrate by mechanism similar to the enzymic catalysis they must be composed of polymer ligands with highly coiled, especially with densely helicoidal, conformations. While catalysts composed of loosely coiled or helicoidal ligands react with the substrate through molecular collision and have relatively lower activities only.Under nitrogen,catalysts from sericin and chitosam reacting with β-naphthol give optically active β-binaphthol,rotating polarized light to right,but the stereiselectivities are rather low.
1987, 5(4): 308-315
Abstract:
The normal vibrational calculation was carried out on cis-polyacetylene(PA) and its model compound, cis, trans-2, 4--hexadiene. Based on the observed IR and Raman frequencies, force constants relevant to the cis-structure were refined. Finally a force field common for cis-PA, trans-PA and three model moleculaes was obtained. The observed spectra of cis-PA were theoretically assigned and the similarities and differences between the cis-and trans-conjugate systems were discussed on the basis of normal coordinate calculation.
The normal vibrational calculation was carried out on cis-polyacetylene(PA) and its model compound, cis, trans-2, 4--hexadiene. Based on the observed IR and Raman frequencies, force constants relevant to the cis-structure were refined. Finally a force field common for cis-PA, trans-PA and three model moleculaes was obtained. The observed spectra of cis-PA were theoretically assigned and the similarities and differences between the cis-and trans-conjugate systems were discussed on the basis of normal coordinate calculation.
1987, 5(4): 316-324
Abstract:
The results of normal vibrational analyses of trans, trans-2, 4-hexadiene and the backbone of trans, trans-1, 4-diphenyl-butadiene were used in the normal mode computation of trans-polyacetylene (PA). Only 8 non-zero calculated frequencies were obtained which obeys the rule of 3N-4. The potential energy distribution (PED) data were in good agreement with the empirical assignment of Shirakawa et al. and Kozmany, but most of the vibrational frequencies of ttrans-PA had contributions from several empirical modes,indicationg the more conplicacy in trans-PA molecular vibration than in the model molecule case.The calculated C=C and C-C stretching frequencies of trans-PA were over 200cm-1higher and lower than the observed ones,respectively,due to the longer effective conjugate length in the trans-PA.This was shown by the dependence of the PED-weighted average frequencies of C=C and C-C stretchings on the force constants f(C=C)2 and f(C-C)2.
The results of normal vibrational analyses of trans, trans-2, 4-hexadiene and the backbone of trans, trans-1, 4-diphenyl-butadiene were used in the normal mode computation of trans-polyacetylene (PA). Only 8 non-zero calculated frequencies were obtained which obeys the rule of 3N-4. The potential energy distribution (PED) data were in good agreement with the empirical assignment of Shirakawa et al. and Kozmany, but most of the vibrational frequencies of ttrans-PA had contributions from several empirical modes,indicationg the more conplicacy in trans-PA molecular vibration than in the model molecule case.The calculated C=C and C-C stretching frequencies of trans-PA were over 200cm-1higher and lower than the observed ones,respectively,due to the longer effective conjugate length in the trans-PA.This was shown by the dependence of the PED-weighted average frequencies of C=C and C-C stretchings on the force constants f(C=C)2 and f(C-C)2.
1987, 5(4): 325-331
Abstract:
An apparatus constructed for measuring permeation properties of polymer membranes using a mixture of gases is described. A gas chromatographic system was applied to determine the individual transport characteristics of component gases without a vacuum line. This paper also discusses some experimental factors effecting the precision of measurement. The results show that there is a linear relationship between the permeation time and the volume of the gas permeated through the membrane within certain permeation period,which depends on the permeation rate(from 10-10 to 10-7 cm3(STP)/cm2.sec.cmHg) of the membrane.The reproducibility has been found to be good with a relative standard deviation of 3.5%.This method is more sensitive,considerably faster and more convenient for determining both the permeability coefficient and the separation factor of a polymer membrane from a chromat ogram using mixed penetrant gases.
An apparatus constructed for measuring permeation properties of polymer membranes using a mixture of gases is described. A gas chromatographic system was applied to determine the individual transport characteristics of component gases without a vacuum line. This paper also discusses some experimental factors effecting the precision of measurement. The results show that there is a linear relationship between the permeation time and the volume of the gas permeated through the membrane within certain permeation period,which depends on the permeation rate(from 10-10 to 10-7 cm3(STP)/cm2.sec.cmHg) of the membrane.The reproducibility has been found to be good with a relative standard deviation of 3.5%.This method is more sensitive,considerably faster and more convenient for determining both the permeability coefficient and the separation factor of a polymer membrane from a chromat ogram using mixed penetrant gases.
1987, 5(4): 332-339
Abstract:
The limiting viscosity number [η] and translational diffusion coefficient D of polyphenylsilsesquioxane (PPSQ) and their dependence on molecular weight Mw were studied by static and dynamic light scattering and viscometry techniques. NMR measurement was also performed to investigate PPSQ's structure. Results show that PPSQ molecules are not rigid rods and do not have fully regular ladder structure but with branches and uncondensed hydroxy groups, and their extensibility decreases with the increase of molecular weight.
The limiting viscosity number [η] and translational diffusion coefficient D of polyphenylsilsesquioxane (PPSQ) and their dependence on molecular weight Mw were studied by static and dynamic light scattering and viscometry techniques. NMR measurement was also performed to investigate PPSQ's structure. Results show that PPSQ molecules are not rigid rods and do not have fully regular ladder structure but with branches and uncondensed hydroxy groups, and their extensibility decreases with the increase of molecular weight.
1987, 5(4): 340-346
Abstract:
Based on relations between the limiting viscosity number, the translational diffusion coefficient and the molecular weight, the shape of polyphenylsilsesquioxane (PPSQ) in dilute solution was simulated with different models. It is found that the oblate ellipsoid of revolution and free-draining random coil are two suitable models, showing that PPSQ is a polymer with rigid chains, and its shape is closer to sphere due to chain branching rather than flexibility.
Based on relations between the limiting viscosity number, the translational diffusion coefficient and the molecular weight, the shape of polyphenylsilsesquioxane (PPSQ) in dilute solution was simulated with different models. It is found that the oblate ellipsoid of revolution and free-draining random coil are two suitable models, showing that PPSQ is a polymer with rigid chains, and its shape is closer to sphere due to chain branching rather than flexibility.
1987, 5(4): 347-352
Abstract:
The steric tacticity of polyphenylsilsesquioxanes (PPS) was studied by exeimer fluorescence spectroscopy. It was found that the fluorescence of PPS come mainly from its intramolecular excimers, The experimental results indicated that the steric-structure of PPS is most probably cisisotactic rather than the cis-syndiotactic as suggested in the literature. With the increase in defect content monomer fluorescence intensity increases because of the enhanced mobility of phenyl groups. Molecular weights and molecular weight distributions do not affect the fluorescence spectra of PPS.
The steric tacticity of polyphenylsilsesquioxanes (PPS) was studied by exeimer fluorescence spectroscopy. It was found that the fluorescence of PPS come mainly from its intramolecular excimers, The experimental results indicated that the steric-structure of PPS is most probably cisisotactic rather than the cis-syndiotactic as suggested in the literature. With the increase in defect content monomer fluorescence intensity increases because of the enhanced mobility of phenyl groups. Molecular weights and molecular weight distributions do not affect the fluorescence spectra of PPS.
1987, 5(4): 353-358
Abstract:
The steric tacticity of polyphenylsilsesquioxanes is discussed based on both structure transformation consideration and the results of calculations, X-ray diffraction patterns, fluorescence emission spectroscopy, and scanning electron microscopy. All of the results show that cis-isotactic conformation is the most probable one for ladderlike polymer polyphenylsilsesquioxane though other conformations such as cissyndiotactic may also be present in the macromolecules depending upon the preparation conditions.
The steric tacticity of polyphenylsilsesquioxanes is discussed based on both structure transformation consideration and the results of calculations, X-ray diffraction patterns, fluorescence emission spectroscopy, and scanning electron microscopy. All of the results show that cis-isotactic conformation is the most probable one for ladderlike polymer polyphenylsilsesquioxane though other conformations such as cissyndiotactic may also be present in the macromolecules depending upon the preparation conditions.
1987, 5(4): 359-365
Abstract:
Solution properties of ladder-like polymer polyphenylsilsesquioxane (PPS) were studied by measurement of intrinsic viscosity, small angle laser light scattering and gel permeation chromatography. It was found that PPS can be modeled with a wormlike continuous cylinder rather than a wormlike coil. A plot of (M2/[η])1/3 vs. M1/2 was employed in obtaining the persistence length (2λ)-1 and effective hydrodynamic diameter. When MW≤5×105, Mark-Houwink equation is adequate in describing the relationship between MW and [η] with α about unity.This implies that PPS chain is semi-stiff.For GPC experiments,it was shown that univeral calibration can be applied in PPS.When molecular weights of PPS are sufficiently high,their molecular weight ditributions are often very broad.
Solution properties of ladder-like polymer polyphenylsilsesquioxane (PPS) were studied by measurement of intrinsic viscosity, small angle laser light scattering and gel permeation chromatography. It was found that PPS can be modeled with a wormlike continuous cylinder rather than a wormlike coil. A plot of (M2/[η])1/3 vs. M1/2 was employed in obtaining the persistence length (2λ)-1 and effective hydrodynamic diameter. When MW≤5×105, Mark-Houwink equation is adequate in describing the relationship between MW and [η] with α about unity.This implies that PPS chain is semi-stiff.For GPC experiments,it was shown that univeral calibration can be applied in PPS.When molecular weights of PPS are sufficiently high,their molecular weight ditributions are often very broad.
1987, 5(4): 366-369
Abstract:
The grafting of copolymer of styrene and 2, 2, 6, 6-tetramethyl-4-piperidinyl methacrylate onto polypropylene during heating was studied by IR and ESR. It is found that the graft reaction is going through the stable free radical > NO mechanism.
The grafting of copolymer of styrene and 2, 2, 6, 6-tetramethyl-4-piperidinyl methacrylate onto polypropylene during heating was studied by IR and ESR. It is found that the graft reaction is going through the stable free radical > NO mechanism.
