Flow-modified permittivity of solutions of poly(n-butyl isocyanate) and poly(n-hexyl isocyanate)

The dielectric behaviour of solutions of poly(n-butyl isocyanate) and poly(n-hexyl isocyanate) in flow have been examined, including, for the latter polymer, fractions of differing molecular weight. The data are analysed in terms of established theories for changes in the permittivity of solutions of rigid macromolecules undergoing shear and are critically compared to dielectrically based information obtained from studies of still solutions. Rotational diffusion coefficients and dipole moments have been measured and the influence of heterogeneity in molecular weight on flow-modified permittivity is examined. The results obtained support the view that the theories for the flow-modified permittivity of rigid macromolecules are generally satisfactory in providing rotational diffusion coefficients and resolved dipoles, but that the influence of molecular shape on the effect is not simply obtained when polydisperse material is involved.     

High birefringence of poly(trimethylene terephthalate) spherulite

Poly(trimethylene terephthalate) (PTT) spherulite shows interference color under polarized light microscope without a sensitive tint plate. The fact indicates that the retardation of PTT spherulite is high, while it was reported that the birefringence in PTT fiber is low. In this study, the reason why the high birefringence is observed in PTT spherulite was discussed. By small area X-ray diffraction measurement, it was confirmed that a-axis of unit cell of PTT crystal was parallel to the radial direction of the spherulite. Based on the result, we calculated the refractive indices of parallel to a-axis and the other orthogonal directions. It was clarified that the refractive index of a-axis is much lower than the others and the intrinsic birefringence for a-axis orientation is high. It is the reason why the PTT spherulite shows high and negative birefringence.     

Flow birefringence and viscosity of cellulose solutions in semi-dilute regime

An attempt was made to study the flow birefringence and the viscosity of the systems of cellulose in aqueous sodium hydroxide and cadoxen solutions. For this purpose alkali-soluble cellulose samples with crystal form I (simply denoted as cellulose I sample), prepared from conifer wood pulp by the steam-explosion method, and alkali-soluble cellulose samples with crystal form of cellulose II (cellulose II sample), regenerated from cuprammonium cellulose solution under specific conditions, were used. The extinction angle χ of aqueous alkali solutions of the cellulose I sample is significantly less shear rate (γ) dependent as compared with that of the cellulose II sample. In the latter system the χ versus γ relations for a given cellulose sample shifted to the higher γ side with decrease in the average molecular weight. The viscosity of the cellulose II sample in aqueous sodium hydroxide solutions is approximately twice that of the cellulose I sample in the same solvent if compared at the same molecular weight, same concentration, and same temperature. The latter solution showed a non-Newtonian property at relatively smaller γ than the former solution did. Spin-lattice relaxation time T₁ (by ¹³C-NMR) of cellulose in cadoxen solution was smaller in cellulose I, suggesting the existence of intra- and intermolecular hydrogen bondings at the C₆ position of cellulose molecules in cellulose I solution. A dynamic light scattering study on cellulose in cadoxen showed that in a 5 wt % solution of cellulose I cellulose particles are dispersed with time into smaller particles and the larger particles could be excluded by ultracentrifuge and in cellulose II solutions the cellulose particles had almost the same size during storage. The above findings indicate that in 5 wt% cellulose I solutions in aqueous alkali or in cadoxen, cellulose I is not dissolved molecularly, but a supra-molecular structure of the solid is at least partly reserved in the above solutions.     

Elongational flow-induced birefringence of polyacrylamide and poly(acrylamide-co-sodium acrylate)

Aqueous solutions of poly(acrylamide-co-sodium acrylate), in up to 1M NaCl, exhibited a flow-induced negative birefringence above a critical elongation flow rate in a crossed-slot device. Aqueous polyacrylamide, on the other hand, exhibited a positive birefringent pattern just above a critical elongation rate. At slightly higher elongation rates a negative birefringent thin-line region centred in the positive birefringent region appeared. This phenomenon was observed for all polyacrylamide concentrations tested (0.001 to 0.5 wt%; 0.5 to 20 times the quiescent overlap concentration). This change in birefringence sign can be qualitatively mimicked using a simple coil deformation model which includes contributions from intrinsic, microform and macroform optical anisotropy terms. Evidence is also given for this alternating birefringence sign pattern possibly being due to an elongational flow-induced change in the microstructure of the polyacrylamide.     

Determination of density and birefringence of poly(ethylene terephthalate) fibers using Raman microscopy

Multiple regression analysis has been used to calibrate polarized Raman spectra of poly(ethylene terephthalate) fibers in terms of density and birefringence. The calibration spans PET fibers having a wide range of density and birefringence values. The calibration required the Raman spectrum in only one polarization direction, that is, with the polarization directions of the incident and scattered light parallel to each other and to the fiber axis. The peak at 631 cm⁻¹, which has been used previously as an internal standard band, could be used for the prediction of density, but not for the prediction of birefringence. The peak at 702 cm⁻¹ was found to be a good internal standard band for both density and birefringence. Density could be predicted with a standard error of prediction of 0.003 g/cc using only the ratio of the intensity of the band at 996 cm⁻¹ to that of 702 cm⁻¹ and the full width at half maximum of the 1725-cm⁻¹ band. Birefringence was predicted with a standard error of 0.01 using the ratios of the intensities of the bands at 996 and 1616 cm⁻¹ to that of the 702-cm⁻¹ band. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 943–952, 1999     

Light‐control birefringence of oriented poly(vinyl cinnamate) by UV irradiation

The research focused on realizing the birefringence of light‐control polymer films. The photoelastic birefringence exhibits when Poly (vinyl cinnamate) (PVCi) films are stretched below their glass transition temperature (T_g). The birefringence of PVCi decreases when the UV irradiation happens because the side chains of the PVCi photo‐react when the oriented films are exposed to UV light. A method to quantify the birefringence ability of the polymer films is created and verified. Using this method, the decrease of the birefringence through the UV irradiation is quantified. The result shows the birefringence of PVCi can be controlled by altering the UV irradiation time. In addition, oriented PVCi films of different esterification degrees were prepared and irradiated at different time, and the birefringence of them was studied to clarify the birefringence mechanism of light‐control polymer films. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dielectric relaxation of poly(n-hexyl isocyanate) in concentrated solutions of polybutadiene

We report the dielectric relaxation in a ternary system in which a trace amount of poly(n-hexyl isocyanate) (PHIC) is dissolved in concentrated toluene solutions of polybutadiene (PB). The dielectric response is due to the rod-like PHIC molecules having high dipole moment along its chain contour. Solutions of PB form entanglement networks which retard the reorientation of the PHIC molecules. With increasing concentration (C_PB) of PB from 0 to 40 wt% the relaxation behaviour changed at a crossover concentration C_PB⁺. In the range below C_PB⁺, the relaxation time τ for reorientation of the PHIC molecules increased on account of the effect of entanglement. However above C_PB⁺, τ decreased and at the same time the relaxation strength decreased with increasing C_PB. The crossover concentration C_PB⁺ depended on the molecular weight M of the PHIC, i.e. C⁺_PB=0.13 at M=29,000, and C_PB⁺=0.25 at M=20,000. The decrease of the relaxation strength can be attributed to the reduction of the effective dipole moment due to the restriction of motions of the PHIC chains in entanglement networks of PB chains.     

注射成型熔接线区域流动诱导双折射行为

带有熔接线的透明聚苯乙烯平板制品通过带嵌件的模具注射成型,利用光弹测试考察了不同工艺条件下的制品双折射行为,探讨了嵌件造成的相邻熔接线区域熔体流动行为及对制品双折射分布的影响。结果表明,保压压力和熔体温度对制品双折射整体分布影响明显;嵌件后熔接缝区域与制品其他区域的双折射行为有较大差异,其变化与熔体相遇后流动行为和熔接部位分子取向分布有关;制品最大双折射值出现在嵌件后一定距离处。热收缩实验进一步验证了上述结果。     

Evaluation of the birefringence of uniaxially oriented poly(2,6-dimethyl 1,4-phenylene oxide)-atactic polystyrene blends

The intrinsic birefringence of atactic polystyrene and poly(2,6-dimethyl 1,4-phenylene oxide) in their compatible blends are obtained from coupled birefringence and infra-red dichroism measurements. The experimental value obtained for poly(2-6-dimethyl 1,4-phenylene oxide) is in reasonable agreement with the value calculated from bond polarizabilities. These results allow evaluation of the angle between the normal to the benzene ring of polystyrene and the chain axis. This angle appears to be constant as a function of draw ratio and poly(2,6-dimethyl 1,4-phenylene oxide) percentage in the 0–35% studied range.     

Functionalization of poly(propylene) by isocyanate groups

Isotactic poly(propylene (PP) was grafted with m-isopropenyl-α,α-dimethylbenzyl-isocyanate (TMI) using tert-butyl cumyl peroxide as free-radical initiator. The amount of grafted TMI increased with increasing initial initiator concentration, whereas the molecular weight of PP decreased. An increase of the amount of grafted TMI resulted in a decrease of the PP melting point, onset-temperature, and heat of fusion. The TMI-grafted PP was used as compatibilizer in PP/polyamide 6 and PP/polyamide 66 blends. Received: 16 October 1997/Accepted: 18 November 1997     

Temperature dependence of photoinduced birefringence in mixed Langmuir-Blodgett (LB) films of azobenzene-containing polymers

The temperature dependence of photoinduced birefringence was investigated for mixed Langmuir-Blodgett (LB) films from the homopolymer poly[4′-[[2-(methacryloyloxy)ethyl]ethyl-amino]-2-chloro-4-nitroazobenzene] (HPDR13) and cadmium stearate (CdSt) and from the copolymer 4-[N-ethyl-N-(2-hydroxyethyl)]amino-2′-chloro-4′-nitroazobenzene (MMA-DR13) and CdSt. Birefringence was achieved by impinging a linearly polarized light on the LB films. The maximum birefringence achieved decreased with temperature as thermal relaxation of the chromophores was facilitated. The buildup curves for birefringence were fitted with biexponential functions representing distinctly different mechanisms with time constants. The first, fast process is thermally activated and may be represented by an Arrhenius process. The decay of birefringence after switching off the laser source was described by a Kohlraush-Williams-Watts (KWW) function, consistent with a distribution of relaxation times for the polymer system. Activation energies were obtained from Arrhenius plots of the rate constant of the exponential functions and KWW function, which showed that the buildup of birefringence was very similar for the two polymer systems. The decay, however, was slower for the LB film from MMA-DR13/CdSt.     

Solution properties of poly(n-hexyl methacrylate) in homologous series of n-alkanes

Summary Dilute solutions of poly(n-hexyl methacrylate) have been studied in the homologous series of alkanes at different temperatures using viscometry. Mark-Houwink relations in solvents widely differing in their thermodynamical quality were established together with the unperturbed dimensions and their temperature coefficient. Received: 24 August 2000/ Revised version: 10 July 2001/ Accepted: 23 December 2001     

Intrinsic birefringence of amorphous poly(bisphenol-A carbonate)

The birefringence of uniaxially oriented poly(bisphenol-A carbonate) (PC) samples stretched over a wide range of temperatures has been measured accurately with a combination of the compensator and the wedge methods. The Hermans' orientation function of anisotropic PC was calculated from the measured dichroic ratio of the infrared absorption band at 1364 cm^-1. Measurements using differential scanning calorimetry, X-ray diffraction, or infrared spectroscopy indicated no stress-induced crystallinity in stretched amorphous PC. At each state having a defined molecular orientation, samples stretched below the glass transition temperature (T_g) always exhibited excess birefringence and slightly higher density. This phenomenon is attributed to bond distortion during stretching, a result of the suppression of large-scale segmental motions of polymer chains below the T_g. The birefringence of samples stretched above the T_g arises exclusively from the orientation effect as a result of greater chain mobility. These measured birefringence values are proportional to Hermans' orientation functions, yielding a linear relationship which allows precise determination of the intrinsic birefringence of amorphous PC as 0.192 ± 0.006.     

Estimation of intrinsic birefringence of poly(ethylene terephthalate) crystal

The intrinsic birefringence of poly(ethylene terephthalate) crystal has been estimated by means of the Orito method using experimental data and using theoretical calculation. The experimental estimation was performed on the basis of the assumption of a two-phase model consisting of crystalline and amorphous phases and the additivity of birefringence contributions — that total birefringence is equal to the sum of the orientation contributions from crystalline and amorphous phases, and of form birefringence. The value experimentally extrapolated by the Orito method is approx. 0.24. On the other hand, the theoretical calculation was carried out in the usual way using the values of bond polarizabilities according to Bunn and the atomic arrangements within the crystal according to Daubeny et al. The calculated value is 0.251. The difference between two results is also discussed.     

Conformational variability of helix sense reversals in poly(methyl isocyanate)

The conformations and energies of several helix sense reversal geometries in poly(methyl isocyanate) (PMIC) have been determined using the PCFF forcefield. In an extension of previous studies, a larger conformational variability for a helix sense reversal has been investigated. In addition to the reversal geometry previously detailed by several authors that results in a relatively small angle deviation from the rod-like polyisocyanate structure, we report the discovery of reversals of similar energy with much larger angle deviations from linearity. The effect of electrostatic interactions as controlled by the value of the dielectric constant, ε, on the conformation and energy of a reversal is also shown to be important. At ε=1.0 (vacuum) the conformations of the reversals with large and small angle ‘kinks’ have similar energies. However, at ε=2.0 (non-polar organic solvent) and ε=3.5 (bulk state) the reversals corresponding to the large angle kinks have lower energies.     

Polymers with pendant isocyanate groups. I. Dual synthesis and properties of poly(styrene-co-styryl isocyanate)

The copolymer poly(styrene-co-styryl isocyanate) was synthesized directly by radical initiation from two different monomer pairs: styrene–cinnamoyl azide and styrene–styryl isocyanate. The copolymerization parameters r₁ = 0.93 ± 0.08, r₂ = ?0.7 ± 0.8 for the first monomer pair and r₁ = 7.8 ± 0.6, r₂ = 0 ± 0.3 for the second pair were determined according to the conventional scheme of copolymerization. The intrinsic viscosities and the thermal behavior of the various copolymers were determined. Further, the chemical reactivity of the pendant isocyanate groups toward alcohol and amines was investigated.     

Polymers with pendant isocyanate groups. II. Dual synthesis and properties of poly(acrylonitrile-co-styryl isocyanate)

The copolymer poly(acrylonitrile-co-styryl isocyanate) was prepared directly in bulk by radical initiation either from the monomer pair acrylonitrile–cinnamoyl azide or from the pair acrylonitrile–styryl isocyanate. The copolymerization parameters, calculated by the conventional scheme, are r₁, = 3.5 ± 0.5; r₂ = 0 ± 0.5, for the first pair and r₁ = 9 ± 0.5; r₂ = 0 ± 0.5 for the second pair. The basic physical properties (solubility, intrinsic viscosity, and thermal behavior) of the new copolymer were determined and the chemical reactions of the isocyanate group with alcohol and with dimethylformamide were investigated.     

Rheological properties of poly(trimethylene terephthalate) in capillary flow

The shear viscosity, extensional viscosity, and die swell of the PTT melt were investigated using a capillary rheometer. The results showed that the PTT melt was a typical pseudoplastic fluid exhibiting shear thinning and extensional thinning phenomena in capillary flow. There existed no melt fracture phenomenon in the PTT melt through a capillary die even though the shear rate was 20,000 s^?1. Increasing the shear rate would decrease the flow activation energy and decline the sensitivity of the shear viscosity to the melt temperature. The molecular weight had a significant influence on the flow curve. The flow behavior of the PTT melt approached that of Newtonian fluid even though the weight‐molecular weight was below 43,000 s^?1 at 260°C. The extensional viscosity decreased with the increase of the extensional stress, which became more obvious with increasing the molecular weight. The sensitiveness of the extensional viscosity to the melt temperature decreased promptly along with increasing the extensional strain rate. The die swell ratio and end effect would increase along with increasing the shear rate and with decreasing the temperature, which represented that the increase of the shear rate and the decrease of temperature would increase the extruding elasticity of the PTT melt in the capillary die. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 705–709, 2005     

现行流量计的特点以及选型

流量是工业生产中一种常见的测量对象,但由于流量计的类型繁多,对设计选型造成了困扰.介绍了工业控制中常用到的几种流量计类型,讨论了其测量原理及主要特点.针对工业生产的不同应用要求,总结了流量计的选型方法和要点.     

Interpretation of intrinsic viscosity/temperature data for solutions of poly(phenyl acrylate) and poly(ethylene oxide)

Measured intrinsic viscosities ([η]) at several temperatures (T) within the interval 280–350 K have been found to increase with T for solutions of poly(phenyl acrylate) (PPA) in ethyl lactate. A decrease of [η] with T was observed for aqueous solutions of poly(ethylene oxide) (PEO) at several temperatures within the range 276–358 K. The results have been treated on the basis of eight excluded volume theories, among which the best consistency was afforded by those of Kurata-Stockmayer-Roig, Fixman, and Stockmayer (Padé). These yielded values of ?3.4 × 10^?3 to ?4.7 × 10^?3 deg^?1 and ?0.9 × 10^?3 to ?2.4 × 10^?3 deg^?1 for the temperatur coefficient of the unperturbed dimensions of PPA and PEO, respectively. The derived θ-temperatures were 287 K as the upper critical solution temperature for PPA in ethyl lactate and 365–382 K as the lower critical solution temperature for aqueous PEO.