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21.
Surface functionalization of the plasma‐pretreated polycarbonate (PC) track‐etched membranes via plasma‐induced thermally graft copolymerization of acrylic acid (AAc) was carried out. The resulting PC membranes with grafted AAc side chains were characterized by X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric (TG) analysis. The morphology of the PC membranes was studied by scanning electron microscopy (SEM). The results showed that the grafted PAAc polymers were formed uniformly inside the pores throughout the entire membrane thickness. With increase in the pore‐filling ratio, the pore diameters of PAAc‐grafted membranes became smaller. The PC‐g‐PAAc membranes exhibit rapid and reversible response of the flux to the environmental pH as pH is switched between 3 and 9. Between pH 3.5 and 5.5, the membranes demonstrate a pH‐valve function as the carboxyl group changes from neutral to charged with a corresponding variation in chain configuration. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Viscosities of ternary systems consist of polycarbonate (PC)/brominated polystyrene (PBrS) in chloroform and their corresponding binary systems were measured at different temperatures (20, 25, and 30°C). All the measurements were carried out at the concentration ranges of 0.1–0.6 g·dL?1. The mass ratio of PC to PBrS was selected as 75:25, 50:50, and 25:75 in the ternary solutions. Two empirical expressions of Huggins and Kraemer equations with three-parameters were used for reproducing of the experimental viscosity data. The fitting parameters were obtained for the corresponding temperatures. The miscibility criteria on the basis of the sign of Δ[η]m based on the difference between experimental and ideal values of [η]m, was calculated by applying the Garcia et al., theoretical equation. The effect of temperature on the viscosity data was also studied. The results from this method were correlated with the miscibility data obtained for the same system by differential scanning calorimeter (DSC) findings. 相似文献
23.
Youngjae Yoo Changhyun Park Jong Chan Won Sung‐Goo Lee Kil‐Yeong Choi Jae Heung Lee 《先进技术聚合物》2007,18(12):1015-1019
In this paper, we showed the simplified continuous process to crystallize the polycarbonate (PC) melts using sonocrystallization which is based on ultrasonic cavitation and ‘hot spot’ theory. High power ultrasonic wave was introduced to crystallize the PC prepolymers which is generally used for solid‐state polymerization (SSP) to obtain the ultra‐high molecular weight PCs. The structure and properties of PC treated with ultrasonic wave such as torque changes and crystallinities were studied. The experimental results showed that ultrasonic wave could improve the crystallinities of PCs and sonication time was proportional to their crystallinity. This is attributed to the decrease of the specific volume and the resulting shrinkage is compensated by a flux of a polymer melt toward the crystallization front. Torque data were collected directly from the Haake internal mixer and crystallinities were evaluated from differential scanning calorimeter (DSC). This process is an environmentally benign process so that no additional solvents or treatments are needed and will be very useful in the conventional solid‐state process which is used industrially. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
24.
Liang B. Liu David Gidley Albert F. Yee 《Journal of Polymer Science.Polymer Physics》1992,30(3):231-238
Positron annihilation lifetime spectroscopy (PALS) is used to probe structural changes in glassy polycarbonate in terms of changes in the hole volume and the number density of holes during fatigue (cyclic stress) aging. The ortho-positronium (o-Ps) pickoff annihilation lifetime τ3, as well as the intensity I3, were measured as a function of cyclic stresses and various previous thermophysical aging histories. It is found that τ3, the longest of the three lifetime components resolved in the PALS of glassy polycarbonate, increases when a cyclic stress is applied. These results indicate that there is a structural change during fatigue aging. The “holes” where o-Ps can localize become larger upon fatigue aging. These results also suggest that a significant distinction exists between structural changes induced by thermophysical aging and fatigue aging. The o-Ps annihilation intensity, which is a relative measure of the hole density in a material, showed a continuous decrease upon fatigue aging, indicating the possibility of hole coalescence, which could be a precursor of crazing. The interaction between thermophysical aging and fatigue aging corresponds very well with the enthalpy relaxation behavior as reported previously, viz., a well-aged sample is much more sensitive to cyclic stress. More importantly, it is hypothesized that fatigue failure initiation is probably closely related to hole size and density fluctuation. 相似文献
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Z. Y. Tan S. L. Sun X. F. Xu C. Zhou Y. H. Ao H. X. Zhang 《Journal of Polymer Science.Polymer Physics》2005,43(19):2715-2724
Polycarbonate (PC) was blended with acrylic impact modifiers (AIMs). The effects of modifiers weight fraction on the Izod impact strength and yield strength of PC/AIM blends were investigated. The samples with 4% modifiers were aged under the Tg of PC in an air‐circulating oven, and the effects of aging time on impact strength, yield strength, modulus, elongation at break, post yield stress drop (PYSD) values, and morphology of fracture surface were investigated. The effects of aging time on the shape of stress–strain curve were also investigated. The aged samples were heat‐treated over the Tg of PC to erase the effects of physical aging. It was found that the drop of impact strength caused by physical aging can be recovered, the increment of yield strength and PYSD value caused by physical aging can only be partly recovered, and the heat‐treatment over the Tg of PC caused further increment of modulus. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2715–2724, 2005 相似文献
28.
Birefringence in polycarbonate: Molecular orientation induced by cooling stresses. I. Free quenching
The residual birefringence distributions in polycarbonate disks quenched in a liquid bath under various conditions are determined. Unbalanced distributions of approximately parabolic shape are obtained in the cross-sections in general. A systematic influence of the initial quench temperature on the imblance of the birefringence distributions is observed, with higher initial temperatures leading to a strong shift of birefringence in the positive direction. The systematic variation of the birefringence distribution with quenching conditions is interpreted in terms of a stress and an orientation contribution. The distributions are predicted correctly by a numerical program making use of the linear stress-optical rule with a different stress-optical coefficient above and below the glass-transition temperature. The contribution of molecular orientation is distinguished experimentally from the stress contribution by annealing experiments. © 1993 John Wiley & Sons, Inc. 相似文献
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T. A. Bullions M. Wei F. E. Porbeni M. J. Gerber J. Peet M. Balik J. L. White A. E. Tonelli 《Journal of Polymer Science.Polymer Physics》2002,40(10):992-1012
Bulk poly(ethylene terephthalate) (PET) and bisphenol A polycarbonate (PC) samples have been produced by the coalescence of their segregated, extended chains from the narrow channels of the crystalline inclusion compounds (ICs) formed between the γ‐cyclodextrin (CD) host and PET and PC guests, which are reported for the first time. Differential scanning calorimetry, Fourier transform infrared, and X‐ray observations of PET and PC samples coalesced from their crystalline γ‐CD‐ICs suggest structures and morphologies that are different from those of samples obtained by ordinary solution and melt processing techniques. For example, as‐received PC is generally amorphous with a glass‐transition temperature (Tg) of about 150 °C; when cast from tetrahydrofuran solutions, PC is semicrystalline with a melting temperature (Tm) of about 230 °C; and after PC/γ‐CD‐IC is washed with hot water for the removal of the host γ‐CD and for the coalescence of the guest PC chains, it is semicrystalline but has an elevated Tm value of about 245 °C. PC crystals formed upon the coalescence of highly extended and segregated PC chains from the narrow channels in the γ‐CD host lattice are possibly more chain‐extended and certainly more stable than chain‐folded PC crystals grown from solution. Melting the PC crystals formed by coalescence from PC/γ‐CD‐IC produces a normal amorphous PC melt that, upon cooling, results in typical glassy PC. PET coalesced from its γ‐CD‐IC crystals, although also semicrystalline, displays a Tm value only marginally elevated from that of typical bulk or solution‐crystallized PET samples. However, after the melting of γ‐CD‐IC‐coalesced PET crystals, it is difficult to quench the resultant PET melt into the usual amorphous PET glass, characterized by a Tg value of about 80 °C. Instead, the coalesced PET melt rapidly recrystallizes during the attempted quench, and so upon reheating, it displays neither a Tg nor a crystallization exotherm but simply remelts at the as‐coalesced Tm. This behavior is unaffected by the coalesced PET sample being held above Tm for 2 h, indicating that the extended, unentangled nature of the chains in the noncrystalline regions of the coalesced PET are not easily converted into the completely disordered, randomly coiled, entangled melt. Apparently, the highly extended, unentangled characters of the PC and PET chains in their γ‐CD‐ICs are at least partially retained after they are coalesced. Initial differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared, and X‐ray observations are described here. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 992–1012, 2002 相似文献