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101.
Yaw-Terng Chern Wan-Ho Chung 《Journal of polymer science. Part A, Polymer chemistry》1996,34(1):117-124
1,3-Diaminoadamantane (I) was used as a monomer with various aromatic dicarboxylic acyl chlorides and dianhydrides to synthesize polyamides and polyimides, respectively. Polyamides having inherent viscosities of 0.10–0.27 dL/g were prepared by low-temperature solution polycondensation. The polyamides were soluble in a variety of solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), pyridine, dioxane, and nitrobenzene. These polyamides had glass transition temperatures in the 179–187°C range and 5% weight loss temperatures occurred at up to 354°C. Polyimides based on diamine I and various aromatic dianhydrides were synthesized by the two-stage procedure that included ring-opening to form polyamic acids, followed by thermal conversion to polyimides. The polyamic acids had inherent viscosities of 0.14–0.38 dL/g. The glass transition temperature of these polyimides were in the 245–303°C range and showed almost no weight loss up to 350°C under air and nitrogen atmosphere. © 1996 John Wiley & Sons, Inc. 相似文献
102.
现有的测定镍的容量分析方法很多[1~3],但准确、简便、快速者不多。目前最常用的是将Ni2+先用丁二酮肟沉淀,过滤,洗涤后,重新溶解,再用EDTA滴定,以红紫酸铵或茜素S为指示剂[4,5],滴定时pH控制要求严格。用丁二肟为滴定剂测镍的安培滴定法也有报导[6-8],但由于操作麻烦,很少在实际中应用。另外,在氨性溶液中用丁二肟碱性溶液直接滴定镍的办法也有报导[9],但因使用外指示剂误差较大。 相似文献
103.
Effect of short-chain alcohols on the oil-in-water microemulsion polymerization of styrene 总被引:4,自引:0,他引:4
The influence of short-chain alcohols, 1-butanol (C4OH), 2-pentanol (C5OH) and 1-hexanol (C6OH), on the formation of oil-in-water styrene microemulsions and the subsequent free-radical polymerization was studied. Sodium
dodecyl sulfate was used as the surfactant. The overall performance of C4OH as the cosurfactant is quite different from C5OH and C6OH. The range of the microemulsion region in decreasing order is C4OH > C5OH > C6OH. The primary parameters selected for the microemulsion polymerization study were the concentrations of cosurfactant and
styrene. Only a small fraction of microemulsion droplets initially present in the reaction system can be successfully transformed
into latex particles and the remaining droplets serve as a reservoir to supply the growing particles with monomer. Limited
flocculation of latex particles also occurs during polymerization and the degree of flocculation is most significant for the
C4OH system.
Received: 24 August 1999/Accepted in revised form: 22 October 1999 相似文献
104.
Chorng‐Shyan Chern Jih‐Cheang Sheu 《Journal of polymer science. Part A, Polymer chemistry》2000,38(17):3188-3199
The effects of 2‐hydroxyalkyl methacrylates (HEMA and HPMA) on the styrene miniemulsion polymerizations stabilized by SDS/lauryl methacrylate (LMA) or SDS/stearyl methacrylate (SMA) were investigated. A mixed mode of particle nucleation (monomer droplet nucleation and homogeneous nucleation) is operative during polymerization. Homogeneous nucleation plays a crucial role in the polymerizations stabilized by SDS/LMA, whereas monomer droplet nucleation becomes more important in the polymerizations stabilized by SDS/SMA. The polymerization kinetics is insensitive to the type of 2‐hydroxyalkyl methacrylates, but the difference in the relative importance of monomer droplet nucleation and homogeneous nucleation is detected. Incorporation of 1‐pentanol (C5OH) into the reaction mixture also shows a significant influence on the polymerizations stabilized by SDS/LMA or SDS/SMA. This is attributed to the formation of a close‐packed structure of SDS and C5OH on the droplet surface, which acts as a barrier to the incoming oligomeric radicals. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3188–3199, 2000 相似文献
105.
Yaw-Terng Chern Wen-Liang Wang 《Journal of polymer science. Part A, Polymer chemistry》1998,36(13):2185-2192
A series of new polyamides 3 were synthesized by direct polycondensation of the 1,6-bis[4-(4-aminophenoxy)phenyl]diamantane (1) with various dicarboxylic acids. The polyamides had inherent viscosities of 0.45–1.90 dL/g and number-average molecular weights (Mn) of 24,000–110,000. Dynamic mechanical analysis (DMA) reveals that polymers 3 have two relaxations on the temperature scale between −100 and 400°C. Their α relaxations occurred at high temperatures, ranging from 338 to 389°C. Moreover, these polymers remained quite stable at high temperatures and maintained good mechanical properties (G′ = ca. 108 Pa) up to temperatures close to the main transition markedly exceeding 350°C. Due to the bulky diamantane elements and the flexible ether segments, the polymers 3 were amorphous and soluble in a number of organic solvents such as pyridine, N-methyl-2-pyrrolidone (NMP), and N,N-dimethylacetamide (DMAc). The polyamides 3 have tensile strengths of 56.7–90.2 MPa, elongation to breakage values of 7.5–27.7%, and initial moduli of 1.8–2.1 GPa. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2185–2192, 1998 相似文献
106.
Polymer miscibility was found for a blend system comprising of a new poly(aryl ether ketone) and a poly(ether imide). Phase homogeneity was preliminarily confirmed using optical and scanning electron microscopy, indicating that the scales of phase homogeneity in the blends were beyond the resolution limits of either microscopy. A composition-dependent, single glass transition temperature (Tg) in the PAEK/PEI blends within the full range of composition was observed using differential scanning calorimetry (DSC). The thermal transition breadth also suggests that the scales of mixing are fine and uniform. 相似文献
107.
A. Gupta B.W. Hussey M.Y. Chern 《Physica C: Superconductivity and its Applications》1992,200(3-4):263-270
The effectiveness of oxygen (O2), nitrous oxide (N2O), and nitrogen dioxide (NO2) as oxidizing agents during in-situ growth of YBa2Cu3O7−δ (YBCO) films on (100) SrTiO3 substrates by pulsed laser deposition has been studied as a function of deposition temperature (700–800°C), and laser wavelength (193,248 and 355 nm), for a wide range of oxidizer gas pressure (0.1–200 mTorr). In general, the superconducting transition temperature of the films has been found to increase with increasing oxidant pressure, with zero-resistance temperature ≈90 K only obtained in films prepared in a relatively high pressure (150–200 mTorr) of oxidizer gas. At lower pressures, the transition temperature while being depressed is quite sensitive to the nature of the oxidant, the laser wavelength and the deposition temperature. Nevertheless, independent of the oxygen source or other growth parameters, an almost linear decrease in transition temperature with a corresponding increase in the c-axis lattice parameter has been observed for all the film. YBCO films have also been deposited in a low pressure background (≤ 1 mTorr) using a combination of atomic oxygen and pulsed molecular oxygen. The results are discussed in terms of the oxygen requirement for kinetic and thermodynamic stability of YBCO during growth of the film by pulsed laser deposition. 相似文献
108.
H.R. Vydyanath S.S. Chern F.A. Kroger 《Journal of Physics and Chemistry of Solids》1973,34(8):1317-1321
Iodine doped single crystals of CdS were grown from the vapor phase. High temperature Hall effect measurements for the crystals equilibrated with Cd and S2 vapors at temperatures between 700 and 1000°C gave the free electron concentration as a function of pCd or pS2 and temperature. The results can be explained on the basis of a model in which the CdS is saturated with iodine at low pCd (=high pS2) but unsaturated at high pCd.The solubility of iodine in CdS is given by ct=1·73×1022pS2?1/8 exp (?1·045 eV/kT) cm?3 atm?1/8=4·62×1019pCd1/4 exp (?0·195 eV/kT) cm?3 atm1/4The formation of pairs (ISVCd)′ from IS· and VCd″ is governed by the equilibrium constant KP(I, V)=4 exp (≤1·1 eV/kT)If Cd diffusion occurs primarily by free vacancies, the Cd* tracer self diffusion leads to a vacancy mobility of (1·2±0·5)×10?5 cm2 sec?1 at 900°C, in agreement with results reported by Woodbury [12], but (7±3) times larger than reported by Kumar and Kroger [10]. 相似文献
109.
A series of random copolymers of methylmethacrylate and methacryloxypropyltris (trimethylsiloxy) silane were synthesized by free radical polymerization under ultraviolet light. The permeabilities of these copolymers to carbon dioxide, oxygen, and nitrogen were determined and correlated with the packing densities of the polymers. Correlation between the permeability and permselectivity of these copolymers is also addressed. 相似文献
110.
Chorng-Shyan Chern Gary W. Poehlein 《Journal of polymer science. Part A, Polymer chemistry》1990,28(11):3055-3071
A new theory, based on the concept of nonuniform distribution of free radicals in polymerizing latex particles, has been developed for the kinetics of two-phase emulsion polymerization reactions. This theory also takes into account the diffusion controlled termination and propagation reactions to describe the gel effect and limiting conversion. The kinetic model permits prediction of the distribution of free radicals in the two polymer phases and rate of polymerization as a function of reaction conditions. Experimental data for polystyrene/polymethyl methacrylate and polymethyl methacrylate/polystyrene (postformed polymer/preformed polymer) in the literature have been used to assess the proposed idea of nonuniform distribution of free radicals in the latex particle. 相似文献