摘要:

AbstractThe synthesis of new hydrogel copolymers and their use for anchoring Pd and Pt species is described. The supported catalysts are effective for the reduction of alkenes, dienes, alkynes, and nitroaromatics under mild conditions. The catalysts have been characterized by chemical analysis, particle size measurement, IR, TGA, and x‐ray photoelectron spectra. Relative reactivities and the effects of substrate structure, solvents, catalyst loading, particle size of the catalysts, and partial pressure of hydrogen have been determined. The kinetics of hydrogenation have been analyzed using concepts useful under slurry reaction conditions. The recycling efficiencies of the catalysts and product analysis to establish selectivities have been assessed. © 1992 John Wiley&Sons, I

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301301

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractStrips of polystyrene held in a flowing O2or N2O atmosphere have been exposed to 240‐600 nm radiation. The extent of photooxidation has been followed by x‐ray photoelectron spectroscopy (XPS). Although N2O is a more reactive gas than O2, it produces a less oxidized polymer surface. This surprising observation can be correlated to the photochemistry occurring at the gas/polystyrene interface. © 1992 John Wiley&Sons,

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301302

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe plasma copolymerization of ethylene (ET) and tetrafluoroethylene (TFE) was investigated by means of IR and XPS analyses. The deposition rates for plasma ET/TFE copolymers, when plotted versus mol % TFE in the feed gas, gave a concave‐downward curve situated above the straight‐line joining the deposition rates for the respective plasma polymers, PPET and PPTFE, with the maximum rate at ∼ 70‐80 mol % TFE. This result, coupled with the finding that normalized absorbances of the CH and CF IR bands of ET/TFE copolymers had maxima at ∼ 20 and 80 mol % TFE, respectively, indicated a positive interaction between ET and TFE such that each monomer “sensitized” the plasma copolymerization of the other. As analyzed by XPS, CF groups dominated over CF2and CF3groups at 5‐70 mol % TFE, but at ≥ 80 mol % TFE, these moieties approached the relative proportions in PPTFE (CF2>CF3>CF). The plot of F/C ratio versus mol % TFE was concave‐upward and situated below the hypothetical straight‐line plot representing noninteracting, independent polymerization of ET and TFE, while the % F in the plasma copolymers was linear with mol % TFE. The F1smean binding energies of the ET/TFE plasma copolymers, which increased monotonically with % F, were consistently higher than those for several commercial polymers of fluorinated olefins at comparable values of % F. This result suggested clustering of CFnmoieties in the plasma copolymers or the presence of F atoms in highly fluorinated environments. ©

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301303

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThermal oxidation of poly(ethylene oxide) (PEO) and its blends with poly(methyl methacrylate) (PMMA) were studied using oxygen uptake measurements. The rates of oxidation and maximum oxygen uptake contents were reduced as the content of PMMA was increased in the blends. The results were indicative of a stabilizing effect by PMMA on the oxidation of PEO. The oxidation reaction at 140°C was stopped at various stages and PMMA was separated from PEO and its molecular weights were measured by gel permeation chromatography (GPC). The decrease in the number‐average molecular weight of PMMA was larger as the content of PEO increased in the blends. The visual appearance of the films suggested that phase separation did not occur after thermal oxidation. The activation energy for the rates of oxidation in the blends was slightly increased compared to pure PEO. © 1992 John Wiley&Sons,

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301304

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractOptically‐active polyurethanes (2a‐2c) were prepared by polyaddition reaction of diamide (1a, 1b) and diester (1c) derivatives of chiral coumarin dimer with 4,4′‐diphenylmethane diisocyanate (MDI) in chloroform and methyl ethyl ketone, respectively. The inherent viscosity of the polyurethanes are between 0.13 and 0.21 dL/g inN,N‐dimethylacetamide (DMAc) at 30°C. Treated silica gels were absorbed with ca. 25 wt % of the polyurethanes, and packed as chiral stationary phases for direct optical resolution of 16 racemates with aromatic groups by high‐performance liquid chromatography (HPLC). Polyurethanes2aand2b, obtained from diamide derivatives, show efficient resolution ability to some of the racemates (α = 1.06‐1.79), especially the atropic (R5) andtrans(R6‐R9) isomers. The recognition ability of the polyurethanes can be attributed to the simultaneous aromatic stacking and hydrogen‐bonding interactions with racemates. © 1992

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301305

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractEmulsion polymerizations of ethylene were run using potassium persulfate as the initiator and either an anionic or a cationic surfactant, usually at five times the critical micellar concentration. The molecular weight distributions had at least two major peaks. The broadly distributed lower molecular weight component is formed in the early stages of polymerization. The higher molecular weight component has a narrow distribution characteristic of termination by the combination of chain radicals. The weight‐average molecular weight of this component was about 400,000 when the surfactant was sodium laurate and 33,600,000 when the surfactant was dodecyl amine hydrochloride. © 1992 John Wiley&Sons, I

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301306

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe influence of porous additives with various structures on the shrinkage of resins used for stereolithographic applications was studied by measuring the dependence of the specific gravity of the charged polymer material as a function of the charge fraction. The investigations were conducted on difunctional monomers photopolymerized either by a radical (acrylate) or a cationic (epoxy) mechanism. The improvement resulting from the incorporation of charges in the formulation is accounted for in a semi‐quantitative way by an adsorption‐desorption equilibrium of monomer molecules between the pores and the bulk phase. Thus, the pores of the charges which are initially filled with monomer molecules play the role of buffers which discharge their content as the photopolymerization develops in the liquid phase. It is also worth mentioning that the viscosities of the photosensitive charged resins used in these experiments are quite suitable for use in stereophotolithography. © 1992 John Wiley&Sons,

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301307

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractExperiments to determine the initial reaction rate constants of acidolytic (co)polycondensations of fully aromatic polyesters were conducted in the melt. The initial reaction rate was determined by constant monitoring of the evolution of acetic acid. Both homo‐polycondensation ofp‐acetoxybenzoic acid (pAcBA) and copolycondensation of 2 parts pAcBA, 1 partp,p'‐bisacetoxybiphenyl (BAcBP), and 1 part terephthalic acid (TPA) were studied in a batch reactor under nonisothermal conditions. Next to this, the effect of the presence of the catalystN‐methylimidazole (NMI) on the (co)polycondensations was checked. From the series of experiments it was concluded that the reactivities of acetoxy groups of pAcBA and BAcBP were equal. Furthermore, it was found that the catalyst NMI showed an accelerating effect in the homo‐ and copolycondensations, thereby acting as a “conventional catalyst.” The postulated reaction mechanism for the (co)polycondensations is in accordance with the reaction mechanism for acidolysis of esters by carboxylic acids as suggested by Loncrini. The reactivity of TPA could not be determined by the method used because of the poor solubility of TPA in the reaction mixture. © 1992 John W

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301308

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA new [(PPh2CH2CH2CH2PPh2)Pd(CH3CN)2](BF4)2/CH3OH catalyst for olefin/carbon monoxide alternating copolymerization has been found which is far more active and more stable than previous monodente phosphine Pd catalysts. Methanol is a coinitiator as well as a chain transfer agent. Protonic acid is not a coinitiator but causes chain transfers. In the absence of methanol, the copolymerization was characterized by long induction period and slow rate © 1992 John Wiley&Sons, Inc

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301309

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractInterpenetrating polymer networks (IPN's), pseudo IPN's and linear blends of urethane‐containing aliphatic polycarbonate (PCU) and polybutadiene (PB) have been prepared and characterized. The simultaneous full IPN's of PCU and PB over the whole composition range (15‐85% by weight PCU) exhibit a single phase morphology even though the linear chain blends are completely immiscible, as determined by DSC and confirmed by transmission electron microscopy (TEM). However, in both pseudo IPN's of PCU and PB there appeared multiple (melting and glass) transitions in DSC measurements and phase separation was observed by TEM. © 1992 John Wiley&Sons,

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301310

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY