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• Physics  (555)
• 1990-1994
• 1970-1974  (555)
• 1972  (555)
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• 1990-1994
• 1970-1974  (555)
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• 1
Electronic Resource
New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: A new class of catalysts for polymerization of cycloalkenes was developed, based on the interaction of these hydrocarbons with π-allylic transition metal complexes. The reaction route (decyclization or double-bond opening) and the microstructure of polyalkenamers obtained is determined primarily by the nature of the transition metal and also by the nature and the number of ligands bound to the metal. π-Allylic complexes of zirconium and chromium catalyze the polymerization of cycloalkenes in both directions. For complexes of the group VI metals the substitution of molybdenum or tungsten for chromium results in complete suppression of the double-bond opening. In the presence of Group VIII metal compounds the polymerization of cycloolefins occurs exclusively at the double bond. The introduction of acidic ligands into the internal sphere of the π-allylic compound does not affect the reaction route but results in a significant rise of the yield of polyalkenamers and enriches the content of trans-1,4-units. Lewis acids act as activators for complexes of all the metals, the halides of molybdenum and tungsten affecting favorably the decyclization. It is assumed that the ring-opening polymerization of cycloolefins proceeds via π-allylic complex formation.
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• 2
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The oxidation of both amorphous and crystalline polypropylene in benzene solution was studied at 100-130°C. tert-Butyl peroxide was used as an initiator. The kinetic behavior of the amorphous and crystalline forms differs slightly; the oxidation rate of the amorphous type is slower for a given polymer and initiator concentration. The oxidation rate of solutions of the crystalline form can be simply described by the expression: R0 = 1.87 × 1013 exp {-29,000/RT} [t-Bu2O2]0.58[polypropylene]0.73, mole/l.-min. Product analyses of the oxidized solutions are incomplete, but the results do show that only ∼40% of the absorbed oxygen is present as hydroperoxide. Further, much of the hydroperoxide is present in low molecular weight polar fragments which are acetone-soluble. These results show that oxidized polypropylene cannot be regarded simply as “polypropylene hydroperoxide” with repeating hydroperoxide groups attached to the polymer chain in 1,3,5… (tertiary) positions.
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• 3
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Some physical properties of linear polydimethylsiloxanes have been studied. The states and transitions in polydimethylsiloxanes have been investigated by using the method of dynamic heat capacity and a thermomechanic method in the temperature range from -150 to +200°C. The temperature dependence of primary and secondary crystallization has been studied by optical, calorimetric, and x-ray methods.
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• 4
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Molecular parameters of sodium amylose xanthate in 1N NaOH solution have been determined by means of light scattering and viscometry. The expansion factor, α, has been determined from the expression due to Orofino and Flory. The value of a of the Mark-Houwink relation, [η] = KMa, has been determined. The Stockmayer-Fixman relationship has been used to evaluate the unperturbed dimension of the chain. The effective bond length b, Kuhn-Kuhn equivalent chain segment length Am and the steric factor σ, i.e., the ratio of the unperturbed dimension to the dimension assuming free rotation of the chain \documentclass{article}\pagestyle{empty}\begin{document}$(\bar R_o^2 )_z ^{1/2} /(\bar R_f^2 )^{1/2}$\end{document} have also been determined. From these data, it is concluded that sodium amylose xanthate in 1N NaOH solution behaves as a loosely coiled molecule.
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• 5
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Radical polymerization of styrene in the presence of various diallyl compounds was carried out at 60°C, with the use of 2,2′-azobisisobutyronitrile as an initiator. The chain transfer constant Cs of the styryl radical to diallyl compounds was determined graphically by solving the Mayo equation. The Cs values of diallyl esters are quite small compared to those of diallyl acetals. The polymerization mechanism of styrene in the presence of diallyl compounds was also discussed in connection with the results obtained previously.
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• 6
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: A series of N-(dialkylaminoalkyl)acrylamides was synthesized by reductive amination of N-(1,1-dimethyl-3-oxobutyl)acrylamide (diacetone acrylamide) and by the reaction of either an alkenylamine or an amino alcohol with acrylonitrile. These monomers homopolymerize and copolymerize readily to form high molecular weight products. The solubility of the monomers and their homopolymers in water ranges from soluble to insoluble at room temperature. The insoluble materials can be quaternized readily to produce water-soluble products. The solubility of the homopolymers in water decreases with increasing temperature. Glass transition and decomposition temperatures of the homopolymers are reported.
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• 7
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 8
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 9
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Acrylic acid has been grafted from aqueous solution onto 70 μ isotactic polypropylene-film previously peroxidized by irradiating in air with both 400 keV electrons and γ-radiation from a 60Co source. Ferrous ion has been used to induce the redox decomposition of the macromolecular peroxy species at temperatures between 0 and 40°C. It has been shown that the effect of low [Fe2+] is to increase grafting rates, but that at [Fe2+] 〉 8 × 10-4 molal the retarding effect of the reducing ion becomes increasingly important. At constant [Fe2+] a pronounced maximum in rate is observed at around 50 wt-% of acrylic acid; this may be related to increased swelling of the polymer matrix at this point. The initial rate of grafting increases as the square root of the preirradiation dose and, in the preirradiation dose rate range, 1.6-8.0 Mrad/sec, is independent of the dose rate. The grafting rate during the later stages of the reaction, however, increases as the preirradiation dose rate decreases. In the temperature range 0-40°C, the overall activation energy is 19 kcal/mole; from this value, the activation energy of initiation has been estimated to be around 20 kcal/mole.
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• 10
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Electron paramagnetic resonance studies were conducted on thermally degraded nylon 6 polymers. A nitroxide radical was observed from nonterminated and amineterminated nylon 6 samples heat-treated in the persence of air. The nitroxide concentration in the latter was about twice that of the former under the same conditions. The nitroxide radical was not observed in acid-terminated nylon 6 samples. A mechanism of nitroxide radical formation was proposed based on the oxidation of secondary amines. A one-line EPR signal was also observed from nonterminated, amine-terminated, and acid-terminated nylon 6 samples heated in the presence of air. This singlet signal was attributed to conjugated systems with unpaired electrons.
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• 11
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: We have investigated the γ-radiation-initiated polymerization of n-butyl acrylate (BA) and of methyl methacrylate (MMA) in aqueous emulsions stabilized with sodium lauryl sulfate (SLS). The reaction rate, as measured by a nonabsolute thermocouple technique, varies as the square root of emulsifier concentration for both monomers. In the case of BA, the dose rate exponent of the reaction rate is 0.7 ± 0.3, whereas the corresponding value for MMA is approximately 0.4. The overall activation energy of the BA polymerization is close to zero, whereas for MMA a value of 4.8 ± 2.1 kcal/mole has been found. The poly(butyl acrylate) molecular weight is effectively independent of soap concentration and of dose rate but decreases as the reaction temperature is increased in the range 30-70°C. The general conclusion drawn from this work is that these radiation-induced emulsion polymerizations differ little from conventionally initiated systems insofar as the reaction kinetics are concerned. Poly(butyl acrylate-g-methyl methacrylate) copolymers have been prepared by a direct irradiation method involving a poly(butyl acrylate) prepolymer seed latex. Some physical properties of this material have been examined.
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• 12
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: 100-MHz NMR spectra are reported for solutions of the 1:1 copolymers of sulfur dioxide with hex-1-ene, cis- and trans-but-2-enes, cyclohexene, cyclopentene, and norbornene, including the deuterated polymers made from hex-1-ene-2-d1, cis- and trans-but-2-ene-2,3-d2, and cyclohexene-3,3,6,6-d4. The resolution of the spectrum of poly-(hex-1-ene sulfone) was very poor in CCl4 as solvent but good in polar solvents. The main-chain CH2 protons are nonequivalent, and their chemical shifts show sensitivity to dyad structure; the α-CH2 protons are also non-equivalent. The spectra of most of the other polymers are discussed in terms of possible preferential modes of addition as well as tacticity effects.
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• 13
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Reactions of dialkyltin mercaptides, thioglycollates, and carboxylates with the poly-(vinyl chloride) model compounds tert-butyl chloride and 3-chlorobut-1-ene have been studied. At 180° the tertiary and allylic chlorine atoms in the model compounds undergo exchange reactions with the SR, SCH2COOR, and OCOR groups attached to tin. In the case of 3-chlorobut-1-ene, the exchange reactions are accompanied by allylic rearrangements. The relevance of these results to the stabilization of poly(vinyl chloride) is discussed.
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• 14
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The magnetic circular dichroism (MCD) spectra of “atactic” and isotactic polystyrene solutions have been found to be sensitive to configurational and conformational differences. The ratio of B terms for “atactic” polystyrene (predominantly syndiotactic) to that of cumene was found to pass through a minimum as the coil expanded in various solvents. The ratio of dipole strengths D also passed through a minimum. For isotactic polystyrene and cumene the ratio of B terms increased with increasing coil size in the range of solvents utilized. The ratio of B terms of isotactic polystyrene over atactic polystyrene was found to go through a maximum as the coil expanded whereas the ratio of dipole strengths was found to continuously decrease. These results have been interpreted on the basis of the change in short range and long range orientation and interaction distances between chromophores during coil expansion. It is concluded that the microscopic conformation of isotactic and atactic polystyrene are very different in very good solvents. The B/D ratio for cumene was found generally to decrease with increasing solvent power.
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• 15
Electronic Resource
New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The equilibrium volatilities at near infinite dilution of various solutes absorbed in molten polystyrene have been determined by a gas chromatographic technique. This method is much more rapid, although, with the present apparatus, probably less accurate than conventional static techniques. The primary parameters obtained from measurements of retention volumes are the Henry's law constants, from which are derived the weight and volume fraction activity coefficients, the Flory-Huggins interaction parameters, and the heats of dilution and solution.Of the solutes investigated, 2-butanone (MEK) was the least, and benzene the most compatible (highest and lowest volume fraction activity coefficients, respectively) with molten polystyrene. A small, but definite, variation of the activity coefficients with polystyrene molecular weight was observed.
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• 16
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Low-temperature polymerizations of fluoral with the use of ionic initiators in inert diluents have produced high molecular weight polyfluoral which is amorphous and tractable. The polymer can be end-capped by standard techniques to give material which is thermally stable to 350-400°C. The stabilized polymer can be fabricated from solution or melt-pressed at temperatures as low as 125°C to give clear films and coatings which are oil-and water-repellent but highly permeable toward oxygen and water vapor.
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• 17
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Investigations on the molecular weight distribution of cyrstalline polypropylene were carried out by column fractionation and gel-permeation chromatography for the purpose of comparing the determination methods. Average molecular weight, standard deviation, skewness, and kurtosis were calculated as statistical parameters from the distribution curve of each, and the number-average and weight-average molecular weights were determined by osmometry and light scattering. The molecular weight distribution curves obtained from column fractionation were found to be narrower than those from gel-permeation chromatography, and it was confirmed that the molecular weight distribution curve obtained from GPC was more accurate and reliable than that from column fractionation by the fact that the average molecular weight from GPC agreed fairly well with that from the absolute methods. On the other hand, no clear difference between these determination methods was observed with respect to skewness and kurtosis of the data, while the standard deviation from GPC seemed to be greater than that from column fractionation.
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• 18
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Polypropylene powder, as formed by typical Ziegler catalysts, can conveniently be hydroperoxidized in aqueous slurry. A cationic surfactant and potassium persulfate are used to achieve wetting and initiate oxidation. It is proposed that specific reaction between the quaternary ammonium cations and persulfate anion generates a water-insoluble persulfate which decomposes to yield a hydrophobic radical species which initiates oxidation. Graft copolymers were prepared by using this polypropylene hydroperoxide, a redox catalyst, and either dimethylaminoethyl methacrylate or n-butyl acrylate. These graft copolymers, dispersed in polypropylene, form two-phase systems in the solid state. Under synthesis conditions which are believed to yield long side chains, the dispersed, more polar polymer was found in larger domains than observed with shorter side chains. Polypropylene spherulites were also distorted, although per cent crystallinity of the continuous polypropylene phase was hardly affected by the presence of graft. Mixtures of poly(propylene-g-butyl acrylate) and polypropylene are rather extensible and of low modulus. Low temperature tensile impact values are only slightly higher than for pure polypropylene. Addition of poly(butyl acrylate) to these blends increases both the low-speed modulud and high-speed tensile impact relative to the two component blends.
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• 19
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The kinetics of reversible polymerization of a polymer system without transfer and termination reactions is investigated theoretically. An analytic solution is obtained that enables one to predict the variation of monomer concentration with respect to time in a closed system. When the polymer system reaches equilibrium, three different relationships are derived between the equilibrium monomer concentration and the ceiling temperature under different conditions. The classical relationship by Dainton and Ivin is a special case of the three derived cases.
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• 20
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate Rp is independent of ceric ion concentration and can be expressed by the equation: Rp = k1 [amine] [monomer] + k2[monomer]2, where k1 and k2 are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.
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• 21
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The deuterium-decoupled methine proton spectra of polyacrylonitrile-β,β-d2 were measured at 156°C in dimethylsulfoxide-d6 solution. Splittings of triad peaks caused by pentad sequences were observed. The isotactic triad resonance was resolved into three peaks and the heterotactic resonance into two peaks, while the syndiotactic resonance was unresolved or resolved into three peaks. The splittings were assigned by comparing the probability of each pentad sequence with observed intensities. The pentad signal shifted to the higher magnetic field with increasing number of meso configurations as neighbors of the central triad. It was observed that the pentad of atactic polyacrylonitrile-β,β-d2 obeyed Bernoullian statistics but that of isotactic polymer obtained by γ-ray irradiation of the canal complex seemingly obeyed first-order Markov statistics.
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• 22
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The radical copolymerization of sulfur dioxide and chloroprene (CP) in benzene was carried out, especially as a function of the total monomer concentration ([SO2] + [CP]). The composition of chloroprene polysulfones varies mainly with total monomer concentration and with polymerization temperature, but depends very slightly on feed composition. The microstructure of chloroprene units in chloroprene polysulfone was such that the trans-1,4 unit was predominantly over the cis-1,4 unit. Thus it would seem possible to rule out both radical copolymerization mechanisms, i.e., propagation of separate monomers as explained by the Lewis-Mayo equation, and propagation processes involving a monomer charge-transfer complex.
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• 23
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The possibility of evaluating with acceptable accuracy the composition of a two-polymer mixture which is well separated by GPC, was studied by using mixtures of high molecular weight polybutadiene (M̄w = 4.5 × 105) and low molecular weight polyiso-butylene (M̄n in the range of 103). It was concluded that a satisfactory evaluation of the composition of a polymer mixture can be achieved, provided that the variations of the refractive index with the molecular weight are taken into account for the low molecular weight polymer (the polyisobutylene).
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• 24
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The degradation of two chlorinated polyethylene compounds CPE 25 (45% chlorine) and CPE 16 (36% chlorine) was studied by following their rates of dehydrochlorination at two temperatures, 150°C and 180°C in pure nitrogen and pure oxygen atmospheres. Studies on the powdered polymers showed that the dehydrochlorination rate of CPE 25 is about fourteen times faster than that of CPE 16 in nitrogen atmospheres and only three to four times faster in oxygen. The molded polymers gave a lower rate of dehydrochlorination than when in the powdered form. This effect is attributed to diffusion factors. The antimony oxide brought about an induction period in the dehydrochlorination reaction during which only a small amount of HCl is evolved, followed by a very fast rate of dehydrochlorination both in oxygen and nitrogen atmospheres. The duration of the induction period increases with increase in the Sb2O3 concentration, but is followed by an accelerated HCl loss which is faster when Sb2O3 concentration is higher. This work provides supporting evidence that SbCl3 was formed and lost during degradation. Mechanisms of dehydrochlorination are suggested for the reaction in the case of pure chlorinated polyethylene and for the polymer containing antimony oxide.
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• 25
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 26
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Soluble ethylene polymerization catalysts derived from (π-C5H5)2Ti(R)Cl and R′AlCl2 where R is ethyl or higher alkyl and R′ may be methyl or ethyl, were studied both by polymerization kinetics at 0°C and by diagnostic experiments. An early acceleration in rate occurred at this temperature in toluene solvent which was due to a solvent dependent increase in catalyst activity, not to a gradual formation of catalyst. No such solvent effect was found in nonaromatic solvents. The subsequent decay in rate, at least at low temperatures, did not depend upon valence reduction. The effect of Al/Ti ratio was studied, and certain discrepancies in the literature were shown to be due to the method of making kinetic measurements. Oxygen, which has previously been reported to affect the polymerization rate with these catalysts, was also found to eliminate the acceleration period in toluene when present in the amount of 1% of the catalyst. These catalysts gave polymers at low temperature for which the active site had long life and which did not undergo chain transfer. Therefore, they approximate many of the characteristics of living polymers.
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• 27
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 28
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New York : Wiley-Blackwell
ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The preparation of vinyl-substituted pyrylium salts and their intermediates is described. These monomers and intermediates have been derived from syntheses based on p-2-hydroxyethoxybenzaldehyde and 4-methoxypyrylium salts. Treatment of the hydroxybenzaldehyde with acetophenone gives a hydroxypyrylium intermediate which, when methacrylated, gives a pyrylium methacrylate. Methacrylation of the hydroxy-benzyldehyde followed by condensation with methylpyrylium salts gives styryl-pyrylium methacrylates. Displacement of the methoxy group in methoxypyrylium salts with ethanolamine derivatives followed by methacrylation yields a series of aminopyrylium methacrylates. The preparation of a divinylpyrylium urethane and a pyrylium-type copolymer is also described.
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• 29
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ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reaction of polydiethynylbenzene with hydrazine is described. The resulting polypyrazole has good tensile properties and good thermal stability. N-Methylhydrazine and hydroxylamine react in a similar way but product properties are inferior. Polypyrazole polymers can easily be modified with acid chlorides or isocyanates.
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• 30
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ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: By using the carbon-13 NMR technique, it is shown that there are no cis-1,4-trans-1,4 linkages in a n-BuLi-catalyzed polybutadiene. The polymer consists of “blocks” of cis-1,4 units and trans-1,4 units separated by isolated vinyl units. Preliminary evidence suggests this might also be true for other types of 1,3-diene polymerization. Some of the implications of this finding on the mechanism of polymerization are discussed. Tacticity triad distributions are readily determined in polybutadienes with high 1,2 addition contents.
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• 31
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ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The radiation-induced grafting of styrene vapor to low-density polyethylene film of 0.063 mm thickness was studied at 23°C at a dose rate of 1.98 × 104 rad/hr. The concentration C of monomer in the film was measured as a function of pre-irradiation exposure time to monomer vapor. The concentration-dependent diffusion coefficient of styrene in polyethylene was calculated to be 4.9 × 10-9 exp {2.0C/C0} cm2/sec, where C0 is the saturation concentration of styrene in the film, and a linear boundary diffusion coefficient for styrene vapor into polyethylene film was found to be 2.0 × 10-7 cm/sec. The rate of grafting was determined as a function of the concentration of styrene absorbed in the film. The maximum graft yield was obtained with an initial styrene concentration in the film of 4 wt-%. Under conditions of low initial monomer concentration, the grafting rate increases with irradiation time. The results are compared with previously published data on grafting of polyethylene from methanol-styrene solutions. They are explained in terms of the viscosity of the amorphous region as a function of styrene content and the resistance to the diffusion of monomer at the film-vapor interface.
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• 32
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ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The effect of stabilizer on the thermal degradation of poly(vinyl chloride) was studied by means of pyrolysis-gas chromatography. The stabilizers used in this study were dibutyltin dilaurate, dibutyltin bis(n-dodecyl mercaptide), barium stearate, and zinc stearate. PVC containing these stabilizers was degraded in a stream of nitrogen at temperatures ranging from 350 to 570°C. It was found that observed drastic reduction of benzene yield from the PVC containing zinc stearate had a close correlation with the formation of crosslinking structures.
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• 33
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ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The polymers deposited from mixtures of argon and the vapors of methane, ethane, propane, and n-butane subjected to excitation in a 30-MHz discharge have been analyzed by infrared absorption techniques and for elemental composition. The polymers show unsaturation, crosslinking, and branching. The stability of the polymers to atmospheric oxidation is discussed.
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• 34
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ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Bismaleimides undergo successive 2 + 2 and 2 + 4 cycloadditions to alkylbenzenes to form polyimides. For the series toluene, ethylbenzene, cumene, tert-butylbenzene, highest yields of polymer are obtained with toluene and tert-butylbenzene with three different bismaleimides. This is explained in terms of inductive and steric effects of the alkyl substituents.
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• 35
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ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The preparation and characterization of functionally terminated polybutadienes by an anionic polymerization technique is described. Prepolymers possessing hydroxyl end-groups were synthesized via vacuum-line methods. Characterization was completed through endgroup, functionality, molecular weight, molecular weight distribution, and microstructural analyses. Emphasis was placed on the reproducibility in the properties of the prepolymers, particularly in their functionality.
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• 36
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ISSN: 0449-296X
Keywords: Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reaction rate of phenol and aqueous formaldehyde in the presence of p-phenolsulfonic acid has been studied. The increase in pH during the reaction, which decreases the reaction rate, can be correlated with the disappearance of polyoxymethylene (formaldehyde), but not as previously supposed solely with the dilution effect of the water formed from the reaction. Gel-permeation chromatography was used to monitor the consumption of phenol and the growth of polymeric species. It has been demonstrated that the formation of a second liquid phase during the novolac process is independent of the amount of catalyst. The liquid two-phase system and its relation to the reaction rate have been examined. The final molecular weight distribution of novolacs is dependent not only on the initial pH of the system, but also on the pH at the onset of devolatilization.
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Methods of preparing new monomers, 2-vinyl and 2-isopropenyloxazoles and 2-isopropenyl-1,3,4-oxadiazoles are described. New methods were developed to synthesize monomers containing an isoxazole or a thiazole ring. Radical homopolymerization and copolymerization with styrene of these monomers were carried out by using AIBN as an initiator. Monomer reactivity ratios r1, r2 and Alfrey-Price Q-e values were determined by the Fineman-Ross and the Mayo-Lewis methods. The localization energy of the β-carbon was calculated by a HITAC-5020 computer, and the monomer reactivity is discussed in terms of Lβ.
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: A new thermally stable polymer with a structure resembling that of graphite has been synthesized by the condensation of 1,4,5,8-tetraaminoanthraquinone and 1,3,6,8-tetraketo-1,2,3,6,7,8-hexahydropyrene (naphthalene-1,8,4,5-diindandione). Prepolymers, with an open structure, were soluble to some extent in concentrated sulfuric acid but were more completely solubilized by methanesulfonic acid. The final polymer with a closed-ring structure, which was obtained by heating the prepolymer having an inherent viscosity of 0.4, was completely insoluble in these acids. Elemental analysis indicated that a high degree of cyclization was achieved, and the final polymer showed good thermal stability. Prepolymers with inherent viscosities in the range 0.11-1.58 have been obtained but, usually, a high viscosity was accompanied by a low acid solubility. Prepolymers with an inherent viscosity of 0.4, which were very soluble (〉90%) in strong acids, were solubilized to a high degree by reduction with sodium dithionite in alkaline, aqueous dimethylacetamide. The highest molecular weight prepolymer (inherent viscosity of 1.30-1.58) was solubilized to a greater extent in this base mixture than in methanesulfonic acid. However, it was not completely soluble, under the conditions employed. The propolymers of higher molecular weight showed some fiber- and film-forming properties.
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• 39
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 40
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: One crystalline form of α,α′-bis(4-acetoxy-3-methoxybenzylidene)-p-benzenediacetonitrile is photopolymerized by a four-center reaction to give a polymer containing alternating benzene and cyclobutane rings. The polymer is highly crystalline and insoluble in most solvents. Location of groups around the cyclobutane ring is deduced from the products obtained on thermal decomposition. Chain contained benzene rings are located in positions 1 and 3; aromatic groups alternate sides of the cyclobutane ring. Special characterization and quantum yield of the polymerization are reported, as well as polymer solution viscosity and alkaline depolymerization of the polymer.
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• 41
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Addition of polar modifiers to alkyllithium-initiated homopolymerizations of butadiene causes substantial changes in the microstructure of the polymers produced. These changes are shown to depend not only on the concentration of modifier, but also on the polymerization temperature. The combined effects of modifier concentration and reaction temperature have been considered, and a method is presented for quickly determining the proper conditions for preparation of a polybutadiene of any 1,2-microstructure within a range of 10-80%. It is also shown that in anionic polar-modified copolymerizations of butadiene-styrene, the reaction temperature is again critical. Within a certain concentration range of modifier, the temperature will influence the rate of styrene incorporation or the randomness of styrene units in the resulting copolymers.
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• 42
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Topics: Chemistry and Pharmacology
Notes: Several novel vinyl polymers containing five fused benzene rings in side chains were synthesized either by polymerization of the appropriate vinyl monomers or by chemical modification of the appropriate polymer. Thus, 3-(α-acryloyloxy)ethylperylene was prepared from perylene by Friedel-Crafts acylation with acetyl chloride and subsequent hydrogenation, followed by the reaction of the resulting alcohol with acryloyl chloride. 3-Acrylamido- or methacrylaminoperylene was prepared by the nitration of perylene, reduction of the resulting 3-nitroperylene, and the reaction with acryloyl or methacryloyl chloride. p-Vinylbenzal-3-acetylperylene was prepared by the condensation and dehydration reaction between p-vinylbenzaldehyde and 3-acetylperylene under alkaline medium, and, in the same manner, p-vinylbenzal-3-aminoperylene was prepared from p-vinyl benzaldehyde and 3-aminoperylene. All these monomers were polymerized with α,α′-azobisisobutyronitrile as catalyst in solution to afford the corresponding vinyl polymers. A vinyl polymer containing perylene-3-acetyl side chain was also prepared by the acetalization of poly(vinyl alcohol) with 3-formylperylene.
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• 43
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Topics: Chemistry and Pharmacology
Notes: The solid-state polymerization of maleimide by γ- and ultraviolet irradiation was carried out in binary systems with succinimide, maleic anhydride, and acenaphthylene. Polymaleimide obtained from the solid-state polymerization of maleimide by γ-rays was amorphous, while that obtained from the solid-state polymerization by ultraviolet rays was highly crystalline. In the maleimide-succinimide system the rate of polymerization reached a maximum nearly at the eutectic composition when the polymerization was carried out by γ-irradiation. With ultraviolet irradiation the rate of polymerization became higher with increasing content of succinimide in the feed. In the maleimide-maleic anhydride system a copolymer of both constituents was formed by γ-irradiation, but almost no homopolymer was produced. On the other hand, two kinds of polymers, a crystalline copolymer and an amorphous one, were produced by ultraviolet irradiation. The results were compared with those obtained from the copolymerization in solution. In the maleimide-acenaphthylene system the main products with ultraviolet irradiation was the dimer of acenaphthylene.
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• 44
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Topics: Chemistry and Pharmacology
Notes: Fibers of benzoxazole-imide ordered copolymers were prepared by cyclodehydrating the amide-phenol units of precursor polyamide-o-hydroxyimide fibers at 375°C in nitrogen. The precursor polyamide-o-hydroxyimides were obtained by the reaction of 3,3′-dihydroxybenzidine with diacid chlorides containing preformed imide rings. The benzoxazole-imide fibers are very thermally stable, especially with respect to retention of tensile properties after heat aging in air. For example, the benzoxazole-imide fibers after heating aging in air for 35 days retained 75% or more of their original tenacities and 50% or more of their original elongations to break. The original fibers did not have high tenacities, probably because of the rather extreme thermal treatment required to cyclodehydrate the amide-phenol units of the precursor fiber. The ultraviolet light stability of one benzoxazole-imide fiber was outstanding for a fiber of the polyheterocycle type: there was no loss in strength or elongation after 140 hr of exposure in a Fade-Ometer. Fibers of ordered amide-imide polymers based on the same imide-containing diacid chlorides used for the benzoxazole-imide polymers were also prepared. They were substantially less thermally stable than their benzoxazole-imide fiber counterparts, as expected.
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• 45
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Unique photodegradable polyamides have been prepared by solution polymerization of diphenyl α-truxillate or δ-truxinate with hexamethylene or nonamethylenediamine, followed by melt polymerization. Photochemical properties of resulted polyamides were studied spectroscopically and are discussed in terms of photoreversibility and monomeric derivatives for comparison. Solution viscosity of the polymer was decreased by irradiation with a high-pressure mercury lamp. The polymers from α-truxillic acid depolymerize by the action of monochromatic light of 224 mμ to give rise to cinnamyl groups faster than those from δ-truxinic acid. On the photodegradation of polyalkylene-δ-truxinamide, two types of scission of cyclobutane were found: symmetrical scission, giving rise to two cinnamyl groups, and a symmetrical scission, giving rise to one trans-stilbene and one fumaramide linkage. The intense absorption peak due to cinnamyl groups at 272 mμ of partially photodepolymerized films diminished by the action of 304 mμ light; this can be accounted for by the recombination of cinnamyl groups into cyclobutane ring and some unidentified crosslinking reactions. The photochemical behavior of cyclobutane in the polyamides studied proved to be consistent with that of monomeric derivatives reported previously. The study on thermal properties of the polymers by DTA and TGA revealed that this type of polyamide is quite stable as high as 350°C unless significant steric effects are involved.
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• 46
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: For unfractionated anionic polymers, the following relationship between the osmometric molecular weight and intrinsic viscosity is valid: M̄n = 13200[η]1.115 (cresol), or M̄n = 13000[η]1.021 (93.8% H2SO4). A comparison of the osmometric and viscometric data with the number of endgroups of a polymer confirmed the finding that under certain conditions, moderately branched molecules can be formed; the above parameters depend on the type of the activator used.
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• 47
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Notes: The effect of the amount of metabisulfite and of the change (spontaneous or deliberate) in the pH of the medium on the viscosity and structure of the polymers is shown. These data as well as evidence on the structure of the polymers formed in the presence of “foreign” aldehydes suggest that in addition to the polymerization proceeding by the radical mechanism, heterolytic processes occur at the carbonyl group. As a result, structures of the semiacetal ester type are formed in the polymer chains of methacrolein.
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• 48
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Notes: Polyurethanes derived from xylylene diisocyanates and trans-1,4-cyclohexanedimethanol were thermally degraded by using the techniques of thermogravimetry and pyrolysis at atmospheric pressure. Quantitative determination of the pyrolysis products such as CO2, diamine, olefin, and starting diol showed that these polyurethanes follow the typical mechanism of degradation via dissociation into starting diol and diisocyanate. Kinetic parameters for the overall degradation reaction were determined using four different methods. The results showed the influence of the experimental technique used when making a comparison of the thermal stability of polymers, as determined by the kinetic parameters of the degradation reactions.
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• 49
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Notes: A comprehensive kinetic scheme is proposed which takes into consideration γ-ray-initiated polymerization via free radical, cationic, or radical-cationic species, or their combinations, and the relative contribution of each depending upon experimental conditions. From this kinetic model, equations describing the kinetics of polymerization and the resulting molecular weight distributions have been derived. The resulting expressions are complex in nature, particularly for the case where a combination of mechanisms is involved. In view of this, a general approach to the problem of generating theoretical molecular weight distributions based on the application of high speed digital computers has been presented. The proposed technique is particularly powerful since no simplifying assumptions or mathematical approximations are required in order to obtain the molecular weight distribution.
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• 50
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Topics: Chemistry and Pharmacology
Notes: The γ-ray initiated polymerization of styrene in the liquid state was investigated over the temperature range 0 to -29°C at constant dose rate. The kinetics and molecular weight distributions were studied for samples prepared by standard techniques and samples subjected to exhaustive drying to remove residual water. In the former case, the rates of reaction were comparable to those for purely free radical polymerization, however, the resulting molecular weight distributions were distinctly bimodal, indicating an additional contribution from the cationic mechanism. On the other hand, the rates of polymerization for rigorously dried samples were 2 to 3 orders of magnitude greater than accepted free-radical values, and the molecular weight distributions were unimodal in nature. The experimental results were compared with theoretical kinetic data and molecular weight distribution data generated from a kinetic scheme taking into consideration polymerization via free-radical, cationic, and radical-cationic species, resulting in the evaluation of a number of quantities of interest. Substitution of determined values for the rate constants and G values results in good agreement between theoretically generated and experimentally determined kinetic data and molecular weight distribution data over the range of experimental conditions studied.
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Notes: Vinyl acetate was polymerized at high initiation rate with 2,2′-azobis(2,4-dimethyl valeronitrile) as initiator at 50°C. In this polymerization, the power dependence of polymerization rate on the initiation rate is smaller than at lower concentration of monomer. This dependence was kinetically analyzed at each given concentration of monomer. Average degree of polymerization of polymer formed depends on the concentration of initiator. This dependence was explained by considering chain and primary radical terminations and transfer to monomer of polymer radical, and the initiator efficiency (=0.503) was deduced. It was found that the chain termination is inversely proportional to solvent viscosity, but the primary radical termination is not inversely proportional to solvent viscosity. Further, the value of the primary radical termination rate constant (=1.4 × 109l./mole-sec) was estimated.
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Notes: Polymerization of methyl methacrylate by cyclic ether hydroperoxide-metal acetylacetonate systems for a number of different metals was carried out to compare with the tert-butyl hydroperoxide-metal acetylacetonate initiating systems. The rate of polymerization of methyl methacrylate with cyclic ether hydroperoxides as initiating systems was much higher than that with tert-butyl hydroperoxide. In cyclic ether hydroperoxide initiating systems, V(III), Co(II,III), Fe(III), Cu(II), and Mn(II) promoted the polymerization rate markedly, and Zn(II), Ni(II), Al(III), and Mg(II) had little or no effect; in the tert-butyl hydroperoxide initiating system only V(III), Co(II), and Mn(II) enhanced polymerization rate, and most of other metals showed little or no effect. Furthermore, noticeable differences in color of solution and appearance during polymerization, and in relation between conversion and the degree of polymerization were observed. The effect of metal acetylacetonates on hydroperoxide initiators in polymerization of methyl methacrylate was also compared with that on the decomposition of hydroperoxides.
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Notes: Substitution of several mole per cent of the hydroxyl groups of poly(vinyl alcohol) by fluorine results in marked changes in polymer properties. These fluoro poly(vinyl alcohols) (PVAF) form thermally reversible gels in water at low polymer concentrations. In solution, a helical conformation or a random coil containing helical sequences is more in accord with the experimental observations than the random coil structure of poly(vinyl alcohol). This helical hypothesis is supported by high heats of crosslinking of the aqueous thermally reversible gels, the difficult solubility of PVAF in H2O, the insolubility of the PVAF-iodine complex under conditions where the PVA-iodine complex remains soluble, the temperature-independent high value for the Huggins k ′ slope constant, the greater stability of the PVAF-iodine complex, the shear dependence of the solution viscosity and our inability to form thermally reversible gels by the introduction of fluorine into other water-soluble polymers which are capable of hydrogen bond formation. Infrared dichroism and deuteration measurements do not differentiate between PVA and PVAF. If this conclusion is correct, PVAF is the first vinyl polymer of which we are aware that maintains a helical conformation in solution.
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Notes: The kinetics of the radiation-induced polymerization of ethylene in the presence of various amounts of medium (tert-butyl alcohol containing 5 vol-% of water) was studied, and the effect of the amount of medium on the polymerization was investigated. The polymerization was carried out by use of a reactor of 100 ml capacity under the following conditions: temperature, 24 ± 3°C; pressure, 200 kg/cm2; dose rate, 2.0 × 104-1.6 × 105 rad/hr. The amount of polymerized monomer and the rate of polymerization were maximum when about 50 ml of the medium was used. Data obtained with the use of 30, 50, and 90 ml of the medium were analyzed kinetically and the rate constants of each elementary reaction were determined by the method based on a reaction mechanism which contains both first- and second-order terminations for the concentration of propagating radical. These results were compared with those obtained with the use of 70 ml of the medium already reported in the previous paper. The dose rate exponents of the rate of polymerization were about 0.7-0.8. It was found that G values for the initiation of ethylene and the medium were 1.5 and 3.8, respectively, and the rate of propagation was proportional to the fugacity of ethylene. It is supposed that the medium plays an important role in the first-order termination, because the apparent rate constant of the reaction was larger when a larger amount of medium was used.
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Notes: The interaction of optically active polymer prepared from L-lysine and adipyl chloride by interfacial polycondensation with D- and L-tryptophan was studied. It was found that selective interaction occurred, and the amount of L-isomer bound to the polymer was greater than that of D-isomer in the range from pH 3.0 to 7.5 at 25°C. At near pH 5.0, the maximum asymmetrical ratio was obtained. The optical rotatory dispersion and viscosity of the polymer were measured. The relationship between conformational differences of the polymer and asymmetric interaction is discussed.
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Topics: Chemistry and Pharmacology
Notes: The thermal degradation of poly-p-oxybenzoate in vacuo as function of temperature has been studied. The energy of activation of the process up to about 30% volatile formation is 59.6 kcal/mole. The degradation is preceded by induction periods, which have been shown to be due to poor heat conductivity of the polymer powder. CO, CO2, phenol, and an unknown compound of molecular weight larger than 200 are the main degradation products found by chromatographic analysis. Infrared spectra of the original polymer, the polymer residue after degradation and of a degradation product solid at room temperature are presented. The possible reactions taking place have been indicated. The heat stability of the polymer in vacuo lies between those of polytetra-fluoroethylene and polyethylene.
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Notes: The influence of γ-irradiation on the melting and two solid-solid transitions, occurring near 19° and 30°C, of polytetrafluorethylene was studied by differential scanning calorimetry. A continuous depression of all three transition temperatures, with increasing dose was observed in a first scan of highly crystalline samples at a heating rate of 20°C/min. Additional information was obtained about the accompanying heats of transition. Values for the number of CF2 units excluded from the crystal lattice per 100 eV energy deposition were calculated by using an equation for the depression of the melting point by chemical impurities. The value obtained of G(-units) = 3.3 ± 0.3 is in agreement with a value of G(chemically damaged units) = 3.0 ± 0.1 previously reported on the basis of scavenging techniques. It is concluded that chemical radiation-induced damage in this polymer may be estimated by reference to changes in the melting temperature. A value of G(-units) = 1.6 ± 0.2 was obtained by reference to the 19°C transition.
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Notes: This paper describes the preparation of a series of novel perfluoroalkylene- and ether-linked aromatic polyimides. Depending on the nature of the precursor diamine, the polyimides were prepared by either melt or solution techniques, the latter via the corresponding poly(amic acids). The polymers were characterized by a variety of methods, and their structure is discussed.
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Notes: Soluble ethylene polymerization catalysts derived from (π-C5H5)2Ti(R)Cl and R ′AlCl2, where R = methyl or phenyl and R ′ = methyl or ethyl, were studied both by polymerization kinetics at 0°C and by diagnostic experiments. It was found that the first insertion of ethylene into the Ti—R bond is difficult when R = methyl or phenyl, and for this reason these catalysts show a different overall behavior than when R = ethyl or higher alkyl.
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Notes: Cyclization of synthetic cis-1,4-polyisoprene was carried out by using TiCl4 and p-toluenesulfonic acid catalyst. The average cyclicity and structure of the polymers cyclized to a different degree was studied by infrared and high-temperature NMR spectroscopy. The methods of synthesizing an average mono-, bi-, tri-, or polycyclic polymer that could be distinguished by high-temperature NMR spectroscopy and followed by gel-permeation chromatography are discussed.
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• 64
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Topics: Chemistry and Pharmacology
Notes: The kinetics of the solid-state polymerization of acrylamide, γ-irradiated at 77°K, has been studied by wide line NMR and by ESR at temperatures above 300°K. This reaction may be followed by the growth of a narrow line superimposed on the NMR spectrum of the monomer. The amplitude of this narrow line has been found to be proportional to the polymer yield. By long continued annealing, the conversion yield approaches a limiting value, generally lower than 50% under most of our experimental conditions. The activation energy of post-polymerization is 19 ± 1 kcal/mole. The radiochemical yield of radicals, determined by ESR, is 0.27 ± 0.03 at 77°K before warming. In the course of annealing above 300°K, the overall concentration of radicals is reduced to about one tenth of its initial value at 77°K. However, the local concentration of the remaining radicals is constant and equal to 1.2 × 1019 spins/g, i.e., more than 100 times their overall concentration. The recombination of radicals does not seem to intervene in the kinetics of post-polymerization, so that it may be assumed that only the radicals remaining after annealing, have actually contributed to the reaction.
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Notes: The post-polymerization of acrylic acid, γ-irradiated at 77°K, has been studied by broad-line NMR and ESR between 240°K and 286°K (mp). The changes in the structure of NMR spectra during the polymerization has been related to the conversion yield checked by gravimetry of the polymer formed. The very fast reaction occurring above ⋍270°K has been followed simultaneously by NMR and thermal analysis. This last method indicates an activation energy of chain propagation of 18.6 ± 2 kcal/mole in satisfactory agreement with the value given by the initial slope of the conversion - time curves. ESR experiments show that, while the average radical concentration decays by a factor of about ten between 77°K and 240°K, the local concentration of radicals persisting after prolonged annealing at T 〉 240°K, remains the same as at 77°K, i.e., 1.4 × 1019 spins/g. A kinetic scheme, assuming an exponential decay of propagation and termination rate constants with chain length, has been proposed to explain the shape of conversion - time curves as well as the almost constancy of the local concentration of growing polymer chains.
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Notes: High molecular weight, 1:1 alternating copolymers of 1-bicyclobutanecarbonitrile with styrene were prepared in tetramethylenesulfone solution by complexing the electron-poor bicyclobutane monomer with zinc chloride. Methyl 1-bicyclobutanecarboxylate under these conditions gave copolymers containing a slight excess of styrene units (ratio 1:1.3 to 1:1.8). High molecular weight homopolymers of 1-bicyclobutanecarbonitrile and of methyl 1-bicyclobutanecarboxylate were prepared similarly. The tendency of the bicyclobutane nitrile to form 1:1 alternating copolymers is as great as that of its vinyl analog, acrylonitrile, and the synthesis of other alternating copolymers from this monomer should be possible.
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• 68
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