摘要:

The behavior of various diaminotetraarylcyclotriphosphazenes N3P3(NH2)2R4on heating has been studied. The homocondensation reaction occurs with elimination of ammonia or aniline when the N3P3(NH2)2(OC6H5)4, N3P3(NH2)2(C6H5)4, or N3P3(NHC5H5)6is heated under various conditions. However, the homocondensation reaction does not proceed in case of N3P3(NH2)2(SC6H5)4because of the high conductivity of this compound.

ISSN:0022-233X    

DOI:10.1080/00222337808069396

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The polymerization of methyl methacrylate and acrylonitrile can be initiated by the chitosan-copper(II) complex and its monomeric form, glucosamine-copper(II) complex, in the presence of carbon tetrachloride. The chitosan complex system was found to be more active for initiating the polymerization of methyl methacrylate than acrylonitrile at neutral pH. On the other hand, the glucosamine complex system showed no activity at neutral pH region, but had high activity at higher pH, because of the reducing endgroup of the glucosamine. Formation of the copper(II) complexes was studied by pH titration and visible spectroscopy. The relationship between complex formation and the activity for initiating the polymerization is discussed.

ISSN:0022-233X    

DOI:10.1080/00222337808069397

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0022-233X    

DOI:10.1080/00222337808069398

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The conductivity of different catalytic and copolymerization systems which were used for the copolymerization of epoxide with cyclic anhydride catalyzed by a tertiary amine, ammonium salt, alkali salt, and the system tert-amine-proton donor compound was conductometrically investigated in different solvents at 120°C. Measurements of the conductivity of the system epoxide-anhydride-tertiary amine as well as that of components and binary solutions indicate that a considerable increase in conductivity appears only in a ternary system. The temporal course of conductivity of the reaction system indicates the ionic character of copolymerization while the conductivity plot shows a maximum. The increase in conductivity in the initial stage of reaction is interpreted as a result of the formation of active centers before reaching a stationary concentration (induction period); the decrease in conductivity is regarded as a consequence of the reduced mobility of macroins due to the increase in molecular weight and macroviscosity of the system and to the dissolving ability of solvent. The absolute value of conductivity of the copolymerization system depends on the polarity of solvent and increases with dielectric constant. Similar results were obtained with the tertiary amine-proton donor catalyst system. The catalytic effect of alkali and ammonium salts brings about rapid dissociation and increase in conductivity of the copolymerization system. AS in catalysis by tertiary amine, the decrease in conductivity is attributed to the decrease in mobility of ions and to a solvent effect. Comparison of maximum conductivities with rate constants for copolymerization points out that the ion pairs of active centers as well as the dissociated salt have a catalytic effect.

ISSN:0022-233X    

DOI:10.1080/00222337808069399

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The copolymerization of an epoxide, 2-hydroxy-4-(2,3-epoxy-propoxy)benzophenone, with cyclic anhydride catalyzed by tertiary amine in different solvents was studied. The copolymerization curves are sigmoidal in character with an induction period. In the region following the induction period, the loss in epoxide or anhydride may be correlated with the kinetic equation of the first order reaction provided the monomers are present in equimolar ratio or anhydride is in excess with respect to epoxide. The rate constant found experimentally after the induction period depends on the first power of the concentrations of amine, epoxide, and anhydride. The activation energy of copolymerization in o-xylene is 58.2 kJ/mole (13.9 kcal/mole) and log A = 3.6. The rate of copolymerization depends on polarity of the solvent and increases with dielectric constant. A reaction scheme has been proposed for the copolymerization of epoxides with cyclic anhydrides catalyzed by tertiary amines which involves the formation of a catalytic center of ionic character by isomerization of epoxide into a derivative of allyl alcohol and its subsequent interaction with tertiary amine and anhydride in equilibrium reactions, In this way, an active center of the carboxylic anion type is formed which reacts with epoxide to give alkoxide anion. This alkoxide anion reacts with anhydride to yield carboxylic anion. By interchange of these reactions, an alternating copolymer-polyester arises. The termination involves the decay of the active center into tertiary amine and carboxylic or hydroxylic endgroups. The kinetic solution of this scheme is in agreement with the experimental results of kinetic measurements and the rate of copolymerization is governed by the equation: -d[epoxide] /dt = kp[amine]0[epoxide]0[anhydride]0[epoxide].

ISSN:0022-233X    

DOI:10.1080/00222337808069400

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Cyclic trimers of n-nonaldehyde (NA), n-decaldehyde (DA), n-undecaldehyde, (UA) and n-dodecaldehyde (DDA) were prepared by reacting the individual aldehydes with protic or Lewis acids. Higher aliphatic aldehydes whose long paraffinic chains dominate the general properties of these compounds do not trimerize readily the trimers, when formed, are purified with difficulty. The cyclic trimers, characterized by IR and NMR spectroscopy, are exclusively the cis isomers and commonly exist in all equatorial conformations. The melting behavior of the cyclic trimers was studied by DSC. The melting endotherms and the enthalpies of fusion increase with increasing chain length. Although the melting temperatures of the cyclic trimers are similar to the melting range of the side-chain crystallization of the corresponding crystalline isotactic polyaldehydes, the transition peaks of the trimers are single peaks and much sharper than the corresponding polymer peaks.

ISSN:0022-233X    

DOI:10.1080/00222337808069401

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Polysilazane thin films were prepared by glow discharge polymerization of hexamethylcyclotrisilazane in mixture with various gases: argon, nitrogen, hydrogen and ammonia. The effect of gas type on thermal stability and chemical structure of glow discharge polysilazane was studied. Thermo-gravimetric measurements performed within a temperature range of 20–1000° C, showed that the best thermal stability was exhibited by polysilazane prepared at the presence of ammonia in the reaction mixture. IR analyses data revealed that polymers prepared from mixture with ammonia or hydrogen contained more Si-H groups than those obtained with argon or nitrogen. It proves that in the presence of ammonia or hydrogen, greater monomer fragmentation through Si-C bonds cleavage takes place. More detailed investigations were carried out for polysilazanes prepared in mixture with ammonia. It was found that thermal stability as well as chemical structure of polymer depend strongly on polymerization conditions, i. e., ammonia contents in the reaction mixture, deposition time, discharge current density. Thermal stability of polysilazane improved with the increase in deposition time and current density. Increasing these parameters caused also the Si-NH-Si bonds content in the polymer to grow. The results prove that ammonia is a reactive comonomer and that the polymerization of hexamethylcyclotrisilazane at the presence of this gas may proceed through the formation of Si-NH-Si bonds.

ISSN:0022-233X    

DOI:10.1080/00222337808069402

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The degradative effects of γ-radiation on diethyl ether solutions of poly(alkyl vinyl ethers) under a variety of conditions were studied by polymer molecular weight measurements. Poly(methyl vinyl ether) (PMVE), poly(ethyl vinyl ether) (PEVE), poly(isopropyl vinyl ether) (PIPVE), and poly(isobutyl vinyl ether) (PIBVE) exhibited similar degradative behavior, with G(SC)values between 0.3 and 0.9 scissions/100 eV at 0°C. Chemically polymerized and radiation-polymerized PEVE samples gave comparable results. Chain degradation was much more pronounced for samples of poly(tert-butyl vinyl ether) (PTBVE) which yielded a G(SC)value of 3.6 at 0°C. Degradation experiments conducted on PEVE in air resulted in significantly higher rates of scission: G(SC)= 5.6 scissions/100 eV at 0°C. Chain scission was not measurably influenced by changing the solvent from diethyl ether to di-isopropyl ether. Increased polymer concentration was found to reduce the rate of polymer degradation.

ISSN:0022-233X    

DOI:10.1080/00222337808069403

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The violet-colored complexes of V(V) and N-methylaminothio-formyl-N′-phenylhydroxylamine are extractable into chloroform. The spectrophotometric studies have shown that 1:3 and 1:4 (metal:ligand) complexes predominate in the acidity range 6.5–9Nand 9.5–10.5NHCl, respectively. The values of stability constants, stepwise and overall, have been calculated by following extended Leden and Yatsimirskii methods. The analytical suitability of the reagent for the microdetermination of vanadium has also been investigated.

ISSN:0022-233X    

DOI:10.1080/00222337808069404

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The probability that a polymeric chain reaches from one crosslink junction to a second is given by the probability that the chain's end-to-end vector is equal in magnitude and direction to the junction-to-junction vector. In calculating this probability, conventional Gaussian theories assume independent probabilities in the three coordinate directions. This assumption of independent probabilities means that the conventional Gaussian chain displacement function cannot refer to a specified direction as is required. In this paper, the directional probability is re-introduced into the Gaussian chain displacement function which leads to a novel strain-energy function. This strain-energy function is shown to be in quantitative agreement with reversible deformation data in extension and in pure shear. No additional parameters are introduced into the new function which allows the independent determination of both the crosslink density and the “front factor” (the ratio of the mean-square end-to-end distances of free and crosslinked chains).

ISSN:0022-233X    

DOI:10.1080/00222337808069405

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor