摘要:

The aqueous heterogeneous polymerization of methyl methacrylate (MMA) initiated by the Ce4+-glycolic acid (GA) redox system was studied at 35 × 0.2°C under a nitrogen atmosphere. The rate of monomer disappearance was proportional to [MMA]1[GA]1[Ce4+]°, and the rate of eerie ion disappearance was found to be directly proportional to [Ce4+] and [GA] but independent of [MMA]. The activation energy was found to be 34 kJ/mol. The molecular weight of polymethyl methacrylate increased with increasing [MMA] and decreased with increasing [oxidant]. The effect of increasing [H2SO4] on polymerization was also studied. The results are compared with those obtained for the aqueous homogeneous polymerization of acrylamide with the same redox pair.

ISSN:0022-233X    

DOI:10.1080/00222338408055670

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A system is discussed in which two kinds of cyclic macromolecules, without and with the active center located on the ring, are formed from linear ones (and vice versa) by two discrete processes: backbiting and endbiting, respectively. Thus, the probability of cyclization is not a function of the distance between one kind of the reacting groups, as in the Jacobson-Stockmayer (J-S) theory, but there are two sets of groups that can react and lead to cyclization. The proportion of the end- to-end process in the linear cyclic macromolecule equilibration decreases with an increase in the average degree of polymerization of the macromolecules, as was assumed, but it differs from the J-S theory. The present treatment gives a quantitative solution of this new system; equations describing the equilibrium distribution of cyclic and linear oligomers are formulated. These equations are solved numerically, and the dependence of the fraction of macrocyclics, the dependence of the number-average degrees of polymerization of the linear and cyclic macromolecules on the initial monomer and initiator concentrations, and the dependence on the equilibrium constant of endbiting are determined.

ISSN:0022-233X    

DOI:10.1080/00222338408055671

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Optical rotation values of the polymers of N-vinylcarbazole (VCZ) obtained by a (+)-D-camphor-10-sulfonic acid (DCS) catalyst were found to increase linearly with an increase in the donor numbers of such solvents as 1,2-dichloroethane, dioxane, and tetrahydro-furan and such additives as N,N-dimethylformamide and tetra-methylurea. Asymmetric induction is considered to be caused by a stereoselective fixation of the growing VCZ cation with the optically active DCS anion, and fixation is assisted by nucleophilic solvation. No optically active VCZ polymer was obtained by using p-toluenesulfonic acid as the catalyst and (2s)-N,N′-carbonyl-N-cyclohexyl-aminomethyl pyrolizine as the additive.

ISSN:0022-233X    

DOI:10.1080/00222338408055672

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Polymers were prepared by condensing p-xylylene dichloride (PXDC) separately with salicylaldehyde (SAL) and o-hydroxy-acetophenone (OHAC) in the presence of anhydrous ferric chloride in dioxane. The polymer samples were characterized by elemental analysis, measurement of their M by vapor pressure osmometry, by nonaqueous conductometric titration in pyridine, by IR spectral study, by TGA in air, and by viscometric study in DMF. The ion-exchange capacities of these polymeric ligands for selected metal ions were measured by the batch equilibration method and compared. Polymeric metal chelates of PXDC-SAL and PXDC-OHAC polymer samples with Cu2+, Ni2+, Co2+, Fe3and Zn2+were prepared and characterized by elemental analyses, by IR spectral study, and by thermal analyses.

ISSN:0022-233X    

DOI:10.1080/00222338408055673

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Polymers were prepared by condensing p-xylylene dibromide separately with salicylic acid andβ-resorcylic acid in the presence of anhydrous ferric chloride in dioxane. The polymer samples_were characterized by elemental analysis, by IR spectral study, by M determined by vapor pressure osmometry, by nonaqueous conducto-metric titration in pyridine, by TGA in air, and by viscosity measurements of polymer solutions in DMF. Polymeric metal chelates of Cu2+, Co2+, Zn2+, Ni2+, and Fe3+with polymer samples were prepared and characterized by elemental analysis, by IR spectral study, and by TGA in air. The chelation ion-exchange properties of the polymer samples were studied by employing the batch equilibration method.

ISSN:0022-233X    

DOI:10.1080/00222338408055674

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Conformational analysis studies on the tertiary structure of cellobiose and methyl-β-cellobioside were carried out by using calculations of van der Waals, H-bond, electrostatic, and torsional energy interactions between the atoms and groups of the molecules. Energy maps as functions of the rotational anglesΨo and Φ° of the glucosidic bond were obtained in increments of 20° and refined in increments of 1°. Two “primary” and one “secondary” conformations of minimum energy were obtained for both cellobiose and methyl-β-cellobioside, some of which are equivalent to results obtained by x-ray diffraction. The H-bond forces are shown to be, together with the van der Waals forces, the predominant factors in the fixation of the conformations of minimum energy. The position and energy contributions of the H-bonds patterns for the favored conformations are identified.

ISSN:0022-233X    

DOI:10.1080/00222338408055675

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Lignin modifications resulting from different photochemical pre-treatments were studied using chemiluminescent methods. In the oxidation of lignin in NaOH solutions at 25°C, the intensity increased with increasing temperature and can be described by an Arrheniustype exponential equation with an activation energy of 25.8 ± 2.7 kJ/ mol. The oxidation of lignin model compounds under these conditions indicated1O2OH′, and O2generation. Chemiluminescence of the luminol/H2O2/Fe2+system was used to study decomposition products of lignin upon irradiation. Unirradiated lignin proved to be an excellent radical trap, an effect initially abolished upon irradiation. At longer irradiation times, however, the radical trapping behavior was restored. The action of the perodidase/H2O2system onlignin was also investigated using chemiluminescence. Behavior very similar to that using luninol was observed. The intensity increases with increasing time of irradiation up to an optimum value. More prolonged irradiation results in total quenching of the cheiluminescemce. This is indicative of depolymerization and posterior aggregation.

ISSN:0022-233X    

DOI:10.1080/00222338408055676

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A composite gel prepared from β-cyclodextrin and starch in a 1:2 ratio and cross-linked by epichlorohydrin was used as a host compound for inclusions. The competitive inclusion between 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy and chloro-substituted acetic acids was monitored by ESR spectroscopy. The triplet signals enabled us to estimate the rotational correlation frequencies of the radical by employing Kivelson's equation. The unusual temperature dependence of the frequencies suggests that gradual loosening of the gel link occurs with an increase of temperature from 30 to 60°c, resulting in increased amounts of the inclusion which cancels the increments of the correlation frequencies. The gel is found to be a better host than β-cyclodextrin for dichloro, monochloro, and un-substituted acetic acids, at least below 50°c. Trichloroacetic acid is included in the gel as much as is dichloroacetic acid, but much more than monochloroacetic acid and acetic acid, which still compete comparably with radical inclusion.

ISSN:0022-233X    

DOI:10.1080/00222338408055677

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Polarographic studies on aqueous solutions of the redox polyelectrolyte poly-m-xylylviologen dibromide were carried out in the 1.70–7.90 pH range. The compound revealed two well-defined, diffusion-controlled cathodic waves with half-wave potentials of -0.482 and -0.906 V vs SCE. The electrode processes were found to be irreversible and independent of pH. The system did not conform to the protonation equilibrium (PXVBr2+ H+˭PXVBr2H+) in contrast to its ortho and para isomeric compounds. A suitable mechanism for the reduction processes is suggested.

ISSN:0022-233X    

DOI:10.1080/00222338408055678

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Thermal stabilities of the H form of sulfonic acid resins from polystyrene electrophilically substituted with phthalic anhydride, pyro-mellitic dianhydride, trimellitic anhydride, and cis-1,2,3,6-tetra-hydrophthalic anhydride have been studied and compared by DTA and TGA. Isothermal degradation studies of these resins at 150 ± 10°C for 72 h in air and nitrogen reveal significant changes in IR, decreases in sulfur content, and increases in ion-exchange capacity values. The pH-metric titration characteristics of the pyro-mellitic-dianhydride-modified sulfonated polystyrene after isothermal heating under the above conditions indicate weak acid behavior, in contrast to the strong acid nature of the original resin.

ISSN:0022-233X    

DOI:10.1080/00222338408055679

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor