摘要:

Continued research on poly(bisbenzimidazobenzophenanthrolines) from one-step condensation of 1, 4, 5, 8-naphthalene tetracarboxylic (NTA) acid and 3, 3′-diaminobenzidene in polyphosphoric acid (PPA) has led to good-quality fibers with outstanding resistance to high temperatures and Fade-O-Meter aging. The condensation of 4, 5-diamino-1, 8-naphthalene dicarboxylic acid derivatives produces low molecular weight polyperimidines which have good stability. The polyimide from condensation of 1, 1′, 5, 5′-diphenyldianhydride is insoluble in all solvents tried and shows moderate thermal stability. The completely soluble ladder polymer from condensation of 1, 4, 5, 8-naphthalene tetracarboxylic acid with 1,2,4,5-tetraamino benzene in polyphosphoric acid has been obtained in high molecular weight (intrinsic viscosities in methane sulfonic acid at 30°C of over 5 dl/g).

ISSN:0022-233X    

DOI:10.1080/10601326808051898

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The distributions of the sequences of methyl methacrylate units are calculated, first by taking into account and then ignoring the effects of the penultimate units on the reactivity of the growing radicals, previously deduced from kinetic measurements. The study of the infrared and NMR spectra of a set of copolymers covering the whole range of composition does support the occurrence of these penultimate effects. Admitting these effects, it is possible to propose the assigments of several bands in the methoxy and α-methyl regions of the NMR spectra.

ISSN:0022-233X    

DOI:10.1080/10601326808051899

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The kinetic scheme proposed by us on the basis of the so-called “penultimate effect” in the termination stage of several copolymerizations is compared to the current opinions in the literature on the termination mechanism for radical polymerizations and copolymerizations. Our treatment agrees both with the chemical and physical models for termination, as it is comprehensive of all physicochemical parameters which can condition the termination-stage kinetics.

ISSN:0022-233X    

DOI:10.1080/10601326808051900

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Eight monomers, considered as suitable for the direct synthesis of iminobenzylidene polymers,, which pass through a tractable, fusible stage, have been synthesized. The polymerization of four of these monomers yielded insoluble, infusible brick-dust polymers. With the exception of p-CH3CONHC6H4CHO and p-C6H5CH˭NC6H5CH˭NC6H5, little advantage accrues to the use of these new monomers in the synthesis of the desired polymers, which appear to be best prepared by polymerizing the trimers of m- and p-aminobenzaldehyde in a solution of benzylideneaniline.

ISSN:0022-233X    

DOI:10.1080/10601326808051901

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The oxidative photolysis of polyvinylpyrrolidone with light of λ = 2537 Å has been studied over a range of oxygen pressures and polymer concentrations. The results show that chain scission and cross linking take place simultaneously. In the range where cross linking is a negligible component, a mechanism based on chain scission due to components which lead to chain scission without intervention of oxygen, and a component which leads to chain scission via hydroperoxide side groups, has been proposed. This mechanism accounts satisfactorily for all observed features of the reaction. The degree of degradation at any one time decreases with oxygen pressure. Cupric ions, with or without oxygen present, have very little influence on the degradation process. However, the UV spectra of PVP in the presence of cupric ions are different from those without them.

ISSN:0022-233X    

DOI:10.1080/10601326808051902

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The Watson-Crick model for DNA has been modified to account for observed physical phenomena associated with DNA. The viscosity data obtained on both partially denatured DNA and on undenatured DNA in various aqueous salt solutions give rise to acidic-type cationic sequences. These results can only be explained if there exist additional bonds other than the hydrogen bonds between base pairs. Considering the experimental data, the only possible type of bond that could exist is an ionic bond between the negatively charged phosphate group and the polar or positively charged nitrogen atom attached to the C'-1 position of the deoxyribose unit. The formation of such an ionic bond produces a natural twist in the DNA strand. The model is also applicable to RNA, although steric factors affect the stability and structure of such an RNA. Values of ΔH for the formation of the DNA and RNA double helix substantiate the proposed models. The most plausible structure for the double-stranded DNA helix is a model where the base pairs are on the surface rather than on the interior of the helix. Hydrophobic bonds do not exist except possibly in the altered structure produced during preparation of the DNA for X-ray analyses. The viscosity results on undenatured DNA in various salt solutions are caused by two factors: a destruction of the ionic bond and a reversal of charge effect on the DNA. The results show that the charge on DNA must change from a negative to a positive charge with addition of salt. The proposed model is applied to replication of DNA and formation of RNA from DNA and associated phenomena.

ISSN:0022-233X    

DOI:10.1080/10601326808051903

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The structure of bovine plasma albumin (BPA) was examined by optical rotatory dispersion studies at both low (pH 1.5 and 2.0) and high (pH 9.0) pH values in various aqueous salt solutions. The resulting cationic sequences were compared to those observed by Pedersen for values of the sedimentation constant. At pH 9.0 the destruction of the “helix” produces an acidic sequence. The relative pH position of the “helix” transition, the fact that addition of salt increases the apparent helical content of BPA, and the observed acidic-type of sequence rule out the possibility of (1)ionic bonds between carboxylate and ϵ-amino groups, (2) hydrophobic bonds, or (3) hydrogen bonds between peptide linkages as major contributing forces in the formation of the helix. The stability of the “helix” in BPA between pH 3.0 and 9.0 must therefore be due to hydrogen bonds between carboxylate ions and hydroxyl groups such as those of serine, threonine, and tyrosine. Repulsive forces between the positively charged groups on BPA strengthen these bonds by preventing the expanded form of BPA from collapsing. At pH 2.0 two types of sequences were observed: The s020, w, [α]Dand a0values gave an acidic-type cationic sequence. The b0(helix content), λcand [λ]233values gave essentially a nonpolar sequence. The nonpolar or hydrophobic salting-out sequences show that the formation of hydrophobic bonds at pH 2.0 hinders the formation of the helix or folded structure. The acidic sequences show that hydrogen bonds between carboxylic acid groups stabilize both the apparent helix or helices and the intermolecular aggregation of the BPA molecules. From a comparison of the S020,w values and the helical content of BPA at pH 9.0 it is also concluded that the formation of these apparent helices or folded structures expands or stiffens the BPA molecule.

ISSN:0022-233X    

DOI:10.1080/10601326808051904

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

At a recent meeting of the Editorial Board held in San Francisco during the spring American Chemical Society meeting, it was decided to institute a section of the journal to be entitled “New Interpretations.”

ISSN:0022-233X    

DOI:10.1080/10601326808051905

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The common measure of relative heterogeneity of a polymer sample is the ratio Mw/Mn, where Mwis the weight-average molecular weight and Mnis the number-average molecular weight [1]. A convenient measure of the absolute heterogeneity of polymer sizes is the variance of the molecular weight distribution. The variance [Var(M)] is formulated in terms of Mwand Mnas follows:

ISSN:0022-233X    

DOI:10.1080/10601326808051906

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0022-233X    

DOI:10.1080/10601326808051897

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor