摘要:

The polymerization of 1,1-dicyclopropylethylene with radical (ABIN) and cationic (A1EtCl2) initiators has been investigated. The structure of the polymers was elucidated by IR and NMR spectroscopy. These studies indicated that the major repeat unit of the polymer obtained by radical initiator is

ISSN:0022-233X    

DOI:10.1080/10601326808051908

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The cationic copolymerizations of α-methylstyrene and cyclopentadiene were carried out and the monomer reactivity ratios were determined. It was found that cyclopentadiene was more reactive than α-methylstyrene, and that the effect of solvent polarity on the monomer reactivity ratio was small. It was deduced from the pKBH+values of cations pertinent to the present investigation that there is little difference between the stabilities of cyclopentenyl cation and cumyl cation. The present experiment seems to be the first example showing that there is little solvent effect even in the copolymerization between monomers of dissimilar structures, if the stabilities of cations are similar.

ISSN:0022-233X    

DOI:10.1080/10601326808051909

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Aqueous solutions of poly(N-isopropyl acrylamide) show a lower critical solution temperature. The thermodynamic properties of the system have been evaluated from the phase diagram and the heat absorbed during phase separation and the phenomenon is ascribed to be primarily due to an entropy effect. From viscosity, sedimentation, and light-scattering studies of solutions close to conditions of phase separation, it appears that aggregation due to formation of nonpolar and intermolecular hydrogen bonds is important. In addition, a weakening of the ordering effect of the water-amide hydrogen bonds as the temperature is raised contributes to the stability of the two-phase system.

ISSN:0022-233X    

DOI:10.1080/10601326808051910

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Tractable azomethine copolymers are difficult to prepare by solution processes. Melt-polymerization techniques have been used to synthesize random, block, and graft azomethine copolymers in which the repeating units correspond to units derived from either A-B monomers or a pair of A-A and B-B monomers. Not all systems yielded tractable copolymers, and these limitations are discussed. The block copolymers are prepared readily by the reaction of appropriate insoluble oligomers with monomers or by the reaction of two different fusible oligomers. The thermal stabilities of the copolymers are high and comparable to azomethine homopolymers.

ISSN:0022-233X    

DOI:10.1080/10601326808051911

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The molecular weight of bovine plasma albumin (BPA) was examined by ultracentrifugal molecular weight determinations at low pH values in various concentrations of guanidinium thiocyanate (GSCN). The electrostatic charge on BPA under such conditions is approximately +100 for a molecular weight of about 70,000. It was shown that the value of Bwas obtained from the equation (1/Mwapp) = (1/Mwext) + Bw(Ca+ Cb)/2 goes through a minimum at concentrations slightly less than 2.5 M GSCN for both dialyzed and undialyzed samples. The results illustrate that the value of the net electrostatic charge on BPA varies with the absolute concentration of salt and BPA. The minimum Bwis due to a reversal of charge phenomenon. At 2.5 M GSCN or higher the net charge on BPA is negative rather than positive because of the association of counterions. The greater the solubility of the counterion, the greater will be the reversal of charge effect. Addition of a more soluble salt therefore reduces the value of Bwfaster than a less soluble salt. The extrapolated molecular weight values of BPA were the

ISSN:0022-233X    

DOI:10.1080/10601326808051912

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Many recent experiments have shown that urea behaves as a zwitterion. By measuring the solubility of urea in various aqueous salt solutions and by obtaining the effect of salts on the dispersing power of urea, the structure of urea and its mechanism for destroying hydrogen and hydrophobic bonds were elucidated. The zwitterion structure of urea was confirmed by means of these ionic sequence studies. The K+ion increases the dispersion power of urea and decreases its solubility more than any of the other monovalent cations because the K+ion forms a more insoluble salt bond with the negatively charged oxygen atom of the urea zwitterion. This salt bond is more insoluble than the urea-urea bond. Hence, more positively charged -NH2groups on urea are liberated by the addition of KCl. The dispersion power of the urea molecule is the result of the interaction of the negatively hydrated domain (B regions) surrounding these -NH2groups with the oxygen atoms involved in the hydrogen bonds between starch molecules. These B regions on urea -NH2 groups are more effective in destroying hydrogen bonds than normal water molecules. That is, the anionic sequences and the solubility of benzene in aqueous urea solutions show that the hydrated -NH2 groups of urea have an effective dielectric constant that is greater than that of water and is approximately equal to that of the hydrated guanidinium ion. However, the urea-urea salt complexes or polymers lower the effectiveness of urea at high urea concentrations. The charge density of the urea anion is between that of the C1- and F- anions and consequently does not contribute to the dispersing power of urea. By destroying water clusters, the -NH, groups of urea increase the domain which hydrocarbons can occupy and hence destroy hydrophobic bonds. The destruction of hydrogen and hydrophobic bonds by urea therefore involves the electrostatic interactions between the urea B regions and the surrounding hydrogen bonds. It is also shown that DMSO behaves as a stronger zwitterion than urea and that it has the properties of a small anionic detergent. Anhydrous DMSO dissolves polar polymers and molecules by complexing its strongly ionized oxygen atom with the polar group. Urea and formamide form aggregates with themselves and therefore are incapable of dispersing polymers in this manner.

ISSN:0022-233X    

DOI:10.1080/10601326808051913

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

ISSN:0022-233X    

DOI:10.1080/10601326808051914

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:10.1080/10601326808051907

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor