摘要:

The monomer reactivity ratios for methyl methacrylate (MMA) with pure meta-divinylbenzene (m-DVB) and with pure para-divinylbenzene (p-DVB), determined with radioactivity assay techniques, are r1(MMA) = 0. 41, r2(m-DVB) = 0.61 and r1(MMA) ≃ 0.62, r2(p-DVB) ≃ 1. 3. The data for the MMA/m-DVB pair give a fairly precise solution of the copolymerization equation and are in accord with previously observed styrene (S)/methyl methacrylate values [8] (r1= 0.52,r2- 0.41). The data for the MMA/p-DVB pair, as was also observed for the S/p-DVB pair, do not give an entirely satisfactory solution for the equation but do indicate a substantial preference of both (p-DVB and MMA or S) radicals for the p-DVB monomer and thus confirm a postulated clustering of p-DVB units.

ISSN:0022-233X    

DOI:10.1080/10601326808051881

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The polymerization of butadiene with an EtAlCl2-TiCl4catalyst system yields cyclopolybutadiene with varying amounts of trans-1, 4 units, depending upon the Al/Ti ratio and the solvent. Apparently different active centers are produced at Ti > Al and Al > Ti ratios. When the catalyst system has Ti > Al, there is a rapid decrease in the initial polymerization rate and the cyclopoly butadiene contains large amounts of methyl groups, 10–12% of trans-1, 4 units, 2–3% of 1, 2 units, and, when the polymerization is carried out in aromatic solvents, aromatic moieties are incorporated in the structure. When the catalyst system has Al > Ti, there is a very slow decrease of the initial polymerization rate, and the cyclopoly butadiene contains up to 40% of trans-1, 4 units, less than 1% of 1, 2 units, and methyl groups and solvent moieties are essentially absent even when the polymerization is carried out in aromatic solvents. Cocatalytic amounts of iodine greatly increase the initial rate of polymerization. The Ti > Al catalyst may promote 1, 3-cation-radical propagation with transoid monomer to yield a perhydrophenanthrene structure while the Al > Ti catalyst may promote 1,2 cation-radical propagation with cisoid monomer to yield a perhydroanthracene structure.

ISSN:0022-233X    

DOI:10.1080/10601326808051882

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Polarographic reduction and electrolytically initiated anionic polymerization of various monomers have been investigated with tetra-n-butylammonium perchlorate in dimethoxyethane.

ISSN:0022-233X    

DOI:10.1080/10601326808051883

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Thermogravimetric procedures are used to obtain the kinetic parameters for the intermolecular condensation of the anomers of D-glucose, D-mannose, and D-galactose. The condensation rates in the temperature range 176–220°C are found sufficiently rapid compared to the rates of mutarotation that significant differences between anomers can be observed.

ISSN:0022-233X    

DOI:10.1080/10601326808051884

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The thermal and oxidative stability of low unsaturation elastomers has been studied as a function of chain and cross-link structure by stress relaxation and oxygen absorption techniques. An ethylene-propylene terpolymer, a propylene oxide copolymer, and an ethylene sulfide-propylene sulfide terpolymer were used.

ISSN:0022-233X    

DOI:10.1080/10601326808051885

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Phase diagrams for the system of methyl ethyl ketone, cyclo-hexane, and styrene-acrylonitrile copolymer were determined. The phase diagrams indicate that the copolymer may be fractionated by chemical composition in this system. Discussions of the thermodynamics are also presented, to show that copolymers can effectively be fractionated into fractions of different compositions if a system can be found in which the difference between the Flory interaction parameters (x parameters) of two constituents of the copolymer with solvent is sufficiently large. Theoretically, the fractionation of copolymer must always occur to a certain extent, depending both on chemical composition and molecular weight. The composition fractionation results of styrene-acrylonitrile copolymers are given to confirm the discussions.

ISSN:0022-233X    

DOI:10.1080/10601326808051886

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Previous developed theories were applied in explaining the mechanism for the salting-in and -out of various amino acids. Glycine is salted-in according to the cationic sequences Li+> Na+> K+> Rb+and Ca2+> Ba2+> Sr2+. The ability of a cation to increase the solubility of an amino acid therefore corresponds to the destruction of the ion-ion bond between the - CO-2and the -NH+2group of the amino acid by forming an insoluble ion-ion bond between the added cation and the - CO−2group. This insolubilizing effect produces a positive charge on the amino acid. If, however, the anion of the added salt forms a relatively insoluble ion-ion bond with the -NH+2group of the amino acid, then the effect is minimized because now both charges on the amino acid are reduced. Consequently, the more insoluble the cation amino acid salt and the more soluble the anion amino acid salt (or vice versa), the greater will be the salting-in effect. Titration of either charged group on the amino acid zwitterion has the same effect, since now the ion-ion bond of the amino acid is again destroyed. Aliphatic and carboxylic acid groups also effect the salting-in sequence, since these groups are salted-out by addition of salt when D±< DH2o. These mechanisms explain how leucine is first salted-out, then salted-in (at 4 M) and finally salted-out again (at 9 M) in LiCl solutions. Urea salts-in hydrophobic amino acids by increasing the dielectric constant and salts-out polar amino acids by increasing the interaction between the two charge groups on the amino acid. Glycine reverses the salting-in effect of NaCl on asparagine by competing for the Na+ion.

ISSN:0022-233X    

DOI:10.1080/10601326808051887

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The salting-out or -in of hydrocarbons, uncharged nitrogen bases, and acids containing polarized hydroxyl groups give different cationic sequences. Also various ionic groups have different solubility sequences. Such neutral or electrostatically charged groups are attached to polymers and are involved as forces which hold together aggregates or helicies in inter- or intramolecular interactions. In aqueous solutions, the addition of various salts can destroy or produce these inter- or intramolecular interactions. Consequently, by applying the ionic solubility sequences, the observed salting-in and -out sequences of low molecular weight molecules, and other solubility criteria to the destruction or formation of such polymer interactions, it is possible to determine the major force or forces which are involved in holding the aggregate or helix together. Such forces involve hydrophobic bonds, hydrogen bonds between neutral bases, hydrogen bonds involving polarized hydroxyl groups, ionic bonds, and/or repulsive forces between electrostatically charged groups. The method is applied to the salting-out of ovalbumin, the destruction of the α-helix of ribonuclease, the collagen-gelatin transformation, the dissociation of hemoglobin, and the retrogradation and solubilization of starch. These five examples involve all the secondary forces considered. The method should find wide applicability because it can be applied to any method of physical measurement involving ionic solutions.

ISSN:0022-233X    

DOI:10.1080/10601326808051888

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A number of polymeric azomethines were synthesized to determined the influence on char yields by the deliberate introduction of cross links in their structures. The linear reference polymer was [˭c(CH3)-C6H4-C(CH3)-NC6H4N˭], considered as having a cross-link density, ρ, of zero. Two series were prepared withpvalues between zero and 1, using 1,3, 5-C6H3(COCH3)3and 1,3, 5-C6H3(NH2)3, respectively, as the cross-linking agents.

ISSN:0022-233X    

DOI:10.1080/10601326808051889

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Cross-linked polymeric azomethines were prepared by carbonyl, amine, and bis exchange reactions with cross-link density values of 0.00, 0.05, 0.25,0. 50, and 1.00, in which the cross-link moieties. The yields at 400, 600, and 1176°C were determined as a function of the cross-link density and compared with the previously reported related polymers prepared by direct reactions. A tentative explanation is offered for the higher yields obtained by some of the exchange reactions.

ISSN:0022-233X    

DOI:10.1080/10601326808051890

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor