摘要:

AbstractThe tensile properties of a range of pure gum natural rubbers has been reviewed, and it has been shown that their principal features can be understood on the assumption that the tensile strength measured in a given test depends directly on the amount of crystallization at break. The most important single factor in determining tensile strength is the degree of cross linking. Cross linking is only needed in order to prevent plastic flow, thus permitting the molecules to be aligned by stretching, and hence to crystallize. A very highly cross‐linked rubber is weak because the load required to stretch it is so high, that the rubber is broken before the elongation becomes large enough to produce crystallization. In general, vulcanization also involves reactions, e.g., the combination of sulfur with the rubber, which inhibit crystallization by producing structural modifications of the rubber. These reduce the tensile strength, especially when the degree of cross linking is large. These ideas readily explain the effects of swelling and of the temperature of test. They are also used in a brief discussion of the phenomena of overcure, reversion, and agin

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020501

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY

摘要:

AbstractThe chemical reactivity of vinyl and diene polymers manifested during aging and degradation is similar to the reactivity manifested during polymerization; namely, the activated intermediates are radicals and the reaction proceeds by a chain mechanism. A discussion of the possible types of aggregative and disaggregative processes involved in aging is presented. On the basis that polymerization and degradation occur by means of the same radical mechanism, experimental evidence is given to indicate that under certain conditions both reactions may occur simultaneously. Viscosity changes of solutions of mono‐ and polystyrene and methyl methacrylate were studied under varying conditions of heat, oxygen, catalysts, light, and photosensitizers. An analysis of the concurrent aggregative and disaggregative reactions involved in aging may be obtained by isolating one reaction from the other, either by various physical methods, such as intermittent and continuous stress relaxation, or by such classical methods as sol‐gel determinations and aging in solution. A comparative study of the rate of oxygen absorption of a large number of polymer types was undertaken to evaluate the factors affecting oxidation. Evidence is presented to show that these factors may be specified by the following: (1) chemical structure of the polymeric material, (2) presence of antioxidants, and (3) compounding and vulcanization. The oxidizability of polymeric materials was also studied in a circulating oxygen absorption apparatus in order to determine the effect of evolved, gaseous oxidation products. A preliminary study of the effect of light on the aging of butyl and GR‐S rubber as measured by oxygen absorption and stress relaxation is pres

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020502

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY

摘要:

AbstractThe emulsion polymerizations of butadiene and styrene and of butadiene alone have been studied at temperature of 90–160°. The effects of changes in catalysts, modifiers, times of polymerization, and other variables have been investigated. The rate of polymerization at 110° is markedly increased over that at 50° and the final product is a less modified and less processable polymer. However, the standard evaluation and road tests indicate this polymer may be a useful

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020505

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY

摘要:

AbstractThe molecular weight‐viscosity relationships for polystyrene are reviewed and it is recommended that the Staudinger relationship be discarded in favor of the conventional modification of it, [η] = KMa. An emulsion‐prepared polystyrene was fractionated and the viscosities and osmotic molecular weight determined. The corresponding relationship between the viscosities in butanone and toluene is observed to follow the above equation. A table containing the molecular weight‐viscosity relationships for polymers is ap

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020506

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY

摘要:

AbstractThe inhibition by quinone and the retardation by hydroquinone derivatives of the peroxide‐induced polymerization of styrene have been studied. We have examined the end products of benzoyl peroxide at 74°C. in benzene, alone and in the presence of quinone and hydroquinone ethers, and in styrene in benzene, both with and without quinone. Absorption spectra have been obtained after several time intervals for some of these systems and for the benzoyl peroxide‐styrene‐benzene system, alone and in the presence of alkyl substituted hydroquinones. Consideration of the end products indicates that quinone interferes but little with the normal initiation process, particularly at low (0.0045 M) concentrations. Inhibition appears to result largely from reaction between the inhibitor and newly initiated chains. Quinone is converted to products—some of which are phenolic—which do not absorb in the visible. The phenolic products may react with the peroxide or radicals from it, interfering with the normal initiation reaction. The hydroquinone derivatives, which are retarders for the polymerization, appear to be converted initially to quinonoid products. The reactions in inhibition and retardation are

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020507

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY

摘要:

AbstractThe correlation between structure and properties of elastomers prepared from dienes, natural rubber, gutta‐percha, as well as those of some significant derivatives of natural rubber, are discussed. The similar influence exerted by methyl groups on the brittle point, elastic recovery, and permeability to gases is demonstrated and separated from the effect caused by insertion of —CH2—CHR— groups in straight‐chain polybutadiene, which takes place during copolymerization or 1,2 addition. The preponderant influence of an unbranched‐chain structure on tensile strength at elevated temperatures and in the swollen state is illustrated. Complex compounds with silver nitrate provide further evidence for the particular symmetry of the natural rubber chain: They are rein forcing agents for synthetic elastomers. The brittle points of hydrochlorides from natural rubber, gutta‐percha, and polyisoprene are compared with those of polyvinyl compounds. Correlation between the structure of molecular units in a polymeric paraffin derivative and its elasticity i

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020508

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020509

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020511

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020513

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1947.120020514

出版商:Interscience Publishers, Inc.    

年代:1947

数据来源: WILEY