摘要:

AbstractSome dynamic mechanical properties of a series of polymethacrylic and polychloroacrylic esters have been measured over a wide temperature range at about 200 c.p.s. using a cantilever vibration method. The sharp changes in dynamic modulus, and the associated mechanical loss maxima, which occur at various temperatures are discussed in relation to the chemical structures of the polymers and in particular to the ester group in their side chains. The main softening region is shown to be influenced by the presence of polar atoms in both the main and the side chains and by the spatial size and flexibility of the side chains. The data further support the recently postulated view that a secondary dispersion occurring just below the main softening region is associated with rearrangements of the CO.Ogroup in the side chains. Some new low temperature transitions are reported, one of which at −30°C. is characteristic only of polycyclohexyl methacrylate and polycyclohexyl chloroacrylate; it is suggested that this is associated with intramolecular flexibility within the cyclohexyl ring. Another process occurring at about −150°C. is found for those polymers whose linear side chain alkyl components possess sufficient flexibility to enable them to take up more than one unique spatial configuration; such flexibility is characteristic of then‐propyl,n‐butyl, andsec‐butyl esters in both series and of the β‐chloroethyl, neopentyl carbinyl, and stearyl esters in the polymethacrylic series. Finally, the strengths of the low temperature relaxation processes, defined in terms of the percentage modulus change, are comp

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188801

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractThe strain distribution around the tip of an incision in a thin test‐piece of highly elastic material is considered. Using the results of a previous paper, relations between this strain distribution and the over‐all forces or strains are derived for two particular types of test‐piece. Experiments designed to check the theory are described, and agreement is found to be satisfactory. The theory is extended qualitatively to the case where the test‐piece is taken to the point of rupture, and experiments are described which confirm the approximate relation derived. The relevance to tearing and to the previously proposed tear criterion is di

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188802

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractA method of investigating the tear behavior of rubber vulcanizates is described. The method, based on the tear criterion of Rivlin and Thomas, involves the determination of the energy required to propagate a tear and its dependence on the rate of propagation. The type of test‐piece employed and the methods of measuring the energy and rate of tear propagation are described and discussed. Two principal types of tearing, indicative of different tear processes, are described. Experimental results for natural rubber and GR‐S gum vulcanizates, obtained over a wide range of temperature and rate of propagation, are given to illustrate the method. The results indicate that the nature of the tear process and the resistance to tearing, as represented by the energy required to propagate a tear, can change appreciably with the rate of propagation and the temperature. The significance of these changes is discus

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188803

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractThe stress relaxation behavior of peroxide and sulphur vulcanized natural rubber has been investigated using a relaxometer of new design. The peroxide vulcanizates do not degrade significantlyin vacuoand degrade by an exponential decrease in stress with time in oxygen. The vulcanizates from the two sulfur recipes used give stress relaxationin vacuoand more rapid relaxation in oxygen. A theoretical analysis provides the shape of stress–time curves anticipated for various modes of network degradation. The present data and other published results are consistent with a mechanism of scission at the crosslinks and not at random along the chains. The peroxide vulcanizates are interpreted as decaying by a first‐order scission of crosslinks and the sulfur vulcanizates by first‐order scission of two types of crosslink. The uncertainties still present in interpreting stress relaxation data are disc

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188804

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractMelting points were determined for several series of linear polyesters containing substituents either in the acid or glycol unit. The number of substituents was progressively increased by preparing copolyesters containing both unsubstituted and substituted glycol or acid units. The following systems were studied: (1) Those with trimethylene and 2‐methyltrimethylene glycols show decreasing melting points as the number of methyl groups is increased, because they introduce tetrahedral asymmetry. If the structrual unit is relatively short, crystallinity is completely destroyed. (2) Those with trimethylene and 2,2‐dimethyltrimethylene glycols show eutectic type melting point curves, since the substituent groups do not introduce asymmetry. The completely substituted polyesters have new crystal structures which give sharp X‐ray patterns. Those from short acids (C2–4) have higher melting points than the unsubstituted polyesters, while the others have lower melting points. The polyesters with an odd number of chain atoms in the unit have higher melting points than the even ones. The ability to pack closely into the crystal lattice appears to be important, a view supported by melting points of certain polyesters of β,β‐dimethylgultaric acid. (3) Those with trimethylene and 2‐methylenetrimethylene glycols and sebacic acid give a eutectic type curve, because of the appearance of a new crystal structure. (4) Those with succinic and α‐methylsuccinic acids and decamethylene glycol give progressively decreased melting points, decreased breaks in heating curves, and an increasingly distorted lattice as the number of methyl groups is increased, because random “head‐to‐head” and “head‐to‐tail” polymerization makes the completely substituted polyester irregular. (5) The polyester ofd‐α,β‐dimethoxysuccinic acid and tetramethylene glycol is highly crystalline because the substituent groups are oriented in a regular manner. Themeso‐polyester did not crystallize because of more random orientation of substituents. Decamethylened‐tartrate si

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188805

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractThe chemical and physical properties of polychloroprenes made at temperatures ranging from −60 to +200°C. are discussed in the light of knowledge of structure gained from analysis of their crystallization behavior and infrared absorption spectra. The properties of polychloroprenes made below 0°C. are shown to be dominated by the preponderance oftrans‐2‐chloro‐2‐butenylene units in their structure,e.g., they are highly crystalline and relatively unreactive. Polychloroprenes made at 10–90°C. show typical elastomeric properties and the chemical reactivity expected from the presence of a higher proportion of the allylic chloride units that result from 1,2‐polymerization. Polychloroprenes made at temperatures over 100°C. contain an even higher proportion of 1,2‐units and hence are unstable chemically. They are generally obtained as crosslinked gels. Chloroprene polymers made by ionic initiation are found to be chemically unstable, low molecular gums or resins. Their structure remai

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188806

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractThe rate of mechanical shear degradation of a 10% solution of Vistanex B‐100 polyisobutene (viscosity‐average molecular weight 1,740,000) in cetane has been studied at 60 and 80°C. at high rates of shear. The rate constants for the reaction at a given rate of shear energy application are found to decrease with temperature in this range. This result is interpreted as arising from a decreased efficiency at higher temperatures in the process of temporarily concentrating mechanical energy by means of intermolecular entanglements. The energy input requirements for degradation are found to increase with tempera

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188807

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractThe dynamic moduli and loss factors have been determined for high molecular samples of GR‐S and natural rubber. Comparison of the two sets of data shows that the general characteristics of the two materials are quite similar. The main differences are that GR‐S shows a higher temperature for the apparent second order transition, and also a higher value for the modulus in the relatively level portion of the highly elastic region. The usual superposition procedures are used for correlating the data. Several indications that the equivalence of frequency and temperature may not be of universal applicability are noted. It is suggested that the higher elastic plateau modulus of GR‐S my, in conjunction with usual levels of vulcanization, lead to a modulus dispersiion with its attendant loss and thus be a contributing factor to the lower resilience and higher heat development characteristic of

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188808

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractThe viscosities of preparations of sodium polymethacrylate and polyvinyl‐n‐butylpyridinium bromide have been measured in water and salt solutions in the Couette viscometer down to very low concentrations and rates of shear. The dependence of reduced specific viscosity upon polymer concentration has been compared with that for DNA in water and salt solutions. It is concluded that there is a finite effect of salts upon the intrinsic viscosity of the synthetic polyelectrolytes in contrast to the result found with DNA. The viscosity behavior of solutions of intermediate concentration is very similar to the of DNA solutions. The shape of the reduced viscosity–concentration plots has been interpreted as arising from the combined effect of interaction and contraction of the molecules with increasing concentr

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188809

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY

摘要:

AbstractAzo dyes of the Congo Red type are known to be amount the most effective gelling agents for polyvinyl alcohol. It has been shown by means of measurements of dilute solution viscosities that all of the dyes effective as gelling agents associate strongly with polyvinyl alcohol, as well as other hydroxylated water‐soluble polymers. This association is not, however, a sufficient condition for the promotion of gelation. Measurements of gel properties of aqueous systems consisting of polyvinyl alcohol and Congo Red or other related dyes have been made. From these measurements it has been possible to draw some conclusions pertaining to the nature of the crosslinks which contribute to the gel structur

ISSN:0022-3832    

DOI:10.1002/pol.1955.120188810

出版商:Interscience Publishers, Inc.    

年代:1955

数据来源: WILEY