摘要:

AbstractThe chemical structure of tread vulcanisates in heavy duty tyres was examined when the tyres were new, after they had been rig‐tested under conditions designed to induce tread‐lift and after they had had service on the road. Considerable changes occurred near the breaker edge; these included a marked decrease in the concentration of polysulphide crosslinks, an increase in the concentration of monosulphide crosslinks, and an increase in the amount of sulphur bound to the rubber network in main‐chain modifications. Experiments with laboratory‐prepared vulcanisates indicated that the structural alterations in the tyres were due to thermal anaerobic reactions induced by heat build‐up and that they may lead to a deterioration in the durability of the tread vulcanisate. Tyre performance may be improved by reducing heat build‐up and/or increasing the thermal stability of the rubber network. The latter could be achieved by the use of modified forms of conventional vulcanisation recipes, or efficient vulcanisation systems that produce thermally stable monosulphide

ISSN:0007-1641    

DOI:10.1002/pi.4980010201

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractThe unique properties that are a direct consequence of chain folding in polymer crystals are described. It is shown that there is a close link between morphology and molecular studies in these entities. It is also shown that the unusual phenomenon of folding persists not only in crystals from very dilute solutions but also in the complex crystalline aggregates of the bulk polymer. Although the experimental crystallisation data can be described exactly in terms of standard nucleation theory, the melting process has proved to be too complex for a simple explanation in terms of thermodynamic principles.

ISSN:0007-1641    

DOI:10.1002/pi.4980010202

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractIn addition to the more conventional methods for promoting the crystallisation of polymers, treatment with certain organic liquids has been found to be effective. In previous work it has been shown that the mechanism of this process is a diffusion‐controlled one and that for thin films of polyethylene terephthalate, the crystallisation is completed by the development of opacity after a well‐defined induction time.After a survey of possible methods it has been shown that an infra‐red technique is the most suitable for measuring the change in crystallinity, although doubt exists as to the reliability of the calculated magnitude of degrees of crystallinity. A comparison has been made between diffusion data and induction times and fair correlation is found to exist between log (diffusion coefficient) and induction

ISSN:0007-1641    

DOI:10.1002/pi.4980010203

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractMeasurements of the intensity of the light scattered from polymer solutions lead to information about geometric parameters such as the molecular weight and radius of gyration of the solute. The intensity changes when an electric field is applied to the solutions, owing to the resulting orientation, deformation and alignment of the polymer molecules. Measurements of these intensity changes lead to the evaluation of such physical parameters as the permanent and induced dipole moments and the relaxation time of the particles.The theory of the effect is outlined briefly for rigid rod‐like and for flexible randomly coiled molecules. Two attractive aspects of the theory are that, in favourable circumstances, some measures of both the solute flexibility and polydispersity are obtainable in addition to the determination of the electrical properties of the polymer. Details of the inexpensive and straightforward modification and operation of an existing photoelectric photometer are mentioned.Representative results are given for three systems. Aqueous dispersions of the needle‐like clay mineral attapulgite illustrate the abundance of molecular information obtainable by the method. Results for polybenzyl glutamate in the helix‐promoting solvent dichlorethane, demonstrate how an appraisal of the α‐helical configuration can be made in terms of the molecular length and dipole moment. Finally, results for polyproline show that, even with poorly characterised samples, useful qualitative information is still readily available. In this case, the molecular flexibility and dipolar nature were clear

ISSN:0007-1641    

DOI:10.1002/pi.4980010204

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractThe interpretation of studies of dielectric relaxation in polymers is often restricted by ignorance of the mode of motion responsible for dipole orientation in an applied field. Relevant information can be drawn from studies of visco‐elastic relaxation, since the visco‐elastic relaxation time is comparable with the dielectric relaxation time when the latter requires some ‘whole molecule’ mode of motion involving simultaneous movement of many chain segments. The dielectric and visco‐elastic relaxation times are expected to differ when the former involves a localised segmental motion.The dielectric relaxation process is shown to involve a localised segmental motion in acrylic polymers, but involves a ‘whole molecule’ rotation in low molecular weight poly(N‐vinylcarbazole). Poly(p‐substituted phenyl acetylenes) exhibit two dielectric relaxation processes. A low frequency relaxation comparable with the visco‐elastic relaxation is ascribed to the backbone double bonds being polarised unidirectionally along the chain, and a high frequency process is ascribed to a localised segmental motion of the substi

ISSN:0007-1641    

DOI:10.1002/pi.4980010205

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractA sample of a commercial low‐density polyethylene was fractionated and values of number −Mnand weight‐averageMw, molecular weights obtained together with intrinsic viscosities [η], measured in decalin at 135° and in a theta‐solvent, diphenyl at 118°. Results are compared with those obtained using samples of high‐density polyethylene, of narrow molecular weight distribution, in decalin at 135° and in diphenyl at 125°.Values of thez‐average mean square radius of gyration (S−2)z, are converted to the weight‐average unperturbed state. The branching parametersgandg1thus obtained, indicate that long‐chain branching increases with increasing molecular weight. Intrinsic ivscosities under theta‐conditions for the low‐density polyethylene fractions lead to a relationship [η]θ=Kw0·20, agreeing with the treatment of Zimm and Kilb.Some of the approximations involved in the estimation of long

ISSN:0007-1641    

DOI:10.1002/pi.4980010206

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractThe measurement of the extent of the crosslinking process in unsaturated polyester resins by infra‐red spectroscopy is discussed. Quantitative use of such methods is considered. The concentration of free unreacted styrene is measured by the absorbence at 915 cm−1, and the fumarate unsaturation by the absorbence at 985 cm−1, after correcting for overlapping styrene. The carbonyl band is used as an internal standard.Comparison of the results with refractive index measurements, solvent extraction and volatility data suggests that this method may be approximately quantit

ISSN:0007-1641    

DOI:10.1002/pi.4980010207

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractReaction conditions for the synthesis of α, α′, β‐trideuterovinyl acetate by the continuous vapour phase catalytic reaction of deuteroacetylene and acetic acid‐d (CH3COOD) are d

ISSN:0007-1641    

DOI:10.1002/pi.4980010208

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractThe solubility of azodiisobutyronitrile (AZDN), which is used as an initiator in emulsion polymerisation was measured in an aqueous phase containing a dissolved monomer and a surfactant. The results show that AZDN solubility is enhanced in the presence of dissolved monomer but that the surfactant alone has no appreciable effect.

ISSN:0007-1641    

DOI:10.1002/pi.4980010209

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980010210

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY