摘要:

AbstractTorsional braid analysis has been used to study the curing reaction of some resin systems based upon tetraglycidyldiaminodiphenylmethane. TBA gives isothermal times to gelation and vitrification and hence the processing window for the particular systems studied at any intermediate isothermal temperature. The activation energies for the processes involved were also derived allowing extrapolation outside the range of the experiments.

ISSN:0007-1641    

DOI:10.1002/pi.4980210302

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractProton spin‐lattice,T1, and spin‐spin,T2, relaxation times of poly(ethylene terephthalate) film annealed at various temperatures were measured using a broad line pulse spectrometer. The value ofT1is closely related to the crystallinity of the sample and only oneT1was observed for each sample, indicating that the spin diffusion is effectively operating. Even in the amorphous sample there are some nuclear spins, the motion of which is strongly restric

ISSN:0007-1641    

DOI:10.1002/pi.4980210303

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe thermal stabilities of four fluoroelastomers, a polyphosphazene elastomer and four polysiloxanes, mainly in the vulcanised state, have been compared by isothermal weight loss experiments in nitrogen, or in air. The overall activation energies for degradation as a function of percentage conversion to volatiles have also been determined. In the majority of cases there was a linear relationship between activation energy and percentage conversion but the slope may be positive, negative or zero.

ISSN:0007-1641    

DOI:10.1002/pi.4980210304

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractMolecular weight has a considerable influence on the mechanical properties and density of polytetrafluoroethylene. Empirical equations have been found relating tensile properties and density to the number‐average molecular weigh

ISSN:0007-1641    

DOI:10.1002/pi.4980210305

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractBenzoyl peroxide labelled with carbon‐14 and tritium has been used for study of the end‐groups in copolymers of α‐methylstyrene (MST) with methyl methacrylate, in particular determination of the relative numbers of benzoate and phenyl end‐groups derived from the initiator. MST is found to be quite reactive towards the benzoyloxy radical. It is deduced that combination is the dominant mode of termination in the copolymerization, that transfer reactions are not important and that there is little abstraction of hydrogen from MST by the benzoyloxy

ISSN:0007-1641    

DOI:10.1002/pi.4980210306

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractPolystyrene (PS)‐polyether sulphone (PES) polymer blend thin films were prepared for investigation in a scanning transmission electron microscope. The microstructures of PS‐PES films (prepared by drawing from solutions at temperatures above ambient) of three different compositions were characterized: (1) 75 wt% PS‐25 wt% PES, (2) 50 wt% PS‐50 wt% PES, and (3) 25 wt% PS‐75 wt% PES. For films prepared at ∼ 40°C all three compositions exhibited microstructures consisting of spherical inclusions, ranging from ∼0.2μm to ∼ 1.2μm in diameter. The microscope used here was equipped with an energy‐dispersive X‐ray spectrometer, and this was employed to determine the chemical content of the inclusions and the matrix material. From X‐ray analysis, it was found that films (1) and (2) consisted entirely of PES‐rich inclusions, while film (3) contained both PS‐rich and PES‐rich inclusions. In addition, these analyses revealed that films (2) and (3) possessed a ‘mixed’ PS‐PES matrix phase. At the other temperatures for film preparation some significant differences in morphology were observed, reflecting the di

ISSN:0007-1641    

DOI:10.1002/pi.4980210307

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractInterpenetrating networks have been prepared using poly(dimethylsiloxane) as the host network and polymethacrylic acid as the guest network, i.e. polymerised and crosslinked in the presence of the siloxane network. These networks were swollen to equilibrium in dilute aqueous potassium chloride solutions and used as membranes to separate a solution of potassium chloride from pure water. The concentration of potassium chloride either side of each membrane was monitored as a function of time by conductivity measurements. From these data, the diffusion coefficient of potassium chloride in the membranes was calculated as a function of polymethacrylic acid content for temperatures of 303, 318 and 333K. Values of the diffusion coefficient were between 3 x 10−7cm2s−1and 19 x 10−5cm2s−1. The activation energy of the diffusive process decreased linearly with the increase in water content of the n

ISSN:0007-1641    

DOI:10.1002/pi.4980210308

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe effects of microbiological attack on the rheological properties of sodium carboxymethylcellulose (NaCMC) solutions are described. The effect of aging on the viscosity of aqueous NaCMC solution was studied by means of a Brookfield viscometer. An aqueous NaCMC solution was allowed to age and was subjected to shearing at different time intervals. Dilatant rheological properties were observed in contrast to the usually pseudoplastic behaviour of a normal NaCMC solution. This is attributed to the effect of shear‐induced recombination of NaCMC macromolecular crystallites produced as a result of chain scission of NaCMC molecules during aging. The recombination of the crystallites gives higher values of viscosity at higher shear rates. A five months aged sample when subjected to shearing for a period of 20 h exhibits different behaviour. After prolonged post‐shearing of this sample, the viscosity measured at shear speeds of 10 rpm and 20 rpm at 72 h and 102h approaches a common value for post‐shearing period. The approach to the Newtonian character is attributed to the shear‐stress‐induced breakdown of the crystalline aggregates. These studies reveal that the aging effects on NaCMC solution have a drastic influence on the rheological p

ISSN:0007-1641    

DOI:10.1002/pi.4980210309

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractEight tungsten‐carbene complex catalysts of the type W(CHCMe3)L1L2L3L4, where the ligands L are various combinations of OCH2CMe3, SO3CF3, OSiPh3, Br and I, have been used, in the presence and absence of GaBr3, to polymerize norbornene and six of its methyl derivatives by ring opening. The microstructure of the polymers was determined from their13C NMR spectra; values ofciscontent,cis‐transblockiness, ring‐dyad tacticity and head‐tail bias were derived as appropriate to each system. The results are discussed in terms of electronic and steric effects in the propagating carbene co

ISSN:0007-1641    

DOI:10.1002/pi.4980210310

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper deals with the effect of addition of epoxidized mowrah oil (EMO) and epoxidized cashew‐nut‐shell liquid (ECNSL) on the properties of glass fibre reinforced conventional epoxy resin, diglycidyl ether of bisphenol‐A (DGEBA) composites. The chemical resistance, tensile strength and flexural strength of the laminates increased, while impact and hardness were found to decrease on using these diluents with DGEBA. Dielectric properties such as breakdown strength, dielectric constant (ϵ′) dielectric loss (ϵ″) and loss tangent (tan δ) were compared. A significant improvement in the properties was observed on addition of 20 parts per hundred grams (phr) of an epoxy fortifier, a condensation product of phenyl glycidyl ether and 4‐hydr

ISSN:0007-1641    

DOI:10.1002/pi.4980210311

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY