摘要:

AbstractCommercial samples of two ethylene—propylene terpolymers (EPDM), two isobutene— isoprene copolymers (IIR), one polyisobutene (PIB) and one chlorosulphonated polyethylene (CSPE) were pyrolysed at temperatures between 770 and 1370 K in a quartz micro‐furnace. Volatile products were analysed by gas chromatography using wide‐boiling‐range and high‐boiling‐point columns with flame ionisation detectors and/or online quadrupole mass spectrometry using helium as carrier. Low molecular weight gases were separated on a crosslinked polystyrene bead column and detected with a katharo‐meter using argon as carrier. Mechanisms are put forward to account for the temperature‐dependence of pyrolysis‐product yields as follows.In the primary pyrolysis (ca 770–870 K) EPDM products arise principally from 1 : 5 : 9(: 13 : 17) intramolecular hydrogen transfer accompanied by some unzipping. There is also evidence for a small amount of transfer to the third carbon atom and of some β‐scission. IIR and PIB yielded isobutene presumably by stepwise cyclic unimolecular elimination. However, a number of other products including telomers, methane, iso‐butane and neopentane are explained by telomerisation of isobutene and intramolecular transfer reactions following random scission; at 870 K, there is already evidence for some aromatisation. CSPE pyrolysis is complicated by preliminary loss of SO2Cl groups and dehydrochlorination to form a polyene. Concomitant crosslinking may involve inter‐molecular elimination of HCl and/or a Diels‐Alder type reaction between two polymer molecules which have already undergone dehydrochlorination. Subsequent thermal degradation of the main chain proceeds principally by 1 : 5 hydrogen transfer.At intermediate temperatures (above 900 K) secondary pyrolysis occurs in which higher alk‐l‐enes formed by primary pyrolysis break down to lower molecular weight products probably by a modified Rice mechanism and associated intramolecular cyclic dissociation. Similar mechanisms are proposed to explain the secondary products from IIR and CSPE.At higher temperatures (above 1000 K) further fragmentation, cyclisation and aromatisation. occur. For all the polymers, hydrogen yields increase sharply and yields of C3/C4products diminish; C2yields show maxima at temperatures about 1100 K. Below 1200 K, benzene is formed in largest yield. Toluene yields fall at temperatures above 1100 K, but naphthalene is formed in increasing yields up to a maximum at about 1220 K. At these higher temperatures, the product spectrum is simplified by the disappearance of molecules of intermediate size leaving only small fragmentation products and rather large polynuclear aromatics (anthracene, etc.).Two main routes are suggested for the formation of cyclic products from EPDM and IIR‐acyclisation of (particularly) methyl‐substituted n‐alkenes/alkanes of sufficiently high carbon number; andbthe reaction of intermediate molecules such as olefin + diene by a Diels‐Alder reaction.At the highest temperatures investigated, high hydrogen yields are accompanied by a substantial drop in total yield of volatilisable products and this is attributed to further con

ISSN:0007-1641    

DOI:10.1002/pi.4980080402

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe ‘dissolved’ oxygen permeabilities (Pd) of a range of hydrogels have been studied at 25 and 34°C (the temperature of the eye). At both temperatures the equilibrium water content (W) was found to be the major controlling factor in determining oxygen permeability and log (Pd) was found to be linearly related toW.The values ofPdat 34°C were found to be approximately twice those at 25°C throughout the range of water contents studied.Available information on corneal oxygen consumption rates is used as a basis for the prediction of oxygen permeability/thickness requirements in continuous wear lenses. These data lead in turn to predicted minimum equilibrium water contents for hydrogels in this, type of appli

ISSN:0007-1641    

DOI:10.1002/pi.4980080403

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractSome of the problems and advantages in the use of non‐hydrogel polymers in contact lenses are discussed together with studies on a series of such polymers which have potential advantages over the established material, poly(methyl methacrylate), in that they are both more flexible and more oxygen‐permeable. Of the polymers examined which are all too hydrophobic for direct use, poly(4‐methylpent‐l‐ene) proved to be the most readily modified in such a way that its surface became sufficiently wettable to sustain a coherent tear film without reducing its optical qualities to an unacceptable level.The ‘dissolved’ and ‘gaseous’ oxygen permeability coefficients of this polymer were studied as a function of film thickness, surface hydrophilicity and temperature. A pronounced boundary layer effect was observed in ‘dissolved’ oxygen permeability studies, although this decreased as the surface was treated to make it more wettable (as indicated by the equilibrium advancing water contact angle).The ‘gaseous’ permeability coefficients of oxygen were found to be some 4‐6 times greater than those for nitrogen. A discontinuity corresponding to the glass transition temperature was observed at 28°C with both permeants and apparent activation energies for permeation were determined both abov

ISSN:0007-1641    

DOI:10.1002/pi.4980080404

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractA wide range of metal oxide—polyacid cements have been studied to determine the influence that the nature of the cation and polymer structure have on their formation and water stability. The formation of water‐stable products depends markedly upon the type of oxide and polyacid employed and some typical examples of rapid‐setting ionomer cements with varying degrees of water resistance have been listed. Poly(ethylenesulphonic acid) has been found to be a poor cement former compared to polycarboxylic acids. The stability in water of these systems appears to be dependent on a number of factors, including the nature of the metal ion—polyanion bonding, the size of the cation and the presence of other potential ligands on the polymer.To aid a fuller understanding of the influence of the cation—polyanion bonds on the properties of cements made from CaO and CdO with poly(acrylic acid) or ethylene‐maleic acid copolymer, stability constants for Ca2+and Cd2+with these polyacids have been determined. Cd2+is bound much more strongly than Ca2+to the macroanions of these polyacids and poly(acrylic acid) appears to be a more effective cation binder than ethylene—maleic a

ISSN:0007-1641    

DOI:10.1002/pi.4980080405

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe salient features of a study of the dynamic wetting behaviour of several polyester tapes are given, together with the complementary fluid and air entrainment phenomena. Analysis of the data shows that there is no significant difference between data from different tape surfaces and that a correlation between Weber and Reynolds number adequately describes the results. A practical empirical formula (r>0.99) is given which relates the air entrainment velocity to fluid properties. This has the form:\documentclass{article}\pagestyle{empty}\begin{document}$$ U_{{\rm air\!\! entr}.} = 0.00957\left({\left. {{\textstyle{{\sigma ^5} \over {\rho .\mu ^4}}}} \right)} \right.^{1/6} + 0.2782{\rm }\!\! m/s $$\end{document}This formula agrees with experimental data for fluids with viscosity in the range 0.004<μ<0.5Nsm−2and surface tension in the range 0.025<σ<0.064Jm−2whilst predicting the air entrainment velocity to within 10% of experimentally determined

ISSN:0007-1641    

DOI:10.1002/pi.4980080406

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe distribution of macromolecules between two liquid phases in solvent/polymer systems depends on molecular weight in a more complicated way than that suggested by classic equations which indicate proportionality between the logarithm of the distribution coefficient and molecular weight or some fractional power thereof. The main reason for the discrepancy must be sought in the fact that in such systems equilibria exist between extremely dilute and relatively concentrated polymer solutions. If both concentration regimes are included in a single free‐enthalpy equation proposed previously, containing no arbitrarily adaptable parameters and smoothly describing the transition between the two states, improved agreement with experiment is obtained, but further developments are needed. The molecular‐weight dependence of the distribution coefficient appears to provide a sensitive means of discovering the parameters that play an important rǒle in the free enthalpy of mi

ISSN:0007-1641    

DOI:10.1002/pi.4980080407

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe copolymerisation of fluoroacrylates with 4‐vinylpyridine is described together with the characterisation and methylation of the copolymers. Determination of the reactivity ratios suggests that the comonomers tend to combine in a random manne

ISSN:0007-1641    

DOI:10.1002/pi.4980080408

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980080410

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980080411

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980080401

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY