摘要:

AbstractSeveral classes of organosilicon polymers are effective precursors for silicon carbide ceramic compositions. These include polydimethylsilane (via a two‐step process), ‘polysilastyrene’, polycarbosilazanes or polysilazanes, and certain siloxanes, plus the branched polycarbosilanes, branched polysilahydrocarbons, and vinylic polysilanes developed at Union Carbide. The latter three classes are prepared by active metal dechlorinations of appropriate chlorosilane blends, leading to recognition of branching at backbone silicon atoms (either as prepared or during processing) as a prerequisite for obtaining useful ceramic yields. Fundamental reactivity differences between the active metals (potassium and sodium) allow the preparation of sodium‐derived vinylic polysilanes. The latter offer certain economic and performance advantages as ceramic pre

ISSN:0007-1641    

DOI:10.1002/pi.4980180602

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractA general survey is presented of the preparation, physical and chemical properties, and structural patterns of transition metal borides and silicides. The appropriateness of their description as inorganic homopolymers stabilised by electron transfer from metal centres is discussed. Finally, applications are outlined, with particular reference to the fabrication of thin films and their use in advanced microelectronic devices.

ISSN:0007-1641    

DOI:10.1002/pi.4980180603

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe formation of network polymers by curing epoxy oligomers with dicyandiamide was investigated. The oligomers had the structureIt was shown that the reaction between hydroxyl and epoxy groups is important in this process. The strength‐deformation properties of the network polymers obtained were studied. Calculations of elastic active network chains were carried out by the method of branching processes. Good agreement was obtained between calculated and experimental dat

ISSN:0007-1641    

DOI:10.1002/pi.4980180604

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThree polymers based uponp‐hydroxybenzoic acid have been studied by thermogravimetry to ascertain their relative thermal stabilities in both inert and oxidising atmospheres. Experiments have been carried out at a rate of temperature rise of 2°C min−1and isothermally at a number of temperatures. The polymers have good thermal stability. They have also been examined by pyrolysis gas chromatography mass spectrometry using two different procedures. In the first, fresh samples were pyrolysed at a number of increasing temperatures, whereas in the second, the same sample was subjected to successive pyrolyses at the same temperature intervals. The results are compared with those of other authors derived using different techni

ISSN:0007-1641    

DOI:10.1002/pi.4980180605

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractPartially metallated polymers of 2‐vinylfluorene in tetrahydrofuran THF and THF‐dimethoxyethane mixtures were studied by electronic absorption spectroscopy. Effects arising from interaction of the ion pairs within the polymer chain were clearly observed. Conversion of the contact ion pairs with lithium and sodium cations into the solvent‐separated ion pairs is influenced by interactions between the solvent‐separated ions pairs. The polymer carbanions with bulky K+and Cs+cations exhibited a shift of λ with increasing carbanion concentration, suggesting the formation of an extended polymer chain in

ISSN:0007-1641    

DOI:10.1002/pi.4980180606

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe paper reports13C nuclear magnetic resonance spectra of novolac resins and the variation of the composition of the reaction mixture during thein situpreparation of resin. It is observed that in the initial stages of the reactionorthosubstitution occurs; however the hemiacetal rather than the methylol derivative is observed. These methylol substituted intermediates are highly unstable and a better appreciation of the relative rates of structure formation can be obtained from an analysis of the methylene bridge region,para‐paraBridges are the first to appear, the next are theortho‐paraand finally theortho‐ortholinkages are observed. Analysis of the relative intensities oforthoandparabridge carbon atoms allows identification of the isomeric composition of the final resin. The proportion of each isomer depends on the catalyst used in synthesis of the

ISSN:0007-1641    

DOI:10.1002/pi.4980180607

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractCloud point curves for several narrow fractions of polystyrene dissolved in cycloheptane, in cyclooctane and in cyclodecane have been established, and the critical solution temperatures extrapolated to give the respective temperatures. All three cycloalkanes are good solvents for the polymer. A comparison is made between the phase behaviour of polystyrene dissolved in cyclic alkanes and inn‐alkanes using free volume polymer solution theor

ISSN:0007-1641    

DOI:10.1002/pi.4980180608

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractSize exclusion chromatography calibrations for polystyrene and poly(ethylene glycol) standard samples in the molecular weight range of (600‐11000) have been obtained in tetrahydrofuran. The Kuhn‐Mark‐Houwink‐Sakurada constants of poly(ethylene glycol) in tetrahydrofuran were determined, and poly(ethylene glycol) chromatograms were evaluated according to primary and universal calibration methods. The molecular weights determined from universal curves were substantially lower than those obtained from primary curves. The Coll and Prusinowski universal calibration procedure gave better results than the calibration of Beno

ISSN:0007-1641    

DOI:10.1002/pi.4980180609

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractAralkyl polymers with ethyl side‐chains were prepared by Friedel‐Crafts reactions. Ethylbenzene and bis(p‐chloromethyl)benzene (BCMB) were reacted together in the presence of stannic chloride to produce polymers of various molecular weights. A study was then carried out of the chlorination of these polymers, using (a) molecular chlorine, (b) molecular chlorine with a peroxide catalyst and phosphorus pentachloride, (c) sulphuryl chloride. The objective was to determine the best conditions for chlorination to occur selectively at the α‐carbon atom of the ethyl group, with minimal chlorination at either the β‐position or the main‐chain methylene groups. Analysis of1H nuclear magnetic resonance spectra of the chlorinated polymers suggests that in most cases chlorination occurs extensively both in the side‐chain and in the main‐chain methylene groups. Conditions were found, however, which favour chlorination at the α‐position. The greatest selectivity was achieved when molecular chlorine, a peroxide catalyst and phosphorus pentachloride were use

ISSN:0007-1641    

DOI:10.1002/pi.4980180610

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980180613

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY