摘要:

This paper describes current studies at the Fire Research Station on the role of smoke and toxic gases in causing injury and death in fires involving polymeric materials used within the structure and contents of buildings. The work involves obscurational studies of smoke, chemical analysis of decomposition and combustion products, pathological studies and, where appropriate, bioassay procedures. Basic details of these studies are presented together with a summary of the work carried out, and conclusions reached, following the fire at the Woolworth's store, Manchester, on 8 May 1979, in which 10 persons lost their lives. This event focused attention in the United Kingdom on the rapid release of smoke and toxic gases from burning furniture and furnishings.

ISSN:0022-233X    

DOI:10.1080/00222338208056462

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Thermal degradation of polyethylene was studied under a wide range of oxidative degradation conditions including flaming combustion. The collection techniques described were designed to isolate the product mixtures so that secondary reactions were minimized. Both pyrolytic and oxidative degradation products were generally obtained. The pyrolysis products included a range of saturated and unsaturated hydrocarbons from C2to C23which did not vary greatly in product ratio with conditions. The oxidative degradation products, including mainly acetone, acetaldehyde, acetic acid and a small amount of acrolein, varied considerably in relative yield.

ISSN:0022-233X    

DOI:10.1080/00222338208056463

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Tert-butoxy radicals, derived from the thermal decomposition of di-tert-butyl peroxalate at 60°C, react with methyl, ethyl, and n-butyl methacrylate by double-bond addition and by hydrogen abstraction from the α-methyl and ester alkyl functions. The proportion of each of these processes, as well as the fraction of tert-butoxy radicals that fragment to give methyl radicals, has been determined by analysis of the products that result on trapping the transient carbon-centered radicals with 1,1,3,3-tetramethylisoindoline-2-oxyl.

ISSN:0022-233X    

DOI:10.1080/00222338208056464

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The selectivity of the reaction of benzoyloxy radicals with styrene has been examined. Analysis of the products formed when benzoyl peroxide is decomposed in styrene at 60°C in the presence of a radical trapping agent (2,2,6,6-tetramethylpiperidine-1-oxyl) shows that the reaction of benzoyloxy radicals with styrene proceeds with 80% “tail” addition, 5% “head” addition, and 15% aromatic substitution. Phenyl radicals (formed by decarboxylation of benzoyloxy radicals) also may add to either the double bond or the aromatic ring of styrene. The importance of the above-mentioned processes to the structure and properties of benzoyl-peroxide-initiated polystyrene is discussed.

ISSN:0022-233X    

DOI:10.1080/00222338208056465

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

A dilatometer capable of being rapidly filled with monomer and initiator solutions mixed under carefully controlled conditions and a modification of an NMR T1program, adapted to store and display on recall the results of frequent sweeps at 30-s intervals of relevant proton resonances of a polymerizing mixture, are reported. These techniques have been applied to the identification of the optimum conditions for efficient, initiation of isotactic polymerization and investigation of the mechanism of propagation. It is shown that heat treatment does not remove the coordinated THF (1 molecule per RMg group) when toluene-soluble “tBuMgBr” or “PhMgBr” initiators are prepared and that the optimum THF concentration is slightly in excess of this. The nature of the solute in the toluene-soluble initiator solutions is discussed. The kinetics of the polymerization change from internal zero order to internal order of one with respect to monomer as the temperature increases from 225–275 K. This is consistent with a previously proposed mechanism in which propagation proceeds through a complex between monomer and the active center.

ISSN:0022-233X    

DOI:10.1080/00222338208056466

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Measurements of the extent of polymerization have been made for photoinitiated polymerization reactions using consistent conditions and a common monomer, butyl acrylate. Three radiation wavelengths were used and it was found that in most cases polymerization proceeded in the order 350 > 300 > 254 nm. From the range of photoinitiators studied it was found that those of the benzoin type, undergoing cleavage, promoted reaction faster than the benzophenone type, requiring a hydrogen abstraction mechanism. At 350 nm, those undergoing a cleavage mechanism showed reaction rates following the order of their ultraviolet absorption. A hydrogen donor such as a tertiary amine was necessary for the benzophenone-type initiators. Hydrogen donors tended to have mixed effects on polymerization produced by benzoin-type initiators. From a broad range of hydrogen donors used with benzophenone it was found that aliphatic tertiary amines were the most effective.

ISSN:0022-233X    

DOI:10.1080/00222338208056467

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

In the simultaneous irradiation procedure, sensitized W radiation is shown to be a complementary initiator to ionizing radiation for the grafting of monomers to polyolefins. Parameters influencing the yield of graft have been considered, including the role of sensitizer, solvent, and the type of monomer. These results indicate why difficulties have been experienced by previous authors in photografting monomers to polymers using analogous procedures. Grafting of styrene to cellulose acetate using ionizing radiation at low total doses is also reported. Difficulties associated with the poor grafting yield to gel beads as opposed to films are considered predominantly in terms of moisture content and swelling of the gel beads. The feasibility of using the polyolefins and cellulose acetate beads modified by the present grafting methods in reagent insolubilization reactions is discussed.

ISSN:0022-233X    

DOI:10.1080/00222338208056468

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The photopolymerization of dimethacrylate-based resins, employed as dental filling materials, is often limited in practice to a depth of 1 or 2 mm. Microhardness studies of these materials indicate that the degree of cure below the surface is relatively constant until a depth is reached at which the extent of polymerization rapidly decreases. Based on the kinetics of photopolymerization, two simple models were derived which appear to be qualitatively consistent with this behavior. One of these models was also in general agreement with the dependence of the depth of cure on the exposure time, radiation intensity, absorption coefficient of the material, and the inhibitor concentration in the resin.

ISSN:0022-233X    

DOI:10.1080/00222338208056469

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Surface tension measurements on a polymerizing system can yield information concerning concentration changes of surface-active species present in the system. Such measurements have hitherto been performed under conditions more or less remote from those obtaining during the actual polymerization. The use of a twin-capillary dilatometer permits, in principle, the simultaneous determination of both conversion and surface tension as a function of time. The design of such a dilatometer is described, the precautions associated with its use examined, and its application to the monitoring of the surface tension of various polymerizing systems discussed.

ISSN:0022-233X    

DOI:10.1080/00222338208056470

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The products of Ziegler-Natta catalyzed reactions, including high density polyethylene, polypropylene, and other thermoplastics and elastomers, have become familiar to all. While an enormous volume of experimental work was completed during the 1950s and 1960s, it has only been during the 1970s that the multiplicity of mechanistic schemes developed have been subjected to scrutiny. The majority of these have been concerned with polymerization of ethylene and α-olefins and because they have been adequately reviewed recently, are discussed only briefly here. A similarly large volume of empirical experimental work has enabled commercial production of polybutadiene using stereoregular catalysts. However, the mechanisms involved are of recent development, largely due to the additional configurational complexity of products, the multicompound nature of the catalyst complex, and the susceptibility of the system to contamination. Advances which have been made during the last decade are highlighted, with particular emphasis on those modifications to catalyst or to polymer structure which are of practical importance. In Australia, all production of stereoregular (high cis) polybutadiene is achieved using an aluminum alkyl halide-cobalt salt based catalyst. The fundamental technology of this process is discussed with emphasis upon process control. In particular, the control of molecular weight, processing behavior, and reduction in cross-linked material are included in more recent developments. In a broader context, technological changes which have been stimulated by such diverse influences as the increased awareness of industrial hygiene, fluctuations in feedstock availability and cost, and the general acceptance of radial ply tires are discussed. Experimental activities currently in progress in Australia, together with challenges still remaining, are examined.

ISSN:0022-233X    

DOI:10.1080/00222338208056471

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor