摘要:

Free-radical polymerization of methyl methacrylate has been conducted in the presence of a new catalytic chain-transfer agent at different temperatures. The new catalyst exhibits a strong chain transfer characteristic, and the chain-transfer coefficient varies from 2.8 × 104to 6.6 × 104and depends on chain length and temperature. The chain-transfer coefficients decrease with increasing chain length but reach a limiting value for chains more than 8 units in length. The activation energy for the chain transfer coefficient is -10.1 kJ/mol for this catalyst.

ISSN:0022-233X    

DOI:10.1080/00222338908052039

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A series of segmented ionene polymers with polytetramethyleneoxide (PTMO) soft segments and dibromoxylene hard segments have been studied by small-angle x-ray scattering (SAXS) and by transmission electron microscopy (TEM). As detected by SAXS, these materials display multiple scattering peaks which have not been observed before in ion-containing polymers. For the ionene having the shortest PTMO soft segments, a “rodlike” structure has been observed by TEM, which is in good agreement with the SAXS results. Interestingly, the morphological texture of this material is affected by solution casting even at a very low content of the ionic component (<6.4 vol%). To the author's knowledge, this work represents the first direct observation of domain structure in ionene elastomeric polymers. Based on these data, a tentative morphological model of this ionene system is proposed.

ISSN:0022-233X    

DOI:10.1080/00222338908052040

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Surface tension data can be used for estimating the solubility of polymers in liquids. By determining the apolar and the polar components of the surface tension of polymers and of solvents, the attractive free energy, δG121, of a polymer (1) in a given solvent (2) can be established. By also taking into account the contactable surface area of two polymer molecules, immersed in a liquid, δG121can be expressed in units of kT. Solubility then is favored when -1.5 kT < δG121< 0 for apolar systems, and when -1.5 kT < δG121for polar systems. In polar solvents, hydrogen bonding can often increase δG121from <-1.5 kT to > + 1.5 kT. Positive values are frequently attained and this strongly shifts the behavior from insolubility to solubility. A number of proteins exemplify this behavior.

ISSN:0022-233X    

DOI:10.1080/00222338908052041

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The diffusion coefficient for ferricyanide anion in perfluorinated ionomer films (Nafion) have been measured. They are low enough to permit the use of ferricyanides to detect the presence of defects in such films.

ISSN:0022-233X    

DOI:10.1080/00222338908052042

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The presence of a compatibilizing agent permits the blending of otherwise incompatible polymers to yield polyblends or alloys with unique properties, generally not attainable from the individual components. Block and graft copolymers possessing segments with chemical structures or solubility parameters which are similar to those of the polymers being blended are effective compatibilizing agents. The latter may be preformed and added to the mixture of polymers undergoing compatibilization or may be generatedin situby reaction between coreactive functional groups on the polymers. The bonding between the segments in the compatibilizing agent, whether preformed or generatedin situ, is generally covalent, ionic, or hydrogen bonding. The compatibilizing agent acts as a polymeric surfactant, lowering surface tension and promoting interfacial adhesion between the dispersed and matrix polymer phases in a polyblend or alloy or between the layers in a laminate formed by extrusion or coextrusion. Numerous polyblends and laminates are discussed as illustrative of the concepts.

ISSN:0022-233X    

DOI:10.1080/00222338908052043

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

An experimental investigation was aimed at understanding extrusion operating parameters and polymer properties important to the skin surface appearance of extruded EPDM products. The purpose of this study was to develop general guidelines that can be applied to the design of new products in sponge and/or dense profiles for a variety of consumer applications, including automotive weatherstrips. In many of these applications, cure and physical properties as well as extrusion performance in terms of high line rates, low swell, and smooth surface appearance are important. This paper concerns the relationships between the hydrodynamics of extrusion and skin appearance as well as the desirable molecular characteristics for achieving smooth skin surface. The study shows that polymers with broader molecular weight distributions have a significant advantage in processing latitude over those of narrow molecular weight distribution, with skin appearance shown to depend on the extent of viscous heating during the forming operation.

ISSN:0022-233X    

DOI:10.1080/00222338908052044

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A new enzyme electrode for the determination ofL-asparagine is constructed by chemical immobilization ofL-aspartase [E.C. 4.3.1.1] on an ammonia-gas-sensing probe.L-Asparagine was determined over a concentration range of 1.6 × 10−5to 1.5 × 10−3Mwith a subnerstian response of -51 mV/decade. The electrode was stable for more than 30 days. The effect of pH, substrate and metal activator concentrations, amount of immobilized enzyme, and interferents on the electrode response are reported.

ISSN:0022-233X    

DOI:10.1080/00222338908052045

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Superior intelligence, creative genius, extraordinary personality, and/or social prominence have been associated with asthma often enough to raise the question of a nonrandom concurrence. With no intent to prove any developmental correlation this article presents such “case reports” (more biographical than biological) for two main reasons: to document the experience of asthma in the life of outstanding persons and to make everyone better acquainted-using asthma as an “excuse”-with the work and the times of some unique human beings.

ISSN:0022-233X    

DOI:10.1080/00222338908052046

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0022-233X    

DOI:10.1080/00222338908052028

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor