摘要:

The large-scale production of polyolefins has been enhanced by the development of very high activity MgCl2-supported Ziegler-Natta catalysts. Higher activities mean lower production costs or, as in the cases of the UNIPOL or SHERIPOL gas-phase processes, new production technologies. However, despite their abundant use by industry and an intensive research effort by academic and industrical laboratories, a complete understanding of the catalyst's behavior is lacking. Not only is the catalyst a complex mixture of components (such as highly reactive aluminum alkyls) possessing multiple site types, but physicochemical phenomena such as mass transfer limitations across the gas/liquid interface in slurry reactors [58], catalyst fragmentation behavior at the start of polymerization [155], monomer transport to the active sites and heat transport away [61–63], and possible monomer sorption equilibria in the amorphous polymer regions [74] can further complicate the observed kinetics. The objective of this paper is to review the recent advances in the field in terms of its structure, mechanism, and kinetics of the catalyst based on the accumulation of results from many laboratories. The first part of the review will examine the make-up of a supported catalyst by breaking it down and analyzing its components. From this a discussion of the active site structure and mechanism will evolve. Finally, the polymerization rate kinetics will be reviewed. There is a vast amount of literature for propylene polymerizations and a dearth of publications about these catalysts with respect to their ethylene polymerization kinetics, so much of the discussion will be in reference to propylene polymerization.

ISSN:1532-1797    

DOI:10.1080/15321799308021560

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Urethane (meth)acrylate (UA) oligomers have been extensively investigated in the past as (a) photo/radiation/laser curable coatings useful for protecting the surface of such materials as metals [1], wood [2], paper, plastics [3], optical fibers [4], concrete [5], and leather [6]; (b) photoresists for the fabrication of microelectronic devices and video discs [7]; (c) sealants [8] and adhesives [9]; (d) biomaterials useful in contact lenses [10] and surgical implants; (e) printing inks [11]; and (f) elastmeric and encapsulating coatings.

ISSN:1532-1797    

DOI:10.1080/15321799308021561

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Polymer systems with intra and/or interchain bridge bonds of various types (covalent, electrostatic, coordination, etc.) have drawn the attention of numerous researchers for many years. A considerable interes in crosslinked polymers is due to the fact that when their topological structure is varied, they can acquire quite different properties; they can be soluble or lose solubility, exibiting a certain extent of swelling capacity. Their physicomechanical properties can also change drastically in the condensed state. The specific propertieis displayed by polymers with bridge bonds extend the possibilities and prospects of using polymer systems in technology, medicine, biotechnology, and agriculture (as construction materials, polymer glasses with high mechanical strength and high thermal stability, rubbers, ion-exchange resins and sorbents, immobilizing media for the stabilization of natural and synthetic catalysts, insoluble polymer reagents which are used, for instance, in peptide synthesis, therapeutic preparations based on modified enzymes, hydrogels with a high degree of swellin, et.). On the other hand, crosslinked polymer systems serve to develop new promising trends in the investigation of chemical, physical, physicochemical, and mechanical properties of polymers.

ISSN:1532-1797    

DOI:10.1080/15321799308021562

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:1532-1797    

DOI:10.1080/15321799308021563

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

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

ISSN:1532-1797    

DOI:10.1080/15321799308021559

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor