ISSN:1042-7147    

DOI:10.1002/pat.1993.220040701

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe polyolefins, especially polypropylene and polyethylene, industry of today is very different from that of 10 years ago. The development of highly active and stereospecific catalysts, represented by Ti/Mg supported catalysts, have made the gas‐phase polymerization process practical.The trend in catalyst development is shifting from an emphasis on improving the stereospecificity and activity toward improving the polymer physical properties, processability and morphology.Many hybrid thermoplastic olefins, such as high‐impact copolymers, propylene–ethylene–butene terpolymers, and very low density polyethylene, have already been developed by utilizing the features of the gas‐phase polymerization process.These hybrid thermoplastic olefins cover a very broad range of products. They cannot be clearly identified as polyethylenes, polypropylenes or elastomers.Incidentally, metallocene catalysts for polyolefins have been under development for the past 15 years, and are now in the early stage of commercialization. These catalysts differ significantly from the conventional heterogeneous catalysts.They can polymerize not only ethylene, propylene and other linear α‐olefins, but also styrene, cycloolefins and functional monomers In addition, they can control the microstructure of polymer molecules by varying the transition metals and the cyclopentadienyl ligands.Because of these features, we have to be confident that the development of metallocene catalysts, or more widely homogeneous catalysts, may be a dominant force throughout the 1990s in the polyolefi

ISSN:1042-7147    

DOI:10.1002/pat.1993.220040702

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractHomogeneous catalysts based on metallocenes/methylaluminoxane are totally absorbed on surfaces of different metals. Because the methylaluminoxane is relatively stable against small molecules such as water covering metal surfaces, the aluminoxane can be fixed on powders without losing its activity. After treatment with the metallocene, active sites are only formed on the surface of the fillers. Upon injection of the olefins they are polymerized in the presence of the metals. Olefins such as ethene and propene, and cycloolefins or dienes, are used.

ISSN:1042-7147    

DOI:10.1002/pat.1993.220040703

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractPolyolefins are basic materials in the plastics. Their application is limited by their low thermostability, adhesion, hardness and other physico‐mechanical properties. The following treatments are known to improve and modify polyolefin properties: the incorporation of inorganic or organic fillers with a greater hardness and rigidity into the polyolefin matrix, the grafting of functional groups to polyolefins, and crosslinking with the formation of a network structure in the polyolefin matrix. In the case of polymers and inorganic materials, the activation of their surface by the functionalizing and fixing of transition metals allows one to perform polymerization of monomers on a surface to obtain a polymer–polymer composites and a highly filled polymer–inorganic compo

ISSN:1042-7147    

DOI:10.1002/pat.1993.220040704

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractEthylene/propylene copolymers were obtained with vanadium‐based catalysts. Different aluminium alkyls were employed as cocatalyst: Al(C2H5)2Cl/promoter, Al(i‐C4H9)3, Al(n‐C6H13)3. and Al(n‐C8H17)3. The influence of the cocatalyst on the molecular weight, the molecular weight distribution and the microstructure of the copolymers was investigated through GPC, DSC,13C–NMR analysis and fractionation.AIR3afforded a polymerization activity that was much higher with respect to Al(C2H5)2Cl/nBPCC, but with the latter cocatalyst system copolymers were obtained with a more homogeneous distribution of the monomers and the absence of crystallinity. A comparison with ethylene/propylene copolymers obtained with a V(Acac)3/Al(C2H5)2Cl/promoter and with a high‐yield Ti‐based catalyst is a

ISSN:1042-7147    

DOI:10.1002/pat.1993.220040705

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe magnesium chloride supported Ziegler–Natta catalysts are able to copolymerize ethylene and styrene in conditions of high activity. Different parameters, including catalyst type, monomer ratio, temperature and Lewis bases, allow variation of the activity and reactivity ratio. The incorporation of styrene in the copolymer remains always rather limited in moles. The products obtained contain less than 20% styrene in weight, and seem very similar in structure to linear low‐density polyethylenes (LLDPE) obtained with the same catalyst: the melting temperature is only about 5°C lower than that of pure polyethylene. The polymer can be fractionated by solvents in a similar manner to LLDPE, and contains a styrene‐enriched fraction, but homopolystyrene production has never been ob

ISSN:1042-7147    

DOI:10.1002/pat.1993.220040706

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractMetallocene‐based homogeneous Ziegler–Natta catalysts produce mono‐olefin‐terminated oligopropenes with narrow molecular weight distributions, controlled stereoregularities, and molecular weights ranging from 100 to 30,000 g/mole in high yield slurry and solution processes. Steric and molecular weight control are influenced by metallocene structures, and by polymerization conditions such as temperature and propene concentration. Predominantly mono‐vinylidene‐terminated oligopropenes are attractive intermediates, and feedstock for the synthesis of a variety of polypropylene materials, including blends, block and graft copolymers. The key step is the chain end functionalization of the vinylideneterminated oligopropenes via double bond conversion reactions, followed by the controlled synthesis of polypropylene block and graft copolymers. In melt and solution processes the olefinic end groups have been converted into a variety of polar functional groups, e.g. hydroxy, carboxy, succinic anhydride, thiol and acrylic groups. The thiol‐terminated oligopropenes are chain transfer agents in radical methylmethacrylate polymerization with chain transfer constant measured to be 0.2. Acrylic monomers and styrene are grown onto the thiol end group via a chain transfer reaction, thus producing a family of block copolymers, e.g. poly(propene‐b‐methylmethacrylate) and poly(propene‐b‐styrene). As demonstrated by SEM fracture surface analysis, the poly(propene‐b‐styrene) block copolymers are efficient dispersing agents for compatibilizing polystyrene/polypropene (70/30) blends. Homo‐ and copolymerization of acrylic oligopropene macromonomers yield novel classes of graft copolymers with pendant isotactic or atactic oligopropene chains. Hydroxy‐terminated oligopropenes are useful initiators in caprolactone polymerization to form poly(propene‐b‐caprolactone) block copolymers. IR spectroscopic studies demonstrate that succinic anhydride‐terminated oligopropenes, obtained by ene‐type addition of maleic anhydride to the olefinic oligopropene end group, react with oligomeric diamine‐terminated polyamide‐6,6 in the melt to yield polypropene‐b‐po

ISSN:1042-7147    

DOI:10.1002/pat.1993.220040707

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe polymerization of 1,3‐butadiene (BD) was carried out in the presence of a catalyst composed of neodymium 2‐ethylhexanoate, triisobutyl aluminum, diisobutyl aluminum hydride (DIBAH), ethylaluminum sesquichloride and acetylacetone. The molecular weight of the BR could be controlled with DIBAH. The reactive polymer was then chemically modified with styreneoxide (STO). The STO content of BR increased with the decrease in the molecular weight of the BR. This polymer was modified by the STO at the chain terminal end. The physical properties of the vulcanizates with the modified BR were measured. The abrasion resistance and the tensile strength were found to be impro

ISSN:1042-7147    

DOI:10.1002/pat.1993.220040708

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractCopolymerization of propylene and nonconjugated dienes such as 1–9 decadiene (α–ω symmetric) and 7‐methyl‐1,6 octadiene (asymmetric) is carried out in the presence of highly active isospecific catalysts for propene polymerization. The incorporation of the diene is random and does not affect the isospecificity of the catalytic system. For a low amount of diene, whatever its structure, an activation effect is observed. For the symmetric diene, the reactivity of the second double bond gives rise to crosslinking.Derivatization through hydroboration or epoxydation is carried out in suspension, using a toluenetetrahydrofuran solvent mixture that is able to swell the polypropylene and dissolve the reactants. After hydroboration the copolymer is transformed into hydroxylated polymer through oxidation in a phase transfer condition. The epoxydized copolymer shows excellent adhesive properties on anodized stainl

ISSN:1042-7147    

DOI:10.1002/pat.1993.220040709

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractVarious anhydride‐terminated isotactic and atactic oligopropenes of number average molecular weights ranging between 1,000 and 10,000 g/mole, prepared by maleinating vinylidene‐terminated propene oligomers obtained with isospecific and nonstereospecific metallocene‐based Ziegler–Natta catalysts, have been evaluated as blend compatibilizers of polypropylene/polyamide‐6 (70 vol%/30 vol%) blends to study the role of blend compatibilizer molecular architecture. When added during processing, as shown by IR spectroscopic analysis, the anhydride‐terminated oligopropenes react with the amine‐terminated polyamide‐6 to yield polypropylene‐block‐polyamide‐6 in situ. Such block copolymers are efficient dispersing agents. While the polyamide dispersion in the polypropylene continuous phase is not affected by blend compatibilizer stereoregularities, both stiffness and yield stress as well as notched Charpy impact strength increase with increasing stereoregularities and molecular weights. With oligopropene molecular weights exceeding 1,150 g/mole, the average size of the dispersed polyamide microphases correlates with the volume fraction of the oligopropene‐block‐polyamide‐6 blend compatibilizer and the dicarboxylic acid

ISSN:1042-7147    

DOI:10.1002/pat.1993.220040710

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY