摘要:

AbstractAfter a general classification of the cationic ring‐opening polymerizations (CROP's) according to their polymerization mechanism, a number of examples of tailored polymers based on CROP are presented. The monomers used for the synthesis of these tailored structures are tetrahydrofuran (THF),N‐tert‐butyl aziridine (TBA), 2‐methyl‐1,3‐oxazoline (MeOX) and 1,3‐dioxolane (DXL).The polymer structures include different block and graft copolymers, macromonomers, star‐shaped polymers, polymer networks and interpenetrating polymer

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230101

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractDendritic polymers are highly branched structures with globular shape and high number of functionalities. In a divergent or convergent stepwise synthesis perfect macromolecules with controlled size and architecture are obtained. From the broad variety of dendrimer structures some examples are given and the properties of these unusual polymers are illustrated. For comparison the hyperbranched polymers, dendritic structures with defects made in a one‐pot polycondensation reaction, are discussed. Differences and conformities of properties like molecular weight distributions, functionalities, solubility, viscosity behavior and glass transition temperatures for both globular polymer structures are explaine

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230102

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractNew developments in the synthesis of telechelics, macromonomers, block‐ and graftcopolymers are presented. Synthetic strategies for them are demonstrated with examples from different fields such as polycondensation, radical, anionic, and cationic polymerization, chain cleavage and criss‐cross‐cycloadd

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230103

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractTailor‐made segmented polymers play a key role in the development of novel polymeric materials exhibiting unsual bulk and surface properties. As a function of molecular architectures of segmented polymers, it is possible to control polymer morphologies and to achieve property synergisms. Selected examples are presented to illustrate basic concepts and recent developments. Segmented reactive liquid rubbers, containing an immiscible silicone segment flanked by two miscible oligo(caprolactone) segments, are efficient epoxy toughening agents. In such nano‐phase‐separated silicone‐modified IPNs impact strength is improved without sacrificing dimensional stability. Compatibilized blends of segmented phenolic polyurethane and nitrile liquid rubbers produce rubber blend microphases dispersed in epoxy prepregs which are used to bond aluminum sheets in structural laminates. Reactive blending technologies are developed to produce segmented polymers as blend compatibilizers during melt processing, e.g., of polypropylene/polyamide 6 blends. Incorporation of oligo(tetrafluoroethene) segments into various condensation polymers modifies thermal and mechanical properties as well as surface tension and gas permeab

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230104

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractLagerstabile Polyurethan‐Einkomponentensysterne auf Basis von flüssigen oder ver flüssigbaren NCO‐reaktiven Kornponenten und festen, feinteiligen, mit einer Diffusions sperrschicht umhullten TDIH‐Partikeln lassen sich therrnisch zu Elastomeren mit hohem Eigenschaftsniveau, insbesondere hoher thermomechanischer Stabilität, ausharten.Die Eigenschaften der Endprodukte lassen sich in einem weiten Bereich durch die Auswahl der NCO‐reaktiven Aufbaukomponenten steuern. Je nach Viskosität bzw. Schmelzverhalten der Ausgangskomponenten erhält man bei Raumtemperatur gut gießbare, rakelfähige oder auch feste, leicht aufschmelzbare reaktionsfähige Gemische, die, abhängig von ihrer Viskosität und dem Verwendungszweck, nach verschiedenen Methoden verarbeitet werden können (Spritzen, Gießen, Rakeln, Spritzguß, Schleuderguß, Slush‐Molding u.ä.)Die Kombination aus praktisch unbegrenzter Lagerzeit und Verarbeitungszeit, rascher. Härtung bei Temperaturen ab ca. 100°C und breiter Variationsmoglichkeit der mechanischen Eigenschaften eröffnen diesen neuen Polyurethan‐Systemen ein weites. Einsatzgebiet mit inter

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230105

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractAlkanes with highly substituted carbon‐carbon bonds can be cleaved in free radicals by homolytic dissociation under the influence of thermal energy. The energy of dissociation is mainly determined by the type and size of the respective substituents. For tetraarylbutane dinitriles the temperatures of decomposition are in the range of other technically used initiators. But nevertheless, these compounds are up to now rather seldom used to initiate free radical polymerizations. This is connected with the special mechanism of initiation: the formed highly substituted alkyl radicals are relatively stable and show only a rather low reactivity against the usually used monomers. Therefore, in the beginning of the polymerization the radical concentration is rather high which leads not only to addition to monomers but also to a pronounced primary radical termination. In some cases this termination process is reversible which results in an unusual polymerization kinetics. Depending on the type of monomer and the degree of reversibility of the primary radical termination, either a period of “dead‐end” polymerization follows or the cleavage of the oligomers at the chain end results in a re‐initiation process with a “normal” polymerization with increased rate. The reaction mechanism, kinetics and some possible applications of such initiating alkanes

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230106

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe free radical copolymerization and multipolymerization of olefins with acrylic monomers in the presence of acids has been studied. It was found that Brönsted acids are as suitable complexing agents for the acrylic comonomer as the up to now exclusively used Lewis acids. The effectiveness of the Brönsted acids, e.g. carboxylic acids, for obtaining alternating copolymers increased with the pKs value, and trifluoroacetic acid turned out to be the acid of choice. The variation of the Lewis acid‐type complexation agents was extended by the zinc chloride diethylether complex which is advantageous over ZnCl2or other Lewis acids because of its good solubility and recycling practicability, which is also a feature of the Brönsted acids. The versatility of the new complexing agent systems was demonstrated in a series of co‐ and multipolymerizations, and ethyl cyanoacrylate was employed for the first time as electron acceptor comonomer. The properties of the copolymers with periodic comonomer sequences varied systematically with their composition, e.g. the glass transition temperature and the degree of crystal

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230107

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractMetallocenes have gained widespread interest as catalysts for olefin polymerization due to their high activity and versatility. A large range of new polymers with narrow molecular weight distribution and different microstructures can be produced with these “single‐site” catalysts. These highly active catalysts which are able to produce 40 tonnes of polyethylene per gram zirconium per hour are even capable of incorporating remarkable amounts of sterically demanding olefins and dienes in copolymerization with ethylene. Isotactic, syndiotactic, stereoblock and isoblock polyolefins are accessible by variation of the metallocene ligands. Similarly, the isotacticity and molecular weight of the generated polyolefins are influenced by the ligand structure. By heterogenization of the metallocene on metal powder or silica polymers with substantially higher molecular weight, higher melting points and other new properties may be attained. Cyclic olefins like cyclopentene, norbornene or dimethanooctahydronaphthalene polymerize without ring‐opening to yield highly melting and poorly soluble polymers. By separation of the racemic catalyst into enantiomers, optically active alkanes and alkenes are accessi‐ble. Trimers are obtained with ee of 95%. These results provide new insights into the mechanism of Ziegler‐Natt

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230108

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractInvestigation of the polymerization process and property modification of metallocene‐based cycloolefin copolymers (COC) shows that this monomer‐catalyst combination enables synthesis of a new class of transparent thermoplastic polymers. Metallocene catalysis offers much opportunity to vary the composition and microstructure of the copolymers. The breadth of the polymer spectrum which can be further widened by polymer modification enables many applications for this new class of thermoplastics. The key parameters that control structure and properties in the COC family are discussed in this pa

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230109

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractWhile metal‐catalysed polymerizations are chain reaction with constant valence of the metal, metal‐catalysed polycondensations are step polymerizations with changing valence of the metal. Taking as examples the Pd‐catalysed vinyl polymerization of norbornene, the alternating copolymerization of ethylene and carbon monoxide, and the Heck reaction, the essential structural prerequisties of the catalyst to control those reactions are presented. Metal‐catalysed polycondensations may occur as one‐ or two‐electron processes. The oxidative polymerization of 2,6‐dimethylphenol, the Heck reaction, and the Ni‐catalysed polyphenylene synthesi

ISSN:0003-3146    

DOI:10.1002/apmc.1994.052230110

出版商:Hüthig&Wepf Verlag    

年代:1994

数据来源: WILEY