摘要:

AbstractAspects of phase transition will be surveyed such as are direct consequences of straightforward thermodynamic considerations yet are not normally taken count of in traditional treatments of phase behaviour even if, as is here shown, they can assume special significance in polymers. The central theme will be the common experience that in most materials, but especially in polymers, the state of ultimate thermodynamic stability is hardly ever attained, consequently that we are dealing with metastable states, the issue of metastability thus becoming the main theme of the present treatise. This metastability can manifest itself either through the phase transformation, even in the thermodynamically stable phase, not reaching completion and/or that phases other than those of ultimate stability appear first often taking on a dominant role. The above two strands are being followed through first separately and finally, with the example of polymer crystallisation, in combination. In the course of it all a variety of phase transformations and numerous potentially intriguing consequences are being touched upon. These are encompassing aspects of liquid‐liquid phase separation, liquid‐crystal formation and crystallisation, the intervention of glass transition, the significance of supercooling, the effect on and influence of the morphology and the connection and interrelation between thermodynamic stability (including metastability) and the rates of the phase transformation, with passing comments on gels and also on some aspects of chain conformation in solution. In the case of the most extensively covered item of crystallisation attention is being drawn to the possibility of stability inversion with phase (here crystal) size. The latter, in terms of ‘Phase Stability Diagrams’, offers a new approach to crystal growth, which in the case of polymers, creates both new perspectives and opens up the possibility of treating so far largely disconnected aspects of the subject within a unifying framework. The survey ends with reference to recent work on amorphisation through pressure pointing to new aspects of material behaviour and to some new and possibly surprising variants of otherwise familiar phase d

ISSN:1022-1360    

DOI:10.1002/masy.19950980103

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractOver the past eight years, early transition metal catalysts for the ring opening metathesis polymerization of cyclic olefins have been developed. These catalysts are simple organometallic complexes containing metal carbon multiple bonds that in most cases polymerize olefins by a living process. These catalysts have been used to prepare a family of near monodispersed and structurally homogeneous polymers. A series of group VIII ROMP catalysts that allow a wide range of functionality to be incorporated into the polymer side chains have recently been prepared. This most important members of this family of complexes are the bisphosphinedihaloruthenium carbene complexes. These catalysts show excellent functional group stability and can be used to prepare well defined telechelic polymers, polyolefins with ordered functionality, and highly functionalized block copolymers.

ISSN:1022-1360    

DOI:10.1002/masy.19950980104

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractRecent progresses in the self assembly of ultrathin polymer films are described. Bilayer membranes of polymeric hydrogen‐bond networks are formed in water. Two‐dimensional networks of organic and inorganic polymers are formed in cast films of synthetic bilayer membranes to give stable multilayer films upon removal of the matrices. The monolayer at the air‐water interface constitutes suitable templates for 2D polymer networks, and it may be either removed or part of the 2D film. Successive adsorption of polycations and polyanions under carefully controlled conditions produces layered polyion complexes in the stepwise manner. Various polymer chains are epitaxially adsorbed onto graphite. All these results indicate that molecularly defined 2D polymer structures are readily avai

ISSN:1022-1360    

DOI:10.1002/masy.19950980105

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractPhotozymes are novel polyelectrolytes made from mixtures of hydrophobic and hydrophilic comonomers. They often contain a relatively high concentration of bound chromophores as photon harvesting or antenna groups, which transport excitation energy to organic substrates located in the interior of the macromolecular coil in aqueous solution. Previous studies have shown that the photocatalytic behavior of these polymers has many similarities to natural enzymes which carry out thermal reactions in biological systems. Mechanistic studies of four photozyme reactions are discussed: (1) the oxidation of perylene to perylenequinones; (2) the dehalogenation of hexachloro‐ and pentachlorobenzene; (3) the high‐yield synthesis of Vitamin D; and (4) the selective photolysis of aliphatic and aromatic keto

ISSN:1022-1360    

DOI:10.1002/masy.19950980106

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractControlled radical polymerizations can be achieved by using either unimolecular or bimolecular exchange between growing radicals and dormant chains. Dormant chains can be represented as either covalent species or organometallic compounds. Systems based on alkoxyamines, organochromium, organoaluminum compounds, and alkyl iodides are discussed in detail. In many systems, straight semilogarithmic plots indicate a constant number of growing radicals. A linear increase of molecular weights with conversion indicates a constant number of chains capable of growth but being predominantly in the dormant state. Some of these systems can be used in the synthesis of block copolymers and for end‐functionalizatio

ISSN:1022-1360    

DOI:10.1002/masy.19950980107

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractNovel copolymerizations for the synthesis of germanium‐containing polymers using a divalent germanium species, germylene, have been developed. The copolymerization involves a redox process between a germylene (Mred) and an oxidant monomer (Mox) such asp‐benzoquinones, cyclic α,β‐unsaturated ketones, and substituted acetylenes. A new germanium‐containing polymer having a germanium‐sulfur bond unit in the main chain has been synthesized by the oxidative addition of a poly(dithioalkylene) toward the germylene. A ligand exchange polymerization has been developed as a new polymerization reaction affording a polygermane. The reaction mechanism of the copolymerization between germylene andp‐benzoquinone derivatives has definitely been established as a biradical polymerization system involving a germyl radical and a semiquinone radical, providing the first clear‐cut evidence for a biradical mechanism in the polymeriz

ISSN:1022-1360    

DOI:10.1002/masy.19950980108

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractAppropriately substituted allylic sulfides, sulfones, bromides, phosphonates, stannanes and peroxides, vinyl ethers and thionocarbonyl compounds are effective chain transfer agents in free radical polymerizations. These compounds function by a radical addition‐fragmentation mechanism by which fragments derived from the chain transfer agents are installed at both ends of polymer chains. This provides a convenient method for preparing both mono‐ and di‐end functional oligomers and polymers. Allylic peroxides fragment to give epoxy end groups while the other allylic compounds give rise to macromonomers by introducing terminal double

ISSN:1022-1360    

DOI:10.1002/masy.19950980109

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe spontaneous thermal reactions of electron‐rich dienes with electrophilic olefins lead to both [4+2] cycloadducts and copolymers. The mechanism proposed for the initiation of the copolymerization involves the formation of a 2‐hexene‐1, 6‐diradical. Structure‐reactivity relationships are

ISSN:1022-1360    

DOI:10.1002/masy.19950980110

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe radical polymerization kinetics and mechanism of sterically hindered dialkyl fumarates (DRF) bearing various ester alkyl groups are described comprehensively. The overall polymerization reactivity of DRF, the initiation mechanism and the reactivity of the primary radicals in the polymerizations with azo initiators, the determination of the propagation and termination rate constants by means of electron spin resonance spectroscopy, the propagation mechanism and the microstructure of the polymers, and the chain rigidity of poly(DRF) and bimolecular termination process are discussed.

ISSN:1022-1360    

DOI:10.1002/masy.19950980111

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThis brief account discusses the development of HCl/TiCl4‐n(OR)n(n= 1–4), the titanium‐based new initiating systems for living cationic polymerizations of vinyl ethers and styrene. The focus of this development is controlling the Lewis acidity of the metal halide components [TiCl4‐n(OR)n] or “activators” in relation to the structure of the monomers. Thus, for vinyl ethers, relatively mild Lewis acids such as TiCl(OiPr)3and TiCl2(OiPr)2are effective, whereas for styrene, a stronger Lewis acid such as TiCl3(OiPr) is employed along with an added salt (nBu4N+Cl−). In both cases, living polymers of controlled molecular weights can be obtained in methylene chloride sol

ISSN:1022-1360    

DOI:10.1002/masy.19950980112

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY