摘要:

AbstractA series of ribo‐ and deoxyribo‐oligonucleotides were synthesized with the sequences CAnG, CUmG AND CTmG (n and m = 5 or 6). These molecules can form RNA, DNA and hybrid double stranded helices containing either perfect base pairing (n = m), or mismatches (n ≠ m). The thermodynamics of formation of these helices has been measured and the destabilization caused by an extra uridylic, thymidylic or adenylic residue has been determined. Nuclear magnetic resonance of exchangeable imino protons has been used to study the conformations of the different helices. The binding of ethidium to the helices has been st

ISSN:0025-116X    

DOI:10.1002/macp.1981.020041981111

出版商:Hüthig&Wepf Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractRecent experimental results concerning the crystal structure and morphology of nascent cis‐poly‐acetylene and pristine trans‐polyacetylene are discussed. The unit cell data of cis‐PA and two different modifications of trans‐PA are reported. The chlorination and the hydrogenation of PA both of which give soluble derivatives under certain experimental circumstances are critically discussed. PA prepared by the Shirakawa technique has a lamellar morphology with some evidence for chain folding and not a fibirillar texture as sometimes assumed. The synthesis and spectral properties of polyenylanions and ‐cations are reported as a new class of polyconjugated macromolecules. The so‐called doping of PA to produce highly conducting phases is explained as a chemical reaction giving rise to intermolecular CT‐interaction.Finally, some new experiments concerning the solution properties of polydiacetylenes and the question of effective conjugation length in polyunsaturated polymer

ISSN:0025-116X    

DOI:10.1002/macp.1981.020041981112

出版商:Hüthig&Wepf Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe influence of tacticity on crystallization under strain (in static and dynamic conditions) and in isotropic state of several hydrocarbon crystal lizable elastomers is considered.The influence of crystallization under strain on the tensile properties in function of crosslinking density and of temperature is demonstrated, however the difference in tensile behaviour noticed among cis 1,4 polyisoprene and other tactic elastomer structures is not completely understood.Some hypotheses are put forward as a basis for future work in this field.

ISSN:0025-116X    

DOI:10.1002/macp.1981.020041981113

出版商:Hüthig&Wepf Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe most recent studies on the structure of ultra‐high modulus polyethylene and polypropylene have been reviewed with the specific purpose of interpreting the mechanical and thermal properties of these materials. In particular, results from X‐ray diffraction measurements, nitric acid etching/GPC experiments, and Raman spectroscopy have been compared for a variety of LPE samples. The X‐ray evidence has been that the average crystal thickness increases as a function of draw ratio, up to values of 500–600 Å. This finding has been confirmed by the GPC analysis on etched samples. In addition, the GPC experiments have provided a full characterization of the crystal‐size distribution of samples of different draw ratio. The disappearance of the LAM lines in the Raman spectra of ultra‐drawn LPE has also been found consistent with a shift of the distribution of crystal thicknesses. It has been concluded that the structure of ultra‐high modulus LPE products is characterized by crystalline continuity over distances much larger than the size of the lamellar crystals. This is achieved by the formation, during the deformation process, of crystalline bridges linking adjacent lamellae. The concentration of these bridges increases with draw ratio and explains quantitatively the increase in Young's modulus. The great chemical interness and thermal stability of these materials have also been interpreted in the light of

ISSN:0025-116X    

DOI:10.1002/macp.1981.020041981114

出版商:Hüthig&Wepf Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe physical structure of semicrystalline polymers influences many of their properties. It has been shown that thermal treatment (rate of cooling and annealing) as well as the action of mechanical forces (drawing) of isotactic polypropylene (PP) resulted in materials with different mechanical properties. In the case of isotropic films the crystallization temperature or annealing temperature from the glass and consequently morphological structure which has been formed, determine the values of modulae, yield stress and viscoelastic properties. Reoptical behaviour has been found to be sensitive to structural differences too. The structure and mechanical properties of highly oriented PP samples which have been obtained by drawing through a flat die have been found to be dependent on parameters characterizing this process (drawing rate, apex angle of die and elongation ratio).

ISSN:0025-116X    

DOI:10.1002/macp.1981.020041981115

出版商:Hüthig&Wepf Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe possibility that polymers containing lath‐like side chains may give rise to crystalline and / or mesomorphic structures as result of the organization of the side groups is discussed with reference to the chemical structure of both main chains and side groups for two families of polymers: 1) the comblike polymers, and 2) the polymers carrying rigid, anisotropic side groups. The role played by the presence of flexible spacers of different length connecting the organizable side groups to the polymer backbones is also discussed. A wide range of polymer structures and properties may be obtained by changing the main chain structure, the length and the flexibility of the spacers, and the nature of the organizable side group

ISSN:0025-116X    

DOI:10.1002/macp.1981.020041981116

出版商:Hüthig&Wepf Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractInfrared dichroism measurements can be used to study the process‐structure‐property relations of a polymer provided the transition‐moment angle and phase absorption characteristics of the individual absorption frequencies are known. The present study describes experimental procedures for determining these intrinsic frequency characteristics using isotactic polypropylene as the semicrystalline polymer example. The study further demonstrates the use of this intrinsic information for characterizing the process‐structure‐property behavior of deformed isotactic polypropylene films. This reveals remarkable similarities in the observed structural response of isotactic polypropylene to different deformation

ISSN:0025-116X    

DOI:10.1002/macp.1981.020041981117

出版商:Hüthig&Wepf Verlag    

年代:1981

数据来源: WILEY