ISSN:0323-7648    

DOI:10.1002/actp.1997.010480901

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe occurrence of banded spherulites in blends of poly(ε‐caprolactone) with poly(styrene‐ran‐acrylonitrile) is studied by means of optical‐, scanning electron‐, environmental scanning electron‐, and atomic force‐microscopy as well as smallangle X‐ray scattering. The measurements reveal that lamellae are confined in fibrils that bend periodically from the center of spherulites in a radial direction. The fibrils show also a regular spacing in the lateral direction. Single bent lamellae can be observed by atomic force microscopy after permanganic etching. The enrichment of amorphous material near to the growth front of the spherulites can be directly observed by polarized light microscopy after temperature jump experiments. The excluded amorphous material on the surface of the growing spherulites has the shape of droplets. This might be the main reason for the initiation of the bending process because the result is a non‐uniform stress distribution acting on the growing lamellae at the interface between spherulites and the surrounding melt. The amorphous material of the blends can be found in three areas as observed by small‐angle X‐ray scattering experiments and microscopical methods: (i) between the lamellae, (ii) excluded from the interlamellar region but within the spherulite, and (iii) for high contents of non‐crystallizable material, it can be excluded from the spherulite. The banding periodicity of spherulites as a function of the crystallization temperature can be described in terms of two models, based either (i) on the inherent twisting of lamellae perpendicular to the axis of a screw dislocation or (ii) on the dependence of the diffusion of amorphous material away from the growth front of lamellae and the temperature dependence of the rate of crystallization. Both models fail at very low supercoolings near to temperatures where the bandi

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480902

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe structure of the crystalline hard domains of polyurethane elastomers based on 1,5‐naphthalene diisocyanate (NDI) has been investigated by X‐ray methods. The specimens were pressed films prepared from NDI and 1,4‐butanediol (chain extender), with poly(oxytetramethylene) as the soft segments. Small angle X‐ray data show that the hard domains are lamellae oriented preferentially with their planes parallel to the film surface. The corresponding wide angle data show that the hard domains are crystalline, and that the degree of crystallinity can be more than 60%. The hard segment chains are relatively extended and are oriented perpendicular to the film surface: they probably form a staggered array in which they are linked in sheets by hydrogen bonds. Molecular models suggest that the hydrogen bonds are shorter, and hence stronger, than those formed in the hard domains of equivalent elastomers based on diphenylmethane diisocyanate (MDI) or dicyclohexylmethane diisocyanate (HMDI). In addition, the stacking of the naphthylene units is unencumbered by the presence of the bridge methylene groups in the latter systems, and these structural features probably account for the higher melting temperature of the hard

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480903

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe size of glass transition cooperativity for 11 polymers and glycerol is determined from heat capacity spectroscopy (HCS) and differential scanning calorimetry (DSC) by using a calorimetric fluctuation formula. The data cover in total the 0.25 ≤x≤ 0.95 part of the reduced temperature interval between the Vogel temperature and a cooperativity onset temperature. A steep cooperativity increase at lower temperature is observed. The data are consistent with the hypothesis that the temperature dependence can be described by the enlargement of a minimal cooperativity at the on

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480904

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractOn the basis of an extended series of monodisperse oligomers of the dialkoxy‐substituted phenyleneethenylenes1a–ithe Eqs. (3) and (4) were conceived in order to determine the limiting values of the energiesEiand the wavelengths λiof the UV/vis absorption. The convergence of theEi, and λivalues with a growing numbernof repeating units permits a precise prediction of theEi,∞ and λi,∞ values of the corresponding polymer1jas well as a statement about the overall effect of conjugation ΔEiand the effective conjugation length ECL. A great variety of different conjugated oligomers2–14can be evaluated by the s

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480905

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe vinylic polymerization of 5‐norbornene‐2‐carboxylic esters with different palladium catalysts to polymers of high molecular weights is reported. Computer simulations based on a force field approach show that these polymers display a rigid statistical chain conformation and are thus a further example of rotationally strongly constrained polymers. The polymers are soluble in a variety of solvents despite their rigidity, they are amorphous, possess glass transition temperatures well above 250°C, and have a high packing density. The dipoles located in the lateral groups perform a secondary relaxation process similar to the case of flexible or rigid rod‐like polymers containing este

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480906

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe polypropylene growth on metallocene/MAO catalysts supported on a silica carrier has been examined by scanning electron microscopy. The kinetic induction period in early polymerization stages can be explained by the formation of a discrete polymer layer only on the outer surface of the catalyst particle. Differences in the fragmentation process at later stages are pointed out, depending on the supporting procedure of the catalyst system.

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480907

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480908

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY