摘要:

Contrary to previous assumptions, the deformation processes occurring in amorphous and partially crystalline high polymers cannot be considered as locally uniform but is anisotropic, with the formation of regularly arranged crazes. Newly developed methods of preparation allow for the first time the obtaining of direct evidence of these superlattice structures in many high polymers subjected to uniaxial, biaxial, or multiaxial stretching. The investigations have led to new concepts of the supramolecular structure of high polymers; they extend our knowledge of the relationships between the technological properties and molecular structures of polymers.

ISSN:0022-2348    

DOI:10.1080/00222347508217858

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The morphological and hydrodynamic properties of three series of anionic polyacrylonitrile fractions (105<Mw< 5 × 106) have been studied in dilute dimethylformamide (DMF) solution. All the observed values of the molecular parameters (Mw,S2wA2, [η], S) are consistent with a trifunctional randomly branched structure characterized by a decrease of branching density with molecular weight. The sample obtained in a strongly dipolar solvent (DMF, −70°C, diphenylmethylsodium) shows a unimodal molecular weight distribution and higher branching densities (2.5 × 10−2to 10−1); on the other hand, the sample obtained in a nonpolar solvent (toluene, −70°C, n-butyllithium) shows a binodal molecular weight distribution and smaller branching densities (10−4to 1.4 × 10−3). These characteristic branched structures may be explained by transfer to polymer as the main branching process, taking into account the polarity of the medium and its thermodynamic quality for the polymer.

ISSN:0022-2348    

DOI:10.1080/00222347508217859

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A study has been made of the relaxation phenomena in a series of poly-γ-n-alkyl-D-glutamates having linear side chains of different lengths in the temperature range from −170 to 250°C. The solid-state films of poly-γ-n-alkyl-D-glutamate were cast from solutions in α-helix and random coil forming solvents. The technique of dynamic mechanical relaxation at various frequencies up to 110 Hz was used in the investigation. X-ray, IR, and density measurements were used as supplements to the mechanical measurements in order to determine the relationships between the mechanical properties and superstructures. Six relaxation regions are discernible in the temperature range investigated, and these are labeled α, β, γ, δ, ε, and ζ in order of decreasing temperature. The following mechanisms are assigned to these relaxations: (1) The α-relaxation arises from the thermal molecular motion of the α-helices in the crystalline region. (2) The β relaxation arises from micro-Brownian segmental motion of the disordered region or the distorted part of the a-helices, (3) The γ and δ relaxations are associated with motions of the entire side-chain groups in the crystalline and the disordered regions, respectively. (4) The ε and ζ relaxations involve the conformational rearrangements of n-alkyl groups including carboxyl group and n-alkyl groups alone, respectively.

ISSN:0022-2348    

DOI:10.1080/00222347508217860

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A model must be judged on the basis of its ability to explain and predict experimental observations. We believe the model presented in this paper for the growth process and resultant morphology has been shown to be capable of explaining a wide variety of experimental observations by a number of different investigators. The assumption is that fiber crystals, once nucleated in an extensional flow field, continue to grow by a chain attachment process in which the highest molecular weight material forms the continuous growth core. Further growth is obtained by the extension and flattening of chains tied to the central backbone and acted upon by the fluid mechanical forces in the shearing flow boundary layer surrounding the growing crystal. A central feature of the model is the realization that complete chain extension and crystallization is not possible due to energetics considerations, and the growing fiber thus must consist of a chain backbone surrounded by a uniform “fuzz” of uncrystallized coils which are attached to the main fiber. The final morphology and properties of the crystals which result from this growth process can then be explained on the basis of this understanding of the growth kinetics.

ISSN:0022-2348    

DOI:10.1080/00222347508217861

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The relaxation spectra for plasticized and phenyl-substituted polystyrenes have been examined in the primary transition region and interpreted in terms of a damped Debye lattice. For all cases examined a broadening of the spectrum occurs. An explanation is sought on a molecular level.

ISSN:0022-2348    

DOI:10.1080/00222347508217862

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A technique is described for determining the temperature-torque profile of a PVC compound in a Brabender Plasticorder mixing chamber from room temperature to the temperature at which degradation occurs. Within this temperature range many PVC compounds show three characteristic peaks in the torque temperature trace. It is suggested that these three peaks are associated with the breakdown of the PVC powder particles (Stage III, 100 to 150 μm), micro-granules (Stage II, 0.5 to 2 μm), and primary particles (Stage I, 10 nm), respectively. The positions and shapes of these peaks are functions of the compound being investigated and as such can be used to characterize the processing behavior of the compound.

ISSN:0022-2348    

DOI:10.1080/00222347508217863

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor