摘要:

The morphology, thermal behavior, and degradation pattern of solution-grown single crystals of polymers with “constitutional” and “configurational” chain defects within macromolecules are examined. Neither evidence of rejection of defects from the crystalline core nor influence of the distribution of the defects in the chain on the thickness of solution-grown single crystal is observed. In contrast with Flory's theory of equilibrium crystallization of random copolymers, some constitutional and configurational chain defects must be incorporated into the crystalline lattice as reticular imperfections. Some models able to explain the manner in which chain defects can be accommodated in the crystalline core of polymer single crystals are suggested and discussed.

ISSN:0022-2348    

DOI:10.1080/00222347508217852

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Conformational energy calculations were employed to determine the effect of hydrogen-fluorine defects on the conformation of the polytrifluoroethylene chain. It was determined that the 31helix was energetically favored for all but the highly syndiotactic polymers, which favored the all-trans conformation. The incorporation of head-to-head linkages into the polymer chain increased the Conformational energy of the 31helix while the Conformational energy of the all-trans form decreased. The energies of these two conformations did not equalize until the head-to-head concentration reached 20 to 30%, depending on the tacticity of the polymer. The trans, gauche, trans, gauche' conformation was also determined to be energetically favorable for the syndiotactic polymer, but both tacticity defects and head-to-head linkages caused a rapid increase in the Conformational energy. This was, therefore, concluded to be unlikely structure when chemical defects are incorporated into the polymer chain.

ISSN:0022-2348    

DOI:10.1080/00222347508217853

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A phenomenological prediction of the creep behavior of cross-linked polymers undergoing simultaneous physical relaxation and chemical network scission is presented. The fundamental assumption underlying this calculation is defined and its physical significance is discussed. The predicted response is related to the behavior of nonreacting polymers through a time-adjustment parameter. The magnitude and time dependence of this parameter depend on both the physical relaxation characteristics and the kinetics of the scission reaction. In the limit of totally elastic systems, a description of the well-known chemorheological behavior ensues.

ISSN:0022-2348    

DOI:10.1080/00222347508217854

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The sorption and diffusion of low molecular weight penetrants proceeds almost exclusively through the amorphous component of the semicrystalline polymer solid. The diffusive transport properties and geometrical distribution of the amorphous component are substantially modified by mechanical and thermal treatment. Deformation of spherulitic material first loosens the structure and then transforms it into a densely packed fibrous structure with a great many taut tie molecules in the amorphous component. Annealing lets the crystals grow in thickness, removes crystal defects, sharpens the boundaries between crystalline and amorphous component, and relaxes the taut tie molecules. The resulting changes of transport properties cannot be described in a satisfactory manner by crystallinity and orientation but requite a detailed consideration of morphology. The elastic tensile deformation enhances sorption and diffusion by reducing the density of amorphous component. The high anisotropy of diffusion and the drastic reduction of sorption and diffusion of fibrous material are the consequence of the microfibrillar morphology with the large fraction of highly aligned and closely packed taut tie molecules which eliminate many sorption sites, enormously reduce the diffusivity, and increase its concentration dependence. The anisotropy may be reduced during plastic deformation of the fibrous material by the increased number of interfibrillar tie molecules.

ISSN:0022-2348    

DOI:10.1080/00222347508217855

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Potential energy calculations have been made for the conformation and packing of chains of the alternating copolymer of ethylene and tetrafluoroethylene. Although the copolymer composition is similar to that of poly(vinylidene fluoride), the conformation and packing of the copolymer are quite different. The calculations indicate that for an isolated chain, a 3, helical conformation is lower in energy than the all-trans planar zigzag. Examination of the potential energy maps indicated that half of the available bond rotations are required to be nearly trans, making the copolymer chains considerably less flexible than poly(vinylidene fluoride) chains. Calculations of the energies for packing the copolymer chains into a crystalline array indicate three possible packing modes. Packing similar to polyethylene packing, poly(vinylidene fluoride) phase I packing, and a third structure proposed by Wilson and Starkweather have been found to have very similar energies. These three packing modes also seem to agree equally well with the experimental data available.

ISSN:0022-2348    

DOI:10.1080/00222347508217856

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The viscoelastic crystalline relaxation process has been newly observed for solid films of poly-γ-methyl-D-glutamate. The temperature range of the crystalline absorption corresponds to the temperature range in which the lattice distance deviates from linear expansion. The viscoelastic crystalline relaxation process was decomposed into the a, mechanism (150 to 170°C) and the α2mechanism (180 to 190°C) which appear principally for solid poly-γ-methyl-D-glutamate cast from solutions in dichloroethane and chloroform, respectively. The contribution from the α1and the α2relaxation processes depends on such structural factors as alignment or packing state of the a-helix chains; these vary with the kind of solvent and the condition of sample preparation. Based on the experimental results for the anisotropy of mechanical loss and the relationships between the peak temperature of tan 6 and the interhelix distance or the peak magnitude of tan δ and the interhelix distance, it seems reasonable to conclude that the α1relaxation process is associated with shear deformation in the interhelix region of the crystalline phase. Also, from a model calculation of the magnitude of the energy dissipation produced by shear deformation of the interhelix region, coaxially vibrations and torsional oscillations of the a-helices are both possible origins of the a, relaxation mechanism. In practice, these molecular motions correspond to the migrational slip and the rotational motion of the α-helices, respectively. The nature of the α2relaxation process is discussed from the viewpoint of the anisotropy of mechanical loss and the stability of the helix core investigated by X-ray and IR techniques. It is concluded that the α2mechanism is associated with tensile or bending deformation of the α-helix chains represented by accordion-like, torsional extension or bending motions.

ISSN:0022-2348    

DOI:10.1080/00222347508217857

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor