Polymer crystallization method

Li et al. (26) reported a polymer crystallization method to modify CNTs and nanofibers with semicrystalline polymers in a periodic manner, leading to a novel nanohybrid shish—kebab superstructure. Zou et al. (27) proposed a "roping and wrapping" method to disperse MWCNTs by non-covalently wrapping with linear polymers. Liang et al. (28) used molding processing technique to modify... 

Secondly, the ultimate properties of polymers are of continuous interest. Ultimate properties are the properties of ideal, defect free, structures. So far, for polymer crystals the ultimate elastic modulus and the ultimate tensile strength have not been calculated at an appropriate level. In particular, convergence as a function of basis set size has not been demonstrated, and most calculations have been applied to a single isolated chain rather than a three-dimensional polymer crystal. Using the Car-Parrinello method, we have been able to achieve basis set convergence for the elastic modulus of a three-dimensional infinite polyethylene crystal. These results will also be fliscussed. 

In order to carry out an experimental study of the kinetics of crystallization, it is first necessary to be able to measure the fraction d of polymer crystallized. While this is necessary, it is not sufficient we must also be able to follow changes in the fraction of crystallinity with time. So far in this chapter we have said nothing about the experimental aspects of determining 6. We shall now briefly rectify this situation by citing some of the methods for determining 6. It must be remembered that not all of these techniques will be suitable for kinetic studies. 

Other crystallization parameters have been determined for some of the polymers. The dependence of the melting temperature on the crystallization temperature for the orthorhombic form of POX (T = 323K) and both monoclinic (T = 348K) and orthorhombic (T = 329K) modifications of PDMOX has been determined (284). The enthalpy of fusion, Aff, for the same polymers has been determined by the polymer diluent method and by calorimetry at different levels of crystallinity (284). for POX was found to be 150.9 J/g (36.1 cal/g) for the dimethyl derivative, it ranged from 85.6 to 107.0 J/g (20.5—25.6 cal/g). Numerous crystal stmcture studies have been made (285—292). Isothermal crystallization rates of POX from the melt have been determined from 19 to —50 C (293,294). Similar studies have been made for PDMOX from 22 to 44°C (295,296). 

Whenever the polymer crystal assumes a loosely packed hexagonal structure at high pressure, the ECC structure is found to be realized. Hikosaka [165] then proposed the sliding diffusion of a polymer chain as dominant transport process. Molecular dynamics simulations will be helpful for the understanding of this shding diffusion. Folding phenomena of chains are also studied intensively by Monte Carlo methods and generalizations [166,167]. 

The most widely used method for preparing extended-chain crystals involves solid-phase polymerization when the monomer exists as a single crystal. The polymerization of single crystals of the monomer permits the preparation of a polymer material with a maximum orientation a polymeric single crystal composed of fully extended macromolecules. Such polymer crystals are needle-shaped22. ... 

The preparation of oriented polymers by the method of the directed polymerization is of interest since it is possible to avoid the complex process of disentangling the macromolecules already packed randomly in the bulk of the unoriented polymer. However, methods involving conversion of these needle-shaped crystals into actual fibres have not yet been developed. 

It should be clear that the Darwin equation with its special LoRENTZ-polariza-tion factor as reported by Warren ([97], Eq. (4.7)) is only valid for unpolarized laboratory sources and the rotation-crystal method. An application to different setup geometries, for example to synchrotron GIWAXS data of polymer thin films is not appropriate. 

Polymer crystals grown from silica gel at room temperature contain 1-D chains of [Er(TMA)(H20)5]n,[4] The use of a highly controlled layer diffusion method gives 2-D [ErfTMA)(H20)3]n. In this material loss of two ancillary aqua groups allows pendant carboxylates of adjacent 1-D polymer strands to connect and create a sheet. Finally the use of hydrothermal conditions (180°C, autogenous pressure. 3 days) allows formation of anhydrous [Er(TMA)]n. This has a 3-D network with no simple topological relationship to the hydrated forms.[5]... 

We must therefore conclude that for slowly crystallizing polymers both methods can be used, and the growth rates and morphologies ob-... 

Vibrational spectra depend on structural parameters and are therefore suitable sources of information about microscopic properties of the vibrating units (molecules, polymers, crystals). Since the relation between structural parameters and spectra is not a direct one, it is necessary to develop model calculation methods. They are presented in this chapter. A more detailed discussion of this subject has been provided by Wilson et al. (1955) and Califano (1976). 

Aerts, J. (1996). Polymer crystal silverware a fast method for the prediction of polymer crystal structures. Polym. Bull, 36, 645-52. [182]... 

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