Amorphous polymers intensity

Figure 4.7 Various representations of the properties of a mixture of crystalline and amorphous polymer, (a) The monitored property is characteristic of the crystal and varies linearly with 0. (b) The monitored property is characteristic of the mixture and varies linearly with 0 between and P, . (c) X-ray intensity is measured with the sharp and broad peaks being P. and P., respectively.

Amorphous polymers prepared by aluminum catalysts had an additional quartet at 6.40, 6.58, 6.64, and 6.74 ppm. The intensity of this quartet varied depending on the nature of the amorphous polymer, and roughly paralleled the content of head-to-head and tail-to-tail linkages determined by chemical means. Thus, this quartet was assigned to a tail-to-tail dyad. 

The 100 MHz H-NMR spectra in benzene-d6 solution afforded additional information. Isotactic polymers prepared by zinc catalysis had a symmetrical quartet at 6.38, 6.48, 6.67, and 6.77 ppm, whereas amorphous polymers prepared by KOH catalysis had an additional quartet of equal intensity at 6.36,6.46,6.60, and 6.70 ppm. Therefore, the former absorption could be assigned to the isotactic dyad and the latter to the syndiotactic one. Amorphous polymers prepared by aluminum catalysis had an additional quartet assigned to a tail-to-tail dyad. 

On the other hand, WAXS measurements of PE melt clearly indicate a range of intermolecular distance correlations of about 25 A [3]. Together with the relatively high density of polymer melts, the fact that the first interchain halo in WAXS patterns of oriented amorphous polymers tends to lie in the equatorial direction and the relatively high WAXS intensity of the interchain halo support the idea of parallel chain segments on the short range scale. 

Photoluminescence intensity of the amorphous polymers was generally much larger than that of the more crystalline polymers. The energy level of the lowest singlet excited state Es was evaluated to be 2.5-2.7 eV for the amorphous polymer pristine films, and 2.0 eV for the more crystalline polymers. The Stokes shifts were also observed to be much larger for the amorphous polymer films compared with those of the more crystalline polymer films. This indicates a larger structural relaxation of the amorphous polymers following photoexcitation. 

Figure 5. Examples of diffraction patterns of amorphous polymers (19). Observed x-ray intensity is plotted vertically.

Numerous amorphous room temperature polymer electrolytes are also known. A variant of PEO which interspaces methylene moieties with ethylene moieties is also amorphous at room temperature. Its repeat structure is (—O—CH2—O—C2H4—). Another intensively studied Li-ion conductive amorphous polymer is known as MEEP. This acronym stands for methoxy-ethoxy-ethoxy-phosphazene. The polymer structure is a repeating (—N=PR2—) phosphazene unit with two alkoxy chains dangling from the phosphorous atoms, i.e., (—N=P—(O—C2H4 —O—C2H4—O—CH3)2—). 

IR spectra of the cis-1,4 isotactic or syndiotactic polymers, in the molten state or in solution, and of the amorphous polymers are practically identical. All are characterized by an intense band at 751.8 cm.-1 (cis double bonds). In the spectra of the solid isotactic or syndiotactic polymers, however, new bands appear which are typical of the crystallinity of the polymers (Figure 1 and 2). The positions of the most intense of these bands are as follows (1) isotactic polymers 746.2 843.8 925.9 1005 cm.-1 (2) syndiotactic polymers 757.5 854.7 925.9 1000 1136 cm."1 It is interesting to observe that the band of the... 

Schmidt, M., Maurer, F.H.J. (2000) Ortho-positronium lifetime and intensity in pressure-densified amorphous polymers . Radiation Physics and Chemistry. 58, 535. 

Any discussion of crazing in molecular terms must take into account the molecular organization in amorphous polymers. Thus, the information available on the structure of amorphous PC will be briefly reviewed in this section. Much of this information results from the enormous efforts that have been invested to resolve the intense controversy concerning the existence of strong intermolecular orientation correlations in conventional polymer melts and glasses (see e.g. the contributions in A comprehensive review has recently been given by Wendorff... 

A third method which recently provided considerable insight into the role of crazes in deformation and fracture of amorphous polymers is the optical interference measurement of crazes (preceding a crack). Since the pioneer work of Kambour, this method has been widely used to determine characteristic craze dimensions and critical displacements. W. Doll gives an overview on recent results and on their interpretation in terms of fracture mechanics parameters (stress intensity factor, plastic zone sizes, fracture surface morphology, fracture energy). 

Most crystalline polymers with metylenic groups in their structure and with a degree of crystallinity below 50% present a sub-glass relaxation whose intensity and location scarcely differ from those observed for the amorphous polymer in the glassy state. The temperature dependence of this relaxation follows Arrhenius behavior, and its activation energy is of the same order as that found for secondary processes in amorphous polymers. 

In this section we will consider polydimethylsiloxane (PDMS) as an example of the type of work that is possible with amorphous polymers. The structure and INS spectrum of PDMS are shown in Fig. 10.21a [40]. The repeat unit shown in Fig. 10.21b was used to model the spectrum using the Wilson GF matrix method [41]. The major features are reproduced skeletal bending modes below 100 cm", the methyl torsion and its overtone at 180 and 360 cm respectively, the coupled methyl rocking modes and Si-0 and Si-C stretches at 700-1000 cm and the unresolved methyl deformation modes 1250-1500 cm. The last are not clearly seen because the intensity of the methyl torsion results in a large Debye-Waller factor, so above 1000 em or so, most of the intensity occurs in the phonon wings. 

In the literature there are reports of radial distribution function analyses performed with polystyrene,6 7 polycarbonate of bisphenol-A,7 8 and a number of other amorphous polymers.9 As an illustration, we present results obtained with atactic polystyrene. Figure 4.2 shows the x-ray scattering intensity data obtained with CuKa radiation. The strong peak at 26 around 20° represents the so-called amorphous halo, whereas the smaller peak at around 10° is called the polymerization peak by some and has attracted interest with regard to its structural origin. The experimentally measured intensity is first corrected for background, polarization, absorption, etc.,... 

The variation with q in the intensity I q) scattered from pure liquids or singlecomponent amorphous polymers is very moderate in the small-angle region, and the extrapolation is easily accomplished. Figure 4.1119 shows the x-ray scattering... 

In this chapter the dilute particulate system, the nonparticulate two-phase system, and the periodic system are discussed in Sections 5.2, 5.3, and 5.5, respectively. Section 5.4 deals with scattering from a fractal object, which may be regarded as a special kind of nonparticulate two-phase system. The soluble blend system is dealt with in Chapter 6. The method discussed in Section 4.2 for determining, for a single component amorphous polymer, the thermal density fluctuation from the intensity I(q) extrapolated to q -> 0 can also be regarded as a small-angle technique. 

According to Equation (4.43), for a single-component liquid the zero-angle scattering intensity 7(0), that is, the intensity of scattering I(q) extrapolated to q - 0, is proportional to the mean square fluctuation ((ANv)2) in the number Nv of atoms present in a macroscopic volume v. In an equilibrium liquid (or an amorphous polymer above Tg) the mean square fluctuation ((ANv)2) is related to the isothermal compressibility of the liquid according to (4.32), so that 7(0) is given by... 

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