Effect of morphology and degree of crystallinity on the infrared absorption spectra of linear polyethylene

Abstract

The infrared absorption spectra of selected crystalline and noncrystalline bands were studied in bulk‐crystallized specimens of linear polyethylene which encompassed the extremely wide density range of 0.92–0.99 g./cm.3. The analysis of the data obtained at room temperature yield degrees of crystallinity by infrared methods which are in very good accord with the values deduced from the density measurements. Studies of the infrared spectra as a function of temperature give fusion curves which are in agreement with those obtained by thermodynamic methods. However, in order to obtain these latter results cognizance must be taken of the large negative temperature coefficient of the specific extinction coefficients of the crystalline bands from room temperature to the melting point. The necessary data to account for this phenomena were obtained from studies of the spectra of the n‐paraffin, C94H190, where molecular crystals are formed. Analysis of the two gauche bands, at 1352 and 1303 cm.−1, which are assigned to the noncrystalline regions demonstrate that for bulk‐crystallized samples of lowest densities the intensity ratio at room temperature is identical to that expected from the pure melt at this temperature. The conclusion is thus reached that the noncrystalline regions in these cases and the pure melt are structurally very similar. For samples of higher density, where the crystallite size is comparable to the extended chain length, the intensity ratio of the two gauche bands is altered. This change could reflect a change in the sequential distribution of gauche bonds. This intensity ratio for crystals formed from dilute solution is very similar to that for the high‐density bulk‐crystallized material and indicates a similarity in structure of the noncrystalline regions in the two cases.

A Raman spectroscopic study of the morphological structure of the polyethylenes

“…As we discuss below this conclusion differs from that reached by Strobl and Hagedorn [7]. It has been well documented that the degree of crystallinity determined from the density is always greater than the corresponding quantity derived from the enthalpy of fusion [18,[31][32][33]. The data in the last two columns of tables 3 and 4 give further support to this conclusion.…”

Surface studies of ultra-high molecular weight polyethylene irradiated with high-energy pulsed electron beams in air

“…19,20 However, in the FTIR/ATR spectrum of PE, these bands are too weak to be used for quantitative analysis. Recently, Zerby et al 21 proposed that the strong doublet at 1473/1463 cm Ϫ1 assigned to the CH 2 -bending vibration can be employed for the quantitative FTIR/ATR evaluation of the crystalline vs. amorphous content in the polymer.…”

The degree of crystallinity of monoclinic isotactic poly(propylene)

“…These include, among others, measurements of density, 9 enthalpy of fusion, 10 small-and wide-angle X-ray scattering, 7,[11][12][13][14] vibrational spectroscopy, 1,[15][16][17][18][19] and NMR using different techniques and nuclei. 20 -24 Properties correlate directly with the degree of crystallinity.…”