Structural Studies of Crystalline Linear Polyethylenes as Revealed by Factor Analysis of Their Raman Spectra

Abstract

Seven samples of linear polyethylene which show quite different levels of crystallinity were prepared and Raman spectra of them were measured. The spectra of these samples show a series of narrow bands superimposed on very broad bands. This pattern is recognized to be the consequence of partial crystallization to give material consisting of lamellar crystallites connected with amorphous material. The narrow peaks are identical to those of crystalline polyethylene. The broad bands are identical to those of a polyethylene melt. Factor analysis of the spectra shows the existence of a third component which has a spectrum quite similar to that of the crystalline region. An estimation of the spectrum of this component is presented. It is based upon combinations of abstract factors and upon subtraction of the contributions by the two prominent components from mixture spectra. The third spectrum, attributed to an interracial region surrounding the crystallites in which partial order exists, closely resembles that of crystalline polyethylene, but with somewhat broader peaks that are shifted in position.