RAMAN LONGITUDINAL ACOUSTIC MODE (LAM) STUDIES OF FOLDED-CHAIN MORPHOLOGY IN POLY(ETHYLENE OXIDE) (PEO) .3. CHAIN FOLDING IN PEO AS A FUNCTION OF MOLECULAR-WEIGHT

We have obtained Raman LAM spectra for a series of PEO fractions crystallized under different conditions and have interpreted these with the aid of results from normal mode calculations. Our LAM, X-ray, and DSC data indicate the existence of folded-chain structures more complex than the previously proposed simple integer-fold lamellae. We find evidence for lamellae consisting of once-folded chains in bilayer arrangements, for lamellae containing mixed integer-fold structures, and for lamellae based on half-integer-fold chains. The once-folded bilayer structures provide a mechanism for transformation, by reptation, to fully extended chains, and we see evidence in the LAM spectra for intermediate stages in this conversion. © 1990, American Chemical Society. All rights reserved.