ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Variable temperature magic angle spinning 13C NMR experiments on linear alkanes and low molecular weight polyethylene allowed the observation of up to six carbon atoms at the chain ends near the surface of the lamellar crystallites. Conformational order-disorder and intermolecular packing effects are reflected by the spectra. The effects are discussed with regard to the peculiar phase behaviour of the n-alkanes and the fringed micella model for low molecular weight polyethylene. The solid-solid transitions of nonadecane and hexatriacontane appear to be correlated with the occurrence of specific non-liquid-like conformational disordering. Thus, conformational defects were observed for the “rotator phase” which depend on the chain length and which vary along the chain. Whilst the center part of the chain remains all-trans ordered, significant gauche defects were observed for the bonds at the chain ends. For a polydisperse low molecular weight linear polyethylene as well as for monodisperse octahexacontahectane reversible liquid-like conformational disordering of the terminal chain segments could be detected when the melting point was approached. Hence, in this case the NMR spectra indicate pre-melting of the lamella surface, while in case of the shorter n-alkanes the occurrence of end-gauche defects is correlated with solid-solid transitions.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1986.021870520
