In the reported study, x-ray line broadening measurements were used to determine the apparent ″mosaic block″ sizes of randomly oriented PE and polyoxymethylene single crystals. Both dried-down and uncollapsed crystals were examined. PE lamellae were grown at 80, 85 and 90 degree C by isothermal crystallization from a 0. 1% solution in xylene. POM crystals were grown at 125 degree C by self seeding from an 0. 05% solution of the polymer in o-dichlorobenzene. It is evident from this present study that crystallite sizes in uncollapsed lamellae are significantly larger than those observed for the same crystals dried down. In the case of uncollapsed lamellae, one can explain the observed crystallite sizes solely on the basis of chain obliquity rather than by invoking the ″mosaic block″ model. It has also been determined that there is an upper limit to the crystallite sizes that can be observed in PE and POM crystals using wide-angle x-ray techniques.
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