Long chain branching indices of low density polyethylenes from size exclusion chromatography and 13C-NMR spectroscopy
1987; Elsevier BV; Volume: 23; Issue: 11 Linguagem: Inglês
10.1016/0014-3057(87)90056-5
ISSN1873-1945
AutoresDaniele C. Bugada, Alfred Rudin,
Tópico(s)Polymer Nanocomposites and Properties
ResumoSize exclusion chromatography (SEC) and 13C-NMR analyses have been used to measure long chain branching indices in low density, free radical-polymerized polyethylenes. Calculation of long chain branching frequency from SEC data requires the assumption of a molecular model. Generally, a randomly branched polymer is assumed, with branches originating at trifunctional branch points. Long chain branch concentrations determined by SEC analysis alone appear to be valid only in a relative sense. The parameters used in the model assumptions vary from polymer to polymer. Despite these limitations, SEC analyses appear to be internally consistent when applied to polyethylenes made by a single manufacturer and process. Comparisons of absolute values of long branch frequency between products from different reactor types require NMR as well as SEC data.
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