Molecular structural parameters such as number-average molecular weight
(Mn), weight-average molecular weight
(Mw), and long-chain branching frequency of low-density polyethylenes (LDPE) synthesized by an autoclave and a tubular reactor were evaluated from GPC and intrinsic viscosity data on the basis of the method developed individually by Drott and by Kurata. In Drott's procedure, the contraction factor g derived for unfractionated materials was used. On the other hand, g derived for fractionated materials was used in the Kurata's procedure. Here
g is the ratio of root-mean square radii of the branched and linear polymers with the same molecular weight. Values of
Mn or
Mw obtained by the two procedures were almost the same but long-chain branching frequencies evaluated by Kurata's procedure were considerably larger than those of Drott's one. In order to evaluate which procedure would provide more adequate long-chain branching frequencies, the long-chain branching frequencies were also evaluated on the basis of
13C-NMR spectra and compared with those obtained by means of GPC and intrinsic viscosity measurements. However we could not obtain a definite conclusion from such a comparison. The relationships among melt index (MI), density, and molecular structural parameters were also investigated. It was found that (i) MI can be predicted from
Mw and long-chain branching frequency, and (ii) the long-chain branching frequency of autoclave resins increases with decrease in their density.
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