THE MOLECULAR-STRUCTURE OF LOW-DENSITY POLYETHYLENE .1. LONG-CHAIN BRANCHING AND SOLUTION PROPERTIES

Light scattering, viscosity, gel permeation chromatography (GPC), and 13C NMR measurements were carried out on fractions of linear high-density polyethylene (HDPE) and branched low-density polyethylene (LDPE). GPC spectra show that the molar mass distribution of branched LDPE can be well fitted by the three-parameter distribution of Hosemann and Schramek. Its nonuniformity coefficient is 10 times larger than one corresponding to the linear polymer of the same molar mass.l3C NMR measurements indicate that the branched LDPE’s contain both short (favorably n-butyl) and long branches. A comparison of the number-average of long branches per 1000 CH2, estimated by13C NMR spectroscopy, with the one calculated by light scattering indicates that the branch points are predominantly tetrafunctional if one assumes random branching. However, an adequate interpretation of the experimental data can also be given by the heterogeneous comb model, developed by Solensky and Casassa. Thus, there exists some doubt concerning the true structure of the branched polymers. Additionally, it seems that LDPE’s, prepared by different companies, possess slightly different structures of branching. The following paper, dealing with the particle scattering factor, will hopefully give a deeper understanding of this problem. © 1990, American Chemical Society. All rights reserved.