THE MOLECULAR-STRUCTURE OF LOW-DENSITY POLYETHYLENE .2. PARTICLE SCATTERING FACTORS

In order to characterize branched low-density polyethylenes (LDPE 1, LDPE 3, and Lupolen 1840 D) by means of light scattering, particle scattering factors for different branched structures were calculated and compared with experimentally determined values. Three models were considered in some detail: (i) heterogeneous combs with branches of equal length; (ii) combs, monodisperse with respect to the molar mass and polydisperse with respect to the length of a branch; (iii) random branched polymer trees of the kind A2-Bx. Additionally, the results were analyzed by means of space correlation functions. For LDPE 1 and LDPE 3 it was found that the comb models describe the observed particle scattering factors quite well. Best-fit values of the number of long branches per molecule, nb, agree well with those derived from the g ratio, which is defined as the ratio of the square radii of gyration of a branched to a linear macromolecule, both containing equal number of segments. The molecular structure of Lupolen 1840 D in some respects is that of a comb and in others is that of a polymer tree, of the kind A2-Bx. Superimposement of particle scattering factors, assigned to these structures, gives the best measure of agreement between theory and experiment. © 1990, American Chemical Society. All rights reserved.