A novel parameter of polymer structure

Abstract

With the aim of finding a simple and reliable method for the determination of the breadth of molecular weight distributions of high molecular weight compounds, W. S. Baharyl If, however, for the moment we assume the existence of two molecular weight ranges of constant (Y and 8 as proposed in eq. (l), a discussion of the ratio of q s and [q] as a means for the determination of heterogeneity indices is possible.Apart from a few trivial assumptions Bahary postulates, first, that the polymer should contain some molecules having a molecular weight greater than the critical value and, second, that the range of intrinsic viscosities to be compared should be narrow.For the general case with finite amountsof polymers on both sides of M,,, ROVbecomes and it is readily seen that, for constant [ q ] , the greater the product of WU~(&)M>M,, the larger the value of ROV, subject to the condition that KI and Kz are of the same order of magnitude. If, however, for easier discussion we examine the validity of ROV for the special case of polymers containing only homologs either below or above M,,, eq. (4) reduces to~s / [ t l l = (Kz/K3)(iffw/B,,)"Bw3.6-" All M > M , (4b) In both cases ROV is not only a function of the ratios of two different molecular weight averages, but also of the absolute weight-average molecular weight. This is the reason, why Bahary' was forced to confine the application of his novel parameter to samples lying within a narrow range of intrinsic viscosities.If [q] and therefore a,, is kept constant, qs, which depends on Gw or aw3.6, respectively, will reflect the high molecular weight ends of the molecular weight distribution,

Molecular heterogeneity characterization in polyglycols

“…With high molecular weight materials a low solution viscosity is needed in the characterization of this coefficient. 20 The samples studied meet all the following conditions necessary for ROV to be operative as a valid heterogeneity index : 2o constant microstruc-…”