Sequential homogeneity, a new quantity characterizing sequence distribution in copolymers
Camillo Tosi, Giuseppe Catinella · Die Makromolekulare Chemie · 1970
Abstract In order to ground on a quantitative basis the concept of “homogeneity” of copolymers, we introduce a novel quantity, which we propose to call “index of sequential homogeneity” and to denote by the symbol Hs. Its derivation is based on a new approach to the description of the statistical properties of copolymers, consisting in the evaluation of the probability Pn of each of the (n + 1) possible compositions of a sequence of n units picked up at random from an infinite copolymer chain we show that, as n increases, the curve of Pn against composition takes on a GAUSSian shape; hence we can calculate the mean square deviation μ of composition from the average. The limit value of μ /n, when n goes to infinity, is defined as the index of sequential homogeneity of copolymers. The dependence of Hs on the copolymer composition and the product of reactivity ratios is discussed, with particular emphasis to the comparison with informational entropy per monomeric unit. Some examples of experimentally measurable quantities concerning ethylene/propylene copolymers (melting temperature, half‐width of the X‐ray band of amorphous copolymers, ratio of IR‐bands characteristic of methyl rocking vibration), which correlate with sequential homogeneity, are also given.