TERMINAL AND PENULTIMATE REACTIVITY RATIOS IN THE STYRENE-ACRYLONITRILE FREE-RADICAL COPOLYMERIZATION SYSTEM IN BULK

The terminal and penultimate model reactivity ratios for the styrene-a crylonitrile monomer system in bulk have been investigated by the simp lex and scanning method. It has been shown that Mayo-Lewis equation ha s an unique solution when determining the reactivity ratios according to the terminal model while for the penultimate model the non-uniquene ss in determination of the reactivity ratios has been found. The numer ical values of the penultimate r-parameters calculated with the simple x method depend on the initial guess for r-parameters. Several sets of penultimate reactivity ratios for the styrene-acrylonitrile system in bulk have been found to be equal from mathematical point of view. The reactivity ratios with comparable standard deviation have an equivale nt graphical representation on the copolymerization diagragm. It has b een also confirmed that the penultimate model is a more appropriate of the models considered to describe the variation of the copolymer comp osition with the monomer feed. Taking into account previous results fo r the styrene-methyl methacrylate system in bulk it is thereby assumed that the occurrence non-uniqueness in determination of the penultimat e model reactivity ratios does not depend on the monomer system.