KINETIC HETEROGENEITY OF POLYMER PRODUCTS OBTAINED IN THE PRESENCE OF MICROHETEROGENIC CATALYTIC SYSTEMS BASED ON GEL CHROMATOGRAMS

Abstract

Background: the polymer product obtained in the presence of microheterogeneous catalytic systems is characterized by fairly molecular weight distribution (MWD), resulted from kinetically nonequivalent active centers (ACs) in the system that initiate the polymerization process. The nature and composition of ACs are determined by setting and solving an inverse problem on the formation of MWD. This problem is acute because revealing the nature of the kinetic heterogeneity explains changes in the molecular and consumer parameters of the product for different catalyst compositions and propagation modes in polymerizations. Aim: This study aimed to develop methods and algorithms for interpreting gel chromatograms to analyze the kinetic heterogeneity of a polymer product obtained industrially in microheterogeneous catalytic systems. Methods: the solution method is based on the assumption that the formed MWD is a superposition of distributions inherent in each type of ACs. Since the problem in the final formulation refers to the Fredholm integral equations of the first kind, the regularization method of A. N. Tikhonov is used for its numerical solution, with the original problem being preliminary discretized. This methodology and the developed software algorithms were used to determine the kinetic heterogeneity of titanium- and neodymium-containing catalytic systems. Results and discussion: The MWD analysis revealed two types of ACs with an average molecular weight of ATi-lnM = 11.3 and BTi-lnM = 13.2 in the titanium catalyst and three types of ACs ANd-lnM = 11.1, BNd-lnM = 12.7 and CNd-lnM = 14 for the neodymium catalyst, respectively. Conclusions: repeated computational experiments under different polymerization conditions and requirements for the preparation of a catalytic system make it possible to reveal a relationship with the resulting heterogeneity of ACs. It allows us to set and solve problems of controlling the molecular characteristics of the resulting polymer product.