MODELING OF THE GLASS-TRANSITION TEMPERATURE OF FREE-RADICAL COPOLYMERS - AN APPROACH FOR CONTROL PURPOSES

A method that allows one to determine the relationship between the evo lution of copolymer composition and the distribution of glass transiti on temperatures is presented in this work. The experimental validation of the model is based on histograms of T-g distributions which were c omputed from DSC thermograms by using a new model-based optimisation t echnique. This technique allows us to obtain both the average T-g of t he overall copolymer and the cumulative distribution of T-g as a funct ion of the degree of advancement of the copolymerisation reaction, eve n in the case of reaction with composition drift. The modelling strate gy was used successfully to analyse the evolution of the T-g with conv ersion of several free radical copolymers of styrene and butyl acrylat e in emulsion. In particular, it has been shown that the value of the glass transition temperature of an ideally alternating copolymer, T-g, used in the Johnston (1973 Macromolecule 6, 453-456) equation, is in fact a function of the copolymer composition, and may vary by as much as 50 degrees C. The model of T-g presented here can be used to contro l profiles of glass transition temperature distributions (not just ave rages) during semi-continuous polymerisation processes. (C) 1998 Elsev ier Science Ltd. All rights reserved.