Analyzing compositional drift transients in copolymerization systems using digital encoding

Abstract

A new methodology termed “Digital Encoding of Polymeric Chains” was developed by Debling and Teymour (Macromol. Symp. 182 (2002) 195). It involves replacing distinguishable features of the chain such as monomer units, branches, functionality, etc., with a numeric code that can be translated into a unique decimal equivalent number. This technique provided a suitable method for the graphical representation of the chain type distribution (CTD), which was not previously possible. CTD represents concentration fractions of all polymer chain types including polymer isomers which are chains of same length and composition, but have different monomeric sequences. This work focuses on the analysis of the transient behavior of CTD in contrast with the compositional behavior for free radical copolymerization chemistry in batch reactors, in semi-batch reactors operated under different compositional drift control policies, and finally in grade transitions of continuous stirred tank reactors (CSTRs). Results show that many time-dependent policies succeed in maintaining a homogenous copolymer composition and CTD; however, for grade transitions in CSTRs, a uniform copolymer composition cannot ensure the same level of uniformity in CTD resulting in the possibility of fairly different product grades than required.