Determination of Molecular Mass during Online Monitoring of Copolymerization Reactions

Abstract

Light scattering determination of weight-average molecular mass M w of a copolymer has historically required that measurements be made in at least three separate solvents of different index of refraction. Recently, however, it was demonstrated that, in principle, the evolution of M w of a copolymer can be followed during copolymerization reactions using automatic continuous online monitoring of polymerization reactions (ACOMP). The continuous measurement of M w by ACOMP is made possible by the fact that ACOMP provides the comonomer concentrations and absolute light scattering intensity at each instant of time during conversion and, hence, also yields the evolution of the average and instantaneous composition distribution. In this work, a workable and practical formalism for determination of M w during reactions, using a single solvent, is developed for the case of N comonomers. The traditional method quickly becomes intractable since the number of solvents required grows as N(N + 1)/2, and the number of auxiliary measurements of differential index of refraction of polymers in the solvents is N(N + 1) 2 /2. The formalism is applied to experimental cases involving copolymerization of styrene and methyl methacrylate, and M w and apparent mass M ap are compared. Results are correlated with traditional multisolvent determinations on endproducts and gel permeation chromatography approaches.

Cationic Copolyelectrolytes: Online Monitoring of the Synthesis and Subsequent Copolymer Characterization

“…For homopolymers, the Zimm40 single contact approximation is generally used to determine M w . In this work, the computed mass comonomer concentrations are used together with data from light scattering measurements in the determination of M w , based on authors previous reported studies 41…”

Fundamental Measurements in Online Polymerization Reaction Monitoring and Control with a Focus on ACOMP

“…They formulated a method requiring light scattering measurements in a minimum of 2 N − 1 solvents to find true $\overline {M} _{{\rm w}} $ , where N is the number of comonomer types (i.e., three solvent minimum for two comonomers, five for terpolymers, etc.). This impractical limitation has been circumvented in ACOMP, since it measures the evolution of average composition drift, so that true $\overline {M} _{{\rm w}} $ can be computed at each instant of synthesis, as recently reported 72…”

“…The dual stream reactor extraction approach ACOMP platform was applied also to batch copolymerization reactions in emulsion, using BA and methyl methacrylate (MMA) as the comonomers. An extended spectrum UV analysis for discerning concentrations of comonomers with similar spectral characteristics was involved 72. On the polymer/monomer stream, the average composition drift and distribution, $\overline {M} _{{\rm w}} $ and reduced viscosity η r,w were measured, and on the colloid stream the particle size distributions were measured.…”

Polymerization Online Monitoring

“…A small stream of reaction mixture is continuously withdrawn from the reactor, continuously diluted with solvent from a reservoir and pumped through several detectors [164][165][166][167][168].…”