MALDI-TOF Mass Spectrometry in the Study of Statistical Copolymerizations and Its Application in Examining the Free Radical Copolymerization of Methyl Methacrylate and <i>n</i>-Butyl Methacrylate

Abstract

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used to obtain bivariate distributions of composition and chain length for a series of copolymers of methyl methacrylate (MMA) and n-butyl methacrylate (BMA) produced by free radical catalytic chain transfer polymerization. The relationship between the bivariate distributions of copolymers and the kinetics of the copolymerization reactions from which they were formed was derived using the terminal copolymerization model. This relationship was used with the mass spectra from the MMA/BMA copolymerizations studied to estimate kinetic parameters which describe the polymerizations. For this copolymerization the reactivity ratios, (catalytic) chain transfer coefficients, and initiator selectivity were determined to be rMMA = 1.09, rBMA = 0.77, CS,MMA = 17 900, CS,BMA = 6150, and SMMA = 0.535, respectively. The reactivity ratios for these polymerizations were also determined from 1H NMR to be rMMA = 0.75 and rBMA = 0.98, using an error-in-variables model (EVM) treatment. The parameters determined from the mass spectra were compared with both the NMR values and literature values, where available, and general agreement is shown.