Evaluation of conversion during the synthesis of aluminum (III) methacrylate-based copolymers using Raman spectroscopy and multivariate curve resolution

Abstract

The present work addresses the use of Raman spectroscopy and multivariate curve resolution–alternating least squares (MCR-ALS) for the evaluation of the reaction conversion in copolymerization of aluminum (III) methacrylate and vinyl monomers (vinyl acetate, ethyl acrylate and methyl methacrylate). For the synthesis of these materials, pseudo-dispersion copolymerizations were carried out in a reaction medium containing 17wt.% of aluminum (III) methacrylate [Al(III)MA] and 83wt.% of vinyl monomers, such as vinyl acetate (VAc), ethyl acrylate (EA) and methyl methacrylate (MMA). Raman spectra were acquired at different reaction times for each monomer used. We used multivariate curve resolution (MCR-ALS) in order to evaluate the reaction conversion and the concentration profiles. The concentration profile of VAc/Al(III)MA reaction shows that the polymerization occurs slowly, in which the conversion stabilizes after 15h of reaction. The concentration profile of EA/Al(III)MA copolymerization shows that high conversions are achieved in a short reaction time. However, as the reaction proceeds (between 4 and 12h), it is possible to observe a decrease of the reaction rate, which is an indication that the modified monomer is polymerizing. The concentration profile of MMA/Al(III)MA copolymerization shows a high conversion in the first 2h of reaction, indicating a possible low incorporation of the modified metal monomer into the growing copolymer chains, due to the differences of reactivity between the monomer species. The use of Raman spectroscopy coupled with MCR-ALS allowed for the evaluation of the conversion rate of three different organic–inorganic copolymers, although it is difficult to determine the conversion of hybrid polymers, the use of chemometric methods and Raman spectroscopy allowed us to compare the conversion rate between the studied copolymers.