Solution Radical Polymerization of Methyl Acrylate and n-tert butylacrylamide under Batch and Semi-batch Operation
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Authors
Kaur, Gagandeep
Date
Type
thesis
Language
eng
Keyword
Batch vs Semi- Batch operation , Radical Polymerization
Alternative Title
Abstract
Free radical polymerisation is one of the most versatile methods to produce materials for diverse applications. With the world inclining towards sustainability, the industry is transitioning from the use of organic solvents to aqueous media. However, radical polymerization kinetics are affected by the use of hydrogen-bonding solvents, and there is limited information regarding the use of water as a solvent for hydrophobic and sparingly soluble monomers. Thus, the radical polymerisation of methyl acrylate (MA) and N-tert-butylacrylamide (t-BuAAm) is studied in water and ethanol (EtOH), as the copolymer product has commercial application in hair sprays and other personal care products, and as textile and paper coatings.
The copolymerization kinetics of the system are being studied in a parallel project by Maryam Agboluaje using an in-situ NMR technique that provides a continuous measure of both monomer conversion and composition. However, the evolution of the polymer molecular weight (MW) cannot be followed over the course of the batch reactions in the NMR tube. Thus, a stirred 250 mL reactor setup has been established, with samples removed over the course of the reaction analyzed by both NMR and size exclusion chromatography to determine monomer conversions and composition as well as copolymer composition and molecular weight distributions (MWDs). The results from the new setup are in good agreement with those from the in-situ NMR technique, and it is determined that there is a significant decrease in polymer average MWs and broadening of the MWD with reaction time.
Semi-batch reactors are used by industry to reduce the variation in polymer properties over the course of a reaction, as well as to better control the heat released by the exothermic reaction. In addition, semi-batch operation provides additional data to probe the influence of solvent on polymerization rate and polymer MWs, as the low monomer concentration maintained under starved-feed operation leads to a different solvent to monomer ratio than in a batch system. Thus, a series of semi-batch reactions have been conducted, to demonstrate that the copolymer can be successfully synthesized without significant drifts in product MW or composition. The effect of batch and semi-batch operating conditions (i.e., reaction temperature, initiator level, solvent to monomer ratio, comonomer composition) are interpreted in terms of the known features of the polymerization kinetics, which includes backbiting and solvent effects on rate. It is found that MA is preferentially incorporated into the copolymer relative to t-BuAAm and the molecular weight increases with increased t-BuAAm content in the system.
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