Radical Copolymerization of Hydroxy-Functional Monomers

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Idowu, Loretta
Coatings , Pulsed Laser Polymerization , Modeling , Reactivity Ratio , Propagation Kinetics , HEMA , HEA , BMA , Semi-Batch , ESI-MS , Solvent Effects , Copolymerization
Solvent-borne acrylic resins are commonly used in automotive coatings formulations due to the superior characteristics they provide to the final products. Hydroxyl-functionality, incorporated by selection of 2-hydroxyethyl methacrylate (HEMA) or 2-hydroxyethyl acrylate (HEA) as monomers, is required to ensure that the low molecular weight chains produced by free radical copolymerization participate in the cross-linking reactions to form the final coating product. Hence, the knowledge of their copolymerization kinetic coefficients is vital for both process and recipe improvements. In the first part of this work, the pulsed laser polymerization (PLP) technique is paired with size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) to provide kinetic coefficients for the copolymerization of HEMA with butyl methacrylate (BMA) in various solvents. These experiments provide insights into the influence of solvent type on the copolymerization reactivity ratios and composition-averaged propagation rate coefficients. In the second part of the study, small scale semi-batch reactions were conducted to investigate the influence of temperature, monomer composition and initiator content on the copolymerization of HEA with BMA. The effect of HEA content and copolymer molecular weight (MW) on resin performance was investigated by determining the amount and MWs of non-functional polymer that could be extracted after forming crosslinked films from the resins. Characterization of the extractable material by NMR, SEC, and by electrospray ionization mass spectrometry (ESI-MS) confirmed that the polymer extracted contained negligible levels of HEA. The experimental results were compared to Predici® and Monte Carlo simulations of the system
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