Hydrogen bonding in radical copolymerization: A kinetic investigation under industrially relevant conditions

Abstract

Radical solution polymerization is a common method to produce a variety of plastics and coatings. Particularly in the automotive industry, large scale semi-batch operations are used to (co)polymerize monomers of the styrenic, acrylate and methacrylate families. To reduce solvent content, traditional non-functional feedstocks have been replaced or augmented with functional monomers like 2-hydroxyethyl methacrylate (HEMA) or 2-hydroxyethyl acrylate (HEA) to produce reactive polymer chains of lowered molar mass. The introduction of such polar and functional reactants affects the radical copolymerization kinetics and introduces solvent dependencies. The goal of this thesis is to identify and characterize these kinetic effects. Using specific kinetic parameters, a comprehensive model will be developed to describe copolymerizations under industrially relevant conditions, while also determining experimental limitations of comonomer incorporation. Due to the limited availability of reliable kinetic parameters, initial studies focused on the determination of copolymerization parameters involving HEA. The IUPAC recommended pulsed laser polymerization (PLP) technique in combination with size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy was used to determine propagation rate coefficients and reactivity ratios for HEA with both butyl methacrylate (BMA) and butyl acrylate (BA). Kinetics systematically diverged from classic kinetic behaviour and were solvent dependent. It was proven that hydrogen bonding causes these deviations by comparing HEA copolymerization to that of methoxyethyl acrylate. Simple terminal model predictions or implicit penultimate unit effects were used to represent chain growth kinetic parameters. Further experimentation was performed to determine the influence of these changing kinetic parameters during production of low molar mass functional HEA copolymers in relevant solvents such as ketones or esters under starved-feed semi-batch operating conditions, similar to those used in industry. H bonding effects on kinetics were found to be well controlled to HEA contents of maximum 50 wt%. The BMA/HEA copolymerization in ketones is very well represented by a comprehensive copolymerization model that considers relevant methacrylate and acrylate side reactions and uses the kinetic chain growth parameters measured by the PLP investigations.