Effect of reaction conditions on the distribution of hydroxyl functional groups in HEA- BMA copolymer
May 20-25, 2018
Non-functional monomer feedstocks containing alkyl meth(acrylate) components such as butyl acrylate (BA) and butyl methacrylate (BMA) have been replaced or augmented with functional monomers such as 2-hydroxyethyl methacrylate (HEMA) and 2-hydroxyethyl acrylate (HEA) to produce reactive polymer chains of lowered molecular weight (MW) for application in solvent-borne automotive coatings. The polar and functional reactants affects the radical copolymerization kinetics and introduces solvent dependencies. A series of BMA/HEA experiments have been performed at 138 °C to determine the influence of these changing kinetic parameters under starved-feed semi-batch operating conditions. A comparison with BMA/BA copolymerization shows that the influence of hydrogen bonding is small, with the semi-batch system well controlled to HEA contents of up to 50 wt%. Thus, the experiments are well represented by a comprehensive generalized copolymerization model formulated in PREDICI® that considers relevant methacrylate and acrylate side-reactions and uses the chain growth parameters measured in previous kinetic investigations.
As well as controlling overall copolymer composition, understanding the distribution of the hydroxyl functional groups among the polymer chains is of importance, as non-functionalized lower-MW chains will not crosslink into the polymer network formed upon application of the coating. A series of BMA/HEA copolymers containing 6.25, 12.5 and 25 wt% HEA were synthesized with weight-average polymer MWs varied between 3000-10000 Da through manipulation of reaction temperature (138 and 160 °C) and initiator loading (2 to 4 mol% relative to monomer) during starved-feed semi-batch operation; at the higher temperature the influence of BMA depropagation becomes more apparent. The amount of non-functional material in the samples is experimentally determined by solvent extraction after forming a crosslinked film, and MWs and HEA contents of the extractable fractions are measured. These experimental results will be compared with predictions from the PREDICI® model as well as a kinetic Monte Carlo representation that calculates how the reactive groups are distributed as a function of polymer chain-length.
 J. E. S. Schier, R. A. Hutchinson, “The influence of hydrogen bonding on radical chain-growth parameters for butyl methacrylate/2-hydroxyethyl acrylate solution copolymerization”, Polym. Chem. 2016, 7, 4567-4574.
 J. E. S. Schier, M. Zhang, M. C. Grady, R. A. Hutchinson, “Modeling of Semi-batch Solution Radical Copolymerization of Butyl Methacrylate and 2-Hydroxyethyl Acrylate”, Macromol. React. Eng.. 2018, submitted.
Loretta A. Idowu, Jan E. S. Schier, Amin Nasresfahani, and Robin A. Hutchinson, "Effect of reaction conditions on the distribution of hydroxyl functional groups in HEA- BMA copolymer" in "Polymer Reaction Engineering X (PRE 10)", John Tsavalas, University of New Hampshire, USA Fouad Teymour, Illinois Institute of Technology, USA Jeffrey Stubbs, HP Inc., USA Jose R. Leiza, University of the Basque Country, Spain Eds, ECI Symposium Series, (2018). https://dc.engconfintl.org/prex/24