Synthesis and characterization of new tetraalkylborate initiators for novel polymerization applications

by Nikolaeva, Ekaterina.

Douglas Neckers, Advisor A system has been developed which carries out the radical polymerization of acrylic esters without direct use of light and/or heat (designated as Remote Cure). This approach may represent a significant innovation in the area of coatings. A novel feature of the proposed system design is to bring the active component of the initiating mixture in a flow of a carrier gas which has unrestricted access to the entire surface of the coating. When brought in contact with the surface, the active ingredient(s) of the curing gas (H2O2 vapor) react with the active coating component(s) (tetraalkyl borate salts) to generate free radicals and initiate the polymerization within the coating. The thesis presents the synthesis and characterization of symmetric and asymmetric tetraalkyl borates used as initiators for remote cure. Some of them are known - NBu4BBu4, NBu4BPhBu3 and NBu4BBuPh3, and some of them have been synthesized for the first time - NBu4BEt4, NBu4B(iPr)4, NBu4BBuEt3 and NBu4B(iPr)Et3. Studies of these borate salts were conducted with the emphasis on their relative reactivity in the Remote Cure process and mechanistic considerations. In Situ studies by FTIR Spectroscopy proved that borate salts, when activated by H2O2 vapors, showed good reactivity in the remote cure process. ATR FTIR studies were made using different peroxides. Only H2O2 showed good remote polymerization activity. From the results of electrochemical experiments, oxidation potentials were determined. These potentials helped to explain the observed reactivity of borate salts in the remote polymerization. In addition, iii nanosecond laser flash photolysis experiments were conducted to aid our understanding of the remote cure. The mechanism for remote cure process has been proposed. The results of radical trapping experiments obtained using GC, GCMS, and NMR allowed us to confirm the proposed mechanism where tetraalkyl borate is being oxidized by H2O2 to produce alkyl radical and trialkylborane, with the former adding to acrylic double bond to start the chain polymerization. iv