Intellectual Merit. In our recent successful GOALI work, we have made significant advances in understanding the spontaneous thermal polymerization of acrylates in the absence of any conventional thermal initiators. By combining efficient first-principles quantum-mechanical density functional theory (DFT) calculations with spectroscopic measurements of polymer samples, we have identified conclusively the mechanisms for monomer self-initiation and chain transfer reactions, including the reaction intermediates and transition states. We also calculated rate constants (frequency factors and activation energies) for the reactions in the gas phase. Now, building on these results, we propose to improve experimental control of the thermal spontaneous (without addition of conventional thermal initiators) polymerization of alkyl acrylates through coordinated and collaborative experimental and theoretical/computational research. To deepen our theoretical understanding, calculations will be performed with increasingly realistic solvent models, including multiple explicit solvent molecules in the quantum region and recently-developed van der Waals DFT functionals, to improve intermolecular potential energy surfaces. Concurrently, batch reactor polymerization experiments will be designed on the basis of the computational results and conducted to evaluate the influence of solvent type, monomer and solvent concentrations, and temperature on polymer-chain microstructural characteristics and polymerization rate.
The specific goals of this project are: (a) We will develop a computationally efficient method of calculating reliable liquid-phase rate constants for spontaneous thermal acrylate polymerization reactions such as monomer self-initiation, co-initiation by monomer and solvent, and chain transfer. (b) We will design and conduct batch polymerization experiments and, using spectroscopic methods, measure the microstructural characteristics of the produced polymer chains to validate and refine our theoretical predictions. (c) Using the developed computational method and batch polymerization experiments, we will study the structure-reactivity relationship for various solvents and monomers with a ketone functional group. (d) We will use these theoretical and experimental understandings to guide our computational screening and experimental validation of novel thermal initiators (solvents that permit rapid but controllable thermal polymerization of acrylates). Our ultimate goal is to design high-performance acrylic resins and chemically self-regulated polymerization processes for the production of acrylic resins at attractive overall cost.
Broader Impacts. The potential impacts of this project are societal (through improved safety), environmental, economic, and in human resource development, among others. Spontaneous thermal polymerization allows for the production of higher quality, environmentally friendlier solvent-borne paints and coatings at lower operating costs. Low molecular weight polymer and oligomer solutions have adequately low viscosity?even at high weight percent solids?thus requiring less solvent to be sprayable and brushable. The reduction or elimination of thermal initiators (e. g. azonitrile or organic peroxides, normally the most expensive component of a resin formula) and the increase of reaction rate both lower the operating costs. The elimination of residual groups due to the thermal initiators in the final product (which adversely affect polymer properties such as resistance to UV radiation) and the use of the quantitative understanding in optimal control of the polymerization reactors improve the resin quality. The PIs and Co-PI will train and mentor two doctoral research assistants as well as six undergraduate (REU) students, who will participate in broad range of research activities from quantum-level computations and supercomputing to laboratory experiments and spectroscopic methods. The project results will be released to the public at conferences and in journal and conference proceedings papers. As in our past research activities, students from under-represented groups will be selected, trained and mentored in this project.
