Solvent-free peroxide-initiated polymer modifications are widely used to improve the physical and/or chemical properties of commodity plastics and elastomers. Although the reactions that underlie polymer grafting are known, our understanding of H-atom transfer reactions in this context is incomplete. Fundamental questions remain unanswered, such as the difference in reactivity between different polymers (polyethylene versus polypropylene and polyisobutylene) and differences in the regiochemical outcomes of grafting reactions upon them. Herein, experimental data pertaining to the H-atom transfers involved in polyolefin graft modifications were obtained to improve our fundamental understanding of these reactions by using radical-trapping techniques and quantum chemical calculations. In this project, experimental measurements of the efficiency of H-atom abstraction by t-butoxyl radicals from polyolefins, and suitable model compounds such as pentane, 2,4-dimethylpentane and 2,2,4,4-tetramethylpentane were determined. Insight is gained from alkyl-trapping experiments to quantify the relative reactivities of the primary, secondary and tertiary positions of the model compounds. Experimental data were compared to quantum chemical calculations, which revealed that entropic effects dictate the regioselectivity and preclude abstraction at the secondary position in favour of the less enthalpically-favourable primary abstraction site. MP2 and CBS-QB3 level calculations were able to reproduce experimental trends in model compound reactivity, while the highly common B3LYP density functional, used in other investigations on the subject, could not. / Thesis (Master, Chemical Engineering) -- Queen's University, 2011-10-20 16:48:38.083

Thesis advisor: Peter X. Zhang / Thesis advisor: James P. Morken / Radical reactions have attracted continuous research interest in recent year considering their diverse reactivities. Hydrogen-atom abstraction (HAA), as one type of the most well-explored radical reactions, has been identified as one of powerful tools for C–H functionalization. Reactions involving 1,4-HAA, which is typically a challenging process both entropically and enthalpically, are rather scarce, while 1,5-HAA have been well demonstrated for variety of synthetic applications. Guided by the concept of metalloradical catalysis (MRC), 1,4-HAA was for the first time utilized as the key step to achieve asymmetric construction of chiral ring structures: cyclobutanones, azetidines and tetrahydropyridines. The design of different D2-symmetric chiral amidoporphyrin as the supporting ligand is the key to all these transformations. The reactions can be conducted under mild conditions, affording corresponding ring structure in good yields with excellent selectivity. Furthermore, The combined computational and experimental studies have shed light on the mechanistic details of these new asymmetric radical intramolecular C–H alkylation processes, which are fundamentally different from existing catalytic systems involving metallocarbenes for concerted C–H insertion. We envision that these asymmetric radical processes via Co(II)-based MRC could become an alternative method for important chiral ring structures synthesis and potentially provide new opportunities for complex molecule construction. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.