Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.

(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)

Computational quantum chemistry applied to nitrogen oxide chemistry and new fire-resistant polymers

Karin Rotem, University of Massachusetts Amherst


Computational quantum chemistry was used as a tool to predict needed thermochemistry and kinetics for two classes of problems: formation and destruction of NOx pollutants and development of new fire-resistant polymers. Of the latter, polycarbodiimides and polyhydroxyamides (PHA's) were studied. Different methods were used: HF/6-31 G(d), BAC-MP4 (bond-additivity corrections to UMP4 energies and HF vibrational frequencies), PM3 semi-empirical, and combinations. On the NOx problem, work focused on using theory to generate improved kinetics in H2/O2/NOx combustion. The results were a set of thermochemical data and highpressure-limit kinetics for NOx formation and destruction. Hartree-Fock structures and frequencies and fourth-order Moeller-Plesset energies were used for reactions of H/N/O-species involving H1N1O1 , N1O2, N2O1, H1N 2O1, and N2O2 surfaces, including NH + NO ↔ N2O + H, N2O + O ↔ NO + NO, N + OH ↔ NO + H, N + O2 ↔ NO + O, and N + NO ↔ N2 + O. Thermochemical results were discussed in the form of potential energy surfaces. In general, BAC-MP4 heats of formation compared consistently well to literature data. The results generated from this work allowed evaluation of pressure-dependent kinetics and, ultimately, a refined group of reactions for the NOx mechanism. Strengths of particular bonds and bonding combinations in polycarbodiimides were calculated. Work focused on effects of R groups, chain size and stereoregularity on bond dissociation energies (BDE). Specifically, five polycarbodiimide systems were studied: (1) R=R′=H, (2) R=R′ =CH3, (3) R=R′=CH2CH 3, (4) R=CH(CH3)(Phenyl), R′=H, and (5) R=CH(CH3)(phenyl), R′=CH 3. Methyl- and ethyl-substituted polycarbodiimides decreased the bond strength of the central C-N bond. Ligands on the amine (backbone) nitrogen weakened its chain C-N bond dramatically. However, a lower barrier reaction has also been identified. Results imply rapid, concerted unzipping of this polymer, a result consistent with experiment. For the polyhydroxyamide (PHA) system, a model cyclization reaction of PHA to polybenzoxazole (PBO) was evaluated. PHA cyclization to PBO has been studied experimentally, but a detailed theoretical reaction surface has never been evaluated. Moreover, a plausible mechanism by which PHA arrives at PBO had not been previously determined. The calculated overall heat of reaction was thermoneutral, and decomposition was determined to occur at 212°C, compared to the 215°C experimental value. The hydrogen-transfer reaction and a four-center concerted transition-state reaction were found to be the limiting steps.

Subject Area

Chemical engineering|Polymers|Chemistry

Recommended Citation

Rotem, Karin, "Computational quantum chemistry applied to nitrogen oxide chemistry and new fire-resistant polymers" (1999). Doctoral Dissertations Available from Proquest. AAI9920647.