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Dissertation
Computational and experimental study of spontaneous thermal polymerization of alkyl acrylates
Doctor of Philosophy (Ph.D.), Drexel University
Sep 2009
DOI:
https://doi.org/10.17918/etd-3131
Abstract
This project is aimed at answering two unanswered fundamental and industriallyimportant questions: What are the species that initiate the spontaneous thermal polymerization of alkyl acrylates? What are the initiation mechanisms? Density functional calculations (B3LYP/6-31G*) level of theory was used to investigate mechanism of spontaneous initiation in thermal polymerization of methyl, ethyl and n-butyl acrylate. Flory and Mayo mechanisms of self initiation were investigated. Potential energy surface maps for [4+2] and [2+2] cycloaddition reactions were constructed. It was found that diradical mechanism of self-initiation occurs in spontaneous thermal polymerization of alkyl acrylates, with the diradical species in a triplet spinstate Hydrogen transfer from the triplet diradical intermediate was found to be the lower energy pathway in comparison to hydrogen abstraction from triplet diradical intermediate and is proposed to generate monoradicals for initiating polymerization. DFT calculations was used to identify the occurrence of diradical mechanism of selfinitiation in spontaneous polymerization of MMA and that the diradical exists in a triplet state. This provided theoretical evidence to existing postulate and experimental observations. Experiments of spontaneous thermal homo-polymerization of methyl, ethyl and n-butyl acrylates in the absence of any known added initiators were conducted at 120 and 140 oC in xylene, dimethyl sulfoxide (DMSO) and cyclohexanone and in the presence of nitrogen and air in a 1 liter reaction calorimeter (RC1 Mettler Toledo). Highest initial monomer conversion was found to occur in cyclohex anone and lowest in DMSO. Highest average molecular weight polymers were found to form in DMSO. Higher initial monomer conversion and lower average molecular weight polymers was found in air than nitrogen. Mass-spectrometric studies were used to identify that the two dominant mechanisms of chain initiation and transfer in spontaneous thermal polymerization of methyl and n-butyl acrylate are monomer self-initiation and fi-scission respectively. The initiation rate constants estimated from macroscopic process modeling and experimental monomer conversion, numberaverage and weight-average molecular weight measurements was in good agreement with rate constant for triplet diradical formation predicted via quantum chemical studies.
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Details
- Title
- Computational and experimental study of spontaneous thermal polymerization of alkyl acrylates
- Creators
- Sriraj Srinivasan - DU
- Contributors
- Masoud Soroush (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Chemical (and Biological) Engineering [Historical]; College of Engineering (1970-2026); Drexel University
- Other Identifier
- 3131; 991014632276604721