Studies concerning two different copolymerization processes are detailed in this
dissertation: propylene oxide/CO2 coupling to afford poly(propylene carbonate) and Nbutylaziridine/
CO coupling to afford poly-??-butylalanoid. The copolymerization of
propylene oxide and CO2 to form the industrially useful poly(propylene carbonate) has
been investigated employing chromium(salen)N3 complexes as catalysts. Unfortunately
the reaction could not be studied in real time via in situ infrared spectroscopy, thereby
obtaining detailed kinetic data, because of the copolymer-limited solubility in most
solvents. Studies employing batch reactor runs concentrating on varying the cocatalyst,
the equivalents of cocatalysts, and the steric and electronic structure of the catalyst
through modification of the salen ligand were undertaken. It was discovered that the
optimal catalyst for copolymer selectivity vs. the monomeric propylene carbonate was
one that contained a salen ligand with an electron withdrawing phenylene backbone and
electron donating tert-butyl groups in the phenolate rings. This catalyst was used to
investigate the effect of altering the nature of the cocatalyst and its concentration. The coupling of carbon monoxide and aziridines has been shown to be selective
for comonomer-alternating enchainment in the presence of PhCH2C(O)Co(CO)4 to
afford poly-??-peptoids. The mechanistic aspects of the reaction of CO and Nbutylaziridine
by means of in situ infrared spectroscopy employing CH3C(O)Co(CO)3L
(L = PPh3 and P(o-tolyl)3) as precatalysts was investigated. It was found the PPh3
precatalyst exists in solution under catalytic conditions as an equilibrium mixture of
CH3C(O)Co(CO)3PPh3 and CH3C(O)Co(CO)4, and affords both poly-??-butylalanoid and
the corresponding lactam as a side-product. By way of contrast, the P(o-tolyl)3
precatalyst which possesses the sterically bulky and labile phosphine ligand, affords only
the acyl cobalt tetracarbonyl species in solution during catalysis with the selective
production of the copolymer. Kinetic studies conducted with CH3C(O)Co(CO)3P(otolyl)
3 showed the coupling reaction to have a first order dependence on catalyst, a first
order dependence on N-butylaziridine, and only a slight dependence on the concentration
of CO over the pressure range 17-69 bar. The working mechanistic model for the
copolymerization reaction involves first aziridine insertion into the cobalt-acyl bond, rate
determining ring opening by the cobaltate species, followed by the migratory CO
insertion.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/2531 |
| Date | 01 November 2005 |
| Creators | Phelps, Andrea Lee |
| Contributors | Darensbourg, Donald J. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 1256669 bytes, electronic, application/pdf, born digital |
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