Studies concerning the formation of industrially useful polycarbonates are the
focus of this dissertation. Of particular importance is the biodegradable polymer,
poly(trimethylene carbonate) which has a wide range of medical applications. The
production of polycarbonates can be achieved by the ring-opening polymerization of
cyclic carbonate, or the copolymerization of carbon dioxide and oxiranes or oxetanes.
For the production of polycarbonates from these monomers, Schiff base metal
complexes have been designed, synthesized, and optimized as catalysts. Detailed kinetic
and mechanistic studies have been performed for the ring-opening polymerization of
cyclic carbonates, as well as the copolymerization of carbon dioxide and oxiranes or
oxetane. In addition, the copolymerization of cyclic carbonates and cyclic esters to
modify the mechanical and biodegradable properties of materials used for medical
devices has been studied using biocompatible metal complexes. In the process for ring-opening polymerizations of trimethylene carbonate or
lactides, Schiff base metal complexes (metal = Ca(II), Mg(II) and Zn(II)) have been
shown to be very effective catalysts to produce high molecular weight polymers with
narrow polydispersities. Kinetic studies demonstrated the polymerization reactions to
proceed via a mechanism first order in [monomer], [catalyst], and [cocatalyst] if an
external cocatalyst is applied, and to involve ring-opening by way of acyl-oxygen bond
cleavage. The activation parameters (ΔH≠, ΔS≠ and ΔG≠) were determined for ringopening
polymerization of trimethylene carbonate, ring-opening polymerization of
lactides, and copolymerization of trimethylene carbonate and lactide.
In the process for copolymerization of carbon dioxide and oxetane, metal salen
derivatives of Cr(III) and Al(III) along with cocatalyst such as n-Bu4NX or PPNX (PPN
= bis(triphenylphosphine)iminium, and X = Br, Cl and N3) have been shown to be
effective catalysts to provide poly(trimethylene carbonate) with only trace amount of
ether linkages. The formation of copolymer is proposed not to proceed via the
intermediacy of trimethylene carbonate, which was observed as a minor product of the
coupling reaction. To support this conclusion, ring-opening polymerization of
trimethylene carbonate has been performed and kinetic parameters have been compared
with those from the copolymerization of carbon dioxide and oxetane.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1433 |
| Date | 15 May 2009 |
| Creators | Choi, Wonsook |
| Contributors | Darensbourg, Donald J. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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