Thesis (MSc)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Polylactides (PLA) are thermoplastic materials known for their biodegradability and biocompatibility, and therefore mostly utilized in biomedical applications. PLA-containing block copolymers further expand their application to include commodity materials and even advanced nanoporous materials. This research part of the thesis focuses on the synthesis and characterization of PLA-containing block copolymers, as well as their corresponding stereocomplexes formed by mixing block copolymers containing PLLA and PDLA segments. This work is divided into three parts. First, by using “living” anionic polymerization of styrene (St) and 2-vinylpyridine (2VP) followed by subsequent ethylene-oxide (EO) termination, well-defined hydroxyl-terminated polystyrene (PS) and poly(2-vinylpyridine) (P2VP) were synthesized. The resulting homopolymers were characterized by 1H nuclear magnetic resonance (NMR), size-exclusion chromatography (SEC), and infrared (IR) spectroscopy. The molecular weights were determined by SEC to be 6,200 and 5,500 g.mol-1 for PS and P2VP, respectively. In the second part, the two homopolymers, PS-OH and P2VP-OH were used as the macroinitiators for the ring-opening polymerization (ROP) of D- and L-lactides (D/L-LA) to obtain PS-b-PDLA and P2VP-b-PLLA, respectively. The targeted molecular weights of PLA blocks were varied to be 5,000, 7,000, and 10,000 g.mol-1 In the final part, quantitative stereocomplex formation was achieved by mixing PS-b-PDLA and P2VP-b-PLLA having equimolar PLAs segments. The physical and chemical properties of the diblockcopolymers and their corresponding stereocomplex, as well as the influence of varying the molecular weights of PLA blocks, were investigated by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), and circular dichroism (CD) spectroscopy.

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The spontaneous polymerization behavior of an acceptor substituted quinodimethane was investigated. High molecular weight homopolymers of 7,8,-di(ethoxycarbonyl)-7,8-dicyanoquinodimethane (DEDCQ) or copolymers of DEDCQ-styrene (St) and DEDCQ-p-methoxystyrene (p-MeOSt) were formed spontaneously in chloroform containing acetic acid. All polymerizations occurred by a radical mechanism. High molecular weight polymers formed at low conversion. Radical homopolymerization of DEDCQ was promoted by ambient light or heat. DEDCQ-p-MeOSt copolymerizations yielded alternating copolymers, which formed rapidly relative to the DEDCQ homopolymers and copolymers (rich in styrene). All of these polymerizations are thought to begin with a bond forming mechanism and propagate by polyaddition. A new acceptor group substituted quinodimethane was synthesized, characterized and copolymerized with electron donating monomers. Oxidation of the dianion of α, α'-dicyano-α, α'-diphenyl-p-xylene yielded 45% 7,8-dicyano-7,8-diphenylquinodimethane. In solution this compound exists in both the trans and cis forms but forms a sharply melting crystalline solid. It was resistant to homopolymerization but did form low molecular weight copolymers with electron rich aromatic monomers.

Aniline Black is perhaps the oldest known synthetic polymer. It has been studied since the mid 19ᵗʰ century, and is still a matter of interest. These interests arise from the fact that Aniline Black is inexpensive, yet has some very unusual and potentially useful electrical properties. The present approach has been a systematic study of Aniline Black related compounds. The model compounds were synthesized in a controlled fashion to dictate exact structure and purity. It is expected that the better the process of formation, the more uniform the structure, and hence a more usable material as an organic semiconductor. In the course of this investigation conclusions were drawn as to the structure/function aspects of the derived compounds. Attempts to alter the structure of model compounds deviated from the hypothesized behavior. Starburst model compounds displayed properties unexpected to the investigators. Available information about starburst polymers is very scarce. This work complements previous work on Aniline Black and related compounds, and adds a new source of knowledge in starburst chemistry. The properties of starburst compounds can be predicted only in part from the chemical makeup of the materials; this study gives some of the predictions based on the morphology. Several new approaches to the synthesis of useful Aniline Black model compounds grew from the knowledge obtained during this research. These will be presented with the body of the work and discussed at the conclusion as to the significance of such an investigation.

The experimental results of the current work have two parts. First the synthesis, characterization, and spontaneous copolymerization of two highly electrophilic imines, tricyanomethanimine and methyl 3-aza-α, β-dicyanoacrylate. 1,1-Dichloro-2,2-dicyanoethylene or methyl 3,3-dichloro-2-cyanoacrylate reacted with excess sodium azide to give the corresponding diazides, which smoothly underwent thermolysis in solution to give a solution of the novel tricyanomethanimine or methyl 3-aza-α, β-dicyano-acrylate. Attempted isolation gave only oligomers, but reactions using solution of these imines succeeded. Cyclopentadiene and 2,3-dimethyl-1,3-butadiene afforded hetero Diels-Alder reactions. N,N-Dimethylaniline with tricyanomethanimine gave a p-substituted derivative, but with methyl 3-aza-α, β-dicyanoacrylate only a charge transfer complex was formed. Imines - p-methoxystyrene copolymers were obtained. These imines are as reactive as TCNE, but in contrast can also polymerize. Second, a new unsymmetrically substituted quinodimethane was synthesized, characterized, and copolymerized with electron donating monomers. Oxidation of the 1-cyano-1-phenylmethylene-4-cyano-4-ethoxycarbonylmethylene with MnO₂ gave mostly poly-7,8-dicyano-7-ethoxycarbonyl-8-phenylquinodimethane (DCEPQ), but depolymerization by sublimation yielded 45% of DCEPQ. This compound was a mixture of cis and trans isomers. It was homopolymerized by anionic initiation. High molecular weight copolymers of DCEPQ-styrene, DCEPQ-p-methylstyrene and DCEPQ-p-methoxystyrene(p-MeOSt) were formed spontaneously in 1,2-dichloroethane. All polymerizations occurred by a radical mechanism. High molecular weight polymers formed at low conversion. DCEPQ - p-MeOSt copolymerizations yielded alternating copolymers. From spontaneous polymerization of DCEPQ with NVC no copolymer was obtained. All of these polymerizations begin with a bond forming mechanism and propagate by polyaddition.

The experimental results of the current work have three parts. First, the synthesis and characterization of several new copolymers by the free-radical copolymerization between several highly substituted electron-deficient olefins and furan, benzofuran, indene, alphamethylstyrene, and divinyl ether is discussed. Electron-poor olefins used included dimethyl cyanofumarate, carbomethoxymaleic anhydride and tricarbomethoxyethene. The spontaneous reactions of these monomer pairs were also investigated in both bulk and solution. Second, the effect of synthesis temperature on the composition of the previously reported (co)polymers of styrene with tricarbomethoxyethene and dimethyl dicyanofumarate are given. A ceiling temperature for the synthesis of this copolymer was found to be 220°C. Attempted copolymerization of tetracarbomethoxyethene gave evidence of a small but detectable amount of reaction. Finally, detailed procedures for the synthesis of dimethyl cyanofumarate, carbomethoxymaleic anhydride and tricarbomethoxyethene are given, including a new synthesis of carbomethoxymaleic anhydride.

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