The equilibrium phase behavior of disperse diblock copolymers is studied using the self-consistent field theory. We first examine how dispersity affects the formation of complex spherical phases in conformationally asymmetric diblock copolymers. For disperse diblock copolymers with Poisson and Schulz-Zimm distributions, the Frank-Kasper σ phase appears at a lower degree of conformational asymmetry than what is predicted in monodisperse systems. We next present a general method of treating molecular weight distributions (MWDs) specified by a set of molecular weight fractions in numerical self-consistent field theory. The procedure is applied to MWDs with similar dispersity indices and different skewness obtained from experimental measurements. We find that consistent with experiments, the domain spacing and equilibrium morphology could vary with the skewness. Lastly, we investigate how the MWD shape characterized by the dispersity index and skewness affects the relative stability of complex spherical phases. The predicted set of complex phases could differ between MWDs with identical dispersity indices and different skewness. In particular, it is found that the formation of the C14 and C15 phases is favored for more positively-skewed distributions. Overall, the work underlines the importance of the MWD shape on the phase behavior of disperse diblock copolymers and the need of considering other statistical measures alongside the dispersity index, such as the skewness. / Dissertation / Doctor of Philosophy (PhD)

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The Digitization Centre has determined that pages x, 30 and 106 are not in this thesis or the vault copy. / Pyrenebutylamide-labeled poly(N-isopropylacrylamide-co-N-acryloyl-L-valine) copolymers have been prepared by two different methods and their physicochemical properties have been compared. One sample was prepared via copolymerization of N-isopropylacrylamide (NIPAM), and N-acryloyl-valine (NAV) with N-[4-(1-pyrenyl)butylacrylamide], the other by post-modification of poly(N-isopropylacrylamide-co-N-acryloyl-L-valine-co-N-acryloxysuccinimide) copolymer with pyrenebutylamine hydrochloride. The polymers were characterized by 1H NMR and FTIR spectroscopy, Differential scanning calorimetry and light Scattering. Though the use of fluorescence spectroscopy several differences between the two types of copolymers were detected. By comparing the extent of pyrene excimer emission and pyrene monomer emission from solutions of the two polymers, it was concluded that the copolymer obtained by direct copolymerization (method 1) had an inherent ''blocky" microstructure, while the copolymers obtained by the post-modification route presented a more random microstructure. Intrapolymeric interaction exists in solutions of low copolymer concentrations. At higher concentrations both inter-and intrapolymeric interactions coexist. The presence of a number carboxylic groups in the PNIP AM chain significantly modifies the conformation properties of the copolymers, compared to poly(N-isopropylacrylamide). The copolymers contract and expand in response to external conditions such as pH and temperature. Their Lower critical solution temperature (LCST) changes with pH. The interactions between polymers and fluorescence quenchers were investigated. The quenching results reveal that hydrophilic cationic quenchers interact strongly with the randomly labeled-copolymer. Hydrophobic cationic species interact strongly with ''blocky" pyrene labeled copolymer. Anionic quencher interacts quite weakly with both copolymers owing to electrostatic repulsion. / Thesis / Master of Science (MS)

Integral membrane proteins represent nearly 25% of protein encoding genes yet account for less than 2 percent of solved structures in protein databases. This underrepresentation is due to the difficulty in membrane protein isolation with the use of detergents. The difficulty in structural characterization following isolation has been alleviated by use of amphipathic polymers that stabilize proteins by maintaining the native protein environment. Of these amphipathic copolymers, SMA2000—a commercially available styrene-maleic anhydride copolymer with a 2:1 styrene to maleic anhydride ratio—has demonstrated broad utility in the isolation and subsequent characterization of a wide range of integral membrane proteins. However, there are some limitations to the use of SMA2000 that may arise from a lack of control of polymer parameters such as sequence, composition, and dispersity. Methyl substituted stilbene and maleic anhydride copolymers with controlled sequences and compositions demonstrated membrane solubilization and protein isolation activity at levels comparable to SMA2000, with several advantages that include an increase in the useable pH range and the size and homogeneity of polymer-lipid particles. Regrettably, the synthesis of methyl substituted stilbene-maleic anhydride copolymers is not without challenges that would make laboratory scale-up difficult. The use of anisole as a polymerization solvent mitigates gelation during poly((E)-4-methylstilbene-alt-maleic anhydride) synthesis. Additionally, unsymmetrical dimethyl-substituted stilbenes and monosubstituted stilbenes ((E)-4-tert-butylstilbene, (E)-4-methoxystilbene, (E)-2-methoxystilbene, methyl (E)-4-carboxylatestilbene, and (E)-4-trifluoromethylstilbene) copolymerize with maleic anhydride without gelation. Rates of conversion reveal that stilbenes with donor substituents copolymerize with maleic anhydride faster than stilbenes with acceptor substituents. The reversible addition–fragmentation transfer (RAFT) controlled radical polymerization technique afforded poly((E)-4-methylstilbene-alt-maleic anhydride) copolymers with controlled sequence, composition, molecular weight, and dispersity. Amphipathic copolymers with fluorescent activity are also desired for membrane protein solubilization. A series of donor-acceptor di-substituted stilbene and maleic anhydride copolymers with fluorescence activity have been synthesized and characterized. These copolymers possess electron-donating and electron accepting substituents on each phenyl ring of the stilbene monomer. These copolymers exhibit red-shifts that vary in position and width with changes in substituent. / Doctor of Philosophy / Proteins embedded in biological membranes—integral membrane proteins—are valuable drug targets due to their significance in a variety of essential cellular functions such as signaling and transport. Structural and functional characterization of integral membrane proteins is necessary to develop drugs that target them. However, despite their importance, integral membrane proteins remain a challenging target for structural characterization. Integral membrane proteins must be removed or solubilized from the lipid bilayer for structural characterization and the typical detergent extraction process often results in protein destabilization or irreversible protein deactivation. Polyanions have emerged as suitable alternatives to the solubilization of integral membrane proteins. Unlike detergents, polyanions solubilize integral membrane proteins with a small portion of the lipid bilayer intact. In this way, the integral membrane protein is removed from the lipid bilayer, but it maintains its structural and functional integrity allowing for structural and functional characterization. Hydrolyzed poly(styrene-co-maleic anhydride) is the most widely used polyanion for integral membrane protein solubilization, however, the sequences and compositions of poly(styrene-co-maleic anhydride) copolymers are not uniform and these inconsistencies have been shown to effect isolated integral membrane protein yield and purity. Hydrolyzed strictly alternating copolymers of substituted-stilbene and maleic anhydride have uniform sequences and compositions and have demonstrated integral membrane protein extraction activity at levels comparable to or greater than the commonly used hydrolyzed poly(styrene-co-maleic anhydride) copolymers. The work described in this dissertation focuses on optimized syntheses and characterization of several substituted-stilbene and maleic anhydride copolymers for the solubilization of integral membrane proteins. The choice of stilbene substituent is shown to affect poly(substituted-stilbene-alt-maleic anhydride) properties such as solubility and fluorescence activity.

Summary of the thesis This works aims at reporting a novel strategy that combines controlled ring-opening polymerization of lactones initiated by a cyclic tin(IV) dialkoxide and intramolecular cyclization by photo-cross-linking of pendant unsaturations next to the propagating sites. No linear species is ever involved in the polymerization, which allows higher molecular weight macrocycles to be prepared with high efficiency. Moreover, the synthetic route is very flexible to the point where macrocyclic polyesters with more complex although well-defined architectures, such as tadpole-shaped and sun-shaped copolyesters, can be tailored. Synthesis of well-defined star- and eight-shaped polyesters and twin tadpole-shaped amphiphilic copolymers has also been explored by using a spirocyclic tin(IV) alkoxide as initiator.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Impact polypropylene copolymers (IPC) are commercially used in a variety of applications. They are very complex materials and extensive studies have been conducted to understand the relationship between their chemical structure, morphology and impact properties. The distribution of ethylene propylene rubber (EPR) within IPC has drawn much attention but visualization of the morphology is difficult. In this study a fluorescent marker was used to probe the distribution of EPR within the crystalline and semi-crystalline fraction. The EPR was removed from a commercial IPC and labelled with a fluorescent marker. In this study a method utilizing the hydrophilic nature of cellulose nanowhiskers (CNW) was developed to label the EPR. CNW were labelled with fluorescein-5’-isothiocyanate (FITC) and rhodamine B (RhB) using a one-step procedure. The labelled CNW were incorporated into the EPR by means of sonication. The mobility of the labelled CNW within the EPR film was investigated by confocal fluorescence microscopy (CFM), and showed that the labelled whiskers did not move within the EPR, thus substantiating the validity of this approach. The labelled EPR was recombined with the crystalline fraction by means of injection moulding and was analysed by CFM, and the distribution of the labelled EPR was evaluated. Confocal fluorescence microscopy showed an even distribution of the labelled rubber throughout the injection moulded sample. The miscibility of two EPRs within the IPC matrix in the melt was also investigated using this technique. CFM showed that the technique has promise to prove miscibility or the lack thereof when chemically similar materials are combined in the presence of morphologically different matrix materials. / AFRIKAANSE OPSOMMING: Impak polipropileen kopolimere (IPK) word kommersieel gebruik in ‘n wye reeks produkte. Die samestelling van hierdie kopolimere is baie ingewikkeld en uitgebreide studies is al gedoen om hul chemiese samestelling op molekulêre vlak te verstaan. Baie studies met betrekking tot die verspreiding van die etileen-propileen rubber (EPR) binne in hierdie impak polipropileen kopolimere is al gedoen, maar visualisering van die morfologie is moeilik en beperk. Hierdie kennis kan bydra tot die verbetering van hul chemiese eienskappe en toepassings. In hierdie studie word ʼn fluorosserende merker gebruik om die verspreiding van die EPR binne die kristallyne en semikristallyne fraksie te ondersoek. Die EPR is verwyder vanuit 'n kommersiële IPK en is gemerk met 'n fluoresserende merker. In hierdie studie is 'n metode ontwikkel om die EPR te merk deur gebruik te maak van die hidrofiliese eienskap van sellulose nanovesels (SNV). Die SNV is gemerk met fluoressien-5'-isotiosianaat (FITC) en rhodamien B (RhB) met behulp van 'n eenstap proses. Die gemerkte SNV is deur middel van sonikasie in die EPR versprei. Die mobiliteit van die gemerkte SNV binne-in die EPR film is ondersoek deur gefokusde fluoressensie mikroskopie (GFM) en het getoon dat die gemerkte vesels nie binne die EPR beweeg nie. Dit bevestig dus die geldigheid van hierdie benadering. Die gemerkte EPR is herkombineer met die kristallyne fraksie deur middel van spuitgiet en is geanaliseer deur GFM en die verspreiding van die gemerkte EPR is geëvalueer. GFM het 'n eweredige verspreiding van die gemerkte rubber regdeur die moster wat gespuitgiet is getoon. Die mengbaarheid van twee EPRs binne-in die IPK matriks is ook ondersoek deur gebruik te maak van hierdie tegniek. GFM het getoon dat hierdie tegniek waarde inhou om te bewys dat twee produkte mengbaar is of nie, al word hulle geherkombineer word met ‘n matriks wat morfologiese van hul verskil.

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

No description available.