Over the years there have been many studies on the theoretical and phenomenalogical aspects of starblock, di- and tri-block copolymer systems with very narrow molecular weight distributions. However, in many real multiblock systems the effect of such variables as; chemical composition distribution, molecular weight distribution and block architecture, among others, are not very well understood. The key to gaining a better understanding of these systems lies in the use of synthetic and process controlled variables. Seven different systems were used to study the effect of various synthetic and process controlled variables. The poly(butene sulfone) (PBS)-polydimethylsiloxane (PDMS) graft copolymers were synthesized by a free radical technique which involves the terpolymerization of butene, SO, and hexenyl functionalized polydimethylsiloxane macromonomers. The surface and bulk morphologies of a series of PBS-g-PDMS compolymers with 1, 5, 10, and 20K PDMS graft molecular weights at 5 and 20Wt.% PDMS incorporation. Additionally, for each graft molecular weight and at each composition, copolymers with a low and a high degree of polymerization of the PBS backbone were analyzed. A two phase morphology was found to exist with PDMS domain size increasing with increasing PDMS graft length. The type of morphology observed was dependent on PDMS composition, and in some cases the degree of polymerization and average number of grafts/backbone. These factors were also found alter the nature of the surface morphology and the related surface properties. The effect of PDMS segment molecular weight, the chemical nature of the polyimide segment, the procedure used to imidized the polyimide and processing conditions on the structure-property relationships in a series of polyimide-PDMS containing approximately 15Wt.% PDMS was studied. It was determined that as the polarity of the polyimide segment increased the morphology shifted to texture with lower surface/volume ratios. Casting the copolymers from an NMP solution favored a more discrete morphology than the thermally treated compression molded samples. The modulus was found to increase as the degree of phase separation increased with increasing PDMS segment size at constant composition. In addition, the solution cast films were found to have a higher modulus than the compression molded analogs. The morphology of a series of methacrylate based block ionomer was investigated. The effect of ionic block length, the architecture of the segments, and variations in the nature of ionic group were studied. SAXS revealed the presence of multiple scattering maxima in the dilbock materials. Both highly ordered and disordered region were observed from TEM analysis. The observed spacing from TEM measurements and SAXS were in good agreement. The interdomain spacings between the ionic domains were found to be a strong function of ionic block length. / Ph. D.

During the past few years, studies involving the synthesis, characterization, and structure-property relations of especially well-defined or "model" block and graft copolymers have received increasing interest among academic and industrial communities. The well-defined nature of such polymers makes them ideal subjects for both fundamental studies and specialty polymer applications. This study addresses the synthesis and characterization of well-defined block and graft copolymers through the use of reactor systems and permeability instrumentation designed specifically for this purpose. The engineering design, construction, operation, and in some cases automation of the above instrumentation is discussed in detail. Examples of the synthesis and permeability characterization of several especially interesting multiphase graft and star block copolymers are provided to demonstrate the utility of the instrumentation described. The primary focus of this work has been to address the effects of varying degrees of microphase separation and morphological development on the physical properties of well-defined block and graft copolymers and their hydrogenated derivatives. The application of gas permeability as an especially sensitive probe of morphology in well-defined poly(methylmethacrylate) -poly(dimethylsiloxane) graft copolymers has been given special emphasis. The synthesis these graft copolymers has been accomplished by the copolymerization of model, methacrylate-functional, poly(dimethylsiloxane) CPDMS) "macromonomers" with methylmethacrylate, using conventional free-radical and novel anionic and group transfer techniques. These techniques are described and referenced with chemical characterization provided. The resulting graft copolymers have PDMS-modified surface and bulk morphologies that dominate particular physical property responses and provide for interesting structure-permeability studies. The characterization of these copolymers to demonstrate their well-defined nature has been performed with a focus on the application of gas permeability as an especially sensitive morphological probe. A review of the relevant literature is followed by detailed experimental procedures, a summary and discussion of results, and descriptive appendices. The appendices include details concerning the design, fabrication, and automation of instrumentation to perform volumetric, equilibrium sorption experiments and computer programs for the acquisition and analysis of permeability data. / Ph. D.

The synthesis of novel well defined graft copolymers is now possible with the recent advent of the macromonomer technique. Copolymers with narrow molecular weight distributions of the backbone as well as the grafts are possible. The anionic alkyl- lithium initiated ring opening polymerization of the hexamethylcyclotrisiloxane has been investigated to prepare polymers of controlled molecular weights and narrow molecular weight distributions. This technique was extended to the preparation of macromonomers and from these macromonomers the synthesis of graft copolymers. These siloxane macromonomers were then incorporated into acrylic and styrenic copolymers via free radical and anionic techniques. A series of graft copolymers were characterized by a variety of methods. The resulting copolymers exhibit interesting thermal properties dependent on graft molecular weight and composition. Well-defined morphologies were observed by TEM analysis, indicative of the unique structures prepared. Graft copolymers offer unique possibilities of structure property relationships, often forming two phase morphologies that give rise to properties of both constituents. This allows the preparation of polymers designed to give optimal characteristics. / Ph. D.

The Variable Temperature Size Exclusion Chromatography (VTSEC) was used to study the dilute solution properties of various homo- and block copolymers as well as polymer blends, focus being primarily on the configuration-dependent properties such as average chain dimensions and hydrodynamic behavior of polymers. The study constituted of three parts. In the first part, the dilute solution properties of a series of poly(alkyl methacrylates) with varying side alkyl(ester) group were investigated as to the effect of the size of the side group on the average chain dimensions at various temperatures. The VTSEC results were found to reveal that the effect of the side group depends on the extent of chain flexibility imparted by the side group. In the second part, VTSEC was employed to investigate the applicability and validity of the various models for block copolymers in solution. For this purpose, several series of samples (all anionically synthesized) with various composition and molecular weight were used: i) poly(alkyl methacrylates), their diblock copolymers and blends and ii) diblock and triblock copolymers of poly(styrene/substituted styrene) and poly(butadiene/isoprene). VTSEC results showed that the applicability of each model to a block copolymer in solution depends on the compatibility among the components, the composition of the samples, the solvating power of the solvent used and the operating temperature. Micellization in the hydrocarbon diblock copolymer solutions was found to occur in selective solvent, its extent depending on the solubility parameter difference between the components, molecular weight, composition and solvent power. In the third part, poly(methyl methacrylate) samples with varying tacticities were studied as to the effect of stereochemical configuration on their dilute solution behavior and found to indicate that both syndiotactic and isotactic stereosequences are required for stereoassociation. Two new VTSEC data reduction procedures were devised in order to correct for the temperature drifts due to instrumentation in the first and to neutralize the effect of molecular weight in the second. In the second, termed as the Molecular Weight-Elution Volume Superposition Procedure, the effect of molecular weight alone was enutralized leaving only the effect of the intrinsic character (such as the size of the side group) of the sample in the elution behavior. Numerical computations, using the Matxrix Generation method based on the Rotational Isomeric State approximation, were carried out for stereoregular chains in order to evaluate their chain dimensions at various temperatures. / Ph. D.

The accuracy and utility of using Inverse Gas Chromatography (IGC) to characterize the microphase structure of block copolymers, and the strength of the thermodynamic interactions between the components of polymer blends and the unlike segments of block copolymers was examined. There were three parts to the study. First, the Scott ternary solution model, which is used for the study of thermodynamic interactions in polymer blends, was extended to low molecular weight mixtures. From vapor-liquid equilibrium data in the literature, the Gibbs free energy of mixing of binary mixtures (G_M ) calculated with the model were compared to experimental values. Mixtures containing ketones, aromatics hydrocarbons, chlorinated hydrocarbons, alcohols and water were studied. With the exception of mixtures containing water and low molecular weight alcohols, a fair to good correlation between theoretical and experimental values was observed. Second, the Gibbs free energy of mixing of nitrocellulose, polyvinyl chloride and poly(vinylidene fluoride) containing blends were measured with the Scott model from IGC data. For the nitrocellulose containing blend, the calculated Gibbs free energy of mixing values were large in magnitude (-2.0 to -5.0 calories/gram) and in fair agreement with the experimental heats of mixing determined from microcalorimetry measurements. For the remaining blends, the IGC data could not be distinguished from the results normally obtained for immiscible blends. The calculated G_M values were small in magnitude relative to the experimental error of the quantities. Concerning the block copolymers, the relative incompatibility of the constituent blocks of perfectly alternating block copolymers of polydimethylsiloxane and bis-A-polycarbonate and styrene-isoprene-styrene triblock copolymers was reflected in the measured G_M values. Overall, it was concluded that IGC is a good method for characterizing thermodynamic interaction between blend and copolymer constituents, but a severe limitation of the method is that the interactions are often too weak to measure accurately. Finally, the microphase structure of the above copolymers were studied by IGC from the retention behavior of hydrocarbon probes below the upper glass transition temperature of the copolymers. The degree of microphase separation, the size of the hard phases and the continuity of the soft phases in the copolymers characterized, and the results obtained were consistent with small angle x-ray, electron microscopy and differential scanning calorimetry data on the same materials. / Doctor of Philosophy

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Block copolymers are very interesting materials but they are quite complex. During polymer synthesis only a certain amount of control can be enforced. As copolymers are made up of two or more different homopolymer segments, and therefore have different end group possibilities, varying block lengths and block sequences, they have complex structures and are therefore difficult to analyse. Different techniques exist by which polymers can be analysed to determine the aforementioned distributions. In order to achieve a complete characterisation of a polymer structure, it is best to first use a separation technique to fractionate the polymer into more homogeneous fractions, and then use identification techniques to analyse these fractions. Polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers were investigated using liquid chromatography at the critical conditions (LCCC) of the copolymers' corresponding homopolymers, two-dimensional liquid chromatography (2D-LC) and FTIR. The block copolymers were analysed using the established LCCC of PS but it was found that even though separation of PS homopolymer and copolymer was obtained, PS blocks of the copolymers contributed to some extent to the retention of the PEO blocks. Some of the block copolymer samples were fractionated at the established critical conditions of PS. These fractions were qualitatively and quantitatively analysed using FTIR spectroscopy. The settings for the 2D-LC analysis were established, using LCCC of PS as the first dimension and as the second dimension SEC, using DMF as eluent. DMF was a suitable solvent to be used for the second dimension because PS, PEO and PS-b-PEO exhibited good solubility in this solvent. THF did not dissolve the block copolymers completely. The same solvent system as used for LCCC of PS was used for LCCC of PEO, but the critical conditions correspond to a different solvent composition. The block copolymers were analysed using the established LCCC of PEO but it was found that even though separation of PEO homopolymer and copolymer was obtained, the PEO blocks of the copolymers contributed to some extent to the retention of the PS blocks. Some of the block copolymer samples were fractionated at the established critical conditions of PEO. These fractions were qualitatively and quantitatively analysed using FTIR spectroscopy. The settings for the 2D-LC analysis were established, using LCCC of PEO as the first dimension and as the second dimension SEC using DMF as eluent was used. Lastly, qualitative and quantitative analyses of the block copolymers were carried out using FTIR spectroscopy. / AFRIKAANSE OPSOMMING: Alhoewel blokkopolimere baie interessante verbindings is, is hulle redelik ingewikkeld. Gedurende die kopolimerisasiereaksie kan daar net 'n sekere mate van kontrole behaal word. Aangesien kopolimere uit twee of meer homopolimeersegmente, met verskillende end-groep moontlikhede, bloklengtes en blokvolgordes bestaan, is dit baie moeilik om hierdie verbindings te analiseer. Verskillende tegnieke kan gebruik word vir die analise van polimere en die bepaling van bogenoemde verspreidings. Ten einde 'n polimeerstruktuur volledig te karakteriseer is die beste manier om eers 'n skeidingstegniek te gebruik om die polimeer in meer homogene fraksies te fraksioneer en dan daarna hierdie fraksies te analiseer. Polistireen-blok-poli(etileenoksied) (PS-b-PEO) kopolimere is ondersoek deur gebruik te maak van vloeistofchromatografie by kritiese kondisies (LCCC) van die kopolimeer se ooreenkomstige homopolimere; twee-dimensionele vloeistofchromatografie (2D-LC) en FTIR. Die blokkopolimere is gekarakteriseer deur gebuik te maak van bevestigde LCCC van PS. Daar is egter gevind dat alhoewel skeiding van die PS homopolimeer en die kopolimeer behaal is, PS blokke van die kopolimere in 'n mate bygedra het tot die retensie van die PEO blokke. Sommige van die blok-kopolimeermonsters is gefraksioneer by die bepaalde kritiese kondisies van PS. Hierdie fraksies is kwalitatief en kwantitatief geanaliseer deur gebruik te maak van FTIR spektroskopie. Die stellings vir die 2D-LC analise is bepaal deur gebruik te maak van LCCC van PS as die eerste dimensie en SEC as die tweede dimensie, met DMF as elueermiddel. DMF was 'n geskikte oplosmiddel vir die tweede dimensie aangesien PS, PEO en PS-b-PEO goed oplosbaar is daarin. Die blokkopolimere was nie volledig oplosbaar in THF nie. Dieselfde oplosmiddelsisteem soos gebruik vir die LCCC van PS is gebruik vir die LCCC van PEO, maar die kritiese kondisies stem ooreen met 'n ander oplosmiddelsamestelling. Die blokkopolimere is geanaliseer deur gebruik te maak van die bevestigde LCCC van PEO, maar daar is bevind dat alhoewel skeiding van die PEO homopolimeer en kopolimeer behaal is, die PEO blokke van die kopolimere in 'n mate bygedra het tot die retensie van die PS blokke. Sommige van die blokkopolimeermonsters is gefraksioneer by die bevestigde kritiese kondisies van PEO. Hierdie fraksies is kwalitatief en kwantitatief geanaliseer deur gebruik te maak van FTIR spektroskopie. Die stellings vir die 2D-LC analise is bepaal deur gebruik te maak van LCCC van PEO as die eerste dimensie en SEC as die tweede dimensie, met DMF as elueermiddel. Laastens is kwalitatiewe en kwanitatiewe analises van die blokkopolimere m.b.v. FTIR spektroskopie uitgevoer.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / The synthesis of complex architectures, namely block copolymers with tailored enduse properties, is currently an important research area in academia and industry. The challenge is finding a versatile polymerization technique capable of controlling the molecular properties of the formed copolymers, which in turn determines their macroscopic properties. Reversible addition-fragmentation chain transfer (RAFT)- mediated living polymerization is a robust technique capable of producing controlled polymer products. With the great advances in living polymerization techniques and the environmental awareness of society there is an increasing demand to produce these polymer products via the RAFT living technique in heterogeneous media. Conventional emulsion and miniemulsion polymerization present various problems when used to produce polymers mediated by the RAFT process. There is an inherent need to find cost effective and flexible operating conditions to conduct RAFT polymerization in heterogeneous media with the ability to produce well-defined block copolymers. In this study the use of three novel trithiocarbonate RAFT agents to produce welldefined AB-type, ABA-type and star block copolymers via the RAFT process was investigated. Optimal operating conditions for the production of living block copolymers in homogenous and heterogeneous media were determined. The main focus was on the development of the RAFT process in heterogeneous media to efficiently produce block copolymer latex products. The RAFT-mediated miniemulsion polymerization system stabilized with non-ionic surfactants was thoroughly investigated. The ability of the ab initio and in situ RAFT-mediated emulsion polymerization systems to produce controlled latexes was demonstrated. Controlled block copolymer products were successfully synthesized in homogenous and heterogeneous media via the RAFT process when the optimum reaction conditions were chosen.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Hybrid A-B type block copolymers of polydimethylsiloxane (PDMS) and polystyrene (PS) were synthesised. Three different synthetic routes, which allowed control over polymer structure, were chosen to synthesise these block copolymers. The first technique, coupling of functional prepolymers, involved using anionic polymerisation to produce PDMS and PS functional prepolymers of controlled structure. These prepolymers were functionalised with either silane or allyl functionality and then coupled using a hydrosilylation reaction with Karstetds platinum catalyst. This technique was the least efficient in block synthesis due to the incompatibility of the disparate prepolymers. The second technique under study, sequential anionic polymerisation, gave excellent block copolymer formation with good control over the chain architecture. The final technique employed atom transfer radical polymerisation (ATRP) of styrene using a bromoisobutyrate functionalised PDMS macroinitiator. Silane functional PDMS molecules underwent a hydrosilylation reaction with allyl-2-bromo-2-methyl-propionate to produce the bromoisobutyrate functionalised polymer in excellent yields. Subsequent ATRP with styrene allowed the successful synthesis of block copolymers of controlled structure. Chromatographic systems that allowed liquid chromatography at the critical conditions (LC-CC) of PS and gradient elution chromatography (GEC) of the products were developed. GEC was used successfully in the monitoring of the presence and removal of PDMS homopolymer present in the block copolymer products. LCCC at the critical point of PS allowed successful chromatographic separation of PS homopolymer from the block material, as well as, the molecular weight distribution of the block material according to the segmental length of the PDMS component. LC-CC coupled to FT-IR using a LC-transform device allowed successful characterisation of the block copolymer chemical composition. Corona treatment was used to modify the surface structure of the block copolymer films. Optical microscopy and slow positron beam studies highlighted the formation of a thin silica like layer on the surface of the films after corona. The positron studies enabled determination of the silica like layer’s thickness. Contact angle studies provided the first evidence of hydrophobic loss and recovery for these PDMS containing hybrid polymer materials after corona treatment. A novel offline coupling technique was developed between LC-CC separation and transmission electron microscopy (TEM) analysis. This allowed easy sample preparation without the difficult bulk extraction procedures needed to remove homo-PS contaminants from the block copolymer. This technique also provided morphological information as a function of PDMS segmental length.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Graft and block copolymers were synthesized using multifunctional and monofunctional macroinitiators to produce the copolymers. The process involved hydroboration of commercially available unsaturated rubbers and chain-end unsaturated macromonomers with 9-borabicyclo [3.3.1] nonane (9-BBN). The resulting secondary alkyl 9-BBN moieties in the starting materials were subsequently exposed to oxygen in the presence of free radical polymerizable monomers to facilitate the formation of graft and block copolymers. This research was initiated by first studying the hydroboration of a model compound, 2-hexene, in order to determine the optimal conditions for the graft reactions. The model compound was subsequently used as a macroinitiator to initiate the polymerization of methylmethacrylate (MMA). The same borane chemistry was extended to the synthesis of polystyrene (PS) block copolymers. Chain-end unsaturated PS macromonomers, synthesized by anionic polymerization, were effectively hydroborated and then polymerized to produce PS-b-PMMA block copolymers. The synthesis of polyolefin graft copolymers was subsequently achieved by hydroboration. Several commercial rubbers with different levels of unsaturated segments were efficiently grafted with vinyl monomers MMA and styrene (St) following the “graft from” approach. The grafted reactions were carried out under various reaction conditions to determine the effect of the following factors: concentration of oxygen, amount of borane and monomer concentration. By controlling these factors, different graft densities were achieved with high graft efficiencies. All reactions produced mixed products including unreacted (non-functional) macroinitiator, homopolymer, graft copolymer and in case of the highly unsaturated polymer a crosslinked gel. Finally, the chemical compositions as well as the molar mass distribution of the graft copolymers were fully characterized by different chromatographic techniques. 1H-NMR and FTIR were also used to confirm the structure of these copolymers. Gradient HPLC was developed and extensively used to characterize the graft copolymers.

Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008. / The research presented in this dissertation was concerned with the living radical polymerization (LRP) of an amphiphilic, water-soluble, bi-substituted and biologically compatible acrylamide derivative, namely n-acryloylmorpholine (NAM). The primary objective of this research was the synthesis of novel block copolymers containing poly(dimethylsiloxane) (PDMS) and various chain lengths of poly(acryloylmorpholine) (polyNAM) using a LRP technique, namely reversibleaddition fragmentation chain transfer (RAFT) polymerization. This is the first report on the synthesis of these block copolymers using RAFT polymerization. These novel siloxane block copolymers were synthesized using a monohydroxyterminated PDMS material which had to first be modified into a thiocarbonylthiocontaining moiety in order for it to be used as macromolecular chain transfer agent (macroCTA) in the RAFT copolymerization with NAM. Suitable reaction conditions for the synthesis of these novel block copolymers had to, firstly, be determined, and secondly, optimized. In order to determine suitable reaction conditions, a series of homopolymerizations with NAM were first performed in order to compare which chain transfer agent (CTA), solvent, temperature etc. could possibly be best suited for the block copolymerizations of PDMS-b-polyNAM. Reported in this work is the first account of the homopolymerization of NAM and 2-(dodecylsulfanyl)thiocarbonylsulfanyl-2-methyl propionic acid (DMP) as CTA using RAFT polymerization. The resulting novel siloxane block copolymers are amphiphilic in nature and the existence of these structures was confirmed by size exclusion chromatography/multiangle light scattering (SEC/MALS), proton nuclear magnetic resonance (1H-NMR) spectroscopy, gel elution chromatography (GEC) and transmission electron microscopy (TEM). Interesting phase behaviour was observed in the latter technique.