Dissertationen zum Thema „Coordinative Chain Transfer Polymerization“

Thesis (Ph. D.)--University of Maryland, College Park, 2008.
Thesis research directed by: Dept. of Chemistry and Biochemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Le nouveau complexe Cp*La(BH4)2(THF)2 a été utilisé en combinaison avec des alkyles magnésiens et aluminiques pour la (co)polymérisation coordinative par transfert de chaîne (CCTP) du styrène et de l’isoprène. En développant ce concept nous avons obtenu la première croissance de chaîne catalysée du styrène et de l’isoprène avec contrôle de la microstructure. L’application de la CCTP à la copolymérisation statistique est une voie nouvelle et originale pour le contrôle de la composition de copolymères.Par ailleurs, une étude mécanistique a été réalisée pour la polymérisation de l’ ε-caprolactone avec des dérivés cationiques de ruthénium [(η5-C5H5)Ru(η6-arène substitué)][PF6]. Nous avons montré que la polymérisation a lieu selon un mécanisme de type monomère activé avec transfert aux alcools, avec modification de l’hapticité du ligand arène
A newly synthesized Cp*La(BH4)2(THF)2 complex in combination with magnesium or aluminum alkyls was used for the coordinative chain transfer (co)polymerization (CCTP) of styrene and isoprene. Using this concept, we have accomplished the first catalyzed chain growth like reaction of styrene and isoprene, with control of the microstructure. The application of CCTP to statistical copolymerization represents a new and original approach to tune the composition of copolymers. In addition, a mechanistic study of the ring-opening polymerization of ε-caprolactone by [(η5-C5H5)Ru(η6-substituted arene)][PF6] complexes shows that the polymerization proceeds via an activated monomer mechanism by transfer to the alcohol with a change of hapticity of the arene ligand

Une série de ligands L1-L11 à base d'iminopyridine/iminoquinoline du type 11-[(Ar)N=C(R)]-R' (Ar = 2,6-Me2-C6H3 ou 2,6-iPr2-C6H3 ou 3,5-(CF3)2-C6H3 ou C6F5, R = H ou Me et R’ = 2-C6H5N ou 2-C6H4N-5-Me ou 2-C9H7N ou 8-C9H7N) et leurs complexes de fer (II) correspondants ont été développés. Les complexes ont été entièrement caractérisés, y compris par diffraction des rayons X pour les nouveaux complexes (6-11), et leurs applications catalytiques ont été étudiées pour la polymérisation coordonnée contrôlée de l'isoprène. La modulation des propriétés stériques et électroniques au sein de cette famille de ligands/complexes s'est avérée influencer la stéréosélectivité et l'activité de la polymérisation de l'isoprène après activation avec divers cocatalyseurs. Les catalyseurs obtenus ont produit des polyisoprènes avec une excellente conversion, une activité élevée et une variété de stéréo-/régio-régularités. Certains de ces catalyseurs ont également été évalués pour la polymérisation coordinative du styrène et ont montré une bonne activité pour la formation de polystyrènes syndiotactiques enrichis. Une autre méthodologie organométallique a été utilisée pour la synthèse de ligands d'aminopyridine (rac-L1H and rac-L2H) et de leurs complexes d'amides de fer correspondants 12 ((L1)2Fe), 13Py et 14Py (LnFe[N(SiMe3)2](Py)) pour leur application dans la (co)polymérisation par ouverture de cycle de L-lactide et ε-caprolactone où les complexes 13Py et 14Py se sont avérés efficaces
A series of iminopyridine-/iminoquinoline-based ligands L1-L11 of type 11-[(Ar)N=C(R)]-R’ (Ar = 2,6-Me2-C6H3 or 2,6-iPr2-C6H3 or 3,5-(CF3)2-C6H3 or C6F5, R = H or Me and R’ = 2-C6H5N or 2-C6H4N-5-Me or 2-C9H7N or 8-C9H7N) and their corresponding iron (II) complexes were developed. The complexes were fully characterized including by X-ray for new complexes (6-11) and their catalytic applications were investigated for the controlled coordinative polymerization of isoprene. The modulation of steric and electronic properties within this family of ligands/complexes has shown to influence the stereo-selectivity and activity of the polymerization of isoprene after activation with various cocatalysts. The resulting catalysts produced polyisoprenes with an excellent conversion, high activity and a variety of stereo-/regio-regularities. Some of these catalysts were also assessed for the coordinative polymerization of styrene and displayed good activity for the formation of syndiotactic enriched polystyrenes. Another organometallic methodology has been utilized for the synthesis of aminopyridine ligands (rac-L1H and rac-L2H) and their corresponding iron amide complexes 12 ((L1)2Fe), 13Py and 14Py (LnFe[N(SiMe3)2](Py)) for their application in the Ring-Opening (Co)polymerizaion of L-lactide and ε-caprolactone where the complexes 13Py and 14Py proved to be effective

Thesis (PhD)--Stellenbosch University, 2004.
ENGLISH ABSTRACT: To comply with the ever growing demands for materials with better properties and complex architectures, polymer chemistry has resorted to the use of living free radical polymerization techniques. Despite the structural control some of these techniques offer, major disadvantages do exist. For example, most require ultra-pure reagents, hence only a small fraction of the monomers used in industry can be polymerized in this way. This rendered these new living techniques less advantageous from a commercial point of view. Recently, a revolutionary new living free radical process, namely the reversible addition-fragmentation chain transfer process, or RAFT process, was developed that combines the control over the polymer produced with the robustness and versatility of a free radical process. However, the RAFT process is not without its problems. In some dithioester mediated polymerizations, significant inhibition and rate retardation effects have been observed. Two main opposing opinions have been proposed in recent literature to explain these phenomena observed. The main point of difference between these two groups is the fate of the formed intermediate RAFT radicals, i.e., slow fragmentation of the formed intermediate radicals together with possible reversible intermediate RAFT radical termination, or fast fragmentation of the formed intermediate radicals together with possible irreversible intermediate RAFT radical termination. Between these opposing two groups, there is a difference of six orders of magnitude for the rate of fragmentation of the formed intermediate RAFT radicals. The work presented in this thesis is an attempt to clarify some of the mysteries, i.e., inhibition and rate retardation observed in some RAFT polymerizations. Experimental evidence to support or contradict the theories of the above mentioned two opposing groups was investigated. The concentration-time evolution of the intermediate radical concentration (cy), for styrene and butyl acrylate polymerizations mediated by cumyl dithiobenzoate (COB) at 70°C and 90 °C, was followed via in situ electron spin resonance spectroscopy (ESR). The concentration-time evolution profiles observed were ascribed to the formation of very short chains during the early stages of the reaction. It was also found that the RAFT process is not particularly sensitive to oxygen. The intermediate and propagating radical (cp) concentrations (and their ratio) for the cumyl dithiobenzoate mediated styrene polymerizations were examined by ESR spectroscopy and kinetics. The system showed strong chain length effects in kinetics, assuming all chains were of similar number average molar mass (Mn). However, unusual behavior with respect to existing mechanistic knowledge was observed in other aspects of the system. The central equilibrium "constant" (Keq) was found to be dependent on both temperature and initial reactant concentrations. The observed intermediate radical concentrations were not consistent with predictions based on existing literature models. It was also found that the time dependence of the intermediate radical concentration varies significantly with the type of RAFT agent used. Unexpectedly, intermediate radicals were detected at very long reaction times in the virtual absence of initiator, enhancing the belief of possible reversible termination reactions involving the intermediate radicals. An extra radical (nonpropagating or intermediate) species was observed (via ESR spectroscopy) to form during some reactions. Its concentration increased with time. The combination of data from several analytical techniques provided evidence for the formation of dead chains by the termination of intermediate radicals in the free radical polymerization of styrene, mediated by a cumyl dithiobenzoate RAFT agent, at 84°C. Experiments done focused on the early stages of the reactions, targeting very low final number average molar mass values, with high initiator concentrations. The formation of these terminated chains did not occur to a significant extent until a large fraction of the chains reached a degree of polymerization greater than unity. This corresponded to the occurrence of a maximum in intermediate radical concentration. In situ 1H nuclear magnetic resonance (NMR) and electron spin resonance spectroscopy was used to directly investigate the processes that occur during the early stages (typically the first few monomer addition steps) of an AIBN-initiated reversible addition fragmentation chain transfer polymerization of styrene, in the presence of a cyanoisopropyl dithiobenzoate and cumyl dithiobenzoate RAFT agent, at 70°C and 84 °C respectively. 1H NMR spectroscopy allowed the investigation of the change in concentration of important dithiobenzoate species as a function of time. Identification and concentrations of the radicals present in the system could be inferred from corresponding ESR spectroscopy data. An apparent "inhibition" effect was observed in both the cyanoisopropyl and cumyl dithiobenzoate mediated polymerizations. This effect could be reduced by increasing the reaction temperature to 84 °C. However, the use of cumyl dithiobenzoate as RAFT agent prolonged this effect. This apparent "inhibition" effect was attributed to selective fragmentation of the formed intermediate radicals during the early stages of the reaction, and to different propagation rate coefficients (kp) of the resulting (different) radicals. A change in the equilibrium coefficient for the systems investigated was ascribed to possible progressively decreasing addition and fragmentation rate coefficients of propagating and intermediate radicals formed during the reaction. The increase in intermediate radical concentration, and thus possible intermediate radical termination, was shown to also be a probable cause of the rate retardation observed in the RAFT mediated systems investigated. To conclude, probable causes of the observed inhibition and rate retardation in some dithiobenzoate mediated systems were investigated. It was found that intermediate RAFT radical termination does occurs, albeit reversibly or irreversibly. A maximum in the intermediate radical concentration, and thus possible intermediate radical termination, was seen to occur during the observed rate retardation. An apparent inhibition effect observed was ascribed to a possible change in termination kinetics, the formation of terminated intermediate radical products and a rapidly changing kp of the propagating radicals.
AFRIKAANSE OPSOMMING: Om te voldoen aan die ewig groeiende aanvraag vir materiale met beter eienskappe en komplekse samestellings, is in die polimeerchemie lewende vry-radikaal polimerisasietegnieke ontwikkel. Ten spyte van die feit dat party van die polimerisasie tegnieke die strukuur van die gevormende polimere kan beheer, bestaan daar tog nadele. Die meeste polimerisasie tegnieke benodig ultra suiwer reagense, dus kan net 'n klein fraksie van die monomere wat deur die industrie gebruik word op so 'n manier gepolimeriseer word. Dus, vanuit 'n komersieële oogpunt, is die nuwe lewende polimerisasietegnieke minder voordelig. Onlangs is 'n revolusionere nuwe lewende vry-radikaal polimerisasieproses, naamlike die RAFT-(eng. reversible addition-fragmentation chain transfer process) proses ontwikkel, wat die beheer oor die geproduseerde polimere, kombineer met die robuustheid en veelsydigheid van 'n vry-radikaalproses. Die RAFT proses is egter nie sonder probleme nie. Beduidende inhibisie en vertraging van die polimerisasie tempo is in sommige dithioester-bemiddelde polimerisasies opgemerk. Daar is hoofsaaklik twee opponerende opinies oor die redes vir die inhibisie en vertragings effekte. Die grootste verskil tussen die twee groepe lê in die lot van die gevormde intermediêre radikaal, m.a.w. stadige fragmentasie van die gevormende intermediêre radikale tesame met moontlike onveranderlike intermediêre radikaalterminasie, of vinnige fragmentasie tesame met moontlike omkeerbare intermediêre radikaalterminasie. Tussen die twee groepe, is daar 'n verskil van ses ordegrotes vir die groote van die tempo van fragmentasie van die gevormende intermediêre radikaal. Die werk wat in die tesis weergee word, is 'n poging om sommige van die geheime van die RAFT proses, m.a.w. inhibisie en vertraging van die polimerisasietempo, op te los. Die ondersoek was gerig op eksperimetele bewyse om die teorieë van die twee opponerede groepe of te bevestig of teen te spreek. Die konsentrasie tyd-verandering van die intermediêre radikaal konsentrasie vir stireen- en butielakrilaatpolimerisasie, bemiddeled deur CDB (eng cumyl dithiobenzoate) by 70 oe and 90 oe, is gevolg deur middel van in situ (lat. vir in die oorspronklike plek, m.a.w. binne-in die ESR masjien) elektronspin-resonans (ESR) spektroskopie. Die vorm van die konsentrasie tyd-profiele is toegeskryf aan die vorming van baie kort polimeerkettings gedurende die vroeë reaksietye. Dit is ook bepaal dat die RAFT-proses nie besonder sensitief was vir suurstof nie. Die intermediêre en die propagerende radikaalkonsentrasie (en hulle verhouding) vir die CDB bemiddelde stireen polimerisasies, is bepaal deur middel van elektronspin-resonans spektroskopie en die kinetika van die sisteem. Die kinetika van die sisteem toon 'n sterk afhanklikheid teenoor die lengte van die polimeerkettings, as aanvaar word dat al die kettings dieselfde numeriese gemiddelde molêre massa het. Des nieteenstaande, is egter onverwagte gedrag in ander aspekte van die sisteem opgemerk. Dit was ook gevind dat die sentrale ewewigs-"konstante" (Keq) afhanklik was van die temperatuur en die oorspronklike reaktant konsentrasie. Die bepaalde intermediêre radikaalkonsentrasie het verskil van voorspelde waardes gebaseer op literatuur modelle. Dit is ook gevind dat die intermediêre radikaalkonsentrasie afhanklik is van die tipe RAFT agent wat in die polimerisasie reaksies gebruik word. Intermediêre radikale is onverwags gevind na baie lang reaksietye, wanner verwag is dat die konsentrasie van die afsetter, en dus ook die intermediêre radikale, baie klein sou wees. Dit het die verwagting dat omkeerbare intermediêre radikaalterminasie kan plaasving, versterk. 'n Ekstra radikale spesie, wat gedurende die reaksie vorm en waarvan die konsentrasie groter word met tyd, is ook deur ESR-spektroskopie geidentifiseer. 'n Kombinasie van verskillende skeikundige tegnieke is gebruik om bewyse te kry vir die vorming van dooie kettings wat ontstaan deur middel van intermediêre radikale terminasiereaksies, in die vry-radikaalpolimerisasie van stireen, wat deur 'n CDB RAFT-agent bemiddeled word by 84°C. Eksperimente is gedoen om die reaksie tydens vroeë reaksietye te ondersoek. Baie hoë afsetter konsentrasies is ook gebruik, wat tot uiters lae numeriese gemiddelde molêre massas van die polimeerkettings gelei het. Beduidende konsentrasies van die dooie kettings is eers gevind nadat 'n graad van polimerisasie van groter as een bereik is. Dit het ooreengestem met 'n maksimum in die konsentrasie van die intermediêre radikale. In situ 1H kern magnetiese-resonans (KMR) en electronspin-resonans spektroskopie was gebruik om 'n RAFT proses, wat gedurende die vroeë reaksie tye (tipies gedurende die eerste paar monomeer toevoegingstappe) te bestudeer, wat deur AIBN (eng azo bis(isobutyronitrile)) afgeset word en bestaan uit stireen en CIDB (eng cyanoisopropyl dithiobenzoate) en CDB RAFT agente onderskeidelik, en by 70°C and 84 °C reageer. 1H KMRspektroskopie was gebruik om die veranderinge in die konsentrasie van die belangrike spesies te bepaal. Die identifikasie en konsentrasie van die radikale kon bepaal word deur middel van ESR data. 'n Skynbare 'inhibisie-effek' is waargeneem in die reaksies wat bemiddeled word deur CIDB en CDB. Die effek is verminder toe die reaksietemperatuur verhoog is na 84°C. Die gebruik van CDB as RAFT agent het egter die effek vergroot. Die skynbare 'inhibisie effek' was toegeskryf aan die selektiewe fragmentasie van die intermediêre radikale gedurende die vroeë reaksietye, en aan verskillende propagasie tempokoëffisiënte (kp) van die verskillende radikale. Die veranderlike sentrale ewewigskoëffisiënte is toegeskryf aan die toevoegings en fragmentasie tempokoëffisiënte van die propagerende en intermediêre radikale wat toenemend afneem. Die is ook getoon dat die toename in die konsentrasie van die intermediêre radikale en dus moontlike intermediêre radikale terminasie, 'n oorsaak kan wees van die vertraging van die polimerisasietempo in die RAFT-bemiddelde reaksies. Ter samevatting, die waarskynlike oorsake vir inhibisie en die polimerisasietempo vertraging opgemerk in sekere dithiobenzoaat-bemiddelde sisteme, is ondersoek. Dit was gevind dat intermediêre radikaalterminasie wel kan gebeur, of dit nou omkeerbaar of onveranderlik gebeur. 'n Maksimum in die konsentrasie van die intermediêre radikale, en dus moontlike intermediêre radikaalterminasie, het voorgekom tesame met 'n vertraging in die polimerisasietempo. Die skynbare inhibisie-effek wat opgemerk was kan toegeskryf word aan 'n moontlike verandering in die terminasie kinetika, die formasie van getermineerde intermediêre radikale en 'n vinnig veranderende propagasie tempokoëffisiënt.

Reversible addition fragmentation chain transfer (RAFT) polymerization is a very versatile way to generate synthetic polymeric materials. Multiblock copolymers have received enormous scientific interest recently due to the ability to mimic the sequence-regulated microstructure of biopolymers. The objective of this thesis was to investigate RAFT polymerization and explore its potential in the synthesis of sequence-controlled multiblock polymeric chains, and their use to tune the micro-structure of the polymers, engineer single chain polymeric nanoparticles, and fabricate functional polymeric nanomaterials. This work firstly addresses the investigation of the enormous ability of sequence-controlled multiblock copolymer to tune the physical properties by altering their microstructure. A series of sequence controlled multiblock copolymers were synthesized by RAFT polymerization using ethylene glycol methyl ether acrylate and tert-butyl acrylate as monomers. These block copolymers were synthesized with an alternating order of the two monomers with a similar total degree of polymerization. The number of blocks was varied by decreasing the length of each block while keeping the ratio of monomers constant. Their microphase separation was studied by investigating the glass transition temperature utilizing differential scanning calorimetry analysis. Small angel X-ray scattering analysis was also applied to investigate the transition of the microphase separation with the variation of the segmentations of these multiblock copolymers. The study found the microstructure was significantly affected by the number of segments of the polymer chain whilst keeping the total length constant. Having demonstrated the enormous potential of sequence controlled multiblock copolymers to access defined microstructures, further studies were focused on mimicking the controlled folding process of the peptide chain to a secondary and tertiary structure using sequence controlled multiblock copolymers. RAFT polymerization was used to produce multiblock copolymers, which are decorated with pendant cross-linkable groups in foldable sections, separated by non-functional spacer blocks in between. An external cross linker was then used to cause the folding of the specific domains. A chain extension-folding sequence was applied to create polymer chains having individual folded subdomains. In order to achieve a further step on the way to copy nature’s ability to synthesize highly defined bio-macromolecules with a distinct three dimensional structure, linear diblock copolymer precursors were synthesized by RAFT polymerization. One block of the precursor with pendant functional groups was folded using an external cross-linker to form tadpole-like single chain nanoparticles (SCNPs). These tadpole-like SCNPs could then self-assemble into a more complex stimuli responsive 3D structure by adaptation to environmental pH changes. The stimuli responsive assemblies were found to be able to dissociate responding to low pH or exposure to glucose.

Thesis (MSc)--Stellenbosch University, 2001.
ENGLISH ABSTRACT: A novel approach to conducting controlled free radical polymerization in aqueous systems using Reversible Addition-Fragmentation Chain Transfer (RAFT) has been studied. When conducting RAFT in aqueous systems, reaction conditions must be chosen such that monomer transport across the aqueous-phase is either eliminated or facilitated. This is to prevent the formation of the red layer associated with RAFT in emulsions. The formation of the red layer is ascribed to the inability of waterinsoluble, dithiobenzoate-endcapped oligomers to be sufficiently transported across the aqueous phase. The novel approach in this study focussed on eliminating monomer transport and comprises two fundamental steps: the synthesis of dithiobenzoate-encapped oligomers in bulk followed by miniemulsification of these oligomers to yield a polymerizable miniemulsion. Dithioesters that act as chain transfer agents in the RAFT -process were synthesized in situ, thereby eliminating laborious and time-consuming organic purification procedures of dithioesters. In situ formation of the RAFT-agents involved conducting the reaction between di(thiobenzoyl) disulfide and conventional azo-initiators of differing structures in the presence of monomer. The structure of the chosen azo-initiator played a role in the efficiency of the RAFT process when the reaction was conducted in the presence of monomer to control the free radical polymerization process. Synthesis of the oligomers was performed by heating di(thiobenzoyl) disulfide and a selected azo-initiator, in the presence of monomer for a specific reaction duration in bulk. After the reaction was stopped, these oligomers were then miniemulsified by adding water, surfactant and cosurfactant, followed by the application of shear to form the resulting mini emulsion. The free radical polymerization of the dithiobenzoate-endcapped oligomers in the miniemulsion proceeded in a controlled manner with molecular weight increasing in a linear fashion with increasing conversion, while polydispersities remained low. The familiar red layer formation associated with RAFT polymerization in conventional emulsions was not observed under these conditions. The effects of changing the cosurfactant (hydrophobe) as well as changing the degree of polymerization of the emulsified oligomers were also investigated and described.
AFRIKAANSE OPSOMMING: Hierdie studie is geloods om 'n nuwe benadering tot die beheerde vry-radikaal polimerisasie in water gebaseerde sisteme te ondersoek. Daar is spesifiek gekyk na die uitvoer van die RAFT (Reversible Addition-Fragmentation Chain Transfer) proses in emulsies. Wanneer RAFT in emulsies toegepas word, moet die toestande waaronder die reaksie uitgevoer word, versigtig opgestel word. Die toestande moet so gekies word dat die vervoer van monomere deur die waterfase óf geëlimineer word óf gefasiliteer word. Dit word gedoen om die faseskeiding in die vorm van 'n rooi laag, wat so kenmerkend van RAFT -polimerisasie in emulsies is, te voorkom. Hierdie faseskeiding vind plaas omdat die vervoer van ditiobensoaat endgroep-bevattende oligomere deur die waterfase tydens interval II, moeilik is a.g.v. hulle oplosbaarheid in water. Die nuwe benadering wat hier bestudeer is, het twee basiese stappe. Eerstens word die ditiobensoaat endgroep-bevattende oligomere in bulk gesintetiseer. Dit word gevolg deur die emulsifisering van die oligomere. Hierna vind verdere polimerisasie van die oligomere plaas deur die dormante oligomere te heraktiveer. Die ditio-esters wat as kettingoordrag agente optree in die RAFT proses, word in situ gesintetiseer. Hierdie modifikasie sny tydrowende organiese suiweringsmetodes uit. Die in situ RAFT agente word gesintetiseer deur di(tiobensoïel) disulfied met verskillende konvensionele azo-inisieerders te laat reageer. Die struktuur van die spesifieke azoinisieerder het wel 'n rol gespeel in die effektiwiteit van die RAFT proses om molekulêre massa te beheer as bg. reaksie in die teenwoordigheid van monomere uitgevoer is. Die sintese van die oligomere is gedoen deur di(tiobensoïel) en 'n azo-inisieerder te verhit in die teenwoordigheid van monomere. Die reaksie is gedoen in bulk en die graad van polimerisasie van die oligomere is beheer deur die reaksie te stop by verskillende tydstippe. Nadat die bulk reaksie gestop is, is hierdie oligomere ge-emulsifiseer deur die oligomere te meng met 'n seep, hidrofoob en water. Hierdie mengsel word dan onderwerp aan 'n vermengingskrag om 'n polimeriseerbare mini-emulsie te vorm. Die voortsetting van die polimerisasie van die oligomere in die mini-emulsie het op 'n beheerde wyse verloop, m.a.w. molekulêre massa wat linieêr toeneem met stygende omsetting. Polidispersiteit indekse van die polimere het deurentyd laag gebly in die stabielste sisteme. Onder hierdie toestande was daar geen kenmerkende rooi laagvorming te bespeur nie. Die effekte wat die verandering van die hidrofoob, asook die verandering van die graad van polimerisasie van die oligomere op die sisteem gehad het, is onder andere ook ondersoek en beskryf.

Thesis (MSc)--Stellenbosch University, 2000.
ENGLISH ABSTRACT: This work involves the study of the effects of Reversible Addition-Fragmentation Chain Transfer (RAFT) agents on the emulsion polymerization of styrene. The feasibility of RAFT as a method for obtaining controlled radical polymerizations in emulsion systems is also investigated. Both seeded and ab initio systems were studied with three RAFT agents of varying structure. Inhibition and retardation effects on addition of various amounts of the RAFT agents to the emulsion systems were observed and the trends noticed. The effect of the RAFT agents on the average number of radicals per latex particle was calculated from reaction rates. The effect of the RAFT agent on the molecular weight and the molecular weight distribution was monitored by gel permeation chromatography. Exit of free radicals from the latex particles proves to be a major feature in the studied RAFT emulsion systems. Fragmentation of the RAFT agent in the latex particles, gives rise to free radical species that can exit from the particle and enter other particles where they can either terminate instantaneously or propagate. The exit and termination processes presumably result in both the inhibition and retardation of the emulsion polymerizations. A linear increase in Mn with conversion is observed, however the low concentration of RAFT agent in the latex particles is responsible for the obtained number average molecular weights being much higher than predicted. The low concentrations of RAFT agents in the latex particles is also responsible for the broad molecular weight distributions that are obtained. Reaction conditions for RAFT experiments should to be chosen so that the effects of exit processes are minimized and that the RAFT agent is primarily situated in the latex particles. These conditions must be met if the RAFT process is to be successful as a method of controlled radical polymerization in emulsions.
AFRIKAANSE OPSOMMING: Hierdie navorsing behels die studie van die effek van In bygevoegde addisie-fragmentasie kettingsoordragsreagent (RAFT1) op die emulsie polimerisasie van stireen. Die uitvoerbaarheid van RAFT as 'n metode om gekontroleerde radikale polimerisasies in emulsiesisteme te verkry is ook ondersoek. Eksperimente met drie RAFTkettingoordragsreagente van gevarieerde strukture is uitgevoer in beide seeded en ab initia sisteme. Die effek van die RAFT-reagent op die inhibisie en vertraging van die emulsie polimerisasie is waargeneem en die invloed van RAFT op die gemiddelde aantal radikale per partikel is bepaal. Die ontwikkeling van die molekulêre massa en die molekulêre massadistribusie is waargeneem deur middel van gel permeasie- kromatografiese tegnieke. Die ontsnapping van vrye radikale vanuit die partikels was 'n belangrike faktor in RAFT emulsiesisteme wat ondersoek is. Hierdie radikale is gegenereer deur die fragmentasie van die oorspronklike RAFT-reagent. Fragmentasie van die RAFT-reagent in die lateks partikels lei tot die vorming van vrye radikale spesies wat uit een partikel kan ontsnap en ander partikels kan binnedring waar dit onmiddellik kan termineer of propageer. Die ontsnappings- en terminasieprosesse van vrye radikale lei oënskynlik tot die inhibering en vertraging van die emulsie polimerisasie. 'n Lineêre verhoging in die gemiddelde molekulêre massa tydens konversie is waargeneem, alhoewel die Mn-waardes baie hoër was as wat verwag is. Die verskil kan toegeskryf word aan die klein hoeveelhede van die RAFT-reagent wat in die partikels teenwoordig is. Hierdie lae RAFT-konsentrasies is ook verantwoordelik vir die breë molekulêre massa distribusie wat waargeneem is. Vir die RAFT-proses om suksesvol te wees in gekontroleerde radikale polimerisasies in emulsies, moet reaksie kondisies so gekies word dat die ontsnapping van vrye radikale tot 'n minimum beperk word en die RAFT-reagent hoofsaaklik in die lateks partikels teenwoordig is.

Free radical emulsion polymerization (FRP) is widely adopted in industry due to its applicability to a wide range of monomers. Despite its many benefits and wide spread use, the fast chain growth and the presence of rapid irreversible termination impose limitations with respect to the degree of control in FRP. Furthermore, producing block copolymers and polymers with complex structures via FRP is not feasible. Closer control of macromolecular chain structure and molar mass, using novel polymerization techniques, is required to synthesize and optimize many new polymer products. Reversible addition fragmentation chain transfer (RAFT)-mediated polymerization is a novel controlled living free radical technique used to impart living characters in free radical polymerization. In combination with emulsion polymerization, the process is industrially promising and attractive for the production of tailored polymeric products. It allows for the production of particles with specially-tailored properties, including size, composition, morphology, and molecular weights. The mechanism of RAFT process and the effect of participating groups were discussed with reviews on the previous work on rate retardation. A mathematical model accounting for the effect of concentrations of propagating, intermediate, dormant and dead chains was developed based on their reaction pathways. The model was combined with a chain-length dependent termination model in order to account for the decreased termination rate. The model was validated against experimental data for solution and bulk polymerizations of styrene. The role of the intermediate radical and the effect of RAFT agent on the chain length dependent termination rate were addressed theoretically. The developed kinetic model was used with validated kinetic parameters to assess the observed retardation in solution polymerization of styrene with high active RAFT agent (cumyl dithiobenzoate). The fragmentation rate coefficient was used as a model parameter, and a value equal to 6×104 s-1 was found to provide a good agreement with the experimental data. The model predictions indicated that the observed retardation could be attributed to the cross termination of the intermediate radical and, to some extent, to the RAFT effect on increasing the average termination rate coefficient. The model predictions showed that to preserve the living nature of RAFT polymerization, a low initiator concentration is recommended. In line with the experimental data, model simulations revealed that the intermediate radical prefers fragmentation in the direction of the reactant. The application of RAFT process has also been extended to emulsion polymerization of styrene. A comprehensive dynamic model for batch and semi-batch emulsion polymerizations with a reversible addition-fragmentation chain transfer process was developed. To account for the integration of the RAFT process, new modifications were added to the kinetics of zero-one emulsion polymerization. The developed model was designed to predict key polymer properties such as: average particle size, conversion, particle size distribution (PSD), and molecular weight distribution (MWD) and its averages. The model was checked for emulsion polymerization processes of styrene with O-ethylxanthyl ethyl propionate as a RAFT based transfer agent. By using the model to investigate the effect of RAFT agent on the polymerization attributes, it was found that the rate of polymerization and the average size of the latex particles decreased with increasing amount of RAFT agent. It was also found that the molecular weight distribution could be controlled, as it is strongly influenced by the presence of the RAFT based transfer agent. The effects of RAFT agent, surfactant (SDS), initiator (KPS) and temperature were further investigated under semi-batch conditions. Monomer conversion, MWD and PSD were found to be strongly affected by monomer feed rate. With semi-batch mode, Mn and increased with increasing monomer flow rate. Initiator concentration had a significant effect on PSD. The results suggest that living polymerization can be approached by operating under semi-batch conditions where a linear growth of polymer molecular weight with conversion was obtained. The lack of online instrumentation was the main reason for developing our calorimetry-based soft-sensor. The rate of polymerization, which is proportional to the heat of reaction, was estimated and integrated to obtain the overall monomer conversion. The calorimetric model developed was found to be capable of estimating polymer molecular weight via simultaneous estimation of monomer and RAFT agent concentrations. The model was validated with batch and semi-batch emulsion polymerization of styrene with and without RAFT agent. The results show good agreement between measured conversion profiles by calorimetry with those measured by the gravimetric technique. Additionally, the number average molecular weight results measured by SEC (GPC) with double detections compare well with those calculated by the calorimetric model. Application of the offline dynamic optimisation to the emulsion polymerization process of styrene was investigated for the PSD, MWD and monomer conversion. The optimal profiles obtained were then validated experimentally and a good agreement was obtained. The gained knowledge has been further applied to produce polymeric particles containing block copolymers. First, methyl acrylate, butyl acrylate and styrene were polymerized separately to produce the first block. Subsequently, the produced homopolymer attached with xanthate was chain-extended with another monomer to produce block copolymer under batch conditions. Due to the formation of new particles during the second stage batch polymerization, homopolymer was formed and the block copolymer produced was not of high purity. The process was further optimized by operating under semi-batch conditions. The choice of block sequence was found to be important in reducing the influence of terminated chains on the distributions of polymer obtained. It has been found that polymerizing styrene first followed by the high active acrylate monomers resulted in purer block copolymer with low polydispersity confirmed by GPC and H-NMR analysis.

Doctor of Philosophy (PhD), Engineerig
Free radical emulsion polymerization (FRP) is widely adopted in industry due to its applicability to a wide range of monomers. Despite its many benefits and wide spread use, the fast chain growth and the presence of rapid irreversible termination impose limitations with respect to the degree of control in FRP. Furthermore, producing block copolymers and polymers with complex structures via FRP is not feasible. Closer control of macromolecular chain structure and molar mass, using novel polymerization techniques, is required to synthesize and optimize many new polymer products. Reversible addition fragmentation chain transfer (RAFT)-mediated polymerization is a novel controlled living free radical technique used to impart living characters in free radical polymerization. In combination with emulsion polymerization, the process is industrially promising and attractive for the production of tailored polymeric products. It allows for the production of particles with specially-tailored properties, including size, composition, morphology, and molecular weights. The mechanism of RAFT process and the effect of participating groups were discussed with reviews on the previous work on rate retardation. A mathematical model accounting for the effect of concentrations of propagating, intermediate, dormant and dead chains was developed based on their reaction pathways. The model was combined with a chain-length dependent termination model in order to account for the decreased termination rate. The model was validated against experimental data for solution and bulk polymerizations of styrene. The role of the intermediate radical and the effect of RAFT agent on the chain length dependent termination rate were addressed theoretically. The developed kinetic model was used with validated kinetic parameters to assess the observed retardation in solution polymerization of styrene with high active RAFT agent (cumyl dithiobenzoate). The fragmentation rate coefficient was used as a model parameter, and a value equal to 6×104 s-1 was found to provide a good agreement with the experimental data. The model predictions indicated that the observed retardation could be attributed to the cross termination of the intermediate radical and, to some extent, to the RAFT effect on increasing the average termination rate coefficient. The model predictions showed that to preserve the living nature of RAFT polymerization, a low initiator concentration is recommended. In line with the experimental data, model simulations revealed that the intermediate radical prefers fragmentation in the direction of the reactant. The application of RAFT process has also been extended to emulsion polymerization of styrene. A comprehensive dynamic model for batch and semi-batch emulsion polymerizations with a reversible addition-fragmentation chain transfer process was developed. To account for the integration of the RAFT process, new modifications were added to the kinetics of zero-one emulsion polymerization. The developed model was designed to predict key polymer properties such as: average particle size, conversion, particle size distribution (PSD), and molecular weight distribution (MWD) and its averages. The model was checked for emulsion polymerization processes of styrene with O-ethylxanthyl ethyl propionate as a RAFT based transfer agent. By using the model to investigate the effect of RAFT agent on the polymerization attributes, it was found that the rate of polymerization and the average size of the latex particles decreased with increasing amount of RAFT agent. It was also found that the molecular weight distribution could be controlled, as it is strongly influenced by the presence of the RAFT based transfer agent. The effects of RAFT agent, surfactant (SDS), initiator (KPS) and temperature were further investigated under semi-batch conditions. Monomer conversion, MWD and PSD were found to be strongly affected by monomer feed rate. With semi-batch mode, Mn and increased with increasing monomer flow rate. Initiator concentration had a significant effect on PSD. The results suggest that living polymerization can be approached by operating under semi-batch conditions where a linear growth of polymer molecular weight with conversion was obtained. The lack of online instrumentation was the main reason for developing our calorimetry-based soft-sensor. The rate of polymerization, which is proportional to the heat of reaction, was estimated and integrated to obtain the overall monomer conversion. The calorimetric model developed was found to be capable of estimating polymer molecular weight via simultaneous estimation of monomer and RAFT agent concentrations. The model was validated with batch and semi-batch emulsion polymerization of styrene with and without RAFT agent. The results show good agreement between measured conversion profiles by calorimetry with those measured by the gravimetric technique. Additionally, the number average molecular weight results measured by SEC (GPC) with double detections compare well with those calculated by the calorimetric model. Application of the offline dynamic optimisation to the emulsion polymerization process of styrene was investigated for the PSD, MWD and monomer conversion. The optimal profiles obtained were then validated experimentally and a good agreement was obtained. The gained knowledge has been further applied to produce polymeric particles containing block copolymers. First, methyl acrylate, butyl acrylate and styrene were polymerized separately to produce the first block. Subsequently, the produced homopolymer attached with xanthate was chain-extended with another monomer to produce block copolymer under batch conditions. Due to the formation of new particles during the second stage batch polymerization, homopolymer was formed and the block copolymer produced was not of high purity. The process was further optimized by operating under semi-batch conditions. The choice of block sequence was found to be important in reducing the influence of terminated chains on the distributions of polymer obtained. It has been found that polymerizing styrene first followed by the high active acrylate monomers resulted in purer block copolymer with low polydispersity confirmed by GPC and H-NMR analysis.

In this thesis, we explored the use of a renewable resource to produce more sustainable polymeric materials. Limonene, a monocyclic terpene existing in many essential oils extracted from citrus rinds, was the renewable monomer investigated. The d-limonene ((+)-limonene) isomer is a major component (~90%) of orange oils from orange juicing and peel processing. Having been used as a flavour and fragrance additive in cosmetics, foods and beverages, as well as a green solvent, limonene is of particular interest in polymerization, because it contains double bonds, which provide the bifunctionality necessary for polymerization. Limonene is also an allylic monomer (CH2=CH-CH2Y), which presents challenges in free-radical homopolymerization and thus, copolymerization was investigated herein to overcome this difficulty. 2-Ethylhexyl acrylate (EHA) and n-butyl methacrylate (BMA) were used in two separate projects, as comonomers with limonene. Using bulk free-radical copolymerization at 80℃, with benzoyl peroxide (BPO) as the initiator, high molecular weight (>100,000) EHA/limonene and BMA/limonene copolymers were produced. Reactivity ratios, important parameters used in the prediction of copolymer composition, were estimated and shown to accurately predict the copolymer composition of subsequent experiments. These can now be used for the application of appropriate semi-batch policies to further enhance limonene incorporation into the copolymers.

Dans le cadre de ce travail de thèse, la polymérisation de type RAFT a été exploitée pour synthétiser des particules de latex magnétiques décorées de polymères stimulables. Cinq (co)polymères hydrophiles ont tout d'abord été préparés via la (co)polymérisation RAFT en solution d'acide acrylique (AA) et de méthacrylate de 2-diméthylaminoéthyle (MADAME). Les agents macromoléculaires obtenus (macroRAFT) : des homopolymères de PAA ou PMADAME ainsi que des copolymères P(AA-co-MADAME), présentent une sensibilité au pH et à la température. Ces macroRAFT hydrophiles ont ensuite été utilisés dans des réactions d’extension de chaîne avec du styrène conduisant à la formation de copolymères à blocs amphiphiles bien définis. Puis, des dispersions aqueuses d’agrégats (clusters) de nanoparticules d’oxyde de fer (OF) ont ensuite été préparées via un procédé de mini-émulsification/évaporation de solvant, en utilisant les copolymères à blocs comme stabilisants. Après optimisation des conditions expérimentales (sonication, concentration de macroRAFT, pH), des agrégats de taille contrôlée (45 à 300 nm) ont pu être obtenus. Ces clusters ont ensuite été utilisés comme semence lors de la polymérisation en émulsion du styrène, conduite en présence d’un agent de réticulation. Les clusters d'OF ont été individuellement encapsulés par une couche de polymère, formant des particules magnétiques stabilisées par le segment hydrophile des copolymères à blocs. Enfin, les particules magnétiques décorées de copolymères de P(AA-co-MADAME) ont été utilisées avec succès pour la capture et le relargage de bactéries grâce à la modulation de leurs propriétés de surface en fonction du pH
In this work reversible addition-fragmentation chain transfer (RAFT) polymerization was exploited to synthesize magnetic latex particles decorated with stimuli-responsive polymer brushes. First, five hydrophilic (co)polymers with various compositions were successfully prepared by RAFT solution (co)polymerization of acrylic acid (AA) and 2-dimethylaminoethyl methacrylate (DMAEMA) for different AA to DMAEMA molar ratios. The obtained macromolecular RAFT agents (macroRAFTs), PAA or PDMAEMA homopolymers and P(AA-co-DMAEMA) copolymers, displayed interesting pH- and thermo-responsive properties. These hydrophilic macroRAFTs were then chain extended with styrene leading to the formation of well-defined amphiphilic block copolymers. An aqueous dispersion of iron oxide clusters was next prepared using a strategy based on emulsification/solvent evaporation in which the block copolymers were used as stabilizers. By varying the experimental conditions (sonication power, macroRAFT concentration and pH of the medium), the cluster size could be controlled from 45 up to 300 nm. These clusters were then used as seeds in styrene emulsion polymerization in the presence of a crosslinker. The iron oxide clusters were individually encapsulated into a polymer shell generating latex particles, stabilized by the hydrophilic segment of the block copolymers, and displaying interesting magnetic properties. At last, these magnetic beads were evaluated as carriers in the magnetic separation of bacteria. The magnetic latex particles decorated with P(AA-co-DMAEMA) copolymers were successfully employed for the capture and trigger release of bacteria, allowing their concentration in a biological sample

It was demonstrated for the first time that RAFT polymerizations of NIPAAm can be carried out directly in water at room temperature without photo initiator under UV radiation. Under these conditions, the controlled/living features could be proven for a large range of monomer/RAFT agent ratios. Moreover, even at a monomer conversion exceeding 80%, polymerization control (PDI<1.2) is maintained. It is also demonstrated that the RAFT polymerization of AA can be carried out without photo initiator in water at ambient temperature in the presence of TRITT at short wavelength. At these wavelengths, the controlled/ living characteristics is maintained even at a monomer to polymer conversions exceeding 80%. UV/Vis spectrometry was employed to monitor the functional group (-S(C=S)S-) changes of the employed trithiocarbonate RAFT agent S,S???-Bis(??,?????-dimethyl-acetic acid)-trithiocarbonate (TRITT) in aqueous solution when exposed to UV radiation. It is shown that the degradation pattern of TRITT alone as well as TRITT in the presence of NIPAAm deviate from each other. Surprisingly, it is found that TRITT completely decomposed at 254 nm while the addition of monomer prevented the decomposition of TRITT at the same wavelength. Nuclear magnetic resonance (NMR) techniques were applied to study the decomposition products of TRITT in solution without the addition of monomer. Methanol-d4 was selected as the solvent. In addition, high-resolution soft ionization mass spectrometry techniques were used to map the product species generated during UV radiation induced RAFT polymerizations of NIPAAm and AA in aqueous media, allowing for the tentative assignment of end groups. The NMR analysis suggests that the decomposition of TRITT in methanol-d4 under UV radiation has three cleavage patterns. These three cleavage patterns (described in the current thesis in detail) all occur at the ???S(C=S)S- group, which is the weakest structural unit in TRITT molecule. iii However, polymerization occurs prior to decomposition, if monomer is present. The mass spectrometric analysis suggests that the initial radicals result from the dissociation of TRITT, as well as monomer. Trithiocarbonate end group degradation leading to the formation of thiol terminated chains is also occurring. In the case of NIPAAm polymerization, a peak which may be associated with a cross termination product of the intermediate radical was observed under both 302 nm and 254 nm wavelength irradiation. Interestingly, this peak does not occur in AA polymerization at any wavelength (nor is it expected to form under conventional RAFT conditions and was not observed in previous mass spectrometry studies in thermal or ??-initiated polymerizations of NIPPAm with TRITT) and thus this assignment should be treated as very tentative only.

Thesis (DSc)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Examples of the use of NMR spectroscopy in the study of radical polymerization processes have been described. The studies presented have made a significant contribution to the understanding of the fundamental mechanistic processes in these polymerization systems. It is pointed out that NMR in conventional radical polymerization is of limited use due to the concurrent occurrence of all elementary reactions (initiation, propagation and termination). Conversely, for living radical polymerization, NMR has great value. In that case, the elementary reactions are somewhat more restricted to specific times of the polymerization process. This allows for example the detailed study of the early stages of chain growth in Reversible Addition-­‐Fragmentation Chain Transfer (RAFT) mediated polymerization. Two different studies are described. The first is related to the early stages of RAFT-­‐mediated polymerization. A process for which we coined the name initialization was studied via in situ 1H NMR spectroscopy. It is shown that in many cases, there is a selective reaction that converts the original RAFT agent into its single monomer adduct. A few different examples and their mechanistic interpretation are discussed. It is also shown that NMR spectroscopy can be a valuable tool for the assessment of a RAFT agent in conjunction with a specific monomer and polymerization conditions. In the second study, 15N NMR, 31P NMR and 1H NMR are used for two different types of experiments. The first is a conventional radical copolymerization in which the growing chains are trapped by a 15N labeled nitroxide to yield a stable product. In the second experiment, a similar copolymerization is conducted under nitroxide-­‐mediated conditions. The nitroxide of choice contains phosphorous, which enables the quantification of the terminal monomer in the dormant chains. Each of the experiments individually provides interesting information on conventional radical copolymerization and nitroxide-­‐mediated copolymerization, respectively. Combination of the experimental data reveals an interesting discrepancy in the ratio of terminal monomer units in active chains and dormant chains. Although not unexpected, this result is interesting and useful from a mechanistic as well as a synthetic point of view. In terms of future perspectives, it is expected that the advanced analytical techniques as described here will remain crucial in polymer science. Present developments in radical polymerization, such as investigations into monomer sequence control, rely on accurate knowledge of kinetic and mechanistic details of elementary reactions. It is expected that such detailed studies will be a main challenge for the next decade of polymer research.
AFRIKAANSE OPSOMMING: Voorbeelde van die gebruik van KMR-­‐spektroskopie in die studie van radikaalpolimerisasies word beskryf. Hierdie studies het ʼn beduidende bydrae gelewer tot die verstaan van die fundamentele meganistiese prosesse in hierdie polimerisasiesisteme. Dit het daarop gewys dat KMR beperkte gebruike het in konvensionele radikaalpolimerisasies as gevolg van die gelyktydige voorkoms van alle basiese reaksies (afsetting, voortsetting en beëindiging). Aan die anderkant het KMR groot waarde vir lewende radikaalpolimerisasie. In hierdie geval is die elementêre reaksies ietwat meer beperk tot spesifieke tye van die polimerisasieproses. Gedetailleerde studies kan byvoorbeeld van die vroeë stadiums van die kettinggroei in Omkeerbare Addisie-­‐Fragmentasie-­‐ KettingOordrag (OAFO)-­‐bemiddelde polimerisasie gedoen word. Twee verskillende studies is beskryf. Die eerste het betrekking op die vroeë stadiums van die OAFO-­‐bemiddelde polimerisasie. 'n Proses wat “inisialisering” genoem is, is bestudeer deur middel van in situ 1H KMR-­‐spektroskopie. Dit is bewys dat daar in baie gevalle 'n selektiewe reaksie is wat die oorspronklike OAFO-­‐agent in sy enkelmonomeeradduk verander voor polimerisasie. 'n Paar ander voorbeelde en hul meganistiese interpretasie is bespreek. Dit is ook bewys dat KMR-­‐spektroskopie 'n waardevolle hulpmiddel kan wees vir die assessering van 'n OAFO-­‐agent in samewerking met 'n spesifieke monomeer en polimerisasie toestande. In die tweede studie is 15N KMR, 31P KMR en 1H KMR gebruik vir twee verskillende tipes van die eksperiment. Die eerste is 'n konvensionele radikaalkopolimerisasie waarin die groeiende kettings vasgevang word deur 'n 15N-­‐gemerkte nitroksied om 'n stabiele produk te lewer. In die tweede eksperiment is 'n soortgelyke kopolimerisasie gedoen onder nitroksied-­‐ bemiddelde toestande. Die gekose nitroksied bevat fosfor wat die kwantifisering van die terminale monomeer in die dormante kettings moontlik maak. Elkeen van die individuele eksperimente lewer interessante inligting oor konvensionele radikale kopolimerisasie en nitroksied-­‐bemiddelde kopolimerisasie, onderskeidelik. ʼn Kombinasie van die eksperimentele data toon 'n interessante verskil aan in die verhouding van die terminale monomeereenhede in die aktiewe en sluimerende kettings. Alhoewel dit nie onverwags is nie, is die resultate interessant en van waarde vanuit 'n meganistiese-­‐ sowel as 'n sintetiese oogpunt. In terme van toekomstige perspektiewe word daar verwag dat gevorderde analitiese tegnieke soos hier beskryf, belangrik sal bly in polimeerwetenskap. Huidige ontwikkelinge in radikaalpolimerisasie, soos ondersoeke na die beheer van monomeervolgorde, maak staat op akkurate kennis van kinetiese en meganistiese besonderhede van die basiese reaksies. Daar word verwag dat sulke gedetailleerde studies ʼn uitdaging sal bied vir die volgende dekade van polimeernavorsing.

The present thesis investigates some long standing problems in radical polymerization (RP). The major aim is to consider the feasibility of using simple techniques to provide more insight into the kinetics of RP. This can contribute to fundamental knowledge of radical polymerizations, particularly with respect to the mode of termination (λ), average termination rate coefficient (), chain-length dependence of termination (CLDT) and chain transfer through in-depth investigations of the rate of polymerization (Rp) and molar mass distribution (MMD), the latter especially via mass spectrometric (MS) analysis. The termination process was first investigated. Observation of changes of (or equivalently Rp) and MMD by a variety of factors such as solvent, monomer and initiator concentrations, temperature, pressure and growing radical size were explored. Non-classical kinetics and chain-length dependency of termination were confirmed. Accessibility of CLDT information was clearly evident. Although observed results meet fully with composite-model expectations, issues such as chain transfer were found to have an effect on the CLDT parameters determined from rate measurements. Specifically, dilute-solution polymerization of methyl methacrylate (MMA) in methyl isobutyrate (MIB) showed evidence of such an effect. Scaling of quantities that are experimentally accessible such as with DPn yield CLDT parameters in good agreement with what has been reported from recent PLP experiments. This was confirmed for several monomers. The temperature dependence of termination was also investigated and found to show evidence for CLDT. In contrast, the variation of with pressure did not demonstrate similarly strong CLDT effects. Evidence for and determination of chain transfer to MIB was also obtained. This was followed up by investigations into the important parameter λ using the MS technique. Surprisingly little is known about λ despite its long history and its apparent importance to polymer properties. Firstly, the robustness of using MS was explored, with the method passing numerous consistency checks. Although no large dependence of MS instrument was found, electrospray-ionization mass spectrometry (ESI-MS) provided best resolution. Second, the type of initiator, the initiator concentration and the solvent were found to have no measurable effect on λ, even when chain transfer occurred. In further work, increasing temperature seemed to have an influence on λ, leading to an increase in the proportion of disproportionation. However, pressure was found to have only a small influence on λ. The effect of monomer on λ was also studied. In the final part of this work, a preliminarily investigation into the viability of using Raman spectroscopic techniques to study auto-acceleration, also called the gel effect, for bulk MMA radical polymerization was presented. The results showed the possibility of using such a technique to follow the reaction to high conversion. The effect of temperature and initiator concentration on auto-acceleration were also presented. The outstanding results of this thesis are: (1) The application of CLDT theory to better understand rate results from low-conversion polymerizations. (2) In particular, the use of CLDT principles to explain termination activation energies across a range of monomers. (3) The validation of the MS method for quantitative determination of mode of termination by carrying out an array of consistency checks. (4) Showing that MS results are consistent with CLDT theory. (5) Utilization of the MS method for the first ever reliable measurement of the variation of mode of termination with temperature, pressure and monomer.

New chain transfer agents based on dithiobenzoate and trithiocarbonate for free radical polymerization via Reversible Addition-Fragmentation chain Transfer (RAFT) were synthesized. The new compounds bear permanently hydrophilic sulfonate moieties which provide solubility in water independent of the pH. One of them bears a fluorophore, enabling unsymmetrical double end group labelling as well as the preparation of fluorescent labeled polymers. Their stability against hydrolysis in water was studied, and compared with the most frequently employed water-soluble RAFT agent 4-cyano-4-thiobenzoylsulfanylpentanoic acid dithiobenzoate, using UV-Vis and 1H-NMR spectroscopy. An improved resistance to hydrolysis was found for the new RAFT agents, providing good stabilities in the pH range between 1 and 8, and up to temperatures of 70°C. Subsequently, a series of non-ionic, anionic and cationic water-soluble monomers were polymerized via RAFT in water. In these experiments, polymerizations were conducted either at 48°C or 55°C, that are lower than the conventionally employed temperatures (>60°C) for RAFT in organic solvents, in order to minimize hydrolysis of the active chain ends (e.g. dithioester and trithiocarbonate), and thus to obtain good control over the polymerization. Under these conditions, controlled polymerization in aqueous solution was possible with styrenic, acrylic and methacrylic monomers: molar masses increase with conversion, polydispersities are low, and the degree of end group functionalization is high. But polymerizations of methacrylamides were slow at temperatures below 60°C, and showed only moderate control. The RAFT process in water was also proved to be a powerful method to synthesize di- and triblock copolymers including the preparation of functional polymers with complex structure, such as amphiphilic and stimuli-sensitive block copolymers. These include polymers containing one or even two stimuli-sensitive hydrophilic blocks. The hydrophilic character of a single or of several blocks was switched by changing the pH, the temperature or the salt content, to demonstrate the variability of the molecular designs suited for stimuli-sensitive polymeric amphiphiles, and to exemplify the concept of multiple-sensitive systems. Furthermore, stable colloidal block ionomer complexes were prepared by mixing anionic surfactants in aqueous media with a double hydrophilic block copolymer synthesized via RAFT in water. The block copolymer is composed of a noncharged hydrophilic block based on polyethyleneglycol and a cationic block. The complexes prepared with perfluoro decanoate were found so stable that they even withstand dialysis; notably they do not denaturate proteins. So, they are potentially useful for biomedical applications in vivo.
Ziel der vorliegenden Arbeit war es, neue Kettenübertragungs Agenzien, basierend auf Dithiobenzoat- und Trithiocarbonatderivaten zu synthetisieren, welche in der "Reversiblen Additions-Fragmentierungs Kettenübertragungs-Polymerisation" (RAFT) eingesetzt werden können. Die neu synthetisierten Verbindungen zeichnen sich durch permanent hydrophile Sulfonatgruppen aus, welche eine pH-unabhängige Löslichkeit in Wasser ermöglichen. Eine dieser Verbindungen trägt ein Fluorophore, wodurch eine asymmetrische doppelte Endgruppenmarkierung sowie die Herstellung von Fluoreszenzmarkierten Polymeren möglich ist. Die Hydrolysestabilität dieser Verbindungen in wässriger Lösung im Vergleich mit dem z. Zeit bekanntesten wasserlöslichen RAFT Agenz (4-Cyano-4-thiobenzoylsulfanylpentansäuredithiobenzoate) wurde unter Anwendung spektroskopischer Methoden (UV-Vis, 1H-NMR) untersucht. Dabei wurde festgestellt, dass diese neue Verbindungen deutlich bessere Hydrolysestabiltäten im pH-Bereich von 1-8 und bis zu einer Temperatur von 70°C besitzen. Die neuen RAFT-Verbindungen wurden ebenfalls bezgl. Ihrer Eignung in der Polymerisation von wasserlöslichen nichtionischen, anionischen und kationischen Monomeren in wässrigem Medium bei 48°C und 55°C getestet. Unter diesen Bedingungen konnten Vinylverbindungen wie z. B. Styrenderivate. Acrylate und Methacrylate kontrolliert polymerisiert werden: Die Molmasse stieg mit dem Umsatz, die Polydispersitäten waren niedrig und die isolierten Polymere zeigten Grad an Endgruppenfunktionalität. Bei der Polymerisation von Methacrylamiden wurde bei Polymerisationstemperaturen unter 60°C nur eine mäßige Kontrolle gefunden.

Es konnte weiterhin die RAFT Polymerisation in Wasser als leistungsstarke Methode zur Herstellung definierter Di- und Triblockcopolymere, einschließlich der Synthese von funktionalen Polymeren mit komplexer Struktur – beispielsweise amphiphiler- und schaltbare (stimuli responsive) Blockcopolymere entwickelt werden. Dies beinhaltet auch Polymere, die einen oder zwei schaltbare hydrophile Polymerblöcke enthalten. Der hydrophile Eigenschaft eines oder mehrer Blöcke kann durch äußere Reize wie pH-Änderung, Temperatur oder Salzgehalt geändert werden. Diese Beispiele demonstrierten die Variabilität des für schaltbare Polyamphiphile notwendigen Designs und zeigten exemplarisch das Konzept für multi-sensitive Systeme.

Thesis (MSc) -- Stellenbosch University, 1999.
ENGLISH ABSTRACT: A free-radical polymerisation process, which has characteristics of a living polymerisation system, as it is capable of producing polymers of pre-determined molecular masses with a narrow molecular mass distribution, is discussed. It is also possible to make blockcopolymers by adding adding different monomers. The basic objective was to describe, discuss and explain the results of the effects of alkyl iodides as chain transfer agents on the seeded emulsion homo- and co-polymerisation of styrene and butyl acrylate. lodoacetonitrile and 1-phenylethyliodide were used as alkyliodides, acting as degenerative chain transfer agents. First, the effects of these alkyl iodides as chain transfer agents on the molecular mass, molecular mass distribution, glass transition temperature, conversion and particle size for the seeded emulsion polymerisation of styrene were studied. Second, the effects of alkyl iodides as chain transfer agents on the kinetics of radical emulsion polymerisation, especially the average amount of radicals per latex particle, were investigated. Third, the possibility of producing block-copolymers by emulsion polymerisation, using alkyl iodides as chain transfer agents, was investigated. To the best of the author's knowledge, results of work carried out in this study offer the first proof that the "living"/controlled radical polymerisation of styrene, with alkyl iodides as chain transfer agents, can be successfully carried out in emulsion. Addition of different alkyl iodides as chain transfer agents, in different concentrations, led to marked changes in the molecular mass, molecular mass distribution, glass transition temperature, conversion and particle size for the seeded emulsion polymerisation of styrene. The molecular masses of the polystyrene that was produced ranged from 156 to 663 577 while the average molecular mass distribution was below 2. Addition of these alkyl iodides to a seeded styrene polymerisation under zero-one conditions led to an average number of free radicals per latex particle that was greater than 1. A styrene seed latex with functional iodine end-groups was created and was successfully co-polymerised with butyl acrylate to produce a perfect styrene-butyl acrylate block-copolymer. This work has industrial importance as it allows the molecular mass, molecular mass distribution and particle size of polymers to be controlled. These factors are directly related to their micro- and macrostructure of polymers.
AFRIKAANSE OPSOMMING: Die vrye-radikaal polimerisasie proses wat die eienskappe van In lewendige polimerisasie sisteem toon, omdat dit moontlik is om 'n polimeer met voorafbepaalde molekulêre massas en 'n baie klein molekulêre massa verspreiding te berei, is bespreek. Dit is ook moontlik om, deur die byvoeging van 'n tweede monomeer, 'n blok ko-polimere te maak. Die doel was om die effekte wat alkieljodiede as ketlingoordragagente op die "seed" homo- en ko-polimerisasie van stireen en butiel akrielaat gehad het te beskryf en te verklaar. Jodoasetonitriel en 1-fenieletieljodied is gebruik as degeneratiewe kettingoordragagente. Eerstens is die uitwerking van hierdie alkieljodiede as kettingoordragagente op die molekulere massa, molekulere massa verspreiding, glas oorgang temperatuur, opbrengs en partikelgrote van die "seed" emulsie polimerisasie van stireen bestudeer. Tweedens is na die uitwerking van alkiekjodiede op die kinetika van In emulsie radikaal polimerisasie gekyk met spesifieke 1