Organic-inorganic hybrid graft copolymers of polystyrene and polydimethylsiloxane

Sutherland, Aimee Celeste (2010-03)

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010.

Thesis

ENGLISH ABSTRACT: Hybrid graft copolymers of polystyrene (PSty) and polydimethylsiloxane macromonomers (PDMS) were synthesised. PSty-g-PDMS was synthesised employing the grafting through technique via a conventionally free radical polymerization (FRP) using a polydimethylsiloxane macromonomer. In this series the amount of PDMS incorporated into the copolymer was varied by varying the macromonomer to styrene ratios as well as the length of the PDMS side chain. This allows for the study of the effect that the macromonomer content and the branching length has on the efficiency of the grafting process. A second series of PDMS-g-PSty was also synthesized where the PDMS forms the backbone and the PSty the grafts. Two synthetic techniques were employed for the formation of these polymers. Firstly, the grafting onto approach was used where functional polystyrene prepolymers with either an allyl or vinyl end-groups were synthesised anionically (living anionic polymerization) prior to the coupling of a functional prepolymer using a hydrosilylation reaction with a Karstedt platinum catalyst. This technique was successful and gave insight to the effect of the polystyrene prepolymer graft length has on the grafting efficiency as well as the functional groups needed on the PDMS backbone. Furthermore, the effect of the viscosity (of the PDMS macromonomer) plays on the grafting efficiency was also elucidated. Lastly, the grafting from approach was employed for the formation of PDMS-g-PSty. ATRP, atom transfer radical polymerization, of styrene using a bromoisobutyrate functional PDMS macroinitiator was used for the synthesis of these copolymers. This was accomplished by reacting commercial silane functional PDMS molecules via a hydrosilylation reaction (using a Karstedt catalyst) with allyl-2- bromo-2-methyl-propionate to give a PDMS macroinitiator with bromoisobutyrate functional groups. This will allow for the initiation and growth of polystyrene branches from the PDMS backbone (employing ATRP with a suitable catalyst and ligand). The formation of the endproduct, PDMS-g-PSty, via this route proved to be extremely difficult and largely unsuccessful. Liquid chromatography (LC) at the critical point (LCCC) of polystyrene was used to separate the graft material from homo-polymers which might have formed as well as from the PDMS macromonomer. This technique allows for a very fast chromatographic analysis of the grafting reaction. Under the critical conditions of PSty it was found that the graft copolymer eluted at a lower retention time than the unreacted macromonomer and PSty homopolymer. Two-dimensional chromatography, where LCCC (1st dimension) was coupled to size exclusion chromatography (2nd dimension), was used for the evaluation of the CCD and MMD (molecular mass distribution) of the graft material. LC was furthermore coupled off-line to FTIR and TEM using an LC interface. LCFTIR gave insight to the microstructure of the material, whilst LC-TEM gave insight to the morphological nanostructure of the material.

AFRIKAANSE OPSOMMING: Hibried ent-kopolimere is gesintetiseer uit polistireen (PSty) en polidimetielsiloksaan (PDMS). PSty-g-PDMS is gesintetiseer deur gebruik te maak van die ent-deur tegniek via ‘n konvensionele vrye radikaal polimerisasie proses (VRP). In die reeks is die hoeveelheid PDMS wat geïnkorporeer is, gevarieer deur die hoeveelheid PDMS tot PSty verhouding te verander asook die lengte van die PDMS sytak. Gevolglik het dit toegelaat vir die studie van die effek wat die makromonomeer inhoud, sowel as die taklengte het op die effektiwiteit van die ent-proses. ‘n Tweede reeks is ook gesintetiseer, waar die PDMS die ruggraat vorm van die ko-polimeer, en die stireen die takke vorm van die ko-polimeer. Dus is PDMS-g-PSty gesintetiseer. Twee sintetiese tegnieke is benut vir die vorming van die kopolimere. In die eerste geval is daar van die ent-op tegniek gebruik gemaak waar funksionele polistireen prepolimere met ‘n alliel of ‘n silaan end-groep gesintetiseer is deur gebruik te maak van ‘n anioniese lewendige polimerisasie voor die koppeling van die PDMS makromonomere deur ‘n hidrosililasie proses met ‘n Karstedt platinum katalisator. Die tegniek was suksesvol en het in diepte insig gegee van die effek wat die molekulêre lengte van die polistireen prepolimeer het op die effektiwiteit van die ent-proses, sowel as die minimum hoeveelheid funksionele groepe wat teenwoordig moet wees op die PDMS ruggraat. Verder is die effek wat die viskositeit (van die PDMS makromonomeer) op die ent-proses het, bekend gemaak. Laastens is daar ook van die ent-vanaf tegniek gebruik gemaak vir die vorming van PDMS-g-PSty. AORP, atoom oordrag radikale polimerisasie, van stireen, deur gebruik te maak van ‘n bromoisobutiraat funksionele PDMS makro-inisieerder, is gebruik vir die sintese van die kopolimere. Die makro-inisieerders is bekom deur gebruik te maak van kommersiële silaan funksionele PDMS, en dit is gereageer deur middel van ‘n hidrosililasie proses met alliel-2-bromo- 2-metiel-propionaat. Dit het PDMS makroinisieerders tot gevolg gehad met bromoisobutiraat funksionele groepe. Gevolglik kon stireen takke vanaf die PDMS ruggraat gegroei word deur gebruik te maak van AORP met ‘n geskikte katalisator en ligand. Die vorming van die end-produk, PDMS-g-PSty, deur middel van hierdie roete was onsuksesvol. Vloeistof chromatografie by die kritiese punt van polistireen was gebruik om die ent-produk te skei van die homo-polimere en PDMS makromonomeer. Gevolglik kon die chemiese samestelling van die ent-produk geëvalueer word. Twee-dimensionele chromatografie, waar vloeistof chromatografie by die kritiese punt van polistireen in die eerste vlak gekoppel was aan grootte uitsluitings chromatografie in die tweede vlak, was benut om die chemiese komposisie sowel as die molekul re massa verdeling van die entproduk te verkry. Verder was vloeistof chromatografie indirek aan Fourier-oordrag infrarooi en transmissie elektron mikroskopie (TEM) gekoppel. Eergenoemde het insig gegee tot die mikrostruktuur van die materiaal, terwyl laasgenoemde insig gegee het tot die morfologiese nanostruktuur van die materiaal.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/3182
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