Synthesis and modification of sequence-controlled styrene-maleic anhydride copolymer

Thesis (MSc)--Stellenbosch University, 2018.ENGLISH ABSTRACT: Recently, there has been an immense fascination with replicating nature’s ability to create polymers with perfectly controlled monomer sequences. The work introduced in this thesis focuses on the synthesis of a sequence-controlled copolymer, along with its subsequent modification. Styrene (Sty) and maleic anhydride (MAnh) are the two monomers used in this study. The fact that this comonomer pair are added one at a time to the growing polymer chain during the addition-fragmentation cycle, along with the inability of MAnh to homopolymerize due to the steric hindrance served as a foundation to synthesize a sequence controlled copolymer consisting of a repeating sequence that comprises one MAnh unit followed by two Sty units. S-butyl-S’-(1-phenyl ethyl) trithiocarbonate (BPT) was selected as a reversible addition-fragmentation chain-transfer (RAFT) agent to synthesize the copolymer. The desired polymer was characterized mainly by 1H NMR spectroscopy, and 13C DEPT NMR spectroscopy, as well as by mass spectrometry (MS) and size exclusion chromatography (SEC). The DEPT results proved that the alternating sequence was suppressed, with 93 % of the Sty-centred sequences being MSS. The thermal studies of the synthesized polymer was compared to SMA2000, which is synthesized by conventional radical polymerization with a Sty:MAnh molar ratio of 2:1. The synthesized sequence-controlled copolymer was modified, along with alternating styrene-maleic anhydride (SMA) derivatives of various molecular weights. The dissociation behaviour of these polymers were investigated and upon functionalization, a zwitterionic window was located for all the polymers. The isoelectric point (pI) was calculated using either the method of determining the maxima of first derivative or by a linear regression method reported by Johansson. The latter method provided more precise pKa values for the polymers, upon correlation with the obtained titration curves. The incorporation of a larger fraction of Sty in the sequence-controlled copolymer, resulted in a higher pI, which allows the pI to be manipulated in future studies. Cell viability tests of the functional groups revealed that the ionic groups present in these polymers, are not cytotoxic to cells.AFRIKAANSE OPSOMMING: Onlangs was daar 'n enorme fassinasie met die replisering van die natuur se vermoë om perfek beheerde volgorde te skep. Die werk wat in hierdie verhandeling aangebied word, fokus op die sintese van 'n volgorde-beheerde kopolimeer, tesame met die behandeling daarvan met 'n nukleofiel. Stireen (Sty) en maleienanhidried (MAnh) is die twee monomere wat in hierdie studie gebruik word. Die feit dat hierdie monomeersisteem een vir een bygevoeg word aan die groeiende polimeerketting gedurende die addisie- fragmentasie siklus, tesame met die onvermoë van MAnh om te homopolymeriseer as gevolg van die steriese hindernis, dien as basis vir die sintese van 'n volgorde- beheerde kopolimeer wat bestaan uit een MAnh-eenheid gevolg deur twee Sty-eenhede. S-butiel-S'-(1-fenieletiel) tritiokarbonaat (BPT) is gekies om die kopolimeer te sintetiseer. Die verlangde polimeer is hoofsaaklik gekenmerk deur 1H NMR spektroskopie, en 13C DEPT NMR spektroskopie, tesame met massaspektrometrie (MS) en grootteuitsluitingschromatografie (SEC). Die DEPT-resultate het bewys dat die wisselende volgorde onderdruk is, met 93% van die Sty-gesentreerde rye MSS. Die termiese studies van die gesintetiseerde polimeer is vergelyk met SMA2000, wat gesintetiseer word deur konvensionele radikale polimerisasie met 'n Sty: MAnh molêre verhouding van 2:1 Die gesintetiseerde volgorde-beheerde kopolimeer is aangepas, saam met afwisselende stireen-maleienanhidried (SMA) afgeleides van verskillende molekulêre gewigte. Die dissosiasiegedrag van hierdie genoemde polimere is ondersoek en op funktionalisasie was 'n zwitterioniese streekvenster vir al die polimere. Die isoelektriese punt (pI) is bereken deur óf die metode van maksima van eerste afgeleide of 'n lineêre regressie metode wat deur Johansson gerapporteer is. Laasgenoemde het meer akkurate pKa-bepaling van die polimere voorsien, in ooreenstemming met die verkryde titrasiekurwes. Die inkorporasie van 'n groter fraksie van Sty in die volgorde-beheerde kopolimeer het gelei tot 'n hoër pI, wat die pI toelaat om in toekomstige studies gemanipuleer te word. Selbaarheidstudietoetse het getoon dat hierdie funksionele groepe nie sitotoksies vir selle is nie.Master