Organocatalytic anionic polymerization of o-phthaldialdehyde and n-butyraldehyde

Thesis (MSc)--Stellenbosch University, 2017.ENGLISH ABSTRACT: Self-immolative polymers (SIPs) can be defined as polymers that are capable of complete head-to-tail depolymerization upon cleavage of an end-cap from the polymer chain-end in response to a trigger/stimulus. The use of SIPs has emerged as an alternative strategy in designing smart materials that are capable of responding to selective signals and provide an amplified response since the depolymerization process converts the entire polymer into its monomeric units and other small molecule products that can play a role in the amplified response. The incorporation of these polymers also offers the opportunity to alter the properties of a material after it has been prepared since the depolymerization of the SIP can cause a change in the shape, internal structure and/or surface properties of the material. Poly(phthaldialdehyde) (PPA), a well-known SIP, has been successfully prepared via non-organometallic catalyst based anionic polymerization in recent years. However, the methods that have been reported require expensive reagents and delicate experimental conditions. Hence, a new facile method for the non-organometallic anionic polymerization of PA was introduced and optimized in this work. The effect of a range of phosphazene and amine base catalysts were investigated. The results showed 1,8-diazabicyclo[5.4.0]undec-7-ene with a catalyst to initiator ratio of four to be the ideal catalytic system. It was further determined that the optimum experimental conditions for the DBU catalyzed system consisted of a 1.0 M monomer concentration, tetrahydrofuran as solvent and a reaction time of ten minutes. It was also shown that carboxylic acids can be used to initiate the polymerization reaction, which has thus far only been achieved using primary alcohols. The optimized method for the preparation of PPA was applied to the preparation of polystyrene-poly(phthaldialdehyde) block copolymers (BCPs). Hydroxyl end-functional polystyrene was prepared via activator regenerated by electron transfer atom transfer radical polymerization to serve as macroinitiator for the BCP reaction. Analysis of these BCPs, revealed that they had been prepared with narrow molecular weight distributions and a good agreement between the theoretical and experimentally obtained molecular weights. A systematic study was carried out to optimize the preparation of poly(butyraldehyde) (PBA), a SIP that has to date only been prepared using organometallic catalysts, by non-organometallic catalyst based anionic polymerization. The results of the study showed the phosphazene base catalyst P2-t-Bu with a catalyst to initiator ratio of 1 to 1 to be the ideal catalytic system for the preparation of PBA. Further investigation revealed a monomer concentration of 1.0 M, a nonpolar solvent such as pentane and a reaction time of ten minutes to be the optimum experimental conditions for the phosphazene base catalytic system.AFRIKAANSE OPSOMMING: Self-immolatiewe polimere (SIPe) word gedefinieër as polimere wat in staat is daartoe om van kop-tot-stert te depolimeriseer na die verwydering van die polimeerketting se eind-groep weens blootstelling aan ‘n sneller/stimulus. Die gebruik van SIPe het na vore gekom as ‘n alternatiewe strategie vir die ontwerp van slim materiale wat in staat is daartoe om te reageer op ‘n spesifieke sein en ook ‘n verstertke reaksie te bied, aangesien die depolimerisasie proses lei tot die afbreek van die polimeer na sy monomeriese eenhede en ander klein molekules wat ‘n rol kan speel in die versterkte reaksie. Die insluiting van hierdie polimere bied ook die geleentheid om die eienskappe van die materiaal te verander nadat dit voorberei is, aangesien die depolimerisasie van die SIP die vorm, interne struktuur en/of oppervlak eienskappe van die materiaal kan teweeg bring. Poli(phthalaldehied) (PPA), ‘n bekende SIP, is relatief onlangs voorberei deur nie-organometaal anioniese polimerisasie. Die metodes wat berig is hiervoor, vereis egter duur reagense en delikate eksperimentele toestande. Dus word ‘n eenvoudiger metode vir die nie-organometaal anioniese polimerisasie van PA in hierdie bekendgestel en geoptimiseer. Die effek van ‘n verskeidenheid fosfor en amien bevattende katalisators was ondersoek. Die resultate het getoon dat 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) met 'n katalisator tot inisieërder verhouding van 4 tot 1 die ideale katalitiese sisteem is. Dit is verder bepaal dat die optimale eksperimentele toestande vir die DBU gekataliseerde stelsel bestaan uit ‘n monomeer konsentrasie van 1.0 M, tetrahudrofuraan as oplosmiddel en ‘n reaksie tyd van 10 minute. Die optimale metode vir die voorbereiding van PPA is toegepas vir die voorbereiding van polistireen-poli(phthalaldehied) blokkopolimere (BKPe). Hidroksiel eind-funksionele polistireen is voorberei om te dien as makroinisieërder vir die ketting groei reaksie. Analise van die BKPe het gewys dat die hulle voorberei is met smal molekulêre gewig verspreiding en ‘n goeie oorenkoms tussen die geteikende en eksperimentele molêre massas. ‘n Sistematiese studie is uitgevoer om die optimale toestande vir die nie-organometaal anioniese polimerisasie van butielaldehied te bepaal. Poli(butieldaldehied) (PBA) is ‘n SIP wat tot dusvêr slegs voorberei is met organometaal kataliste. Die resultate van die studie het aangedui dat die fosfor bevattende katalis P2-t-Bu met ‘n katalisator tot inisieërder verhouding van 1 tot 1 die ideale katalitiese sisteem is. Dit is verder bepaal dat ‘n momomeer konsentrasie van 1.0 M, pentaan as oplosmiddel en ‘n reaksie tyd van 10 minute lei tot die beste resultate vir die spesifieke sisteem