Thermoresponsive hydrogels from poly(ethylene glycol)-based graft poly(dimethyl siloxane) amphiphilic copolymers with tunable lower critical solution temperatures
| dc.contributor.advisor | Mallon, Peter | en_ZA |
| dc.contributor.author | Roman, Stacey Kelly | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. | en_ZA |
| dc.date.accessioned | 2021-03-03T10:07:56Z | en_ZA |
| dc.date.accessioned | 2021-04-22T10:13:36Z | en_ZA |
| dc.date.available | 2021-09-03T03:00:10Z | en_ZA |
| dc.date.issued | 2021-03 | en_ZA |
| dc.description | Thesis (MSc)--Stellenbosch University, 2021. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: This study aimed to investigate poly(oligo(ethylene glycol) methyl ether methacrylate)-graft-poly(dimethyl siloxane) copolymer materials as potential precursor materials to produce polymer nanofibre hydrogels. This study initially consisted of finding the optimal ratio between OEGMA and EGMA, as the OEGMA by itself was found unsuitable for this particular study. Various factors were taken into account when determining the optimal ratio, such as the physical state and the processing ability of the product. The optimal ratio was determined to be 40 OEGMA:60 EGMA. Thereafter, a comprehensive sample library of poly(OEGMA-co-EGMA)-g-PDMS was successfully synthesised using conventional free radical polymerisation to yield amphiphilic graft terpolymers. Three different molar mass PDMS macromonomers were used, namely 1000, 5000 and 10 000 g/mol. The sample library systematically varied the PDMS content by copolymerisation ratio and graft length. Thus, the terpolymers were investigated to determine the influence of PDMS incorporation as well as the PDMS chain length on the hydrogel properties. The PDMS acts as the physical cross-links between polymer chains via the formation of hydrophobic domains. The presences of these physical cross-links allowed the material to be physically stable in water, where it swelled and prevented complete dissolution. The sample library was characterised using 1H-NMR spectroscopy, ATR-FTIR spectroscopy, SEC, TGA and DSC. The results of this study show that although not all of these materials showed hydrogels with dimensional stability, there is nevertheless a relationship between the swelling ability of the material and the graft content. It was found that the swelling ability of the materials in both water and hexane is dramatically affected by the length of the PDMS graft chain lengths. The longer chain length samples show higher swelling ratios for a given weight percent of PDMS, due to the formation of larger hydrophobic domains. Remarkably, the results show that at a constant 40 OEGMA:60 EGMA ratio the lower critical solution temperatures of the terpolymers could be varied within a 23 °C range from 39 to 62 °C. The mechanical properties of the hydrogel materials were determined using rheology. Interesting results were obtained owing to the varied tunable properties across the entire sample library. A desired product can be tuned by their physical appearance, the mechanical strength, the LCST and the degree of swelling due to the complex amphiphilic solid state morphology. The terpolymer sample library was also electrospun to yield microfibres, however they were not found to be long continuous fibres, but rather moisture sensitive discontinuous fibres especially when compared to that of the hydrophobic copolymer PEGMA-g-PDMS. Unfortunately due to the lack of dimensional stability of these polymers this specific terpolymer series cannot be viably used to produce nanofibres as confirmed by rheology and preliminary investigations using the electrospinning technique. | en_ZA |
| dc.description.abstract | AFRIKAANS OPSOMMING: Die doel van hierdie studie was om poli(oligo (etileenglikol) metieletermetakrylaat)-ent-poli(dimetiel siloksaan) kopolimere as moontlike voorlopers vir nano-vesel hidrogels te ondersoek. Die aanvanklike uitdaging was om die optimale verhouding van OEGMA tot EGMA te bepaal, aangesien die OEGMA op sigself ongeskik vir hierdie spesifieke studie was. Verskeie faktore was in ag geneem by die bepaling van die optimale verhouding, soos die fisiese toestand en die verwerkings vermoë van die resulterende produk. Die optimale verhouding was bepaal as 40 OEGMA: 60 EGMA. Daarna was 'n omvattende reeks amfiliele entterpolimere van poli(OEGMA-co-EGMA)-g-PDMS suksesvol gesintetiseer deur middel van konvensionele vrye radikale polimerisasie. PDMS makromonomere van drie verskillende molêre massas, naamlik 1000, 5000 en 10 000 g / mol, was gebruik om die entterpolimere te maak. Die PDMS-inhoud in die entterpolimeer reeks was stelselmatig aangepas volgens kopolimerisasie verhouding en entlengte. Dus was die invloed van PDMS-inkorporasie sowel as die PDMS-kettinglengte op die hidrogel-eienskappe van die entterpolimere ondersoek. Die PDMS dien as fisiese verknoping tussen polimeerkettings deur die vorming van hidrofobiese domeine. Die aanwesigheid van hierdie fisiese dwarsverbindings verleen hierdie entterkopolimere stabiliteit in water, sodoende kon swelling plaasvind sonder die gevolg van totale ontbinding. Die entterpolimeer reeks was met behulp van 1H-NMR-spektroskopie, ATR-FTIR spektroskopie, SEC, TGA en DSC gekarakteriseer. Die resultate van hierdie studie het getoon dat alhoewel nie al hierdie materiale hidrogels met dimensionele stabiliteit vertoon het nie, daar tog 'n verband tussen die swelvermoë van die materiaal en die entinhoud bestaan. Daar was gevind dat die swelvermoë van die materiale in beide water en heksaan dramaties beïnvloed word deur die lengte van die PDMS-entkettings. Die monsters met langer kettinglengtes het hoër water absorbsie verhoudings vir 'n gegewe gewig persentasie van PDMS getoon. Dit kan toegeskryf word aan die feit dat groter hidrofobiese domeine wat verder uitmekaar versprei is, vorm. Dit was opvallend dat die resultate getoon het dat die laer kritieke oplossings temperatuur van die entterpolimere met 'n konstante verhouding van 40 OEGMA: 60 EGMA binne 23 °C van 39 tot 62 °C kan wissel. Die meganiese eienskappe van die hidrogel materiale was met behulp van reologiese studies bepaal. Interessante resultate was verkry as gevolg van die uiteenlopende verstelbare eienskappe opgemerk deur die entterpolimeer reeks. Die gewenste produk kan verstel word in terme van fisiese voorkoms, die meganiese sterkte, die LCST en die mate van water absorbsie as gevolg van die komplekse amfifiele vaste toestands morfologie. Pogings was aangewend om mikrovesels te lewer deur gebruik te maak van die elektro-spin tegniek. Daar was egter gevind dat lang ononderbroke vesels nie vervaardig kon word nie, maar eerder vogsensitiewe diskontinue vesels, veral in vergelyking met die van die hidrofobiese kopolimeer, PEGMA-g-PDMS. As gevolg van die gebrek aan dimensionele stabiliteit van hierdie entterpolimere, kon hierdie spesifieke terpolimeer reeks nie doeltreffend gebruik word om nanovesels te vervaardig nie, soos bevestig deur reologiese studies en die elektro-spin tegniek. | af_ZA |
| dc.description.version | Masters | en_ZA |
| dc.embargo.terms | 2021-09-03 | en_ZA |
| dc.format.extent | xx, 112 pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/110313 | en_ZA |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University, 2021 | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Thermoresponsive hydrogels | en_ZA |
| dc.subject | Copolymers | en_ZA |
| dc.subject | Addition polymerization | en_ZA |
| dc.subject | Thermoresponsive polymers | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | Thermoresponsive hydrogels from poly(ethylene glycol)-based graft poly(dimethyl siloxane) amphiphilic copolymers with tunable lower critical solution temperatures | en_ZA |
| dc.type | Thesis | en_ZA |