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Synthesis, structure and crystallization behavior of amphiphilic hetero-arm molecular brushes with crystallizable poly(ethylene glycol) and n-alkyl side chains
Thesis (PhD)--Stellenbosch University, 2020.
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2020
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| _version_ | 1867614138839072768 |
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| access_status_str | Open Access |
| author | Barnard, Elaine |
| author2 | Klumperman, Bert |
| author_browse | Barnard, Elaine Klumperman, Bert |
| author_facet | Klumperman, Bert Barnard, Elaine |
| author_sort | Barnard, Elaine |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2020. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/108406 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:47:17.083Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2020 |
| publishDateRange | 2020 |
| publishDateSort | 2020 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/108406 Synthesis, structure and crystallization behavior of amphiphilic hetero-arm molecular brushes with crystallizable poly(ethylene glycol) and n-alkyl side chains Barnard, Elaine Klumperman, Bert Pfukwa, Rueben Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. Crystallization Amphiphilic molecular brushes Self-assembly (Chemistry) Nanostructures UCTD Thesis (PhD)--Stellenbosch University, 2020. ENGLISH ABSTRACT: This study describes the synthesis of hetero-arm amphiphilic molecular brushes (AMBs) and their selfassembly into well-ordered nanostructures in the solid and solution-state. Firstly, a series of hetero-arm AMBs were prepared using the grafting through synthetic approach, via conventional free radical terpolymerization of macromonomers containing either poly(ethylene glycol) (PEG) or n-alkyl chains of different lengths, i.e., polar 4-vinyl benzyl-PEG methyl ethers (VB-PEG), tert-butyl diphenyl silyl poly(ethylene glycol) methacrylate (TBDPSi-PEGMA), and apolar N-alkyl maleimides (MI-Cm). By varying the PEG side chain degree of polymerization (DP = 12, 16 and 20) and n-alkyl chain lengths (C10, C12, C16 and C20), AMBs with varying combinations of hydrophilic/hydrophobic side chain lengths were produced. The self-assembly behaviour of these hetero-arm AMBs in arm-selective solvents was investigated in relation to the hydrophilic/hydrophobic side chain lengths, choice of common solvent, and method of solvent switching (dialysis versus evaporation). Well-ordered micro and nanostructures of various morphologies were obtainable, and the assemblies were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Fluorescence Microscopy. Two fluorescent studies were employed with the first study investigating the possibility of core entrapment of hydrophobic guests, using a fluorescent dye perylene red. A second study investigated the capability of using the azide moieties (N3-PEGMA side chains) as reactive handles for attaching fluorescent conjugates on the hydrophilic chain ends which will subsequently form part of the coronas upon self-assembly in aqueous media. Furthermore, the effect of side chain length on AMB phase behavior, semicrystalline morphologies and crystallization kinetics in the solid state, was elucidated via differential scanning calorimetry, polarized light optical microscopy and x-ray diffraction experiments. SAXS results indicated that all materials exhibit a phase segregated lamellar structure in the melt. Most of the AMB materials prepared were double crystalline, i.e., contained crystals from alkyl and PEG chains. AMB crystallization was constrained by the AMB architecture, the frustration being most evident in AMBs with combinations of either low DPPEG, or short alkyl chain lengths. Large, well-developed spherulites, implying break-out crystallization, were only observed for the AMBs with the combination of the longest PEG chain (DP = 20) and longest alkyl chain length (C20). A peculiar behaviour was found when spherulitic growth rates and overall crystallization rates of the PEG chains, within this particular AMB sample, were determined as a function of crystallization temperature. In both cases, a distinct minimum with decreasing temperature was observed, probably caused by the challenges encountered in crystal packing of the PEG side chains, tethered to an amorphous backbone, which also contained already crystallized C20 chains. This minimum is analogous to that observed in the crystallization of long chain n-alkanes, or high molar mass polyethylenes with bromine pendant groups that has been attributed to a self-poisoning effect; this is the first observation of this phenomenon in AMBs. AFRIKAANSE OPSOMMING: Hierdie studie beskryf die sintese van hetero-arm amfifiele molekulêre borsels (AMBs) en hul selfsamestelling in goed-geordende nanostrukture in die vaste toestand en in ‘n oplossing. Eerstens is 'n reeks hetero-arm AMBs voorberei met behulp van die ‘enting deur’ sintetiese benadering, via konvensionele radikaalterpolimerisasie van makromonomeers wat of poli(etileenglikol) (PEG) of nalkielkettings van verskillende lengtes bevat, m.a.w polêre vinielbensiel-beëindigde-poliëtileenglikol (VB-PEG), tersiêre-butieldifeniel-siliel-poliëtileenglikol metakrilaat (TBDFSi-PEGMA) en apolêre N-alkiel maleïenamied (MI-Cm). Deur die PEG-sykettinggraad van polimerisasie (DP = 12, 16 en 20) en n-alkielkettinglengtes (C10, C12, C16 en C20) te wissel, is AMBs met wisselende kombinasies van hidrofiliese/ hidrofobiese sykettinglengtes geproduseer. Die selfsamestelling gedrag van hierdie hetero-arm AMBs in armselektiewe oplosmiddels is ondersoek met betrekking tot die hidrofiliese/hidrofobiese sykettinglengtes, die keuse van 'n algemene oplosmiddel en die metode van oplosmiddel-uitruiling (dialise teenoor verdamping). Goed-geordende mikro- en nanostrukture van verskillende morfologieë kon verkry word en die samestellings is gekarakteriseer deur skandeer-elektronmikroskopie (SEM), transmissie-elektronmikroskopie (TEM) en fluoresserende mikroskopie (‘n fluoresserende kleurstof is ingesluit). Twee fluoresserende studies is gebruik om ondersoek in stel van die moontlikheid om 1) die AMBs te gebruik as hidrofobiese gasheers en 2) die vermoë van die azied-groepe (N3-PEGMA-sykettings) om as reaktiewe handvatsels gebruik te word. Die handvatsels kan gebruik word om fluoresserende molekules aan die hidrofiliese kettingpunte te heg, wat dan deel sal vorm van die koronas tydens selforganisasie in waterige oplossings. Verder is die effek van syketting lengtes van die AMB se fase gedrag, semikristallyne morfologieë en kristallisasie-kinetika in die vaste toestand toegelig deur middel van differensiële skandering kalorimetrie (DSK), gepolariseerde lig optiese mikroskopie (PLOM) en x-straaldiffraksie eksperimente. Die x-straaldiffraksie resultate het aangedui dat alle materiale 'n fase gesegregeerde lamellêre struktuur in die smelt het. Die meeste AMB-materiale wat gesintitiseer is was dubbelkristallyn d.w.s. bevat kristalle van beide alkiel- en PEG-kettings. Die AMB-kristallisasie is beperk deur die AMB-argitektuur; die frustrasie was die duidelikste in AMBs met kombinasies van lae DPPEG- of kort alkielketting lengtes. Groot, goed ontwikkelde sferuliete – wat uitbreekkristallisasie impliseer – is slegs vir die AMBs waargeneem met die kombinasie van die langste PEG-ketting (DP = 20) en die langste alkielkettinglengte (C20). 'n Eienaardige gedrag is raakgesien toe sferulitiese groei- en algehele kristallisasietempo van die PEG-kettings binne hierdie spesifieke AMB-monster as 'n funksie van die kristallisasie temperatuur bepaal is. In albei gevalle is 'n duidelike minimum met 'n dalende temperatuur waargeneem, waarskynlik veroorsaak deur die uitdagings wat die kristalverpakking van die PEG-sykettings ondervind, vasgemaak aan 'n amorfe ruggraat, wat ook reeds gekristalliseerde C20-kettings bevat. Hierdie minimum is analoog aan dié wat waargeneem word by die kristallisasie van lang-ketting n-alkane, of poliëtileen met 'n hoë molêre massa en broom eind-groepe. Hierdie verskynsel word toegeskryf aan 'n selfvergiftigings effek en is die eerste waarneming van hierdie verskynsel in AMBs. Doctoral 2020-02-19T07:07:53Z 2020-04-28T15:12:32Z 2020-02-19T07:07:53Z 2020-04-28T15:12:32Z 2020-02 Thesis http://hdl.handle.net/10019.1/108406 en_ZA Stellenbosch University xviii, 132 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Crystallization Amphiphilic molecular brushes Self-assembly (Chemistry) Nanostructures UCTD Barnard, Elaine Synthesis, structure and crystallization behavior of amphiphilic hetero-arm molecular brushes with crystallizable poly(ethylene glycol) and n-alkyl side chains |
| title | Synthesis, structure and crystallization behavior of amphiphilic hetero-arm molecular brushes with crystallizable poly(ethylene glycol) and n-alkyl side chains |
| title_full | Synthesis, structure and crystallization behavior of amphiphilic hetero-arm molecular brushes with crystallizable poly(ethylene glycol) and n-alkyl side chains |
| title_fullStr | Synthesis, structure and crystallization behavior of amphiphilic hetero-arm molecular brushes with crystallizable poly(ethylene glycol) and n-alkyl side chains |
| title_full_unstemmed | Synthesis, structure and crystallization behavior of amphiphilic hetero-arm molecular brushes with crystallizable poly(ethylene glycol) and n-alkyl side chains |
| title_short | Synthesis, structure and crystallization behavior of amphiphilic hetero-arm molecular brushes with crystallizable poly(ethylene glycol) and n-alkyl side chains |
| title_sort | synthesis structure and crystallization behavior of amphiphilic hetero arm molecular brushes with crystallizable poly ethylene glycol and n alkyl side chains |
| topic | Crystallization Amphiphilic molecular brushes Self-assembly (Chemistry) Nanostructures UCTD |
| url | http://hdl.handle.net/10019.1/108406 |
| work_keys_str_mv | AT barnardelaine synthesisstructureandcrystallizationbehaviorofamphiphilicheteroarmmolecularbrusheswithcrystallizablepolyethyleneglycolandnalkylsidechains |