Annerike Cronje on LinkedIn: For future work it is necessary to modify the xanthate end groups to allow… (2024)

After all the lab work the final task to finish the honours project was to write a short ChemComm.

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Conclusion of my Honours project:PVP brushes were formed using the so called grafting from polymerization method. Aqueouse RAFT/MADIX polymerization with sodium sulphite yielded the most uniformey distributed polymer brushes. The xanthate end groups were then converted to aldehyde end groups, and the PVP brush was successfully labelled with 6-aminofluorescein.In future work we will attempt to selectively trap CTC’s that overexpress epithelial cell adhesion molecules (EpCAM) by immobilizing anti-EpCAM antibodies onto a benzylguanine functionalized PVP polymer brush. The effect of the polymer chain length and the antiEpCAM surface density on the adhesion of the CTCs wil

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Two other polymerization methods were then investigated. First the aqueous RAFT/MADIX polymerization was done with sodium sulphite instead of ascorbic acid to ensure a basic polymerization environment with a pH between 8 and 10. Then another polymerization was done in THF as the solvent, to ensure solubility of both the monomer and the RAFT agent. AIBN was used as the initiator for this polymerization and the reaction was done at 60 °C.The aqueous RAFT/MADIX polymerization done with sodium sulphite formed a thick continuous layer of polymer on the glass surface whereas, the polymerization done in THF showed little polymer attached to the glass surface with an inconsistent polymer distribution as seen in Fig 3. This could be due to the polymerization system being much more sensitive to moisture, and other impurities (such as those present in the RAFT agent) which could cause insufficient initiation of the surface grafted RAFT agent. The aqueous RAFT/MADIX polymerization done with sodium sulphite gave the best results and was therefore used for the rest of the project.Next it was attempted to vary the length of the polymer brushes, by using different NVP to RAFT ratios similar to those previously described in Table 1. An interesting phenomenon was observed on the surface of these polymer brushes. For the lowest molecular weight brush,large bubbles and small particles formed on the surface of the polymer layer. For the intermediate molecular weight polymer brush, clusters of particles formed and for the largest molecular weight polymer brush, the most uniform film was formed.Tetraethyl orthosilicate is known to polymerize in water in a 2-step reaction, which includes fast hydrolysis followed by condensation, when the polymerization is base catalysed .The tri-methoxysilane groups on the RAFT agent molecules could therefore couple through this mechanism and form multifunctional macro-RAFT molecules, which would explain the particles that formed. Any cleaved off tri-methoxy silane groups could also undergo polymerization. The polymerization system would therefore be complex and include simultaneous growth of the PVP on the glass surface, particle formation and growth, and possible polymerization of silica, causing an entangled network to form on the glass surface.

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To investigate the physisorption ability of PVP onto the glass surface a standard RAFT agent that does not contain the trimethoxy silane group was used. Furthermore a “grafting to” polymerization was done where the trimethoxysilane functional RAFT agent was simply added to the polymerization mixture and was compared to a ”grafting from” polymerization where the same RAFT agent was first attached to the glass slide before polymerization. SEM/EDS images is shown in Fig 1. As expected PVP shows no physisorption to the glass slide, as seen by comparing a with b and the “grafting to” method is much less effective than the “grafting from” method when comparing c with d. The “grafting from” method however does not form a continuous film covering the whole glass slide.In an attempt to increase the coverage of the glass slide, higher concentrations of RAFT agent for the attachment step were investigated. To vary the RAFT agent surface density on the glass slides, different molar concentrations of the RAFT solution were used as shown in table 2. After polymerization each slide was analysed by SEM/EDS as shown in Fig 2. It is clear that increasing the concentration of the RAFT solution increases the coverage of the PVP on the glass surface, however none of the glass slides was uniformly covered with the polymer.Two main reasons were thought to cause this problem. The first was that cleavage of the tri-methoxysilane group that attached the polymer to the glass slide occurred, due to the ascorbic acid used in the aqueous RAFT/MADIX polymerization which created a harsh acidic environment. This was supported by results obtained for a polymerization that was done with a 5:1 ratio of excess ascorbic acid to RAFT agent with a pH of 3 where the SEM/EDS image showed very little polymer on the glass surface. The second reason could be due to the insolubility of the RAFT agent in the aqueous solution used for the polymerization

RAFT/MADIX polymerization was chosen for this project given that O-ethylxanthates were shown to be efficient RAFT/MADIX agents which lead to high yields, controlled molecular weight and low dispersities, in aqueous RAFT/MADIX polymerisation. The use of aqueous RAFT/MADIX polymerization also has the added advantage of ease of execution at ambient temperature and pressure.The ability of the impure RAFT agent to control the molecular weight of PVP was investigated by varying the monomer to RAFT ratios as shown in Table 1. The molecular weight was determined from 1H-NMR by taking the ratio of peak (e) to peak (f) multiplied by the molar mass of the NVP repeat unit. Although the molecular weight determined by 1H-NMR did not correspond very well to the theoretical molecular weight as seen in Table 1, a definite trend in molecular weight was observed. The RAFT agent would therefore be sufficient to vary the length of the polymer brush and was used for the rest of the project.The typical procedure for the formation of the polymer brush started with a pre-treatment to clean the glass slide and activation under UV light, followed by attachment of the RAFT agent to the glass slide, and finally aqueous RAFT/MADIX polymerization of NVP in a “grafting from” process.

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The first step of my honours project was to synthesise a RAFT agent:The xanthate based RAFT agent was designed to mimic the most common “initiator” used in SI-ATRP for brush formation onto glass surfaces. The O-ethyl xanthate was chosen as the leaving group due to its previous success in the polymerization of NVP.The RAFT agent [3(trimethoxysilyl)propyl] propenamide O-ethylxanthate was synthesized successfully in a 2-step reaction, but could not be purified completely, evident from the small impurity peaks in the 1H-NMR spectra. Attempted aqueous work-up lead to hydrolysis of the trimethoxysilane group and column chromatography always resulted in the desired product remaining in the column due to the tri-methoxysilane groups that reacted with the column particles.

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If you have 3 minutes check out my honour project proposal on polymers brushes thethered to a glass surface for antibody immobalization and selective cell trapping.

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What I learned in Special topics in polymer science 754:1.Raw materialsa. Polyethylenes:LDPE, HDPE, LLDPE,PP, PS, ABS, nylon, PC, PETb.Grading of polymersc. Additivesd. Mixing methodse. Polymer formulationsg. Polymer processing2. Degradation and stabilization of polymersa. Autoaxidationb. Stabilizationc. Photodegradation3. Processing of polymersa. Extrusionb. Injection mouldingc. Extrusion blow mouldingd. Injection blow mouldinge. Compression mouldingf. Rotational moulding4. Theories of adhesion based on :a. adsorptionb. diffusionc. Electrostatic interactionsd. Simple mechanical interlockinge. Chemical bondingf. Weak boundary layers5. Types of adhesivesa. Set by chemical reactions, epoxies, polyurethanes, unsaturated polyesters, phenol- formaldehydes.b. Moisture cured: silicones, Pur/ isocyanates, cyanoacrylatesc. Heat cured: Aromatic polyamides, nylons, poly(vinylacetals)d. Set by evaporation: rubber cement, neoprene cement, SBR, vinyl polymers.6.Reinforced polymers7. Elastomer technology and vulcanizationa. Vulcanization principles and processb. Reinforcement of elastomers by fillers8. Green chemistry9. ⁠Functions of surface coatingsa. Paints and its componentsb. Protective coatings

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Physical Polymer Science 744:1. Polymers in solution part Aa. Constitution,Configuration, Conformationb. Influence of tacticity on propertiesc. Micro and macro - confirmationd. Chain statisticse. Polymer coil modelsf. Polymer dispersity in sizeg. Dimensions of branched polymers2. Polymers in solution Part Ba.Fluory-Huggins lattice theory for macromoleculesb.solubility parameter of polymersc. Polymer miscibilityd. Phase seperation in copolymer blends3. Fundamentals of Viscometrya.Intrinsic viscosityb. Viscosimetric behavior of neutral and ionic polymersc. Viscosimetric equipmentd. Molar mass analysis by viscosimetrye. Polymer coil dimensions from viscosimetry4. Light scatteringa.scattering from solutions of large moleculesb. Zimm plotsc. SEC- MALLS6. Physical behaviour of polymersa. Elasticityb. Visco-elaticityc. Crystallization7. Polymer melt flow and viscoelestic effects8. ⁠Deformation and failure of polymers9. ⁠The ultimate or end-use properties of polymeric products10. ⁠Degradation of polymers11. ⁠Processing of polymers

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