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Title: Synthesis and aqueous solution properties of new hydrophilic/hydrophilic diblock copolymers.
Author: Bailey, Lindsey.
Awarding Body: University of Sussex
Current Institution: University of Sussex
Date of Award: 2000
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Well-defined block copolymers of oligo (ethylene glycol) methacrylate (OEGMA)/2-(dimethylamino)ethyl methacrylate (DMA) and OEGMAl2-(diethylamino)ethyl methacrylate (DEA) have been synthesised via group transfer polymerisation (GTP). The crude diblock copolymers were contaminated with either DMA or DEA homopolymer which could be removed by selective precipitation of the copolymers into n-hexane. Polymers with a range of molecular weights and block compositions were synthesised and characterised by gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy (NMR), which indicated that well-defined copolymers with narrow molecular weight distributions had been produced. DMAlOEGMA copolymers were derivatised with either methyl iodide or 1,3-propanesultone in order to produce copolymers with a permanent cationic or betaine block. The degree of quaternisation was greater than 95 %, as calculated from NMR and / or elemental analyses. Photon correlation spectroscopy (PCS) was used to examine micellisation of the copolymers in aqueous solution. DMAlOEGMA copolymers with relatively high DMA contents reversibly formed micelles with DMA cores and OEGMA coronas above the lower critical solution temperature (LCS1) of the DMA bloc~ cooling these micellar solutions caused the micelles to completely dissolve. IH NMR spectra indicated that the degree of hydration of the hydrophobic block did not change as the solution was heated to micellisation temperature, in other words, the micelle cores were highly hydrated, even at high temperature. 'Anomalous' aggregation of certain copolymers was also observed; this phenomenon may be due to copolymer compositional heterogeneity. DMAlOEGMA copolymers were surface active even at room temperature, where the DMA is still hydrophilic; increasing the solution temperature above the LeST does not appear to affect the surface activity significantly. The aqueous solution properties of a DMAlOEGMA copolymer were compared to those of a DMAlethylene oxide (EO) copolymer with the same DMA block length and ethylene glycol content and micellisation was only observed for the DMAIPEO copolymer. It is thought that that the PEO block is able to stabilise the hydrophobic micelle cores because the linear arrangement of the ethylene glycol residues allows the formation of a closepacked, uniform micelle corona. In contrast, when the ethylene glycol residues were arranged into short, branched chains (OEGMA), stabilisation of the micelle did not occur due to poor packing efficiency of OEGMA blocks in a micelle corona. Micellisation of the quaternised copolymers was observed in concentrated salt solution at high temperature. Under these conditions the positively charged DMA block remained soluble and the OEGMA residues were 'salted out'. A reduction in the solvation and mobility of the OEGMA block in the micelle core was indicated by a decrease in the NMR signals due to these residues. At pH 3 the DEAlOEGMA copolymers were fully soluble due to protonation of the amine residues. As the pH was raised, the DEA residues became deprotonated, and therefore insoluble, and micelles with a DEA core and OEGMA corona were formed. NMR spectroscopy indicated that the DEA micelle cores were significantly, but not completely, dehydrated at pH 9. This micellisation was also reversible: addition of acid caused micellar dissolution. The surface activity of these copolymers is strongly dependent on pH: at low pH the surface activity is negligible but the copolymers are very surface active at pH 7, with limiting surface tensions as low as 35 mN mol for I % copolymer solutions. In both DMAlOEGMA and DEAlOEGMA copolymer micelles the degree of hydration of the micelle core, as seen by NMR. is higher than might be expected. Micelles with both DMA and DEA cores have been shown by other authors to be significantly more dehydrated than observed here. It can therefore be concluded that the presence on OEGMA corona affects the degree of hydration of the micelle core. In particular, it is thought that the highly branched corona-forming OEGMA block prevents the close packing of the hydrophobic chains which is required to form a completely dehydrated micelle core. Standard industrial tests were performed on DMAlOEGMA and DEAlOEGMA copolymers to assess their performance as novel polymeric surfactants. Both copolymers were found to be poor wetters over a range of temperatures and pH values. The foaming capacity of DMAlOEGMA was poor, but the DEAlOEGMA copolymer has high foaming capacity at certain pH and temperatures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Organic chemistry Chemistry, Organic