It was demonstrated for the first time that RAFT polymerizations of NIPAAm can be carried out directly in water at room temperature without photo initiator under UV radiation. Under these conditions, the controlled/living features could be proven for a large range of monomer/RAFT agent ratios. Moreover, even at a monomer conversion exceeding 80%, polymerization control (PDI<1.2) is maintained. It is also demonstrated that the RAFT polymerization of AA can be carried out without photo initiator in water at ambient temperature in the presence of TRITT at short wavelength. At these wavelengths, the controlled/ living characteristics is maintained even at a monomer to polymer conversions exceeding 80%. UV/Vis spectrometry was employed to monitor the functional group (-S(C=S)S-) changes of the employed trithiocarbonate RAFT agent S,S???-Bis(??,?????-dimethyl-acetic acid)-trithiocarbonate (TRITT) in aqueous solution when exposed to UV radiation. It is shown that the degradation pattern of TRITT alone as well as TRITT in the presence of NIPAAm deviate from each other. Surprisingly, it is found that TRITT completely decomposed at 254 nm while the addition of monomer prevented the decomposition of TRITT at the same wavelength. Nuclear magnetic resonance (NMR) techniques were applied to study the decomposition products of TRITT in solution without the addition of monomer. Methanol-d4 was selected as the solvent. In addition, high-resolution soft ionization mass spectrometry techniques were used to map the product species generated during UV radiation induced RAFT polymerizations of NIPAAm and AA in aqueous media, allowing for the tentative assignment of end groups. The NMR analysis suggests that the decomposition of TRITT in methanol-d4 under UV radiation has three cleavage patterns. These three cleavage patterns (described in the current thesis in detail) all occur at the ???S(C=S)S- group, which is the weakest structural unit in TRITT molecule. iii However, polymerization occurs prior to decomposition, if monomer is present. The mass spectrometric analysis suggests that the initial radicals result from the dissociation of TRITT, as well as monomer. Trithiocarbonate end group degradation leading to the formation of thiol terminated chains is also occurring. In the case of NIPAAm polymerization, a peak which may be associated with a cross termination product of the intermediate radical was observed under both 302 nm and 254 nm wavelength irradiation. Interestingly, this peak does not occur in AA polymerization at any wavelength (nor is it expected to form under conventional RAFT conditions and was not observed in previous mass spectrometry studies in thermal or ??-initiated polymerizations of NIPPAm with TRITT) and thus this assignment should be treated as very tentative only.
| Identifer | oai:union.ndltd.org:ADTP/258481 |
| Date | January 2008 |
| Creators | Song, Wentao, Chemical Sciences & Engineering, Faculty of Engineering, UNSW |
| Publisher | Awarded by:University of New South Wales. Chemical Sciences & Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Song Wentao., http://unsworks.unsw.edu.au/copyright |
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