This thesis work has focused on the study of itaconate monomers and photo-initiation processes in acrylate, methacrylate and itaconate monomer systems. Novel information pertaining to photo-initiator derived radical species and their reactivity, as well as the behaviour of itaconate polymerization systems is presented in detail. The knowledge gained from the photo-initiation studies is utilized as a precursor to mark polymer chains using nitrones as radical spin traps and the applicability of this technique discussed. The sterically hindered monomers dimethyl itaconate (DMI), di-n-butyl itaconate (DBI) and dicyclohexyl itaconate (DCHI) were polymerized via reversible addition fragmentation chain transfer (RAFT) free radical polymerization. The RAFT mediated polymerization of these monomers displayed hybrid living behaviour (a mix of conventional and living free radical polymerization characteristics) of varying degrees depending on the molecular structure of the RAFT agent employed. DCHI was also polymerized using atom transfer radical polymerization (ATRP). The resulting molecular weight distributions are broad for the RAFT mediated systems (1.2 ≤ PDI ≤ 3.4). The molecular weight distributions generated via the ATRP of DCHI are narrower (1.2 ≤ PDI ≤ 1.5). Chain transfer to monomer constants for the itaconate monomers DMI, DBI and DCHI have been determined at 60 ??C (CDMI = 1.4⋅10-3, CDBI = 1.3⋅10-3 and CDCHI = 1.0⋅10-3) and are relatively large in comparison to similar 1,1-disubstituted systems, suggesting that the transfer to monomer reaction is significant. PREDICI?? simulations confirm that a significant chain transfer to monomer step results in broad molecular weight distributions. Viscosity of the polymerizing system has also been shown to be an important factor in the resulting width of the molecular weight distributions. Chain extension of RAFT capped pDCHI and pDBI yield molecular weight distributions that progressively shift to higher molecular weights. Thermogravimetric analysis (TGA) of pDCHI-block-pStyrene copolymers indicates thermal degradation in two separate steps for the pDCHI and pStyrene blocks. Conventional pulsed laser polymerization coupled with size exclusion chromatography (PLP-SEC) as well as multi-pulse pulsed laser polymerization (MP-PLP) has been employed to study the depropagation kinetics of DMI, DBI DCHI and di(4-tert butylcyclohexyl) itaconate (DBCHI). The effective rate coefficient of propagation, kp eff, was determined for DMI, DBI and DCHI in bulk and solution of cyclohexanone (DCHI), N-methylformamide (DMI and DBI) and anisole (DBCHI) for monomer concentrations between 0.7 < cM 0 < 7.1 mol L-1 in a wide temperature range (0 < T < 90 ??C). The resulting Arrhenius plots (i.e. ln kp eff vs. 1/RT) displayed a significant curvature in the higher temperature regimes and were analyzed in their respective linear and curved sections to yield the activation parameters of the forward and reverse reaction. Mark-Houwink-Kahn Sakurada parameters for pDBI and pDBCHI were determined in tetrahydrofuran at 40 ??C using triple detection gel permeatation chromatography. High resolution Electrospray Ionization - Quadrupole Ion Trap Mass Spectrometry (ESIMS) was applied to study the polymeric product spectrum generated by the pulsed laser polymerization (PLP) of methyl methacrylate (MMA), methyl acrylate (MA), butyl acrylate (BA) and DMI at temperatures ≤ 0 ??C in the presence of various photo-initiators including 2,2-dimethoxy-2-phenylacetophenone (DMPA), benzoin, benzil, benzoin ethyl ether (BEE) 2,2-azobisisobutyronitrile (AIBN) and bis(2,4,6-trimethyl-benzoyl)- phenylphosphinoxide (Irgacure 819) to study the reactivity of primary and potential secondary derived radical fragments from photolytically induced fragmentation. Termination products, both combination and disproportionation, were identified with high accuracy. Results have been compiled in a user friendly table presenting the reactivity of the various photolysis product fragments towards the different monomers. Energy deposition into the MA/photo-initiator systems is found to have no influence on the product distributions of the MA polymers produced via photo-initiation under the conditions examined. For various photo-initiators employed, products congruent to that of chain transfer to monomer species in the DMI photo-polymerizations are observed, conclusively illustrating that chain transfer to monomer is a significant reaction pathway in itaconate free radical polymerizations. Both the benzoyl and acetal fragments generated as a result of DMPA photo cleavage were found to initiate and highly likely terminate polymerization. Under the conditions studied, the acetal radical produced upon DMPA photolysis fragment further to yield methyl radicals which seem to act predominantly as terminating moieties. Both the benzoyl and ether fragments produced as a result of benzoin photo cleavage were found to act as initiating and probable terminating species, indicating that the ether radical fragment does not act exclusively as a terminating species. Additionally, increasing laser intensity and/or irradiation repetition rate (i.e., energy deposition into the system) results in more complex product distributions of the MMA polymers produced via photo-initiation (with the exception of AIBN). Temperature was determined to have a minor influence on the resulting product distribution under the conditions examined. Polymerization systems utilizing Irgacure 819 give complex product spectra due to the formation of second generation radical species resulting in several initiator fragments incorporated into a single polymer chain. A novel method utilizing PLP in free radical polymerization has been developed for marking of polymer chains with radical spin traps. By introducing a so-called marker (nitroxide derived from a nitrone), which specifically terminates propagating radicals via combination, a polymer subdistribution is generated which can be measured by ESI-MS and may potentially be utilized to determine propagation rate coefficients of ultimate accuracy. The general methodology of the technique in which such marker radicals are generated via reaction of an initiating radical with a nitrone is demonstrated on the examples of butyl acrylate (BA) and vinyl acetate (VAc).
| Identifer | oai:union.ndltd.org:ADTP/236187 |
| Date | January 2008 |
| Creators | Szablan, Zachary Peter, Chemical Sciences & Engineering, Faculty of Engineering, UNSW |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
Page generated in 0.003 seconds