Studies on the ring-opening metathesis polymerization of functionalised bicyclic olefins using well-defined molybdenum initiators
This thesis describes studies into the living ring-opening metathesis polymerization (R.O.M.P.) of several fluorinated norbomenes and norbomadienes, using a series of well-defined initiators of general formula Mo(N-2,6-i-Pr(_2)-C(_6)H(_3))(CHR)(OR')(_2).Chapter 1 highlights areas of R.O.M.P. and of fluoropolymers of relevance to the general themes of the thesis. Chapter 2 describes the R.O.M.P. of 2,3-bis(trifluoromethyl)bicyclo[2.2.1] hepta-2,5-diene, using both Mo(N-2,6-i-Pr(_2)-C(_6)H(_3))(CHCMe(_2)Ph)(OCMe(_3))(_2) and Mo(N-2,6-i-Pr(_2)-C(_6)H(_3))(CHCMe(_2)Ph)(OCMe(CF3)(_2))(_2). In the former case a very high trans polymer has previously been reported; by changing the ancillary alkoxide ligands to hexafluorobutoxides the geometry of die polymer is completely reversed to very high cis. Dielectric measurements on both materials have been carried out and these have been used to determine the tacticity of the polymers in conjunction with high frequency (^13)C N.M.R. spectroscopy. This information has then been considered in terms of mechanistic implications. Chapter 3 details how an equilibrium mixture of the two initiators used in the previous chapter can provide access to any desired cis and trans content poly[1,4- (2,3-bis(trifluoromethyl) cyclopentenylene) vinylene]. The (^13)C N.M.R. spectra of a series of such intermediate samples are assessed and the observed splitting of the methylene resonance is described. This information is combined with preliminary dielectric measurements to arrive at a full unambiguous assignment of polymer microstructure. Chapter 4 continues the theme of controlling the stereoregular nature of poly[l,4-(2,3-bis(trifluoromethyl)cyclopentenylene) vinylene] synthesized from the four-coordinate 'Schrock' initiators. A series of experiments are described which investigate the effect of chiral components at or near the metal centre in an attempt to increase the selectivity of one face of the active site towards the approach of the monomer. Most of these are found to be ineffective in terms of changing the tacticity of the polymer produced. However, the employment of chiral bidentate alkoxides has been found to exhibit some influence which is described. Chapter 5 reports on the synthesis of three other related fluoropolymers using similar techniques to those employed in the previous chapters. (^13)C N.M.R. spectroscopy has again been used to determine the stereoregularity of the polymers prepared. Attention is then turned to the first-ever syntheses of fluorinated block- copolymers via living R.O.M.P.. These species have been fully characterised and indeed shown to possess genuine block structures. Chapter 6 presents experimental details for chapters 2-5.