Copolymerization of High Strain and Low Strain Monomers by Ring-Opening Metathesis Polymerization

Abstract

Ring-opening metathesis polymerization is an attractive method for synthesizing polymers of defined molecular weight and narrow polydispersity. However, elucidating the kinetics of the copolymerization of monomers is an important step that must be made prior to studying and creating polymers with desirable properties tailered to specific applications. This thesis determined the reactivity ratios of two copolymerizations using the first-generation Grubbs catalyst: the copolymerization of exo-oxanorbornene anhydride and cyclooctene and the copolymerization of exo-oxanorbornene anhydride and cyclopentene. The reactivity ratios determined are rOxaN = 0.82 ± 0.07 and rCOE = 0.004 ± 0.013, and rOxaN = 0.32 ± 0.10 and rCP = 0 ± 0.02, respectively. These reactivity ratios were determined by fitting experimental data to the classical copolymerization model accredited to Mayo, Lewis et al., Wall et al., and Alfrey et al. for the exo-oxanorbornene anhydride and cyclooctene copolymerization and to the reversible copolymerization model derived by Torre et al. for the exo-oxanorbornene anhydride and cyclopentene copolymerization. Because the reactivity ratios for both copolymerizations are below unity, both have azeotropic compositions. These were found to be "!"#$ = 0.846 and "%!& = 0.154 for the copolymerization of exo-oxanorbornene anhydride and cyclooctene and "!"#$ = 0.594 and "%' = 0.406 for the copolymerization of exo-oxanorbornene anhydride and cyclopentene. Both copolymerizations additionally exhibited “livingness” with an initial decrease in the polydispersity indices, after which they began to increase due to cross metathesis reactions occurring within and between polymer chains. These findings can be used to predict the resulting polymer chain sequence for different monomer feed ratios and the conversions to which this sequence can be maintained before secondary metathesis becomes significant. With the determined azeotropic composition, compositionally uniform chains can also be made with these copolymerizations. These characteristics can open doors to creating copolymers of controlled structure, functionality, and material properties.