synthesis of polypseudorotaxanes and polyrotaxanes via ring-opening olefin metathesis polymerization of [2]catenanes
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In the first part of this dissertation is described a novel synthetic method to access polypseudorotaxanes, a type of mechanically interlocked polymer where many macrocycles are threaded onto an acyclic polymer backbone that lacks bulky end groups. Synthesis of well-defined polypseudorotaxanes is an attractive area in the field of polymer chemistry due to the unique properties of these molecules. Our group reported a novel synthetic strategy to obtain new main-chain polypseudorotaxanes via entropy-driven ring-opening metathesis polymerization (ED-ROMP) of [2]catenanes. In our synthetic method, a Sauvage-type [2]catenane was polymerized via ED-ROMP to provide a reasonably high molecular weight main-chain polypseudorotaxane. Key to this approach, the monomer, a Sauvage-type [2]catenane, was prethreaded and the resulting polymeric assembly was robust enough to keep the macrocycles on the polymer backbone. These advantages of the Sauvage-type [2]catenane allowed us to access a polypseudorotaxane with effectively saturated with threaded macrocycles via ED-ROMP. In the second part of this dissertation is described the first random entropy-driven ring-opening metathesis copolymerization of a macrocyclic olefin monomer and an olefinic [2]catenane comonomer to control the linear number density of threaded macrocycles in main-chain polypseudorotaxanes. It has been known that the density of the threaded macrocycles influences the physical properties of the polypseudorotaxanes. So far, most polypseudorotaxanes have been synthesized via either solution-phase treatment of polymer with macrocycles or various polymerizations of monomers in the
presence of macrocycles. However, these methods cannot control the macrocycle density on the polymer backbone. In this method, we exactly control the specific average linear number density of macrocycles threaded on the polymer backbone from 0% to 100% saturation by adjustment of the monomer feed ratio. In the third and fourth parts of this dissertation, we introduce synthetic methods to access polyrotaxanes with terminal stoppers and polyrotaxanes with internal stoppers. Polyrotaxanes are compounds in which multiple cyclic molecules are threaded and trapped on a polymer chain containing bulky end groups. The synthesis of polyrotaxanes with terminal stoppers was achieved via ring-opening metathesis polymerization (ROMP) of a [2]catenane with a modified initiator containing a bulky end group followed by termination with a chain transfer agent containing a bulky stopper. The synthesis of polyrotaxanes with internal stoppers was accomplished by copolymerization of a [2]catenane and a comonomer containing a bulky group in the presence of Grubbs’ catalyst.