Solid-state olefin metathesis.

摘要

While organic reactions are most often performed in the liquid or melt state, the investigation of solid-state organic conversions and solid-state polymerization (SSP) have received varying degrees of attention for several decades now. Solid-state polymerization is traditionally divided into two classes: crystal-to-crystal polymerization, well established by Wegner; and equilibrium polycondensation of semicrystalline polymers, which is widely used in industry. The principles governing these two types of polymerization are quite different, for the former is based on topological chemistry, while the latter is thought to occur in the amorphous region of semicrystalline polymers.; Olefin metathesis is an astonishing chemical phenomenon, whereby a single chemical reaction has become widely used and studied in several, very different fields of chemistry, in both academic and industrial settings. The principle mission of this work is to demonstrate that a particular mode of olefin metathesis, acyclic diene metathesis (ADMET), can operate in the solid state using the same principles used for semicrystalline condensation polymers in industry. Experiments were aimed at mimicking the industrial processes, including a prepolymerization period in the melt state, extrusion of this prepolymer to a smaller particle size, and flow of an inert gas (or vacuum) through the reaction vessel to aid in condensate removal. In most cases of ADMET, the condensate that is released is ethylene, which gives it a distinct advantage over polyester, polyamide, and polycarbonate industrial processes in that the condensate is extremely volatile (BP = -104°C), and therefore high temperatures are not required for condensate removal to drive the equilibrium toward high polymer.; The "benchmark" hydrocarbon monomer, 1,9-decadiene, was chosen for the initial work because it lacks any polar or protic functionality that could react or complex with the metathesis catalysts. Steady increase in molecular weight was observed in the solid state, as low as room temperature, with the first- and second-generation Grubbs ruthenium catalysts. Similar trends of molecular weight increase were observed with monomers of varying functionality and architecture, which included ketone and alcohol functionalized monomers and a polystyrene graft copolymer. Conclusions with potential industrial implications were drawn from thermal analysis. We believe that low molecular weight oligomer and unreacted monomer act as plasticizers for the promotion of solid-state polymerization. In experiments where these species were removed, no significant molecular weight increase was observed. (Abstract shortened by UMI.)