Chain-growth polymerization ring opening metathesis

In 1991 we introduced olefin metathesis as a tool for direct synthesis of PV polymers and copolymers [2]. In general, two ways exist for a metathesis chain growth process ring opening metathesis polymerization of a cyclic olefin (ROMP) and metathesis polycondensation of an acyclic diene (ADMET). We have tested both possibilities (s. Eqs. 1 2) [2-5]. A stable, tungsten based Schrock-type alkylidene complex W(=NPh - ) (=CHPh"- ) [OCMe(CF3)2l2 (THF) (described by Grubbs et al [6]) served as catalyst (Scheme 1). 

The reactive intermediates used in chain-growth polymerizations include radicals, carbanions, carbocations, and organometallic complexes. Of the three common metal catalyzed polymerizations - coordination-insertion, ring-opening metathesis and diene polymerization - the last appears to possess the greatest tolerance toward protic solvents. The polymerization of butadiene in polar solvents was first reported in 1961 using Rh salts [18]. It was discovered that these polymerizations could be performed in aqueous solution with an added emulsifier (sodium dodecyl sulfate, for example). 

Dense carbon dioxide represents an excellent alternative reaction medium for a variety of polymerization processes. Numerous studies have confirmed that CO2 is a potential solvent for many chain growth polymerization methods, including free-radical, cationic, and ring-opening metathesis polymerizations. Carbon dioxide has also been demonstrated to be an effective solvent for step-growth polymerization techniques. Advances in the design and synthesis of surfactants for use in CO2 will allow compressed CO2 to be utilized for a wide variety of polymerization systems. These advances may enable carbon dioxide to replace hazardous VOCs and CFCs in many industrial applications, making CO2 an enviromentally responsible solvent of choice for the polymer industry. 

ADMET is a step-growth polymerization, a process very different from ring-opening metathesis polymerization (ROMP), which is a chain-growth polymerization process [19]. 

Monitoring and evaluation of the crossover reaction in ring-opening metathesis polymerization (ROMP) via MALDI methods were reported recently by Binder et al. [97]. The crossover reactions as well as the polymerization kinetics of the various monomers were studied in the presence of different catalysts by kinetic analysis and MALDI MS. Whereas the classical kinetic analysis enabled the qualitative monitoring of the chain-growth reaction, MALDI method allowed the monitoring of the reaction directly at the point of the crossover reaction, thns enabling a better evalnation of the different monomers and catalysts employed in the polymerization reactions. 

---