IN-SITU CATALYST SYSTEMS FOR RING-OPENING METATHESIS POLYMERIZATION

Several new in situ tungsten catalyst systems for ring-opening metathe sis polymerizations (ROMP) by reaction injection molding (RIM) have be en developed by adding BF3 promoter to binary catalyst systems, by usi ng metal hydride cocatalysts, and by altering the ligands on the proca talyst metal center. BF3 etherates improved catalyst efficiency and re duced induction times for formation of active catalysts from reaction of aryloxytungsten complexes [e.g., (ArO)(y)WXx)] with organotin hydri des. Coordinatively unsaturated cationic intermediates, such as [(ArO) (y)WXx-1](+) BF3X-, are proposed to facilitate formation of the active catalysts. Tougher poly(dicyclopentadiene) (polyDCPD) composites were produced using < 5 wt % of styrene-butadiene block copolymers due to formation of small ''shell-core'' rubber morphologies when BF3 promote r was added to the catalyst system. Nonalkylating metal hydrides besid es R3SnH, including (PPh3)(2)CuBH4, (PPh3CuH)(6), and Cp2ZrClH, were s hown to be cocatalysts. The optimum 2 : 1 stoichiometric ratio of orga notin hydride cocatalyst to tungsten, revealed by BF3-promoted catalys t systems, and W-V EPR resonances (g approximate to 1.7) observed in t he reaction of aryloxytungsten with organotin hydride are consistent w ith an overall reduction and reoxidation mechanism for formation of th e active metathesis catalysts. Some tungsten complexes derived from 9- hydroxyffuorene, 2,2'- (and 4,4')-biphenols, and 1,4-hydroquinones wer e found to be very reactive procatalysts, even in the absence of cocat alyst in some cases. These procatalysts also were paramagnetic, charac terized by unusual EPR spectra consistent with W-V (g = 1.6-1.9) and ' 'ligand-centered'' (g = 2.003) resonances. Valence tautomeric species, analogous to catecholate-semiquinonate complexes, are proposed. (C) 1 997 John Wiley & Sons, Inc.