Synthesis and crossover reaction of TEMPO containing block copolymer via ROMP

We report on the block copolymerization of two structurally different norbornene monomers (±)-endo,exo-bicyclo[2.2.1]-hept-5-ene-2,3-dicarboxylic acid dimethylester (7), and (±)-endo,exo-bicyclo[2.2.1]-hept-5-ene-2,3-dicarboxylic acid bis(1-oxyl-2,2,6,6-tetramethyl-piperidin-4-yl) ester (9) using ruthenium based Grubbs' type initiators [(PCy₃)₂Cl₂Ru(benzylidene)] G1 (PCy₃ = tricyclohexylphosphine), [(H₂IMes)(PCy₃)Cl₂Ru(benzylidene)] G2 (H₂IMes = 1,3-bis(mesityl)-2-imidazolidinylidene), [(H₂IMes)(py)₂Cl₂Ru(benzylidene)] G3 (py = pyridine or 3-bromopyridine) and Umicore type initiators [(PCy₃)₂Cl₂Ru(3-phenylinden-1-ylidene)] U1 (PCy₃= tricyclohexylphosphine), [(H₂IMes)(PCy₃)Cl₂Ru(3-phenylinden-1-ylidene)] U2 (H₂IMes = 1,3-bis(mesityl)-2-imidazolidinylidene), [(H₂IMes)(py)Cl₂Ru(3-phenylinden-1-ylidene)] U3 (py = pyridine or 3-bromopyridine) via ring opening polymerization (ROMP). The crossover reaction and the polymerization kinetics were investigated using matrix assisted laser desorption ionization mass spectroscopy (MALDI-TOF) and nuclear magnetic resonance (NMR), respectively. MALDI showed that there was a complete crossover reaction after the addition of 25 equivalents of the second monomer. NMR investigation showed that U3 gave a faster rate of polymerization in comparison to U1. The synthesis of block copolymers with molecular weights up to M(n) = 31 000 g/mol with low polydispersities (M(w)/M(n) = 1.2) is reported.