Rh complex catalyzed alternating copolymerization of alkylallene or aryloxoallene with carbon monoxide: Influence of monomer structures on the reaction rate

Substituted 1,2-dienes such as cyclohexylallene, (3-phenylpropyl)allene, 1,1-dimethylallene, 1-methyl-1-phenylallene, 4-(t-butyl)phenoxyallene and (4-allenyloxy)azobenzene underwent alternating copolymerization with carbon monoxide (at approximately 1.05 atm) in the presence of a catalytic amount of Rh-complex, Rh[η3 - CH(Ar)C{C(=CHAr)CH2C(=CHAr) - CH2CH2-CH=CHAr}CH2] (PPh3)2 (A, Ar=C6H4OMe-p), to produce unsaturated polyketones - CO - C(=CRR′) - CH2 - n (R, R′=H, cyclo-C6H11; H, (CH2)3Ph; Me, Me; Me, Ph; H, OC6H4-t-Bu-4; H, OC6H4 - N=N - C6H5). NMR spectra indicated that the polymers are mainly composed of the repeating units formed via insertion of 2,3-bond of allene monomer and carbon monoxide into the polymer end. The polyketone prepared from 4-(allenyloxy)azobenzene and carbon monoxide was not fully characterized by NMR due to its low solubility in organic solvents. Molecular weights Mn (determine by GPC, based on polystyrene standards) of the five soluble polymers range from 7 200 to 27 700. Plotting molecular weights of the polyketones during polymerization showed a significant difference in the reaction rates depending on the allene monomers; the polymerization rate decreases in the order 1,1-dimethylallene > phenylallene > cyclohexylallene. Copolymerization of mixtures of 4-(allenyloxy)azobenzene and 4-methoxyphenylallene and of 4-(allenyloxy)azobenzene and 4-(t-butyl)phenoxyallene with carbon monoxide afforded soluble random copolyketones with Mn = 11 100-15 400.