Anionic copolymerization of isocyanates with ketenes

Diphenyl‐, phenylethyl, and phenylmethylketene have been copolymerized with phenyl isocyanate by use of sodium naphthalene in dimethylformamide (DMF) at −45°C. Reactivity ratios of phenyl isocyanate (r2) with diphenylketene (r1) were r1 = 0.10, r2 = 0.29; with phenylethylketene (r1) were r1 = 1.6, r2 = 0.10; and with phenyl methyl ketene (r1) were r1 = 4.8, r2 = 0.02. The same initiator and solvent system were used for homopolymerization of phenylethylketene and copolymerization with m‐chloro‐, p‐chloro‐, p‐methoxy‐, and m‐methoxyphenyl isocyanate as well as with phenyl isocyanate. Molecular weights ranged from 1740 to 4000. The effect of substituents on the order of isocyanate incorporation into the copolymer was m‐Cl = p‐Cl > m‐MeO > H > p‐MeO. Phenylethylketene was also copolymerized with m‐methoxyphenyl, p‐methoxyphenyl, and p‐tolyl isocyanate in tetrahydrofuran (THF) at −78°C. Molecular weights ranged from 2800 to 10,500. The least reactive isocyanate was incorporated into the copolymer to a greater extent in this solvent than in the more polar DMF. DTA showed the presence of crystallinity only in polymers of high isocyanate content. The ketenes copolymerized less readily with alkyl isocyanates, such as ethyl, n‐butyl, n‐hexyl, and cyclohexyl isocyanate, than with the aromatic isocyanates when sodium naphthalene was used in either DMF or THF.