Synthesis and Conformation of Optically Active Poly(phenyl isocyanate)s Bearing an ((S)-(α-Methylbenzyl)carbamoyl) Group

Novel optically active aromatic isocyanates, 3-(( S )-(α-methylbenzyl)carbamoyl)phenyl isocyanate (( S )-3MBCPI) ([α] 365 25 +63°) and 4-(( S )-(α-methylbenzyl)carbamoyl)phenyl isocyanate (( S )-4MBCPI) ([α] 365 25 +181°), were synthesized and homopolymerized or copolymerized with m -methoxyphenyl isocyanate ( m MeOPI) with an anionic initiator in THF at −98 °C. Poly(( S )-3MBCPI) showed a very large levorotatory specific rotation ([α] 365 25 −1969°) and an intense CD absorption due to a predominantly one-handed helical conformation of the polymer main chain. Copolymers of ( S )-3MBCPI with m MeOPI showed much larger specific rotation than that expected from the ( S )-3MBCPI content. The intensity of the specific rotation of the copolymer of [ m MeOPI]/[( S )-3MBCPI] = 91/9 greatly increased with a decrease in temperature, but that of poly(( S )-3MBCPI) showed almost no change, suggesting that poly(( S )-3MBCPI) may take a perfectly single-handed helical conformation in solution even at room temperature. Poly(( S )-4MBCPI) showed a large dextrorotatory specific rotation opposite to that of poly(( S )-3MBCPI). This rotation of poly(( S )-4MBCPI) gradually increased in THF with time from [α] 365 25 +1000° to a constant value ([α] 365 25 +2059°). The GPC and CD analyses of the polymer suggest that this change in specific rotation with time may be caused by a slow conformational change. Poly(( S )-3MBCPI) and poly(( S )-4MBCPI) exhibited chiral recognition toward (±)-1,1‘-bi-2-naphthol in 1 H NMR spectroscopy.