Synthesis and conformation of optically active poly(phenyl isocyanate)s bearing an ((S)-(α-methylbenzyl)carbamoyl) group

Novel optically active aromatic isocyanates, 3-((S)-(alpha-methylbenzyl)carbamoyl)phenyl isocyanate ((S)-3MBCPI) ([alpha](365)(25) +63 degrees) and 4-((S)-(alpha-methylbenzyl)carbamoyl)phenyl isocyanate ((S)-4MBCPI) ([alpha](365)(25) +181 degrees), were synthesized and homopolymerized or copolymerized with m-methoxyphenyl isocyanate (mMeOPI) with an anionic initiator in THF at -98 degrees C. Poly((S)-3MBCPI) showed a very large levorotatory specific rotation ([alpha](365)(25) -1969 degrees) and an intense CD absorption due to a predominantly one-handed helical conformation of the polymer main chain. Copolymers of (S)-3MBCPI with mMeOPI showed much larger specific rotation than that expected from the (S)-3MBCPI content. The intensity of the specific rotation of the copolymer of [mMeOPI]/[(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 [alpha](365)(25) +1000 degrees to a constant value ([alpha](365)(25) +2059 degrees). 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 H-1 NMR spectroscopy.