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

Abstract

Novel optically active aromatic isocyanates, 3-((S)-(α-methylbenzyl)carbamoyl)phenyl isocyanate ((S)-3MBCPI) ([α]36525 +63°) and 4-((S)-(α-methylbenzyl)carbamoyl)phenyl isocyanate ((S)-4MBCPI) ([α]36525 +181°), were synthesized and homopolymerized or copolymerized with m-methoxyphenyl isocyanate (mMeOPI) with an anionic initiator in THF at −98 °C. Poly((S)-3MBCPI) showed a very large levorotatory specific rotation ([α]36525 −1969°) 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 [α]36525 +1000° to a constant value ([α]36525 +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 1H NMR spectroscopy.