Synthesis and conformational characteristics of poly(phenyl isocyanate)s bearing an optically active ester group

Optically active phenyl isocyanates (1-9) bearing an optically active ester group were synthesized and polymerized with an achiral anionic initiator. The resulting polymers from 1 and 4-9 showed, a much greater specific rotation than that of the corresponding monomer and an intense circular dichroism (CD) band caused by the main-chain absorption, indicating that these polymers have a predominantly one-handed helical conformation in solution. On the other hand, the polymers obtained from 2 and 3 showed a much smaller specific rotation and a weaker CD band than poly-1, which suggests that, as the distance between the polymer main chain and the asymmetric center on the side chain increases, the asymmetric center cannot effectively induce an excess of one helical twist sense of the polymer main chain at room temperature, However, the specific rotation and CD intensity of poly-2 greatly increased because of a predominantly one-handed helical conformation at low temperatures. The polymers obtained from 3-9 did not shaw such a temperature effect on conformational change. Specific rotation of the copolymers of chiral 8 and achiral 10 changed from a positive to a negative value with an increase in the content of the optically active unit. The helicity of the copolymer may depend on the composition.