Helical structure of oligo- and poly(m-substituted phenyl isocyanate)s bearing an optically active end-group

Abstract

Oligomerization of phenyl isocyanate derivatives, such as m-methoxyphenyl isocyanate (mMeOPI), 3.5-dimethylphenyl isocyanate (3,5MePI), and m-chlorophenyl isocyanate (mClPI), bearing a substituent al meta position was carried out by using the lithium amide (Li-(-)-MMP) of (S)-(-)-2-(methoxymethyl)pyrrolidine as an initiator to obtain the oligomers containing an optically active group at the initial chain end (α-end). When the reaction was terminated with HCl-methanol. the oligomers of various degree of polymerization (DP) were isolated for mMeOPI and 3,5MePI. but were not for mClPI. However. oligo(mClPI)s were obtained when the reaction was terminated with acetic anhydride to introduce an acetyl group at the α-end. The obtained oligomers were separated in terms of DP using supercritical fluid chromatography (SFC) and the specific rotation of each oligomer was estimated. The highest specific rotation [α]36525 was observed at DP = 13-14 for oligo(mMeOPI), DP=15 for oligo(3,5MePI), and DP=10 for oligo(mClPI). These results suggest that the one-handed helical structure can persist to a longer distance as the electron-donating power of the meta substituents increases.