Synthesis and asymmetric polymerization of chiral maleimides bearing an aza crown ether

Abstract

Chiral N-substituted maleimide derivatives bearing L-phenylalanine-or L-leucine-introduced aza crown ether ((S)-A15C5PAMI, (S)-A15C5LMI) were synthesized from maleic anhydride, corresponding amino acids and aza crown ether, and polymerized with an organometal/chiral ligand. The number-average-molecular weights and the specific optical rotations of the polymers were 700-5600 and À105.81 to À38.31, respectively. The specific optical rotations of all polymers tended to a positive direction, Keywords: amino acid; anionic polymerization; asymmetric polymerization; aza crown ether; maleimide INTRODUCTIONThe synthesis of optically active polymers is interesting from the standpoints of the formation process, stereoregularity and asymmetric functionality. The optical activity of these polymers is dependent on the main chain forming a one-handed helical structure. The main chain structure of these optically active polymers is very important for special functions such as molecular recognition and asymmetric catalysis. To artificially form a one-handed helical structure, it is necessary to synthesize an optically active polymer by asymmetric polymerization. For example, Okamoto and coworkers [1][2][3][4] reported that the polymers obtained from the asymmetric polymerization of methacrylate derivatives bearing bulky substituents showed substantial optical activity on the basis of one-handed helical conformations.N-Substituted maleimides (RMIs) have been well known as a type of attractive monomer that provides optically active polymers through asymmetric anionic polymerization. 5,6 Because the RMI has a 1,2-disubstituted structure, poly(RMI) can be presumed to produce four types of structures: threo-diisotactic, threo-disyndiotactic, erythrodiisotactic and erythro-disyndiotactic. Erythro-diisotactic and erythro-disyndiotactic structures cannot be formed with cis-additional reactions because of steric hindrance among monomeric units due to carbonyl groups in the imide rings. 7 Trans-additional structures, that is, threo-diisotactic and threo-disyndiotactic structures, can be formed during the polymerization of RMI. Threo-disyndiotactic structures show no optical activity because the (S, S)-and (R, R)-configurational pairs exist at equivalent levels in the polymer main chains. Poly(RMI) with a threo-diisotactic structure can show optical activity when one of the asymmetric carbon pairs in the monomer unit exists in excess. Furthermore, the high continuity of the same configurational pair

Use of biomass sericin as matrices in functionalized graphene/sericin nanocomposites for the removal of phenolic compounds

“…To synthesize maleimide, a formerly explained process was used [ 15 ]. Also, functionalized graphene with maleimide was prepared according to our previously described paper [ 16 ], for preparation of maleimide functionalized graphene (MG), 1.0 g of pristine graphite, and 1.0 g of maleimide (MI) was dispersed into 20 mL of 1,2-Dichlorobenzene under ultrasonic for 1 h. The resultant mixture was kept at 50 °C and maintained for 5 days.…”

Homopolymerization and copolymerization of N‐substituted maleimides with chiral anionic initiators

“…Oishi and coworkers have also widely investigated the polymerization of RMIs. However, they all used just two methods to achieve optically active poly(RMI): (1) polymerization of chiral N ‐substituted maleimides (RMIs); (2) polymerization of achiral N ‐substituted maleimides (RMIs) with chiral anionic initiators consisting of chiral ligand/organometal complexes . Chiral initiators directly initiate anionic polymerization of RMIs, especially carbon anionic chiral initiators, to obtain an optically active poly(RMI) in the absence of chiral ligand are rarely reported.…”