N-substituted-synthesis And Polymerization Of The Oxazoline Phenyl Maleimide

N-substituted maleimides are characteristic of a rigid imide-ring and high polymerizing ability. They are often used for improving vinyl- or acrylate-polymers via copolymerization with these monomers. On the other hand, Oxazoline - a heterocyclic compound containing both oxygen and nitrogen atom - is an important functionality as a protecting group in organic synthesis. As a ligand, oxazolines have been extensively used in coordination chemistry. Especially, the optically active oxazolines have played a significant role in control the stereochemistry in many asymmetric transformations. In recent years, the synthesis and application of optically active polymers with chiral oxazoline residues are topics attracting much attention. According to the modifiable property of the maleimides matrix, we introduce oxazoline group.In the present work, we have developed an effective synthesis for a novel type of N-[0-(4-alkyloxazol-2-yl)phenyi]maleimides, .including N-[o-(4,4-dimethyl-4,5-dihydro -1,3-oxazol-2-yl)phenyl]maleimide (DMOEMI), (±)-7V-[o-(4-ethyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl]maleimide ((±)-EOPMI), and (R)-7V-[o-(4-ethyl-4,5-dihydro-l,3-oxazol-2-yl)phenyl]maleimide((R)-EOPMT). In the key step - the cyclization of amic acid - for preparation of N-[o-(4-alkyloxazol-2-yl)phenyl]maleimides, a variety of reaction parameters, such as catalyst, time, temperature were examined in detail. It has been demonstrated that the hexamethyldisilane/zinc chloride (HMDS/ZnCk) binary system exhibited an excellent catalytic activity for the cyclization reaction and a higher yield of 62% was obtained for DMOPMI under following conditions:[HMDS]/[ZnCl2]/[amic acid] = 1.5:1.1:1 in molar ratio, 60℃ 2.5 h, and THF as media. By similar procedures, both (±)-EOPMI and (ft)-EOPMI were also synthesized hi moderate yields. The products were characterized by FT-DR, 1H NMR, and elemental analysis.The polymerization behavior was studied briefly by both .radical and anionic initiating mechanism for the above monomers. As a representative, poly(DMOPMI) with Mw of 1.0 x 104was obtained in high yield of 96.3% under an anionic initiating condition. The results on FT-IR and 1H NMR spectra of the polymer indicated that the addition polymerization mainly took place in the C=C double bond in the maleimide ring. The polymerization of DMOPMI and racemic (?-EOPMI initiated by a chiral w-butyllithiurn/(-)-Sparteine in THF to yield the corresponding polymer with a very low optical activity, suggesting that a weakly asymmetric induction took place in main chain.The results on polymerization of chiral monomer (R)-EOPMI showed that the resultant polymers have relatively low molecular weights and low specific rotation, obviously, the activity of polymerization of (±)-EOPMI and (R)-EOPMI are lower than DMOPMI. The addition polymerization mainly also took place in the C=C double bond of the maleimide ring. Polymerization of racemic (±)-EOPMI were also performed with n-butyllithium and chiral ligand(Sp) in THF to obtain chiral polymers. These results suggested that asymmetric anionic polymerization taken place in main chain. The polymers from (R)-EOPMI were obtained by both radical and anionic initiators show specific rotation.Preliminary studies were carried out on the coordination ability of these polymers. The results indicated that nano magnetite composites can be prepared by in situ oxidization of iron salt in the presence of poly(DMOPMI).