Chiral methacrylates, that is, cholesteryl (ChMOC) and l‐menthyl (MnMOC) N‐(2‐methacryloyloxyethyl)carbamates, were synthesized from 2‐methacryloyloxyethyl isocyanate and cholesterol and l‐menthol, respectively. Radical polymerizations of ChMOC and MnMOC gave number‐average molecular weights for poly(ChMOC) and poly(MnMOC) of up to 3.74 × 104 and 9.39 × 104, respectively, and the specific rotations ([α] 25435) were −43.1° to −47.7° and −87.6° to −89.0°, respectively. Temperature dependence of the specific optical rotation was observed for poly(ChMOC) but not for poly(MnMOC). The hydrogen bonds based on urethane segments for poly(ChMOC) were stronger than those for poly(MnMOC) according to IR spectra. In addition, the chiroptical properties of poly(ChMOC) were slightly affected by temperature in the presence of trifluoroacetic acid acting as an inhibitor for the formation of hydrogen bonds. Therefore, poly(ChMOC) may have a regular conformation due to hydrogen bonds and interaction between cholesteryl groups. Radical copolymerizations of ChMOC with styrene, methyl methacrylate, N‐cyclohexylmaleimide, and N‐phenylmaleimide were performed with 2,2′‐azobisisobutyronitrile in tetrahydrofuran at 60 °C. Monomer reactivity ratios and Alfrey–Price Q–e were determined. Chiroptical properties of the copolymers were influenced by co‐units. Thermal and X‐ray diffraction analyses were performed for the homopolymers and copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4315–4325, 2000
ABSTRACT:New chiral methacrylate, (S)-2-methoxy-1,1'-binaphthyl-2'-(N-methacryloyloxyethy])carbamate (MBi-MOC), was synthesized from 2-methacryloyloxyethyl isocyanate and 1,1'-binaphthalene-2,2'-diol. Radical polymerizations of MBiMOC were performed in several solvents to obtain the corresponding chiral polymers. Specific optical rotation of poly(MBiMOC) changed by the measurement temperature, which may be attributed in part to change of conformation caused by hydrogen bonds between urethane segments. From the results of copolymerizations of MBiMOC with styrene and methyl methacrylate, monomer reactivity ratios (r1, r2) and Alfrey-Price Q-e were determined and chiroptical properties of the copolymers were affected by co-units. Three types of chiral stationary phases (CSPs), poly(MBi-MOC)-coated-silica gel (CSP-I), poly(MBiMOC)-bonded-silica gel (CSP-II), and (S)-MeBinol-bonded-silica gel (CSP-III) were prepared from silica gel, MBiMOC, and (S)-MeBinol. The CSPs resolved racemates some using n-hexane/2-propanol as mobile phase for high performance liquid chromatography (HPLC). Difference in chiral resolution ability between CSP-I, CSP-II, and CSP-III was observed, suggesting that the chiral recognition ability ofpoly(MBiMOC) may be based on the higher-ordered structure of the polymer.KEY WORDS 2-Methacryloyloxyethyl Isocyanate/ Radical Polymerization/ Monomer Reactivity Ratios I Chiral Stationary Phase/ High Performance Liquid Chromatography/ Recently, a wide variety of chiral stationary phases (CSPs) have been developed for the separation of enantiomers by high performance liquid chromatography (HPLC). 1 Although many kinds of synthetic chiral polymers have been applied to the CSPs, there have been few reports on preparation of CSPs for HPLC from polymethacrylates bearing a chiral pendant group. 2 The reason may be that low chiral recognition ability of the chiral pendant group used and/or the absence of the stable higher-ordered structure of the polymers. 2 Only Tamai and Miyano et al. 3 synthesized optically active polymethacrylates bearing a 1,1'-binaphthalene moiety as pendant group, and investigated on optical resolution ability as a chiral adsorbent for HPLC. However, the chiral recognition ability of the polymers was conferred by mainly interaction between the individual 1,1'-binaphthalene units and the racemates. 3 It is well known that polymethacrylamides bearing a chiral pendant group are served as CSPs with outstanding recognition ability due to conformation controlled by hydrogen bonds between amide groups. Blaschke et al. 4 and Arlt et al. 5 reported the synthesis of many chiral polymethacrylamides from a-amino acids and their chiral recognition ability. We reported previously on the synthesis of new chiral polymethacrylates bearing urethane moieties as source of hydrogen bonds from 2-methacryloyloxyethyl isocyanate (MOI) and their chiral recognition ability. 6 MOI is a difunctional monomer with both a reactive isocyanate group and a polymerizable double bond, and is covenient and widely used for c...
Chiral poly(acrylamide) macromonomers (PMB-1, PMB-2, PPAE-1, and PPAE-2) were synthesized from 2-methacryloyloxyethyl isocyanate and prepolymers, that is, poly[(S)-methylbenzyl acrylamide] or poly(L-phenylalanine ethylester acrylamide with a terminal carboxylic acid or hydroxy group. Radical homopolymerizations of poly(acrylamide) macromonomers were carried out under several conditions to obtain the corresponding optically active polymers. A strong temperature dependence on the specific optical rotation was observed for poly(PPAE-2) in comparison with that for the corresponding prepolymer. This might have resulted from a change in the conformation caused by hydrogen bonds between polymer-graft branches in the polymacromonomer. Radical copolymerizations of poly(acrylamide) macromonomers with styrene and methyl methacrylate were performed with azobisisobutyronitrile in tetrahydrofuran at 60°C. Chiroptical properties of the copolymers were slightly influenced by comonomer units. Chiral stationary phases were prepared by the radical polymerization of poly-(acrylamide) macromonomers in the presence of silica gel containing vinyl groups on the surface. Some racemic compounds such as menthol and mandelic acid were resolved on the chiral stationary phases for high-performance liquid chromatography. The conformation based on hydrogen bonds between polymer-graft branches in the polymacromonomers may play an important role in chiral discrimination.
Four new chiral methacrylates bearing urethane bonds and N, N-dibenzylamino groups (RMOC) were synthesized from 2-methacryloyloxyethyl isocyanate (MOil and four chiral alcohol derivatives of a-amino acids, Lvaline, L-leucine, D-phenylglycine, and L-phenylalanine. Radical polymerizations of RMOC were performed under various conditions to obtain the corresponding poly(RMOC) with number average molecular weights (Mn) of 2.4 X 10 4-6.4 X 10 4 • Poly(RMOC) has hydrogen bonds based on urethane segments in solvent and exhibited negative (levo) rotation. Specific optical rotations of poly(RMOC) were slightly influenced by solvent and temperature. Radical copolymerizations of RMOC with styrene (ST) and methyl methacrylate (MMA) were performed with AIBN in toluene at 60°C. Monomer reactivity ratios (r 1 , r 2) and Alfrey-Price Q-e were determined. Chiroptical properties of the copolymers were scarcely affected by co-units of ST and MMA. Chiral stationary phases (CSPs) for high performance liquid chromatography (HPLC) were prepared from poly(RMOC) and silica gel and optical resolution ability was investigated. CSPs resolved some racemic compounds (1-5) using methanol/water as mobile phase.
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