Chromatographic Properties of a “Comb-like” Chiral Stationary Phase Prepared via Atom Transfer Radical Polymerization

A “comb-like” chiral stationary phase was developed using surface-initiated technique via atom transfer radical polymerization (ATRP). Chlorinated silica gel was produced as the ATRP initiator in a one-step reaction with thionyl chloride. This initiation method results in a hydrolytically stable initial Si–C bond for poly(glycidyl methacrylate) (pGMA) chains grafted on the surface of silica gel. β-Cyclodextrin (β-CD) was immobilized on the pGMA chains with ring opening reaction to prepare the chiral stationary phase. This “comb-like” chiral stationary phase with the different pGMA chain length was evaluated by enatioseparation of structurally diverse racemic compounds under reversed-phase high-performance liquid chromatography. The chromatographic results demonstrate the effective chiral separation ability of the new chiral stationary phase.

     

Synthesis of Dendritic-Linear Block Copolymers by Atom Transfer Radical Polymerization

Polymers and copolymers with complex, yet well-defined architectures are drawing significant attentions in the search for materials with excellent properties. Of these macromolecular structures, dendritic-linear block copolymers consisting of covalently bound linear and dendritic segments have shown interesting solution, solid-state, and interfacial properties. As a novel polymerization approach, atom transfer radical polymerization (ATRP) has been attracting increasing interest recently, sin…     

Homo‐ and Copolymerization of Phenacyl Methacrylate via the Atom Transfer Radical Polymerization Method

The homo‐ and copolymers via atom transfer radical (co)polymerization (ATRP) of phenacyl methacrylate (PAMA) with methyl methacrylate (MMA) and t‐butyl methacrylate (t‐BMA) was performed in bulk at 90°C in the presence of ethyl 2‐bromoacetate, cuprous(I)bromide (CuBr), and 2,2′‐bipyridine. The polymerization of PAMA was carried out at 70, 80, and 100°C. Also, free‐radical polymerization of PAMA was carried out at 60°C. Characterization using FT‐IR and ¹³C‐NMR techniques confirmed the formation of a five‐membered lactone ring through ATRP. The in situ addition of methylmethacrylate to a macroinitiator of poly(phenacyl methacrylate) [Mn=2800, Mw/Mn=1.16] afforded an AB‐type block copolymer [Mn=13600, Mw/Mn=1.46]. When PAMA units increased in the living copolymer system, the Mn values and the polydispersities were decreased (1.1<Mw/Mn<1.79). The monomer reactivity ratios were computed using Kelen‐Tüdös (K‐T), Fineman‐Ross (F‐R) and Tidwell‐Mortimer (T‐M) methods and were found to be r₁= 1.17; r₂= 0.76; r₁=1.16; r₂=0.75 and r₁=1.18; r₂=0.76, respectively (r₁=is monomer reactivity ratio of PAMA). The initial decomposition temperatures of the resulting copolymers were measured by TGA. Blends of poly(PAMA) and poly(MMA) obtained via the ATRP method have been characterized by differential thermal and thermogravimetric analyses.     

Synthesis of Fullerene-end Functionalized Poly（methyl methacrylate） via Reverse Atom Transfer Radical Polymerization

The use of the reverse atom transfer radical polymerization （RATRP） to end-functionalize poly（methyl methacrylate） （PMMA） with fullerenes, e.g. C60 and C70 was described in this paper. The Cl-terrninated PMMA was prepared via RATRP with designed molecular weight and narrow molecular weight distributions, and then directly used to react with fullerenes to produce C60（C70） terminated PMMA polymers in the presence of CuBr/Cu/bipy or FeCl2/bipy catalysts. The resultant polymers exhibit good solubility in some common organic solvents, e.g. THF, CHCl3 and toluene, and were well structurally characterized by a variety of physical techniques.     

Reverse Atom Transfer Radical Polymerization of (-)-Menthyl Methacrylate

The reverse atom transfer radical polymerization(RATRP)of (-)-menthyl methacrylate ((-)-MnMA) with AIBN(AIBM/CuCl2/bipyridine(bipy) or (-)sparteine((-)Sp)=1/2/4 initiating system in THF has been studied.The dependence of the specific rotation on molecular weight was investigated.     

Synthesis and Characterization of Star Polymer with Comb-like Poly(lauryl methacrylate) Arms by Atom Transfer Radical Polymerization via One-pot ‘Arm-First’ Method

Atom transfer radical polymerization (ATRP) was used to prepare core crosslinked star polymers with comb-like poly (lauryl methacrylate) (LMA) arms by one-pot “arm-first” method, involving the synthesis of comb-like PLMA arms, followed by their crosslinking, using a mixture of LMA monomer and ethylene glycol dimethacrylate (EGDMA) crosslinker. By adjusting the feeding time and level of EGDMA, a series of star-like polymers with various comb-like arms length and number can be obtained. The molecular architecture including radius of gyration (Rg), hydrodynamic radius (Rh) and intrinsic viscosity (η_i) etc. were characterized by a triple-detector gel permeation chromatography (GPC) equipped with a refractive index detector, viscometer detector and a multi-angle static laser light scattering (MALLS) detector. The thermal property and shearing stability of these star-like polymers were also investigated.     

Preparation of Medium Cation Exchange Stationary Phase of Polymeric Matrix and Their Chromatographic Properties

Based on the monodisperse poly（glycidyl methacrylate-co-ethylenedimethacrylate） beads （PGMA/EDMA） with macropore as a medium, a new hydrophilic medium cation exchange （MCX） stationary phase for HPLC was synthesized by a new chemically modified method. The stationary phase was evaluated with the property of ion exchange, separability, reproducibility, hydrophilicity, effect of salt concentration, salt types, column loading and pH on the separation and retention of proteins in detail. It was found that it follows ion exchange chromatographic （IEC） retention mechanism. The measured bioactivity recovery for lysozyme was （96 ± 5）%. The dynamic protein loading capacity of the synthesized MCX packings was 21.8 mg/g. Five proteins were almost completely separated within 6.0 min at a flow rate of 4 mL/min using the synthesized MCX resin. The MCX resin was also used for the rapid separation and purification of lysozyme from egg white with only one step. The purity and specific bioactivity of the purified lysozyme was found more than 95% and 70345 U/mg, respectively.     

A New Initiator Cholesteryl Chloroformate for Cupper-Based Atom Transfer Radical Polymerization of Methyl Methacrylate

The polymerization of metyl methacrylate (MMA) was studied in detail by use of CuCI/L as a catalyst and cholesteryl chloroformate (CC) as an initiator. It was found that the atom transfer radical polymerization of MMA could proceed when L equals to a multidentate aliphatic amine ligand, N,N,N‘,N“,N“-penta(methyl acrylate)diethylenetriamine (MA5-DETA), and no polymerization was occurred while L=2,2‘-bipyridine and 1,10phenanthroline. The linear proportionality of the molecular weights to the conversions and straight lines observed in ln[M]0/[M] versus time plots indicated that the present polymerization system had the typical controlled polymerization characteristics.     

Synthesis of Highly Branched Poly（ε-caprolactone） by Self-condensing Atom Transfer Radical Polymerization of Macroinimers

Fréchet et al.1 in 1995 prepared hyperbranched vinyl polymers by the technique named self-condensing vinyl polymerization (SCVP) of initiator-monomers (“inimers”) having the general structure AB*, where A stands for a double bond and B* for an initiati…     

N-Chlorosuccinimide(NCS):A Novel Initiator for Atom Transfer Radical Polymerization of Methyl Methacrylate

Atom transfer radical polymerization （ATRP） of methyl methacrylate （MMA） was achieved, using N-chlorosuccinimide （NCS） as an initiator together with catalytic system CuCl/PMDETA （N,N,N＇,N＇,N＂-pentamethyldiethylenetriamine）, CuCl/MA5-DETA （N,N＇,N＇,N＂-penta（methylacrylate）diethylenetriamine）, and CuCl/bipy （bipy= 2,2＇-bipyridyl） respectively. The results indicated that the polymerization possessed typical controlled/living radical polymerization characteristics. The analysis for terminal group of obtained polymer by ^1H NMR proved that NCS is an initiator for ATRP. In comparison with NBS, the polymerization rate was slower and the resulted polymer had narrower molecular weight distribution （MWD） when NCS was employed as the initiator.     

Study on Synthesis of Star‐Shaped Poly(ethylene oxide) by Atom Transfer Radical Polymerization

Star‐shaped poly(ethylene oxide) (PEO) was prepared by atom transfer radical polymerization (ATRP) with a 2‐bromoisobutyryl PEO ester as a macroinitiator. Divinylbenzene (DVB) and ethylene glycol dimethacrylate were employed as the coupling reagents. Several factors pertinent to star polymer formation are: type of coupling reagents and solvents, feed ratio of DVB to the macroinitiator, and reaction time. These were studied and used to optimize the star formation process. The optimum yield of star polymer was ca. 90–98%.     

Chromatographic and Spectroscopic Studies on β-Cyclodextrin Functionalized Ionic Liquid as Chiral Stationary Phase: Enantioseparation of Flavonoids

In this study, β-cyclodextrin functionalized ionic liquid was prepared by adding 1-benzylimidazole onto 6-monotosyl-6-deoxy-β-cyclodextrin (β-CDOTs) to obtain β-CD-BIMOTs. β-CD-BIMOTs were then bonded onto the modified silica to produce chiral stationary phases (β-CD-BIMOTs-CSP). The performance of β-CD-BIMOTs-CSP was evaluated by observing the enantioseparation of flavonoids. The performance of β-CD-BIMOTs stationary phase was also compared with native β-CD stationary phase. For the selected flavonoids, flavanone and hesperetin obtained a high resolution factor in reverse phase mode. Meanwhile, naringenin and eriodictyol attained partial enantioseparation in polar organic mode. In order to understand the mechanism of separation, the interaction of selected flavonoids and β-CD-BIMOTs was studied using spectroscopic methods (¹H NMR, NOESY and UV–Vis spectrophotometry). The enantioseparated flavanone and hesperetin were found to form an inclusion complex with β-CD-BIMOTs. However, naringenin and eriodictyol were not enantioseparated due to the formation of hydrogen bonding at exterior torus of β-CD-BIMOTs.

     

Atom Transfer Radical Polymerization of Styrene with 5‐Chloromethyl‐2‐hydroxy‐benzaldehyde as Initiator

Abstract

Atom transfer radical polymerization (ATRP) of styrene (St) proceeded using 5‐chloromethyl‐2‐hydroxy‐benzaldehyde as initiator, CuCl as catalyst, and N,N,N′,N′,N′‐pentamethyldiethyltriamine (PMDETA) as ligand. The results show that the polymerization is a first order reaction with respect to monomer concentration. The polymerization displayed living character as evidenced by a liner increase of monomer weight with conversation and a relatively narrow distribution (M _n/M _w ranges from 1.25 to 1.50). The end structure of PSt was analyzed by ¹H‐NMR, and PSt initiated MMA to form block copolymer (PSt‐b‐PMMA), which also proved that the polymerization could be controlled. The effects of reaction temperature and monomer to initiator mole ratio on the polymerization displayed living character were discussed.     

Three‐Arm Star Homo‐ and Block Co‐Polymers Via Atom Transfer Radical Polymerization

Star homopolymers of some vinyl monomers such as methyl methacrylate, n‐butyl methacrylate and styrene (MMA, nBMA, St.) were prepared by using a N,N,N′N′‐tetramethylethylenediamine ligand/CuBr catalytic system via atom transfer radical polymerization (ATRP). A three armed benzene based core was successfully used as initiator. Low polydispersities and regular molecular weight values were obtained in most cases, especially at low conversions. MMA and BMA showed comparable behavior where controlled and true ATRP was observed even at high conversions. However, styrene monomer recorded irregular high polydispersities at high conversions in spite of the relatively low molecular weight values. Some block copolymers were obtained using MMA homopolymer as macroinitiator with the same strategy of ATRP. ¹H‐NMR confirmed the structures of the resulting polymers. Transmission electron microscopy (TEM) proved the nano‐structure of the star polymers. The thermal behavior of the MMA star homo and copolymers was studied. The effect of the star shape on thermal behavior was very clear with respect to the linear ones.     

Enantioselective Synthesis of α-Alkoxy-Phosphonates by Chiral Phase Transfer Catalysis

Abstract

Enantioselective PTC phosphorylation of aldehydes performed in a two phase (aq. NaOH/toluene) system mediated by chiral crown ether incorporating one or two sugar units. To avoid the rearrangement of hydroxy phosphonate 3 to nonchiral mixed phosphate ester 4 the hydroxy phosphonate was trapped by alkylation to give 5.     

Synthesis of Poly （styrene-b-isoprene-b-styrene） via Nitroxide-mediated Radical Polymerization by a Novel Alkoxyamine

Bifunctional alkoxyamine bis-TIPNO derived from 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxyl （TIPNO） and α, ω-alkyl bromide by atom transfer radical addition（ATRA） was employed as “biradical initiator” for nitroxide-mediated radical polymerization（NMRP） of isoprene and styrene. The kinetics study for the polymerization of styrene at different time showed living features. The poly（styrene-b-isoprene-b-styrene） （SIS） copolymers have two glass transition temperatures, indicating the immiscibility of the corresponding blocks.     

Enantioseparation of Novel Chiral Tetrahedral Clusters on a Chiral Stationary Phase (CSP) by High Performance Liquid Chromatography

In recent years, the synthesis of chiral tetrahedral clusters has been studied extensively and various types are accessible , which are a kind of organometallic compounds with greatly growing interest due to their potential application to asymmetric reaction catalysts. As an efficient     

Liquid Chromatographic Resolution of Racemic α-Hydroxycarboxylic Acids on Ligand Exchange Chiral Stationary Phases

Two ligand exchange chiral stationary phases (CSPs) based on (S)-leucinol derivative, sodium N-((S)-1-hydroxymethyl-3-methylbutyl)-N-undecylaminoacetate, and (R)-phenylglycinol derivative, sodium N-((R)-2-hydroxy-1-phenylethyl)-N-undecylaminoacetate, covalently bonded to silica gel have been successfully applied in the resolution of nine -hydroxycarboxylic acids. The latter was more effective than the former, the separation factors () being 1.05 to 2.12 while the resolution factors (R_S) varying from 0.18 to 5.29 on the latter. The chromatographic resolution behaviors were dependent on the type and the content of organic modifier and the content of CuSO₄ in aqueous mobile phase and the column temperature. A possible chiral recognition mechanism was also proposed based on the chromatographic resolution behaviors.