Optically Active 4‐Substituted (S)‐2‐Phenyl‐2‐oxazolines

(R)‐4‐Hydroxymethyl‐2‐phenyl‐2‐oxazoline (R)‐ 1 ) was prepared from (L)‐serine. The respective tosylate ((S)‐ 2 ) was converted into sulfides (S)‐ 4 and (S)‐ 5 , and sulfone (S)‐ 6 , useful starting materials for the elaboration of additional chiral centers. A previously reported [ α]_D ²⁵ value for (R)‐ 4 is corrected.     

Chiral separation of D,L‐tyrosine through nitrocellulose membrane

Enantioselective membrane was prepared using nitrocellulose as membrane material. The flux and permselective properties of membrane using water solution of D ,L ‐tyrosine as feed solution were studied. The top surface and cross‐section morphology of the resulting membrane were examined by scanning electron microscopy. The optical resolution of over 85% enantiomeric excess was achieved when the enantioselective membrane was prepared with 25 wt % nitrocellulose and 15 wt % N,N‐dimethylformamide in the casting solution of methanol, 10°C temperature of water bath for the gelation of the membrane, and the operating pressure and the feed concentration of the D ,L ‐tyrosine were 6 kgf/cm² and 0.25 mg/mL, respectively. Since the nitrocellulose contains a large amount of chirality active carbons on the backbone structure and is possible to form helical structure, it is considered to be the reason for the enantioselectivity of the membrane. This is the first report that nitrocellulose can be used as a membrane material. This work indicates that the large‐scale purification of chiral molecules from racemic mixtures will be realized by the enantioselective membrane technique in the near future and that the enantioselective nitrocellulose membrane could soon become very attractive for industrial uses. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of operation conditions in the pervaporation of ethanol–water mixtures with poly(1‐trimethylsilyl‐1‐propyne) membranes

Poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) is known to show preferential permeation of ethanol in the pervaporation of ethanol–water mixture. Although this polymer presents good characteristics for the separation of organic–water solutions, operation conditions and membrane characteristics, such as thickness, affect its pervaporation performance. The effect of temperature and feed concentration on pervaporation was studied. During pervaporation of 10 wt % ethanol–water solution, the separation factor (α_H2O^EtOH) remains almost constant, whereas the permeation flux (F) increases exponentially with operation temperature. On the other hand, the separation factor decreases, whereas the permeation flux increases with ethanol content in the feed mixture. The membrane thickness also affects the performance of PTMSP polymer films: selectivity increases sharply with membrane thickness up to 50 μm, whereas it remains constant for thicker membranes. The permeation flux decreases with membrane thickness in the whole range studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94:1395–1403, 2004     

DNA adsorption on poly(N,N‐dimethylacrylamide)‐grafted chitosan hydrogels

In this study, poly(N,N‐dimethylacrylamide) grafted chitosan (PDMAAm‐g‐CT) hydrogels were prepared for deoxyribonucleic acid (DNA) adsorption. Instead of directly grafting the N,N‐dimethylacrylamide (DMAAm) monomer onto the chitosan (CT) chains, poly(N,N‐dimethylacrylamide) with carboxylic acid end group (PDMAAm‐COOH) was firstly synthesized by free‐radical polymerization using mercaptoacetic acid (MAAc) as the chain‐transfer agent and then grafted onto the CT having amino groups. The synthesis of PDMAAm‐COOH and its grafting onto the CT chains were confirmed by attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. From gel permeation chromatography measurements, the number‐average molecular weight (M _n) and polydispersity index of PDMAAm‐COOH were found as 2400 g/mol and 2.3, respectively. The PDMAAm‐g‐CT hydrogels were utilized as the adsorbents in DNA adsorption experiments conducted at +4°C in a trisEDTA solution of pH 7.4. The hydrogels produced with higher PDMAAm‐COOH content exhibited higher DNA adsorption capacity. The DNA adsorption capacity up to 4620 μg DNA/g dry gel could be achieved with the PDMAAm‐g‐CT hydrogels prepared in 80.0 wt % PDMAAm‐COOH feed concentration. This value is approximately seven times higher than that of CT alone. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of polymers blend ratio binder on electrochemical and morphological properties of PC/S‐PVC‐based heterogeneous cation‐exchange membranes

In this research, heterogeneous cation exchange membranes were prepared by the casting‐solution technique using polycarbonate (PC) and S‐polyvinylchloride (S‐PVC) as binders along with cation exchange resin as functional group agent. The effect of blend ratio (PC to S‐PVC) of polymer binder on structure and electrochemical properties of the prepared membranes were elucidated. The morphology of the prepared membranes was investigated by scanning electron microscopy (SEM) and scanning optical microscopy (SOM). The images show that the addition of PC ratio in the casting solution results in formation of a membrane with more inner cavities and micro voids. The electrochemical properties and mechanical strength tests were conducted. Water content, ion exchange capacity, ion permeability, flux, current efficiency, and oxidative stability of the prepared membranes initially were decreased by increasing the PC ratio in the casting solution and then it began to increase. The blending of S‐PVC and PC polymers results in membranes with lower mechanical strength. Membrane potential, surface charge density, perm‐selectivity, cationic transport number, electrical resistance, and energy consumption were initially improved by the increment of PC ratio in the casting solution and then it decreased. The membrane with 70% PC exhibited the highest flux, maximum current efficiency, and minimum energy consumption. However, the selectivity of this membrane was low compared with the other prepared membranes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Chemoenzymatic Preparation of Enantiopure Homoadamantyl β‐Amino Acid and β‐Lactam Derivatives

Racemic cis‐10‐azatetracyclo[7.2.0.1^2,6.1^4,8]tridecan‐11‐one was prepared from homoadamant‐4‐ene by chlorosulfonyl isocyanate addition. The transformation of the β‐lactam to the corresponding β‐amino ester followed by Candida antarctica lipase A‐catalyzed enantioselective (E>>200) N‐acylation with 2,2,2‐trifluoroethyl butanoate afforded methyl (1R,4R,5S,8S)‐5‐aminotricyclo[4.3.1.1^3,8]undecane‐4‐carboxylate and the (1S,4S,5R,8R)‐butanamide with>99% ee at 50% conversion. Alternatively, transformation of the β‐lactam to the corresponding N‐hydroxymethyl‐β‐lactam and the following Pseudomonas cepacia (currently Burkholderia cepacia) lipase‐catalyzed enantioseletive O‐acylation provided the (1S,4S,6R,9R)‐alcohol (ee=87%) and the corresponding (1R,4R,6S,9S)‐butanoate (ee>99%). In the latter method, competition for the enzyme between the (1R,4R,6S,9S)‐butanoate, 2,2,2‐trifluoroethyl butanoate and the hydrolysis product, butanoic acid, tended to stop the reaction at about 45% conversion and finally gave racemization in the (1S,4S,6R,9R)‐alcohol with time.     

Optically Pure 1,2‐Bis[(o‐alkylphenyl)phenylphosphino]ethanes and Their Use in Rhodium‐Catalyzed Asymmetric Hydrogenations of α‐(Acylamino)acrylic Derivatives

Optically pure (S,S)‐1,2‐bis[(o‐alkylphenyl)phenylphosphino]ethanes 1a–d were prepared in four steps from phenyldichlorophosphine via phosphine‐boranes as the intermediates. The rhodium complexes 5a–d of these diphosphines were used for the asymmetric hydrogenations of α‐(acylamino)acrylic derivatives including β‐disubstituted derivatives. Markedly high enantioselectivity (78–>99%) was observed for the reduction of β‐monosubstituted derivatives. β‐Disubstituted derivatives were also reduced in considerably high enantioselectivity (up to 90%). The single crystal X‐ray analysis of the rhodium complex 5c of (S,S)‐1,2‐bis[phenyl(5′,6′,7′,8′‐tetrahydronaphthyl)phosphino]ethane ( 1c) revealed its δ‐type structure with face orientation of the two tetrahydronaphthyl groups and edge orientation of the two phenyl groups. This conformation corresponds to that of the rhodium complex of 1,2‐bis[(o‐methoxyphenyl)phenylphosphino]ethane (DIPAMP); the rhodium complex of (R,R)‐DIPAMP, whose chirality at phosphorus is opposite that of 5c , exhibits a λ‐type structure with the face orientation of the two o‐methoxyphenyl groups and the edge orientation of the two phenyl groups. The conformational similarity of these rhodium complexes as well as the stereochemical outcome in the asymmetric hydrogenations means that the coordinative interaction of the methoxy group of DIPAMP with rhodium metal is not the main factor that affects asymmetric induction.     

Cyclometalated N‐Heterocyclic Carbene‐Platinum Catalysts for the Enantioselective Cycloisomerization of Nitrogen‐Tethered 1,6‐Enynes

Platinum(II) complexes which combine six‐membered N‐heterocyclic carbene‐containing metallacyclic units and monodentate chiral phosphines have been prepared. The key step of their synthesis is the intramolecular oxidative addition of N‐2‐iodobenzylimidazolylidene‐platinum(0)‐diene complexes in the presence of the chiral phosphorus ligands. The platinum(II) metallacycles have been used as well‐defined pre‐catalysts for the enantioselective cycloisomerization of nitrogen‐tethered 1,6‐enynes into 3‐azabicyclo[4.1.0]hept‐4‐enes. High enantiomeric excesses have been obtained with either Monophos or phenyl‐Binepine based catalysts (ees=82–96%), although phenyl‐Binepine outperforms Monophos in these reactions. The absolute configuration of the final 3‐azabicyclo[4.1.0.]heptenes has been established by X‐ray diffraction studies. The method has been extended then to the cycloisomerization of dienynes with enantiotopic vinyl groups. An (S)‐phenyl‐Binepine‐platinum(II) complex allows total diastereoselectivity and high enantioselectivity levels to be attained in these reactions (ees up to 95%) which represent the first enantioselective desymetrizations achieved via enyne cycloisomerizations.     

Synthesis and properties of polyamides based on 5,5′‐bis[4‐(4‐aminophenoxy)phenyl]‐hexahydro‐4,7‐methanoindan

A new diamine 5,5′‐bis[4‐(4‐aminophenoxy)phenyl]‐hexahydro‐4,7‐methanoindan ( 3 ) was prepared through the nucleophilic displacement of 5,5′‐bis(4‐hydroxylphenyl)‐hexahydro‐4,7‐methanoindan ( 1 ) with p‐halonitrobenzene in the presence of K₂CO₃ in N,N‐dimethylformamide (DMF), followed by catalytic reduction with hydrazine and Pd/C in ethanol. A series of new polyamides were synthesized by the direct polycondensation of diamine 3 with various aromatic dicarboxylic acids. The polymers were obtained in quantitative yields with inherent viscosities of 0.76–1.02 dl g⁻¹. All the polymers were soluble in aprotic dipolar solvents such as N,N‐dimethylacetamide (DMAc) and N‐methyl‐2‐pyrrolidone (NMP), and could be solution cast into transparent, flexible and tough films. The glass transition temperatures of the polyamides were in the range 245–282 °C; their 10% weight loss temperatures were above 468 °C in nitrogen and above 465 °C in air. © 2000 Society of Chemical Industry     

Access to Enantiopure α‐Alkyl‐β‐hydroxy Esters through Dynamic Kinetic Resolutions Employing Purified/Overexpressed Alcohol Dehydrogenases

α‐Alkyl‐β‐hydroxy esters were obtained via dynamic kinetic resolution (DKR) employing purified or crude E. coli overexpressed alcohol dehydrogenases (ADHs). ADH‐A from R. ruber, CPADH from C. parapsilosis and TesADH from T. ethanolicus afforded syn‐(2R,3S) derivatives with very high selectivities for sterically not impeded ketones (‘small‐bulky’ substrates), while ADHs from S. yanoikuyae (SyADH) and Ralstonia sp. (RasADH) could also accept bulkier keto esters (‘bulky‐bulky’ substrates). SyADH also provided preferentially syn‐(2R,3S) isomers and RasADH showed in some cases good selectivity towards the formation of anti‐(2S,3S) derivatives. With anti‐Prelog ADHs such as LBADH from L. brevis or LKADH from L. kefir, syn‐(2S,3R) alcohols were obtained with high conversions and diastereomeric excess in some cases, especially with LBADH. Furthermore, due to the thermodynamically favoured reduction of these substrates, it was possible to employ just a minimal excess of 2‐propanol to obtain the final products with quantitative conversions.     

pH‐ and temperature‐sensitive microfiltration membranes from blends of poly(vinylidene fluoride)‐graft‐poly(4‐vinylpyridine) and poly(N‐isopropylacrylamide)

The copolymer poly(vinylidene fluoride)‐graft‐poly(4‐vinylpyridine) (PVDF‐g‐P4VP) was prepared through the graft copolymerization of poly(vinylidene fluoride) with 4‐vinylpyridine. Through the blending of the PVDF‐g‐P4VP copolymer with poly(N‐isopropylacrylamide) (PNIPAm) in an N‐methyl‐2‐pyrrolidone solution, PVDF‐g‐P4VP/PNIPAm membranes were fabricated by phase inversion in aqueous media. Elemental analyses indicated that the blend concentration of PNIPAm in the blend membranes increased with an increase in the blend ratio used in the casting solution. Scanning electron microscopy revealed that the membrane surface tended to corrugate at a low PNIPAm concentration and transformed into a smooth morphology at a high PNIPAm concentration. The surface morphology and pore size distribution of the microfiltration membranes could be regulated by the blend concentration of the casting solution, temperature, pH, and ionic strength of the coagulation bath. X‐ray photoelectron spectroscopy revealed a significant enrichment of PNIPAm on the membrane surface. The flux of aqueous solutions through the blend membranes exhibited a pH‐ and temperature‐dependent behavior. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4089–4097, 2006     

Highly Enantioselective Phase‐Transfer Catalytic α‐Alkylation of α‐tert‐Butoxycarbonyllactams: Construction of β‐Quaternary Chiral Pyrrolidine and Piperidine Systems

A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers.     

Organosoluble and light‐colored fluorinated polyimides based on 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]propane and aromatic dianhydrides

A novel fluorinated diamine monomer, 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]propane (2), was prepared through the nucleophilic substitution reaction of 2‐chloro‐5‐nitrobenzotrifluoride with 2,2‐bis(4‐hydroxyphenyl)propane in the presence of potassium carbonate, followed by catalytic reduction with hydrazine and Pd/C. Polyimides were synthesized from diamine 2 and various aromatic dianhydrides 3a–f via thermal imidization. These polymers had inherent viscosities ranging from 0.73 to 1.29 dL/g. Polyimides 5a–f were soluble in amide polar solvents and even in less polar solvents. These films had tensile strengths of 87–100 MPa, elongations to break of 8–29%, and initial moduli of 1.7–2.2 GPa. The glass transition temperatures (T_g) of 5a–f were in the range of 222–271°C, and the 10% weight loss temperatures (T₁₀) of them were all above 493°C. Compared with polyimides 6 series based on 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane (BAPP) and polyimides 7 based on 2,2‐Bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane (6FBAPP), the 5 series showed better solubility and lower color intensity, dielectric constant, and lower moisture absorption. Their films had cutoff wavelengths between 363 and 404 nm, b* values ranging from 8 to 62, dielectric constants of 2.68–3.16 (1 MHz), and moisture absorptions in the range of 0.04–0.35 wt %. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 922–935, 2005     

Yeast‐mediated enantioselective synthesis of chiral R‐(+)‐ and S‐(−)‐1‐phenyl‐1‐butanol from prochiral phenyl n‐propyl ketone in hexane–water biphasic culture

BACKGROUND: The hydrophobic phenyl n‐propyl ketone was used as a model compound to examine alcohol dehydrogenase activity in Saccharomyces cerevisiae mediated cell culture. Parameters such as pH, hexane‐to‐water volume percentage, and the amount of cofactor Zn²⁺ ion for either cell growth or reduction were studied to see their effect on the enantioselectivity toward the product R‐(+)‐ or S‐(?)‐1‐phenyl‐1‐butanol. RESULTS: The pH for cell growth in aqueous culture was 7.0, while the pH for reduction in the aqueous portion of the biphasic culture was 5.0. Without Zn²⁺ ion the biphasic cultures of middle to high hexane‐to‐water volume percentage exhibited an R‐(+)‐1‐phenyl‐1‐butanol enantiomeric excess of 53.7% to > 99%. Without Zn²⁺ ion the biphasic cultures at low hexane‐to‐water volume percentage possessed an S‐(?)‐1‐phenyl‐1‐butanol enantiomeric excess of 14.5–46.5%. Exclusively, the enantioselectivity for biphasic cultures containing Zn²⁺ ion was an S‐(?)‐1‐phenyl‐1‐butanol enantiomeric excess of 27.5% to > 99%. Reduction mediated in aqueous culture with varied amount of Zn²⁺ ion by the yeast Candida utilis also showed an S‐(?)‐1‐phenyl‐1‐butanol enantiomeric excess of 79.2–95.4%. CONCLUSION: The enantioselectivity of S. cerevisiae mediated biphasic culture reduction of phenyl n‐propyl ketone can be manipulated through the cofactor Zn²⁺ ion and the hexane volume percentage of the biphasic culture. Copyright © 2008 Society of Chemical Industry     

Influence of the coagulation‐bath temperature on the phase‐separation process of poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) solutions and membrane structures

A poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) (PVDF‐g‐PNIPAAm) copolymer was synthesized, and flat‐sheet membranes were prepared via the phase‐inversion method with N,N‐dimethylformamide (DMF) as the solvent and water as the coagulation bath. The effects of the coagulation‐bath temperature on poly(vinylidene fluoride) (PVDF)/DMF/water and PVDF‐g‐PNIPAAm/DMF/water ternary systems were studied with phase diagrams. The results showed that the phase‐separation process could be due to the hydrophilicity/hydrophobicity of poly(N‐isopropylacrylamide) at low temperatures, and the phase‐separation process was attributed to crystallization at high temperatures. The structures and properties of the membranes prepared at different coagulation‐bath temperatures were researched with scanning electron microscopy, porosity measurements, and flux measurements of pure water. The PVDF‐g‐PNIPAAm membranes, prepared at different temperatures, formed fingerlike pores and showed higher water flux and porosity than PVDF membranes. In particular, a membrane prepared at 30°C had the largest fingerlike pores and greatest porosity. The water flux of a membrane prepared in a 25°C coagulation bath showed a sharp increase with the temperature increasing to about 30°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Sulfonated poly(ether ether ketone)‐induced porous poly(ether sulfone) blend membranes for the separation of proteins and metal ions

Asymmetric ultrafiltration (UF) membranes were prepared by the blending of poly(ether sulfone) (PES) and sulfonated poly(ether ether ketone) (SPEEK) polymers with N,N′‐dimethylformamide solvent by the phase‐inversion method. SPEEK was selected as the hydrophilic polymer in a blend with different composition of PES and SPEEK. The solution‐cast PES/SPEEK blend membranes were homogeneous for all of the studied compositions from 100/0 to 60/40 wt % in a total of 17.5 wt % polymer and 82.5 wt % solvent. The presence of SPEEK beyond 40 wt % in the casting solution did not form membranes. The prepared membranes were characterized for their UF performances, such as pure water flux, water content, porosity, and membrane hydraulic resistance, and morphology and melting temperature. We estimated that the pure water flux of the PES/SPEEK blend membranes increased from 17.3 to 85.6 L m^?2 h^?1 when the concentration of SPEEK increased from 0 to 40 wt % in the casting solution. The membranes were also characterized their separation performance with proteins and metal‐ion solutions. The results indicate significant improvement in the performance characteristics of the blend membranes with the addition of SPEEK. In particular, the rejection of proteins and metal ions was marginally decreased, whereas the permeate flux was radically improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Pervaporation of volatile organic compounds/water mixtures through poly(1H,1H,9H‐hexadecafluorononyl methacrylate)‐filled poly(1‐trimethylsilyl‐1‐propyne) membranes

Poly(1‐trimethylsilyl‐1‐propyne) (PMSP) is a glassy polymer that contains many microvoids. The permselectivity of the PMSP membrane is controlled by the microvoids, and its permeation behavior is different from rubbery polymer membranes. PMSP membrane was filled with poly(1H,1H,9H‐hexadecafluorononyl methacrylate) (PHDFNMA), and the solution‐diffusion mechanism during pervaporation was investigated. Separation performance was increased due to the introduced hydrophobic polymer, PHDFNMA, as compared to the PMSP membrane. For the 62 wt % PHDFNMA‐filled PMSP membrane, the permselectivity was significantly enhanced. The microvoids in the PMSP membrane play an important role in permselectivity. As the feed of ethyl butanoate (EBU) concentration increased and the EBU quantity sorbed into the PHDFNMA‐filled PMSP membrane increased, the diffusion of water was prevented; in turn, the water flux decreased. At a low feed concentration, the diffusivity of the EBU molecule was much lower than that of water due to the larger molecular size of EBU. As EBU was sufficiently sorbed into the membrane, the diffusion of water was prevented by the EBU molecules; in turn, the permselectivity of EBU significantly increased. At a high‐feed EBU concentration, the diffusion of water increased, and the diffusion of EBU decreased to a constant as the PHDFNMA‐filled PMSP membrane was plasticized. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1054–1060, 2002     

Preparation and pervaporation performance of 3,3‐bis[4‐(4‐aminophenoxy)phenyl] phthalide based polyimide membranes

A series of novel solvent‐soluble polyimides based on the diamine of 3,3‐bis[4‐(4‐aminophenoxy)phenyl] phthalide (BAPP) were prepared. The effects of the dianhydride structures on the pervaporation performance of aqueous alcohol mixtures through these polyimide membranes were studied. The BAPP‐based polyimide membranes exhibited water permselectivity during all process runs. The permeation rate increased with the addition of bulky groups to the polyimide backbone. The effects of the feed solution concentration, feed solution temperature, and carbon atom number of the feed alcohol on the pervaporation performance were also investigated systematically. Optimum pervaporation results, a separation factor of 22 and a permeation rate of 270 g/m² h, were obtained for a 90 wt % feed aqueous ethanol solution through a 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride polyimide membrane at 25°C. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2046–2052, 2005     

Lower critical solution temperatures of thermo‐responsive poly(N‐isopropylacrylamide) copolymers with racemate or single enantiomer groups

BACKGROUND: Thermo‐responsive copolymers with racemate or single enantiomer groups are attracting increasing attention due to their fascinating functional properties and potential applications. However, there is a lack of systematic information about the lower critical solution temperature (LCST) of poly(N‐isopropylacrylamide)‐based thermo‐responsive chiral recognition systems. In this study, a series of thermo‐responsive chiral recognition copolymers, poly[(N‐isopropylacrylamide)‐co‐(N‐(S)‐sec‐butylacrylamide)] (PN‐S‐B) and poly[(N‐isopropylacrylamide)‐co‐(N‐(R,S)‐sec‐butylacrylamide)] (PN‐R,S‐B), with different molar compositions, were prepared. The effects of heating and cooling processes, optical activity and amount of chiral recognition groups in the copolymers on the LCSTs of the prepared copolymers were systematically studied. RESULTS: LCST hysteresis phenomena are found in the phase transition processes of PN‐S‐B and PN‐R,S‐B copolymers in a heating and cooling cycle. The LCSTs of PN‐S‐B and PN‐R,S‐B during the heating process are higher than those during the cooling process. With similar molar ratios of N‐isopropylacrylamide groups in the copolymers, the LCST of the copolymer containing a single enantiomer (PN‐S‐B) is lower than that of the copolymer containing racemate (PN‐R,S‐B) due to the steric structural difference. The LCSTs of PN‐R,S‐B copolymers are in inverse proportion to the molar contents of the hydrophobic R,S‐B moieties in these copolymers. CONCLUSION: The results provide valuable guidance for designing and fabricating thermo‐responsive chiral recognition systems with desired LCSTs. Copyright © 2008 Society of Chemical Industry     

Influence of the comonomers (styrene and methyl acrylate) on the rate of photocrosslinking of 4‐{[‐3‐(4‐hydroxybenzylidene)‐2‐oxocyclohexylidene]methyl}‐ phenyl acrylate

[2,6‐Bis(4‐hydroxybenzylidene)cyclohexanone] (HBC) was prepared by reacting cyclohexanone and p‐hydroxybenzaldehyde in the presence of acid catalyst. Acrylated derivative of HBC, 4‐{[‐3‐(4‐hydroxybenzylidene)‐2‐oxocyclohexylidene]methyl}phenyl acrylate (HBA), was prepared by reacting HBC with acryloyl chloride in the presence of triethylamine. Copolymers of HBA with styrene (S) and methyl acrylate (MA) of different feed compositions were carried out by solution polymerization technique by using benzoyl peroxide (BPO) under nitrogen atmosphere. All monomers and polymers were characterized by using IR and NMR techniques. Reactivity ratios of the monomers present in the polymer chain were evolved by using Finnman–Ross (FR), Kelen–Tudos (KT), and extended Kelen–Tudos (ex‐KT) methods. Average values of reactivity were achieved by the following three methods: r₁ (S) = 2.36 ± 0.45 and r₂ (HBA) = 0.8 ± 0.31 for poly(S‐co‐HBA); r₁ = 1.62 ± 0.06 (MA); and r₂ = 0.12 ± 0.07 (HBA) for poly(MA‐co‐HBA). The photocrosslinking property of the polymers was done by using UV absorption spectroscopic technique. The rate of photocrosslinking was enhanced compared to that of the homopolymers, when the HBA was copolymerized with S and MA. Thermal stability and molecular weights (M_w and M_n) were determined for the polymer samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2494–2503, 2004