High‐quality poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] synthesized by a solid–liquid two‐phase reaction: Characterizations and electroluminescence properties

Poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] (MEH‐PPV) with a molar mass of 26–47 × 10⁴ g mol^?1 and a polydispersity of 2.5–3.2 was synthesized by a liquid–solid two‐phase reaction. The liquid phase was tetrahydrofuran (THF) containing 1,4‐bis(chloromethyl)‐2‐methoxy‐5‐(2′‐ethylhexyloxy)benzene as the monomer and a certain amount of tetrabutylammonium bromide as a phase‐transfer catalyst. The solid phase consisted of potassium hydroxide particles with diameters smaller than 0.5 mm. The reaction was carried out at a low temperature of 0 °C and under nitrogen protection. No gelation was observed during the polymerization process, and the polymer was soluble in the usual organic solvents, such as chloroform, toluene, THF, and xylene. A polymer light‐emitting diode was fabricated with MEH‐PPV as an active luminescent layer. The device had an indium tin oxide/poly(3,4‐ethylenedioxylthiophene) (PEDOT)/MEH‐PPV/Ba/Al configuration. It showed a turn‐on voltage of 3.3 V, a luminescence intensity at 6.1 V of 550 cd/m², a luminescence efficiency of 0.43 cd/A, and a quantum efficiency of 0.57%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3049–3054, 2004     

Alternating π‐conjugated copolymer of dithiafulvene with 2,2′‐bipyridyl units

A π‐conjugated polymer containing a dithiafulvene unit and a bipyridyl unit was prepared by cycloaddition polymerization of aldothioketene derived from 5,5′‐diethynyl‐2,2′‐bipyridine. Ultraviolet–visible (UV–vis) absorption spectra showed that the π‐conjugation system of the polymer expanded more effectively than that of a benzene analogue of poly(dithiafulvene) obtained from 1,4‐diethynylbenzene. Cyclic voltammetry measurements indicated that the dithiafulvene–bipyridyl polymer was a weaker electron‐donor polymer than the benzene analogue. These results supported the idea that the incorporation of the electron‐accepting bipyridyl moiety into conjugated poly(dithiafulvene) induced an intramolecular charge‐transfer (CT) effect between the units. Treatment of the dithiafulvene–bipyridyl polymer with bis(2,2′‐bipyridyl)dichlororuthenium (II) [Ru(bpy)₂Cl₂] afforded a ruthenium–polymer complex. A cyclic voltammogram of the complex showed broad redox peaks, which indicated electronic interaction between the dithiafulvene and tris(bipyridyl) ruthenium complex. The dithiafulvene–bipyridyl polymer formed CT complexes with 7,7,8,8‐tetracycanoquinodimethane (TCNQ) in dimethyl sulfoxide. The UV–vis absorption indicated that the resulting CT complex contained anion radical of TCNQ and partially charge‐transferred TCNQ. The polymer showed an unusually high electrical conductivity of 3.1 × 10^?4 S/cm in its nondoped state due to the effective donor–acceptor interaction between the bipyridine unit and the dithiafulvene unit. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4083–4090, 2001     

Novel,organosoluble, light‐colored fluorinated polyimides based on 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl or 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐1,1′‐binaphthyl

Two series of fluorinated polyimides were prepared from 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl ( 2 ) and 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐1,1′‐binaphthyl ( 4 ) with various aromatic dianhydrides via a conventional, two‐step procedure that included a ring‐opening polyaddition to give poly(amic acid)s, followed by chemical or thermal cyclodehydration. The inherent viscosities of the polyimides ranged from 0.54 to 0.73 and 0.19 to 0.36 dL/g, respectively. All the fluorinated polyimides were soluble in many polar organic solvents, such as N,N‐dimethylacetamide and N‐methylpyrrolidone, and afforded transparent and light‐colored films via solution‐casting. These polyimides showed glass‐transition temperatures in the ranges of 222–280 and 257–351 °C by DSC, softening temperatures in the range of 264–301 °C by thermomechanical analysis, and a decomposition temperature for 10% weight loss above 520 °C both in nitrogen and air atmospheres. The polyimides had low moisture absorptions of 0.23–0.58%, low dielectric constants of 2.84–3.61 at 10 kHz, and an ultraviolet–visible absorption cutoff wavelength at 351–434 nm. Copolyimides derived from the same dianhydrides with an equimolar mixture of 4,4′‐oxydianiline and diamine 2 or 4 were also prepared and characterized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2416–2431, 2004     

Direct Catalytic Asymmetric Mannich‐type Reaction of α,β‐Unsaturated γ‐Butyrolactam with Ketimines

We report a direct catalytic asymmetric Mannich‐type addition of α,β‐unsaturated γ‐butyrolactam to α‐ethoxycarbonyl ketimines promoted by a soft Lewis acid/Brønsted base cooperative catalyst. A thiophosphinoyl group on the nitrogen of ketimines was crucial for both electrophilic activation and α‐addition of γ‐butyrolactams. The obtained aza‐Morita–Baylis–Hillman‐type products bear an α‐amino acid architecture with a tetra‐substituted stereogenic center.     

A rapid and sensitive LC–MS/MS method for quantification of quercetin‐3‐O‐β‐d‐glucopyranosyl‐7‐O‐β‐d‐gentiobioside in plasma and its application to a pharmacokinetic study

A rapid and sensitive LC–MS/MS method with good accuracy and precision was developed and validated for the pharmacokinetic study of quercetin‐3‐O‐β‐d ‐glucopyranosyl‐7‐O‐β‐d ‐gentiobioside (QGG) in Sprague–Dawley rats. Plasma samples were simply precipitated by methanol and then analyzed by LC–MS/MS. A Venusil® ASB C₁₈ column (2.1 × 50 mm, i.d. 5 μm) was used for separation, with methanol–water (50:50, v/v) as the mobile phase at a flow rate of 300 μL/min. The optimized mass transition ion‐pairs (m/z) for quantitation were 787.3/301.3 for QGG, and 725.3/293.3 for internal standard. The linear range was 7.32–1830 ng/mL with an average correlation coefficient of 0.9992, and the limit of quantification was 7.32 ng/mL. The intra‐ and inter‐day precision and accuracy were less than ±15%. At low, medium and high quality control concentrations, the recovery and matrix effect of the analyte and IS were in the range of 89.06–92.43 and 88.58–97.62%, respectively. The method was applied for the pharmacokinetic study of QGG in Sprague–Dawley rats. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel fluorinated aromatic polyimides derived from 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,5‐ditrifluoromethylphenyl)‐2,2,2‐trifluoroethane and various aromatic dianhydrides

A novel fluorinated aromatic diamine, 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,5‐ditrifluoromethylphenyl)‐2,2,2‐trifluoroethane (9FMA), was synthesized by the coupling reaction of 3′,5′‐ditrifluoromethyl‐2,2,2‐trifluoroacetophenone with 2,6‐dimethylaniline under the catalysis of 2,6‐dimethylaniline hydrochloride. A series of fluorinated aromatic polyimides were synthesized from 9FMA and various aromatic dianhydrides, including pyromellitic dianhydride, 3,3′4,4′‐biphenyl tetracarboxylic dianhydride, 4,4′‐oxydiphthalic anhydride, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), and 4,4′‐hexafluoroisopropylidene diphthalic anhydride, via a high‐temperature, one‐stage imidization process. The inherent viscosities of the polyimides ranged from 0.37 to 0.74 dL/g. All the polyimides were quickly soluble in many low‐boiling‐point organic solvents such as tetrahydrofuran, chloroform, and acetone as well as some polar organic solvents such as N‐methyl‐2‐pyrrolidinone, N,N′‐dimethylacetamide, and N,N′‐dimethylformamide. Freestanding fluorinated polyimide films could be prepared and exhibited good thermal stability with glass‐transition temperatures of 298–334 °C and outstanding mechanical properties with tensile strengths of 69–102 MPa and elongations at break of 3.3–9.9%. Moreover, the polyimide films possessed low dielectric constants of 2.70–3.09 and low moisture absorption (<0.58%). The films also exhibited good optical transparency with a cutoff wavelength of 303–351 nm. One polyimide (9FMA/BTDA) also exhibited an intrinsic negative photosensitivity, and a fine pattern could be obtained with a resolution of 5 μm after exposure at the i‐line (365‐nm) wavelength. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2665–2674, 2006     

High‐Yielding Synthesis of the Anti‐Influenza Neuraminidase Inhibitor (−)‐Oseltamivir by Two “One‐Pot” Sequences

The efficient asymmetric total synthesis of (?)‐oseltamivir, an antiviral reagent, has been accomplished by using two “one‐pot” reaction sequences, with excellent overall yield (60 %) and only one required purification by column chromatography. The first one‐pot reaction sequence consists of a diphenylprolinol silyl ether mediated asymmetric Michael reaction, a domino Michael reaction/Horner–Wadsworth–Emmons reaction combined with retro‐aldol/Horner–Wadsworth–Emmons reaction and retro Michael reactions, a thiol Michael reaction, and a base‐catalyzed isomerization. Six reactions can be successfully conducted in the second one‐pot reaction sequence; these are deprotection of a tert‐butyl ester and its conversion into an acyl chloride then an acyl azide, Curtius rearrangement, amide formation, reduction of a nitro group into an amine, and a retro Michael reaction of a thiol moiety. A column‐free synthesis of (?)‐oseltamivir has also been established.     

Efficient synthesis and dehydration reaction of trichloromethylated 2‐(3‐phenyl‐5‐hydroxy‐4,5‐dihydro‐1H‐pyrazol‐1‐yl)‐4‐aryl‐5‐alkylthiazoles

A convenient method for the synthesis of a novel series of 11, specifically substituted, noncondensed 5,5‐bicycles 2‐[3‐phenyl‐5‐hydroxy‐5‐trichloromethyl‐4,5‐dihydro‐1H‐pyrazol‐1‐yl]‐4‐aryl‐5‐alkylthiazoles ( 3a–k ; 65–94% yield) from the reactions of 3‐phenyl‐5‐hydroxy‐5‐trichloromethyl‐4,5‐dihydro‐1H‐1‐pyrazolethiocarboxyamide ( 1 ) with substituted 2‐bromo‐4′‐acetophenones ( 2a–f ) and 2‐bromo‐4′‐propiophenones ( 2g–k ) is reported. Dehydration of compounds 3a–k with a mixture of concentrated sulfuric acid/chloroform furnished the corresponding 2‐[3‐phenyl‐5‐trichloromethyl‐1H‐pyrazol‐1‐yl]‐4‐aryl‐5‐alkylthiazoles ( 4a–k ) in good yields (61–93%). © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:132–137, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10113     

Donor–acceptor‐integrated conjugated polymers based on carbazole[3,4‐c:5,6‐c]bis[1,2,5]thiadiazole with tight π–π stacking for photovoltaics

An original strategy to construct a new donor–acceptor (D–A)‐integrated structure by directly imposing “pull” unit on the “push” moiety to form fused ring architecture has been developed, and poly{N‐alkyl‐carbazole[3,4‐c:5,6‐c]bis[1,2,5]thiadiazole‐alt‐thiophene} (PCBTT) with D–A‐integrated structure, in which two 1,2,5‐thiadiazole rings are fixed on carbazole in 3‐, 4‐ and 5‐, 6‐position symmetrically and thiophene is used as bridge, has been synthesized. The interaction between pull and push units has fine tuned the HOMO/LUMO energy levels, and the resulting copolymer covers the solar flux from 300 to 750 nm. The interaction between pull and push units is worth noting that due to the fused five rings inducing strong intermolecular interaction, an extremely short π–π stacking distance of 0.32 nm has been achieved for PCBTT both in powder and solid states. This is the shortest π–π stacking distance reported for conjugated polymers. Additionally, an obvious intramolecular charge transfer and energy transfer from donor units to acceptor units have been detected in this D–A integration. A moderate‐to‐high open‐circuit voltage of ～0.7 V in PCBTT:[6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM) (w/w = 1/2) solar cells is achieved due to the low‐lying HOMO energy level of PCBTT. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

3,4‐Dithiaphosphole and 3,3′,4,4′‐Tetrathia‐1,1′‐Biphosphole π‐Conjugated Systems: S Makes the Impact

Conjugated systems based on phospholes and 1,1′‐biphospholes bearing 3,4‐ethylenedithia bridges have been prepared using the Fagan–Nugent route. The mechanism of this organometallic route leading to intermediate zirconacyclopentadienes has been investigated by using theoretical calculations. This study revealed that the oxidative coupling leading to zirconacyclopentadienes is favored over oxidative addition within the S? C≡C bond both thermodynamically and kinetically. The impact of the presence of the S atoms on the optical and electrochemical behavior of the phospholes and 1,1′‐biphospholes has been systematically evaluated both experimentally and theoretically. A comparison with their “all‐carbon” analogues is provided. Of particular interest, this comparative study revealed that the introduction of S atoms has an impact on the electronic properties of phosphole‐based conjugated systems. A decrease of the HOMO–LUMO separation and a stabilization of the LUMO level were observed. These general trends are also observed with 1,1′‐biphospholes exhibiting σ–π conjugation. The P atom of the 3,4‐ethylenedithiaphospholes can be selectively oxidized by S₈ or O₂. These P modifications result in a lowering of the HOMO–LUMO separation as well as an increase of the reduction and oxidation potentials. The S atoms of the 3,4‐ethylenedithia bridge of the 2,5‐phosphole have been oxidized using m‐chloroperoxybenzoic acid. The resulting 3,4‐ethylenesulfoxide oxophosphole was characterized by an X‐ray diffraction study. Experimental and theoretical studies show that this novel chemical manipulation results in an increase of the HOMO–LUMO separation and an important decrease of the LUMO level. The electropolymerization of 2‐thienyl‐capped 3,4‐ethylenedithiathioxophosphole and 1,1′‐biphosphole is reported. The impact of the S substituents on the polymer properties is discussed.     

Simultaneous determination of trifolirhizin, (–)‐maackiain, (–)‐sophoranone,and 2‐(2,4‐dihydroxyphenyl)‐5,6‐methylenedioxybenzofuran from Sophora tonkinensis in rat plasma by liquid chromatography with tandem mass spectrometry and its application to a pharmacokinetic study

A new liquid chromatography with tandem mass spectrometry method was developed and validated for the simultaneous determination of trifolirhizin, (–)‐maackiain, (–)‐sophoranone, and 2‐(2,4‐dihydroxyphenyl)‐5,6‐methylenedioxybenzofuran from Sophora tonkinensis in rat plasma using chlorpropamide as an internal standard. Plasma samples (50 μL) were prepared using a simple deproteinization procedure with 150 μL of acetonitrile containing 100 ng/mL of chlorpropamide. Chromatographic separation was carried out on an Acclaim RSLC120 C₁₈ column (2.1 × 100 mm, 2.2 μm) using a gradient elution consisting of 7.5 mM ammonium acetate and acetonitrile containing 0.1% formic acid (0.4 mL/min flow rate, 7.0 min total run time). The detection and quantitation of all analytes were performed in selected reaction monitoring mode under both positive and negative electrospray ionization. This assay was linear over concentration ranges of 50–5000 ng/mL (trifolirhizin), 25–2500 ng/mL ((–)‐maackiain), 5–250 ng/mL ((–)‐sophoranone), and 1–250 ng/mL 2‐(2,4‐dihydroxyphenyl)‐5,6‐methylenedioxybenzofuran) with a lower limit of quantification of 50, 25, 5, and 1 ng/mL for trifolirhizin, (–)‐maackiain, (–)‐sophoranone, and 2‐(2,4‐dihydroxyphenyl)‐5,6‐methylenedioxybenzofuran, respectively. All the validation data, including the specificity, precision, accuracy, recovery, and stability conformed to the acceptance requirements. The results indicated that the developed method is sufficiently reliable for the pharmacokinetic study of the analytes following oral administration of Sophora tonkinensis extract in rats.     

TiCl3‐Mediated Synthesis of 2,3,3‐Trisubstituted Indolenines: Total Synthesis of (+)‐1,2‐Dehydroaspidospermidine, (+)‐Condyfoline,and (−)‐Tubifoline

2,3,3‐Trisubstituted indolenine constitutes an integral part of many biologically important monoterpene indole alkaloids. We report herein an unprecedented access to this skeleton by a TiCl₃‐mediated reductive cyclization of tetrasubstituted alkenes bearing a 2‐nitrophenyl substituent. The proof of concept is demonstrated firstly by accomplishing a concise total synthesis of (+)‐1,2‐dehydroaspidospermidine featuring a late‐stage application of this key transformation. A sequence of reduction of nitroarene to nitrosoarene followed by 6π‐electron‐5‐atom electrocyclization and a 1,2‐alkyl shift of the resulting nitrone intermediate was proposed to account for the reaction outcome. A subsequent total synthesis of (+)‐condyfoline not only illustrates the generality of the reaction, but also provides a mechanistic insight into the nature of the 1,2‐alkyl shift. The exclusive formation of (+)‐condyfoline indicates that the 1,2‐alkyl migration follows a concerted Wagner–Meerwein pathway, rather than a stepwise retro‐Mannich/Mannich reaction sequence. Conditions for almost quantitative conversion of (+)‐condyfoline to (?)‐tubifoline by way of a retro‐Mannich/1,3‐prototropy/transannular cyclization cascade are also documented.     

Thermal cycloaddition reaction of symmetrical and unsymmetrical α‐diazo‐β‐diketones with 4‐aryl‐2‐methyl‐2,3‐dihydro‐1,5‐benzothia/diazepines

Symmetrical and unsymmetrical α‐diazo‐β‐diketones undergo thermal Wolff rearrangements to generate α‐carbonylketenes to participate as dienes in Diels–Alder reactions with 4‐aryl‐2‐methyl‐2,3‐dihydro‐1,5‐benzothia/diazepines to give, whereapplicable, regiospecific cycloadducts, 4a,5,6,12‐tetrahydro‐1H/1H,7H‐1,3‐oxazino[3,2‐d][1,5]benzo‐thia/diazepin‐1‐ones. A mechanism of formation of the regiospecific cycloadducts is suggested. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 35–40, 1999     

Synthesis and characterization of multiblock copolymers composed of poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one) outer blocks and poly(L‐lactide) inner blocks

Ethylene glycol (EG) initiated, hydroxyl‐telechelic poly(L ‐lactide) (PLLA) was employed as a macroinitiator in the presence of a stannous octoate catalyst in the ring‐opening polymerization of 5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one (MBC) with the goal of creating A–B–A‐type block copolymers having polycarbonate outer blocks and a polyester center block. Because of transesterification reactions involving the PLLA block, multiblock copolymers of the A–(B–A)_n–B–A type were actually obtained, where A is poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one), B is PLLA, and n is greater than 0. ¹H and ¹³C NMR spectroscopy of the product copolymers yielded evidence of the multiblock structure and provided the lactide sequence length. For a PLLA macroinitiator with a number‐average molecular weight of 2500 g/mol, the product block copolymer had an n value of 0.8 and an average lactide sequence length (consecutive C₆H₈O₄ units uninterrupted by either an EG or MBC unit) of 6.1. For a PLLA macroinitiator with a number‐average molecular weight of 14,400 g/mol, n was 18, and the average lactide sequence length was 5.0. Additional evidence of the block copolymer architecture was revealed through the retention of PLLA crystallinity as measured by differential scanning calorimetry and wide‐angle X‐ray diffraction. Multiblock copolymers with PLLA crystallinity could be achieved only with isolated PLLA macroinitiators; sequential addition of MBC to high‐conversion L ‐lactide polymerizations resulted in excessive randomization, presumably because of residual L ‐lactide monomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6817–6835, 2006     

Catalytic Asymmetric Intramolecular Homologation of Ketones with α‐Diazoesters: Synthesis of Cyclic α‐Aryl/Alkyl β‐Ketoesters

A catalytic asymmetric intramolecular homologation of simple ketones with α‐diazoesters was firstly accomplished with a chiral N,N′‐dioxide–Sc(OTf)₃ complex. This method provides an efficient access to chiral cyclic α‐aryl/alkyl β‐ketoesters containing an all‐carbon quaternary stereocenter. Under mild conditions, a variety of aryl‐ and alkyl‐substituted ketone groups reacted with α‐diazoester groups smoothly through an intramolecular addition/rearrangement process, producing the β‐ketoesters in high yield and enantiomeric excess.     

Synthesis and properties of fluorinated polyimides based on 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐2,5‐di‐tert‐butylbenzene and various aromatic dianhydrides

A novel fluorinated diamine monomer, 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐2,5‐di‐tert‐butylbenzene ( 2 ), was prepared through the nucleophilic substitution reaction of 2‐chloro‐5‐nitrobenzotrifluoride and 2,5‐di‐tert‐butylhydroquinone in the presence of potassium carbonate, followed by catalytic reduction with hydrazine and Pd/C. Fluorinated polyimides ( 5a – 5f ) were synthesized from diamine 2 and various aromatic dianhydrides ( 3a – 3f ) via thermal or chemical imidization. These polymers had inherent viscosities of 0.77–1.01 dL/g. The 5 series polyimides were soluble in N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, and N,N‐dimethylformamide and were even soluble in dioxane, tetrahydrofuran, and dichloromethane. 5 (C) showed cutoff wavelengths between 363 and 404 nm and yellowness index (b*) values of 6.5–40.2. The polyimide films had tensile strengths of 93–114 MPa, elongations to break of 9–12%, and initial moduli of 1.7–2.1 GPa. The glass‐transition temperatures were 255–288 °C. The temperatures of 10% weight loss were all above 460 °C in air or nitrogen atmospheres. In comparison with a nonfluorinated polyimide series based on 1,4‐bis(4‐aminophenoxy)‐2,5‐di‐tert‐butylbenzene, the 5 series showed better solubility and lower color intensity, dielectric constants, and moisture absorption. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2272–2284, 2004     

Development and validation of LC‐MS/MS method for the estimation of β‐hydroxy‐β‐methylbutyrate in rat plasma and its application to pharmacokinetic studies

A simple, sensitive and specific high‐performance liquid chromatography mass spectrometry (LC‐MS/MS) method was developed and validated for the quantification of β‐hydroxy‐β‐methyl butyrate (HMB) in small volumes of rat plasma using warfarin as an internal standard (IS). The API‐4000 LC‐MS/MS was operated under the multiple reaction‐monitoring mode using the electrospray ionization technique. A simple liquid–liquid extraction process was used to extract HMB and IS from rat plasma. The total run time was 3 min and the elution of HMB and IS occurred at 1.48 and 1.75 min respectively; this was achieved with a mobile phase consisting of 0.1% formic acid in a water–acetonitrile mixture (15:85, v/v) at a flow rate of 1.0 mL/min on a Agilent Eclipse XDB C₈ (150 × 4.6, 5 µm) column. The developed method was validated in rat plasma with a lower limit of quantitation of 30.0 ng/mL for HMB. A linear response function was established for the range of concentrations 30–4600 ng/mL (r > 0.998) for HMB. The intra‐ and inter‐day precision values for HMB were acceptable as per Food and Drug Administration guidelines. HMB was stable in the battery of stability studies, viz. bench‐top, autosampler freeze–thaw cycles and long‐term stability for 30 days in plasma. The developed assay method was applied to a bioavailability study in rats. Copyright © 2012 John Wiley & Sons, Ltd.     

Library synthesis and characterization of 3‐aminopropyl‐terminated poly(dimethylsiloxane)s and poly(ϵ‐caprolactone)‐b‐poly(dimethylsiloxane)s

Libraries of 3‐aminopropyl‐terminated poly(dimethylsiloxane) (APT–PDMS) and poly(?‐caprolactone)–poly(dimethylsiloxane)–poly(?‐caprolactone) (PCL—PDMS–PCL) triblock copolymers were synthesized. Preliminary experiments were carried out to select an appropriate catalyst and route for the poly(dimethylsiloxane) synthesis, and trial experiments were conducted to verify the successful synthesis of the intended polymer compositions. Then, a series of APT–PDMS oligomers were synthesized with an automated combinatorial high‐throughput synthesis system to cover a molecular weight range of 2500–50,000 g/mol. Trial PCL—PDMS–PCL triblock copolymers were synthesized with the automated reactor system and characterized in detail with rapid gel permeation chromatography, high‐throughput Fourier transform infrared, nuclear magnetic resonance, and differential scanning calorimetry. Finally, two library synthesis experiments were carried out in which the lengths of both the poly(dimethylsiloxane) and poly(?‐caprolactone) blocks in the PCL—PDMS–PCL triblock copolymers were varied. The results obtained from these experiments demonstrated that it was possible to synthesize libraries of well‐defined APT–PDMS oligomers and PCL—PDMS–PCL triblock copolymers with an automated high‐throughput system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4880–4894, 2006     

Ring‐opening polymerization of ϵ‐caprolactam and ϵ‐caprolactone via microwave irradiation

A novel process for synthesizing nylon‐6 and poly(?‐caprolactone) by microwave irradiation of the respective monomers, ?‐caprolactam and ?‐caprolactone, is described. The ring opening of ?‐caprolactam to produce nylon‐6 was performed in a microwave oven by the forward power being controlled to about 90–135 W in the presence of an ω‐aminocaproic acid catalyst (10 mol %) and for periods of 1–3 h at temperatures varying from 250 to 280 °C. The ring opening of ?‐caprolactone to produce poly(?‐caprolactone) was performed in a microwave oven by the forward power being controlled to about 70–100 W for a period of 2 h in the presence of stannous octoate with and without 1,4‐butanediol over a temperature range of 150–200 °C. The yields, conditions of the reactions, and properties of the products generated relative to the thermal processes are discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2264–2275, 2002     

Synthesis and properties of ortho‐linked aromatic polyimides based on 1,2‐bis(4‐aminophenoxy)‐4‐tert‐butylbenzene

A bis(ether amine) containing the ortho‐substituted phenylene unit and pendant tert‐butyl group, 1,2‐bis(4‐aminophenoxy)‐4‐tert‐butylbenzene, was synthesized and used as a monomer to prepare polyimides with six commercial dianhydrides via a conventional two‐stage procedure. The intermediate poly(amic acid)s had inherent viscosities of 0.78–1.44 dL/g, and most of them could be thermally converted into transparent, flexible, and tough polyimide films. The inherent viscosities of the resulting polyimides were in the range of 0.46–0.87 dL/g. All polyimides were noncrystalline, and most of them showed excellent solubility in polar organic solvents. The glass‐transition temperatures of these polyimides were in the range of 222–259 °C in differential scanning calorimetry and 212–282 °C in thermomechanicl analysis. These polyimides showed no appreciable decomposition up to 500 °C in thermogravimetric analysis in air or nitrogen. A comparative study of the properties with the corresponding polyimides without pendant tert‐butyl groups derived from 1,2‐bis(4‐aminophenoxy)benzene is also presented. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1551–1559, 2000