Synthesis,characterization, and thermal properties of alternate copolymers containing N,N′‐bis(diphenylsilyl)tetraphenylcyclodisilazane

Hexamethyldisilazane was used as the starting material to synthesize N,N′‐bis(hydroxydiphenylsilanyl)tetraphenylcyclodisilazane (BHPTPC). By condensation polymerization of BHPTPC with α,ω‐bis(dialkylamino)dimethylsiloxane, a series of alternate copolymers containing N,N′‐bis(diphenylsilyl)tetraphenylcyclodisilazane was synthesized. GPC studies show that the highest molecular weight was obtained at a ratio of 1.005 : 1 (BHPTPC: α,ω‐bis(dimethyl amino)dimethylsiloxane). Data of DSC indicate that the temperature of glass transition (T_g) and temperature of melting point (T_m) decreased with the increasing of dimethylsiloxane segments units. Three stages of degradation were found in the thermogravimetric analysis curves. The activation energy of the copolymer (with m = 2, 3, and 7) was calculated by using Flynn–Wall–Ozawa method. The activation energy of the copolymer with m = 2, 3, and 7 at second stage is 214, 211, and 184 kJ/mol, respectively. Isothermal gravimetric analysis shows that for the same temperature and the same time, the weight loss of the alternate copolymer was greatly less than that of common polydimethylsiloxane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 611–617, 2007     

Highly Efficient and Enantioselective Iridium‐Catalyzed Asymmetric Hydrogenation of N‐Arylimines

A catalytic method employing the cationic iridium‐(S_c,R_p)‐DuanPhos [(1R,1′R,2S,2′S)‐2,2′‐di‐tert‐butyl‐2,2′,3,3′‐tetrahydro‐1H,1′H‐1,1′‐biisophosphindole] complex and BARF {tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate} counterion effectively catalyzes the enantioselective hydrogenation of acyclic N‐arylimines with high turnover numbers (up to 10,000 TON) and excellent enantioselectivities (up to 98% ee), achieving the practical synthesis of chiral secondary amines.     

Synthesis and characterization of a novel siloxane‐imide‐containing polybenzoxazine

A novel siloxane‐imide‐containing polybenzoxazine based on N,N′‐bis(N‐phenyl‐3,4‐dihydro‐2H‐benzo[1,3]oxazine)‐5, 5′‐bis(1,1′,3,3′‐tetramethyldisiloxane‐1,3‐diyl)‐bis(norborane‐2,3‐dicarboximide) (BZ‐A1) was successfully synthesized. The thermal properties of BZ‐A1 are superior to those of conventional polybenzoxazines lacking siloxane groups. Polymerized BZ‐A1 possesses extremely low surface free energy (γ_s = 15.1 mJ m^?2) after curing at 230 °C for 1 h. Moreover, the surface free energy of polymerized BZ‐A1 is more stable than conventional bisphenol A‐type polybenzoxazine during thermal curing and annealing processes, indicating that polymerized BZ‐A1 is more suitable for applications requiring low surface free energy materials for high temperatures over long periods of time. Copyright © 2010 Society of Chemical Industry     

Recent Developments in Enantioselective Metal‐Catalyzed Domino Reactions

Since the first definition of domino reactions by Tietze in 1993, an explosive number of these fascinating reactions has been developed, allowing the easily building of complex chiral molecular architectures from simple materials to be achieved in a single step. Even more interesting, the possibility to join two or more reactions in one asymmetric domino process catalyzed by chiral metal catalysts has rapidly become one challenging goal for chemists, due to economical advantages, such as avoiding costly protecting groups and time‐consuming purification procedures after each step. The explosive development of enantioselective metal‐catalyzed domino including multicomponent reactions is a consequence of the considerable impact of the advent of asymmetric transition metal catalysis. This review aims to update the last developments of enantioselective one‐, two‐ and multicomponent domino reactions mediated by chiral metal catalysts, covering the literature since the beginning of 2006. Abbreviations: Ac: acetyl; AQN: anthraquinone; Ar: aryl; bdpp: 2,4‐bis(diphenylphosphino)pentane; BINAP: 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl; BINEPINE: phenylbinaphthophosphepine; BINIM: binapthyldiimine; BINOL: 1,1′‐bi‐2‐naphthol; BIPHEP: 2,2′‐bis(diphenylphosphino)‐1,1′‐biphenyl; Bn: benzyl; Boc: tert‐butoxycarbonyl; Box: bisoxazoline; BOXAX: 2,2′‐bis(oxazolyl)‐1,1′‐binaphthyl; BPTV: N‐benzene‐fused phthaloyl‐valine; Bu: butyl; Bz: benzoyl; Cat: catechol; Chiraphos: 2,3‐bis(diphenylphosphine)butane; cod: cyclooctadiene; Cy: cyclohexyl; DABCO: 1,4‐diazabicyclo[2.2.2]octane; dba: (E,E)‐dibenzylideneacetone; DBU: 1,8‐diazabicyclo[5.4.0]undec‐7‐ene; DCE: dichloroethane; de: diastereomeric excess; DHQ: hydroquinine; DHQD: dihydroquinidine; DIFLUORPHOS: 5,5′‐bis(diphenylphosphino)‐2,2,2′,2′‐tetrafluoro‐4,4′‐bi‐1,3‐benzodioxole; DIPEA: diisopropylethylamine; DMF: dimethylformamide; DMSO: dimethyl sulfoxide; DOSP: N‐p‐dodecylbenzenesulfonylprolinate; DPEN: 1,2‐diphenylethylenediamine; dtb: di‐tert‐butyl; dtbm: di‐tert‐butylmethoxy; E: electrophile; ee: enantiomeric excess; Et: ethyl; FBIP: ferrocene bis‐imidazoline bis‐palladacycle; Fc: ferrocenyl; FOXAP: ferrocenyloxazolinylphosphine; Hex: hexyl; HFIP: hexafluoroisopropyl alcohol; HMPA: hexamethylphosphoramide; iPr‐DuPhos: 1,2‐bis(2,5‐diisopropylphospholano)benzene; Josiphos: 1‐[2‐(diphenylphosphino)ferrocenyl]ethyldicyclohexylphosphine ethanol adduct; L: ligand; MCPBA: 3‐chloroperoxybenzoic acid; Me: methyl; Me‐DuPhos: 1,2‐bis(2,5‐dimethylphospholano)benzene; MEDAM: bis(dimethylanisyl)methyl; MOM: methoxymethyl; Naph: naphthyl; NMI: N‐methylimidazole; MWI: microwave irradiation; Norphos: 2,3‐bis(diphenylphosphino)‐bicyclo[2.2.1]hept‐5‐ene; Ns: nosyl (4‐nitrobenzene sulfonyl); Nu: nucleophile; Oct: octyl; Pent: pentyl; Ph: phenyl; PHAL: 1,4‐phthalazinediyl; Pin: pinacolato; PINAP: 4‐[2‐(diphenylphosphino)‐1‐naphthalenyl]‐N‐[1‐phenylethyl]‐1‐phthalazinamine; Pr: propyl; Py: pyridyl; PYBOX: 2,6‐bis(2‐oxazolyl)pyridine; QUINAP: 1‐(2‐diphenylphosphino‐1‐naphthyl)isoquinoline; QUOX: quinoline‐oxazoline; Segphos: 5,5′‐bis(diphenylphosphino)‐4,4′‐bi‐1,3‐benzodioxole; Solphos: 7,7′‐bis(diphenylphosphino)‐3,3′,4,4′‐tetrahydro‐4,4′‐dimethyl‐8,8′‐bis‐2H‐1,4‐benzoxazine; SPRIX: spirobis(isoxazoline); SYNPHOS: 6,6′‐bis(diphenylphosphino)‐2,2′,3,3′‐tetrahydro‐5,5′‐bi‐1,4‐benzodioxin; Taniaphos: [2‐diphenylphosphinoferrocenyl](N,N‐dimethylamino)(2‐diphenylphosphinophenyl)methane; TBS: tert‐butyldimethylsilyl; TC: thiophene carboxylate; TCPTTL: N‐tetrachlorophthaloyl‐tert‐leucinate; TEA: triethylamine; Tf: trifluoromethanesulfonyl; TFA: trifluoroacetic acid; THF: tetrahydrofuran; TMS: trimethylsilyl; Tol: tolyl; Ts: 4‐toluenesulfonyl (tosyl); C₃‐Tunephos: 1,13‐bis(diphenylphosphino)‐7,8‐dihydro‐6H‐dibenzo[f,h][1,5]dioxonin; VAPOL: 2,2′‐diphenyl‐[3,3′‐biphenanthrene]‐4,4′‐diol     

Forgotten monomers: access to α‐modified N‐vinylpyrrolidone polymers via C‐alkylation

Alkylation of N‐vinylpyrrolidone using lithium diisopropylamide and bis(2‐bromoethyl) ether was carried out to obtain 3‐(2‐(2‐bromoethoxy)ethyl)‐1‐vinyl‐2‐pyrrolidone ( 2 ). The derivative 2 represents a versatile starting molecule for further modification via nucleophilic displacement yielding, for example, the bicyclic 2‐vinyl‐8‐oxa‐2‐azaspiro[4.5]decan‐1‐one ( 4 ) or the ammonium salt 3‐diethoxy‐N,N′‐((dimethylbenzyl)ammonium bromide)‐1‐vinyl‐2‐pyrrolidone ( 10 ). Via free radical polymerization of 4 and 10 , the corresponding homopolymers were obtained. Copolymerization of 4 and 10 with N,N′‐diethylacrylamide yielded water‐soluble materials. The thermosensitive solubility of copolymers poly[(2‐vinyl‐8‐oxa‐2‐azaspiro[4.5]decan‐1‐one)‐co‐(N,N′‐diethylacrylamide)] and poly[(3‐diethoxy‐N,N′‐((dimethylbenzyl)ammonium bromide)‐1‐vinyl‐2‐pyrrolidone)‐co‐(N‐vinylpyrrolidone)] in water was investigated. © 2015 Society of Chemical Industry     

Preparation and properties of thermally stable copolyimides based on novel second‐order nonlinear–optical chromophore containing diamines

Thermally stable copolyimides were prepared from two novel second‐order nonlinear optical chromophores containing diamines, 4‐nitro‐4′‐[N‐(4,6‐di‐β‐aminoethylamino)‐1,3,5‐triazin‐2‐yl]aminoazobenzene (M1) and 4‐nitro‐4′‐[N‐(4,6‐di‐4‐aminophenylamino)‐1,3,5‐triazin‐2‐yl]aminoazobenzene (M2); two codiamines, 4,4′‐diamino‐3,3′‐dimethyl diphenylmethane (MMDA) and bis‐(3‐aminopropyl)‐1,1′,3,3′‐tetramethyldisiloxane (SiDA); and 3,3′,4,4′‐diphenyl ether tetracarboxylic acid dianhydride (OPDA). All copolyimides possess high glass transition temperatures (T_g's) between 237 and 271°C. Copolyimides based on M2 do not exhibit an obvious change in T_g as the M2 content is increased, while those based on M1 show a slight decrease in T_g as the M1 content is increased. All copolyimides exhibit high thermal decomposition temperatures. The copolyimides are soluble in aprotic solvents such as NMP, DMAc, DMF, DMSO, and 1,4‐butyrolactone. Some are even soluble in common low boiling point solvents such as THF and chloroform. The refractive index of a copolyimide is increased as the chromophore content is increased, while the birefringence of a copolyimide does not exhibit strong dependence on the chromophore content. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1619–1626, 2000     

Phosphorus‐containing epoxy resins: Thermal characterization

Three novel aromatic phosphorylated diamines, i.e., bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl} pyromellitamic acid (AP), 4,4′‐oxo bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AB) and 4,4′‐hexafluoroisopropylidene‐bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AF) were synthesized and characterized. These amines were prepared by solution condensation reaction of bis(3‐aminophenyl)methyl phosphine oxide (BAP) with 1,2,4,5‐benzenetetracarboxylic acid anhydride (P)/3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride (B)/4,4′‐(hexafluoroisopropylidene)diphthalic acid anhydride (F), respectively. The structural characterization of amines was done by elemental analysis, DSC, TGA, ¹H‐NMR, ¹³C‐NMR and FTIR. Amine equivalent weight was determined by the acetylation method. Curing of DGEBA in the presence of phosphorylated amines was studied by DSC and curing exotherm was in the temperature range of 195–267°C, whereas with conventional amine 4,4′‐diamino diphenyl sulphone (D) a broad exotherm in temperature range of 180–310°C was observed. Curing of DGEBA with a mixture of phosphorylated amines and D, resulted in a decrease in characteristic curing temperatures. The effect of phosphorus content on the char residue and thermal stability of epoxy resin cured isothermally in the presence of these amines was evaluated in nitrogen atmosphere. Char residue increased significantly with an increase in the phosphorus content of epoxy network. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2235–2242, 2002     

Synthesis and properties of polysiloxane containing N,N′-bis(diphenylsilyl)tetraphenylcyclodisilazane

A new kind of polysiloxane containing N,N′-bis(diphenylsilyl)tetraphenylcyclodisilazane was prepared by the anionic polymerization with a “seed solution” as initiator. The synthesis of monomers N,N′-bis(hydroxydiphenylsilyl)tetraphenylcyclodisilazane (BHPTPC), N,N′-bis(chlorodiphenylsilyl)tetraphenylcyclodisilazane (BCPTPC), and 1,3-dichloro-1,1,3,3-tetraphenyldisilazane (DCTPS) are all reported in this study. The synthesized polysiloxane containing N,N′-bis(diphenylsilyl)tetraphenylcyclodisilazane was characterized by ¹H–NMR, ²⁹Si–NMR, gel permeation chromatography (GPC), and intrinsic viscosity. The thermal stability of the polysiloxane was studied by isothermal gravimetric analysis (IGA). The results demonstrated that the synthesized polysiloxane containing N,N′-bis(diphenylsilyl)tetraphenylcyclodisilazane had excellent thermal stability. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 929–933, 2001     

Synthesis and characterization of new optically active poly(amide‐imide‐urethane) thermoplastic elastomers,derived from 4,4′‐(hexafluoroisopropylidene)‐N,N′‐bis(phthaloyl‐L‐leucine‐p‐aminobenzoic acid) and PEG‐MDI

A new class of optically active poly(amide‐imide‐urethane) was synthesized via two‐step reactions. In the first step, 4,4′‐methylene‐bis(4‐phenylisocyanate) (MDI) reacts with several poly(ethylene glycols) (PEGs) such as PEG‐400, PEG‐600, PEG‐2000, PEG‐4000, and PEG‐6000 to produce the soft segment parts. On the other hand, 4,4′‐(hexafluoroisopropylidene)‐N,N′‐bis(phthaloyl‐L ‐leucine‐p‐amidobenzoic acid) (2) was prepared from the reaction of 4,4′‐(hexafluoroisopropylidene)‐N,N′‐bis(phthaloyl‐L ‐leucine) diacid chloride with p‐aminobenzoic acid to produce hard segment part. The chain extension of the above soft segment with the amide‐imide 2 is the second step to give a homologue series of poly(amide‐imide‐urethanes). The resulting polymers with moderate inherent viscosity of 0.29–1.38 dL/g are optically active and thermally stable. All of the above polymers were fully characterized by IR spectroscopy, elemental analyses, and specific rotation. Some structural characterization and physical properties of this new optically active poly(amide‐imide‐urethanes) are reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2288–2294, 2004     

Effects of polymethylvinylsilicone oil with side tetraphenylphenyl groups on the radiation resistance of addition‐type silicone rubber

Polymethylvinylsilicone oil with side tetraphenylphenyl groups (called C₂ gum for short) as a low molecular additive was used in two kinds of addition‐type silicone rubber, polymethylvinyl silicone rubber and poly (dimethyl‐diphenyl) silicone rubber, and the radiation resistance of silicone rubbers obtained was investigated by γ‐rays radiation with the dose rate of 117 Gy/min at doses up to 350, 500, and 850 kGy, respectively. Moreover, the average molecular weight between crosslinks and mechanical properties of silicone rubbers after irradiated in air and N₂ were determined by toluene‐swelling method and on a XLS‐A rubber test instrument, respectively. The results show that C₂ gum can effectively improve the radiation resistance of silicone rubber. When C₂ gum is used in poly(dimethyl‐diphenyl) silicone rubber, phenyl groups and tetraphenylphenyl groups may have synergistic effect, and the radiation resistance is improved greatly. The suitable amount of C₂ gum used in silicone rubber is 10– 14 phr. The crosslinking density of vulcanizates irradiated in N₂ is higher than that of vulcanizates irradiated in air because of the oxidative degradation. The radiation protection mechanism of C₂ gum was also discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4144–4148, 2007     

Microwave assisted novel synthetic route for polyfluorenes containing triphenylamine and solubilizing alkyl moiety for blue emitting diodes

A series of blue electroluminescent polyfluorenes (PFs) containing triphenylamine and various alkyl moieties were synthesized using an Ni(0) mediated C?C Yamamoto coupling reaction assisted by microwaves. The synthesized PFs were characterized by various spectroscopic techniques. Their absorption and photoluminescence properties were investigated in solvent and found to possess characteristic electronic absorption and emission spectra. These PFs were found to emit in the blue region (407?415 nm) with high quantum yield in the range 0.41?0.73. Cyclic voltammetry studies of the PFs revealed that the compounds were stable under redox conditions with highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital in the range 5.24–5.29 eV and 1.98?2.01 eV, respectively. The E_HOMO for the PFs was similar to the most widely used hole transporting materials N,N′‐Di(1‐naphthyl)‐N,N′‐diphenyl‐(1,1′‐biphenyl)‐4,4′‐diamine (NPD), N,N′‐Bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine (TPD) and N²,N²,N²′,N²′,N⁷,N⁷,N⁷′,N⁷′‐octakis(4‐methoxyphenyl)‐9,9′‐spirobi[9H‐ fluorene]‐2,2′,7,7′‐tetramine, Spiro‐OMeTAD (spiro‐OMe‐TAD). The thermal stability observed for the PFs accounts for their use under ambient conditions. The electrochemical studies of the fabricated polymer light emitting diodes suggest that the PFs have potential to be used as hole transporting and blue electroluminescent materials for optoelectronic devices. © 2017 Society of Chemical Industry     

Synthesis and characterization of novel optically active poly(imide–urethane)s derived from N,N′‐(pyromellitoyl)‐bis‐(L‐leucine) diisocyanate and aromatic diols

N,N′‐(Pyromellitoyl)‐bis‐(L ‐leucine) diacid was reacted with ethyl chloroformate in the presence of triethylamine followed by reaction with activated sodium azide and gave N,N′‐(pyromellitoyl)‐bis‐(L ‐leucine) diacylazide in high yield. This diacylazide was heated in dry benzene and gave the unstable N,N′‐(pyromellitoyl)‐bis‐(L ‐leucine) diisocyanate ( 5 ) in quantitative yield. Thus, diisocyanate 5 was generated in situ and polycondensation reaction of this monomer with several aromatic diols, such as 4,4′‐dihydroxybiphenyl, 1,4‐hydroquinone, bisphenol A, phenolphthalein and 1,4‐dihydroxyanthraquinone, was performed in dry toluene under refluxing in the presence of 1,4‐diazabicyclo[2.2.2]octane (triethylenediamine) as a catalyst. The polymerization reactions proceeded within 48 h, producing a series of optically active poly(imide–urethane)s with good yield and moderate inherent viscosity in the range 0.18–0.28 dl g^?1. All of the above polymers were fully characterized by infrared spectra, elemental analyses and specific rotation. Some structural characterization and physical properties of these optically active poly(imide–urethane)s are reported Copyright © 2003 Society of Chemical Industry     

Synthesis,properties and pyrolysis of siloxane‐ and imide‐modified epoxy resin cured with siloxane‐containing dianhydride

Hydrosilylation of nadic anhydride with tetramethyl disiloxane yielded 5,5′‐(1,1,3,3‐tetramethyl disiloxane‐1,3‐diyl)‐bis‐norborane‐2,3‐dicarboxylic anhydride (I), which further reacted with 4‐aminophenol to give N,N′‐bis(4‐hydroxyphenyl)‐5,5′‐bis‐(1,1,3,3‐tetramethyl disiloxane‐1,3‐diyl)‐bis‐norborane‐2,3‐dicarboximide (II). Epoxidation of II with excess epichlorohydrin formed a siloxane‐ and imide‐modified epoxy oligomer (ie diglycidyl ether of N,N′‐bis(4‐hydroxyphenyl)‐5,5′‐bis(1,1,3,3‐tetramethyl disiloxane‐1,3‐diyl)‐bis‐norborane‐2,3‐dicarboximide) (III). Equivalent ratios of III/I of 1/1 and 1/0.8 were prepared and cured to produce crosslinked materials. Thermal mechanical and dynamic mechanical properties were investigated by TMA and DMA, respectively. It was noted that each of these two materials showed a glass transition temperature (T_g) higher than 160 °C with moderate moduli. The thermal degradation kinetics was studied with dynamic thermogravimetric analysis (TGA) and the estimated apparent activation energies were 111.4 kJ mol^?1 (in N₂), 117.1 kJ mol^?1 (in air) for III/I = 1/0.8, and 149.2 kJ mol^?1 (in N₂), 147.6 kJ mol^?1 (in air) for III/I = 1/1. The white flaky residue of the TGA char was confirmed to be silicon dioxide, which formed a barrier at the surface of the polymer matrix and, in part, accounted for the unique heat resistance of this material. Copyright © 2005 Society of Chemical Industry     

Polyurethane foams with the contribution of products of hydroxyalkylation of N,N′‐bis(2‐hydroxyalkyl)oxamides with alkylene carbonates—obtaining and properties

In the reactions of N,N′‐bis(2‐hydroxyethyl)oxamide (BHEOD) with an excess of ethylene carbonate (EC) and N,N′‐bis(2‐hydroxypropyl)oxamide (BHPOD) with an excess of propylene carbonate (PC), the hydroxyethoxy and hydroxypropoxy derivatives of oxamide (OD) were obtained, respectively, distinguished by an increased thermal stability. First time, these derivatives were used as polyol components to obtain foamed polyurethane plastics with the contribution of 4,4′‐diisocyanate diphenylmethane (MDI). The rigid polyurethane foams of a slight water uptake, good stability of dimensions, enhanced thermal stability, and compression strength were obtained. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Palladium(II) Complexes of C2‐Bridged Chiral Diphosphines: Application to Enantioselective Carbonyl‐Ene Reactions

(11bR,11′bR)‐4,4′‐(1,2‐Phenylene)bis[4,5‐dihydro‐3H‐dinaphtho[2,1‐c:1′,2′‐e]phosphepin] [abbreviated as (R)‐BINAPHANE], (3R,3′R,4S,4′S,11bS,11′bS)‐4,4′‐bis(1,1‐dimethylethyl)‐4,4′,5,5′‐tetrahydro‐3,3′‐bi‐3H‐dinaphtho[2,1‐c:1′,2′‐e]phosphepin [(S)‐BINAPINE], (1S,1′S,2R,2′R)‐1,1′‐bis(1,1‐dimethylethyl)‐2,2′‐biphospholane [(S,S,R,R)‐TANGPHOS] and (2R,2′R,5R,5′R)‐1,1′‐(1,2‐phenylene)bis[2,5‐bis(1‐methylethyl)phospholane] [(R,R)‐i‐Pr‐DUPHOS] are C₂‐bridged chiral diphosphines that form stable complexes with palladium(II) and platinum(II) containing a five‐membered chelate ring. The Pd(II)‐BINAPHANE catalyst displayed good to excellent enantioselectivities with ee values as high as 99.0% albeit in low yields for the carbonyl‐ene reaction between phenylglyoxal and alkenes. Its Pt(II) counterpart afforded improved yields while retaining satisfactory enantioselectivity. For the carbonyl‐ene reaction between ethyl trifluoropyruvate and alkenes, the Pd(II)‐BINAPHANE catalyst afforded both good yields and extremely high enantioselectivities with ees as high as 99.6%. A comparative study on the Pd(II) catalysts of the four C₂‐bridged chiral diphosphines revealed that Pd(II)‐BINAPHANE afforded the best enantioselectivity. The ee values derived from Pd(II)‐BINAPHANE are much higher than those derived from the other three Pd(II) catalysts. A comparison of the catalyst structures shows that the Pd(II)‐BINAPHANE catalyst is the only one that has two bulky (R)‐binaphthyl groups close to the reaction site. Hence it creates a deep chiral space that can efficiently control the reaction behavior in the carbonyl‐ene reactions resulting in excellent enantioselectivity.     

Monomers for adhesive polymers, 8a crosslinking polymerization of selected N‐substituted bis(acrylamide)s for dental filling materials

The free‐radical polymerization of bis‐(N‐ethylacrylamido)‐ethylenglycol ( I ), N,N′‐dimethyl‐1,6‐bis (acrylamido)‐hexan ( II ), and N,N′‐diethyl‐1,3‐bis(acrylamido)‐propan ( III ) were investigated. The cross‐linking polymerization was followed in bulk by using the ampoules technique and gravimetry. Polymerizations exhibited an abnormal kinetic behavior. For the monomer II , for example, the reaction order to 2,2′‐ azobisisobutyronitril (AIBN) initiator of 1.28, and the polymerization overall activation energy of 151 kJ/mol between 50 and 75°C were determined. The increasing temperature and decreasing initiator concentration resulted in an increase of double bonds consumption in the formed polymer network. At 75°C the residual unsaturation was under 2%, compared with 9.9% at 50°C. The monomer conversion‐time dependences were complemented also with differential scanning calorimetry (DSC) recording the heat released during polymerization. The extension of peak time with decreasing the instant heat flow rate at this point sort the studied bis(acrylamide)s according the reactivity in the following sequence: monomer III > I > II . The polymer samples sol–gel analyses in ethanol allowed the determination of the molecular weight M_c between the network crosslinks. The presence of microgel particles at the very beginning of polymerization and the changes in chain conformation with temperature we consider as the way in which was affected the polymerization kinetics of these monomers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of novel polyaspartimides derived from 2,2′‐dimethyl‐4,4′‐bis(4‐maleimidophenoxy)biphenyl and various diamines

A novel bismaleimide, 2,2′‐dimethyl‐4,4′‐bis(4‐maleimidophenoxy)biphenyl, containing noncoplanar 2,2′‐dimethylbiphenylene and flexible ether units in the polymer backbone was synthesized from 2,2′‐dimethyl‐4,4′‐bis(4‐aminophenoxy)biphenyl with maleic anhydride. The bismaleimide was reacted with 11 diamines using m‐cresol as a solvent and glacial acetic acid as a catalyst to produce novel polyaspartimides. Polymers were identified by elemental analysis and infrared spectroscopy, and characterized by solubility test, X‐ray diffraction, and thermal analysis (differential scanning calorimetry and thermogravimetric analysis). The inherent viscosities of the polymers varied from 0.22 to 0.48 dL g⁻¹ in concentration of 1.0 g dL⁻¹ of N,N‐dimethylformamide. All polymers are soluble in N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide, dimethylsulfoxide, pyridine, m‐cresol, and tetrahydrofuran. The polymers, except PASI‐4, had moderate glass transition temperature in the range of 188°–226°C and good thermo‐oxidative stability, losing 10% mass in the range of 375°–426°C in air and 357°–415°C in nitrogen. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 279–286, 1999     

A Double Prodrug with Improved Membrane Permeability over the Parent Chelator HBED Provides Superior Cytoprotection against Hydrogen Peroxide

The clinical use of N,N′‐bis(2‐hydroxybenzyl)ethylenediamine‐N,N′‐diacetic acid (HBED) has been hindered by its lack of bioavailability. N,N′‐bis(2‐boronic pinacol ester benzyl)ethylenediamine‐N,N′‐diacetic acid methyl, ethyl, and isopropyl esters 7 a – c , respectively, and their dimesylate salts 8 a – c , are double prodrugs that mask the two phenolate and two carboxylate donors of HBED as boronic esters and carboxylate esters, respectively. Their activation by chemical hydrolysis and oxidation, their passive diffusivity, and their cytoprotective capabilities have been investigated here. 8 a – c hydrolyzed in minimum essential medium at 37 °C with half‐lives of 0.69, 0.81, and 2.28 h, respectively. The intermediate formed, 9 [N,N′‐bis(2‐boronic acid benzyl)ethylenediamine‐N,N′‐diacetic acid], then underwent oxidative deboronation by H₂O₂ to give HBED (k=1.82 m ^?1 min^?1). Solubility measurements in mineral oil and in phosphate buffer indicated that 7 a had a better balance between lipid and aqueous solubilities than did HBED. 7 a was also able to passively diffuse across a lipid‐like silicone membrane (log flux=?0.36), whereas HBED‐HCl was not. 8 c provided better protection to retinal cells than did HBED against a lethal dose of H₂O₂ (84 % vs. 28 % protection, respectively, at 44 μm ). These results suggest that the double prodrugs have better membrane permeability than does HBED, and therefore could be therapeutically useful for improving the delivery of HBED.     

Efficient Inhibition of Telomerase by Nickel–Salophen Complexes

Four nickel(II)–salophen complexes containing alkyl‐imidazolium chains connected at the ortho or meta positions were prepared: N,N′‐bis(2‐hydroxy‐4‐methyl‐3H‐imidazol‐1‐iumbenzylideneamino)phenylenediamine ( 1 ), N,N′‐bis(2‐hydroxy‐3‐methyl‐3H‐imidazol‐1‐iumbenzylideneamino)phenylenediamine ( 2 ), N,N′‐bis(2‐hydroxy‐3‐methyl‐3H‐imidazol‐1‐iumbenzylideneamino)methyl‐3H‐imidazol‐1‐iumphenylenediamine ( 3 ), and N,N′‐bis(2‐hydroxy‐4‐methyl‐3H‐imidazol‐1‐iumbenzylideneamino)methyl‐3H‐imidazol‐1‐iumphenylenediamine ( 4 ). They protect G‐quadruplex DNA (G₄‐DNA) against thermal denaturation and show K_A values in the range of 7.4×10⁵ to 4×10⁷ m ^?1 for G₄‐DNA models. Complex 4 exhibits an IC₅₀ value of 70 nm for telomerase inhibition.     

Synthesis and ring‐opening polymerization of macrocyclic aromatic sulfide oligomers

A series of macrocyclic(arylene sulfide) oligomers were synthesized by reaction of 4,4′‐oxybis(benzenethiol) with a number of difluoro compounds in dimethylformamide (DMF) in the presence of anhydrous K₂CO₃ under high dilution conditions. The difluoro compound can be 4,4′‐difluorobenzophenone, bis(4‐fluorophenyl)sulfone or 1,3‐bis(4‐fluorobenzoyl)benzene. Detailed structural characterization of these oligomers by matrix‐assisted laser desorption and ionization‐time of flight‐mass spectroscopy (MALDI‐TOF‐MS) demonstrated their cyclic nature. The MALDI‐TOF‐MS technique has proved to be a powerful tool to analyze these cyclics. These cyclic oligomers are amorphous and highly soluble in DMF and N,N′‐dimethyl acetamide. Moreover, these cyclic(arylene sulfide) oligomers readily underwent ring‐opening polymerization in the melt at 285 °C in the presence of 2,2′‐dibenzothiazole disulfide, affording linear, high molecular weigh poly(aromatic sulfide)s. These polymers are insoluble in most common solvents. Copyright © 2004 Society of Chemical Industry