Synthesis and characterization of poly(L‐lactide‐co‐ε‐caprolactone) (B)‐poly(L‐lactide) (A) ABA block copolymers

ABA triblock copolymers of L ‐lactide (LL) and ε‐caprolactone (CL), designated as PLL‐P(LL‐co‐CL)‐PLL, were synthesized via a two‐step ring‐opening polymerization in bulk using diethylene glycol and stannous octoate as the initiating system. In the first‐step reaction, an approximately 50:50 mol% P(LL‐co‐CL) random copolymer (prepolymer) was prepared as the middle (B) block. This was then chain extended in the second‐step reaction by terminal block polymerization with more L ‐lactide. The percentage yields of the triblock copolymers were in excess of 95%. The prepolymers and triblock copolymers were characterized using a combination of dilute‐solution viscometry, gel permeation chromatography (GPC), ¹H‐ and ¹³C‐NMR, and differential scanning calorimetry (DSC). It was found that the molecular weight of the prepolymer was controlled primarily by the diethylene glycol concentration. All of the triblock copolymers had molecular weights higher than their respective prepolymers. ¹³C‐NMR analysis confirmed that the prepolymers contained at least some random character and that the triblock copolymers consisted of additional terminal PLL end (A) blocks. From their DSC curves, the triblock copolymers were seen to be semi‐crystalline in morphology. Their glass transition, solid‐state crystallization, and melting temperature ranges, together with their heats of melting, all increased as the PLL end (A) block length increased. Copyright © 2005 John Wiley & Sons, Ltd.     

From poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N‐isopropylacrylamide) triblock copolymer to poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide) hydrogels: Synthesis and rapid deswelling and reswelling behavior of hydrogels

Poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N‐isopropylacrylamide) (PNIPAAm‐b‐PEO‐b‐PNIPAAm) triblock copolymer was synthesized via the reversible addition‐fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) process with xanthate‐terminated poly(ethylene oxide) (PEO) as the macromolecular chain transfer agent. The successful synthesis of the ABA triblock copolymer inspired the preparation of poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide) (PNIPAAm‐b‐PEO) copolymer networks with N,N′‐methylenebisacrylamide as the crosslinking agent with the similar approach. With the RAFT/MADIX process, PEO chains were successfully blocked into poly(N‐isopropylacrylamide) (PNIPAAm) networks. The unique architecture of PNIPAAm‐b‐PEO networks allows investigating the effect of the blocked PEO chains on the deswelling and reswelling behavior of PNIPAAm hydrogels. It was found that with the inclusion of PEO chains into the PNIPAAm networks as midblocks, the swelling ratios of the hydrogels were significantly enhanced. Furthermore, the PNIPAAm‐b‐PEO hydrogels displayed faster response to the external temperature changes than the control PNIPAAm hydrogel. The accelerated deswelling and reswelling behaviors have been interpreted based on the formation of PEO microdomains in the PNIPAAm networks, which could act as the hydrophilic tunnels to facilitate the diffusion of water molecules in the PNIPAAm networks. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Behavior of 3(2‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones and 3(3‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones as alkylating agents: A comparative study

3(2‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones and 3(3‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones were prepared as a mixture of (E) and (Z) stereoisomers by condensing pyridine‐2‐carboxaldehyde and pyridine‐3‐carboxaldehyde with 3‐aroylpropionic acids. The reaction of the furanones 6 and 7 with anhydrous aluminium chloride in benzene led to the formation of 4,4‐diaryl‐1‐(2‐pyridinyl)but‐1,3‐diene ( 8 ) and 4,4‐diaryl‐1‐(3‐pyridinyl)but‐1,3‐diene ( 9 ) as mixtures of geometrical (E,E‐ and E,Z‐) stereoisomers via an intermolecular alkylation mode. When the reaction was carried out in tetrachloroethane as a solvent, the reaction of 6 gave 5‐arylquinoline‐7‐carboxylic acid via intramolecular alkylation mode. This may be considered as a novel method for the synthesis of quinoline derivatives. J. Heterocyclic Chem., (2011).     

A highly efficient synthesis of (Z)‐1‐aryl‐2‐silyl‐1‐ stannylethenes and their conversion to (E)‐2‐ arylethenyl‐, (Z)‐2‐(2‐pyridyl)ethenyl‐ and allenyl‐silanes

A Pd(dba)₂–P(OEt)₃ combination allowed the silastannation of arylacetylenes, 1‐hexyne or propargyl alcohols with tributyl(trimethylsilyl)stannane to take place at room temperature, producing (Z)‐2‐silyl‐1‐stannyl‐1‐substituted ethenes in high yields. Novel silyl(stannyl)ethenes were fully characterized by ¹H‐, ¹³C‐, ²⁹Si‐ and ¹¹⁹Sn‐NMR as well as infrared and mass analyses. Treatment of a series of (Z)‐1‐aryl‐2‐silyl‐1‐stannylethenes and (Z)‐1‐(3‐pyridyl)‐2‐silyl‐1‐stannylethene with hydrochloric acid or hydroiodic acid in the presence of tetraethylammonium chloride (TEACl) or tetrabutylammonium iodide (TBAI) led to the exclusive formation of (E)‐trimethyl(2‐arylethenyl)silanes with high stereoselectivity. A similar reaction of (Z)‐1‐(2‐anisyl)‐2‐silyl‐1‐stannylethene also produced E‐type trimethyl[2‐(2‐anisyl)ethenyl]silane, while (Z)‐trimethyl [2‐(2‐pyridyl)ethenyl]silane was produced exclusively from (Z)‐1‐(2‐pyridyl)‐2‐silyl‐1‐stannylethene. Protodestannylation of (Z)‐1‐[hydroxy(phenyl)methyl]‐2‐silyl‐1‐stannylethene with trifluoroacetic acid took place via the β‐elimination of hydroxystannane, providing trimethyl(3‐phenylpropa‐1,2‐dienyl)silane quite easily. The destannylation products were also fully characterized. Copyright © 2007 John Wiley & Sons, Ltd.     

Nanofiltration membranes based on poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)‐graft‐poly(styrene sulfonic acid)

Graft copolymers comprising poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) backbone and poly(styrene sulfonic acid) side chains, i.e. P(VDF‐co‐CTFE)‐g‐PSSA were synthesized using atom transfer radical polymerization (ATRP) for composite nanofiltration (NF) membranes. Direct initiation of the secondary chlorinated site of CTFE units facilitates grafting of PSSA, as revealed by FT‐IR spectroscopy. The successful “grafting from” method and the microphase‐separated structure of the graft copolymer were confirmed by transmission electron microscopy (TEM). Wide angle X‐ray scattering (WAXS) also showed the decrease in the crystallinity of P(VDF‐co‐CTFE) upon graft copolymerization. Composite NF membranes were prepared from P(VDF‐co‐CTFE)‐g‐PSSA as a top layer coated onto P(VDF‐co‐CTFE) ultrafiltration support membrane. Both the rejections and the flux of composite membranes increased with increasing PSSA concentration due to the increase in SO₃H groups and membrane hydrophilicity, as supported by contact angle measurement. The rejections of NF membranes containing 47 wt% of PSSA were 83% for Na₂SO₄ and 28% for NaCl, and the solution flux were 18 and 32 L/m² hr, respectively, at 0.3 MPa pressure. Copyright © 2008 John Wiley & Sons, Ltd.     

Assembly of Three 2D Metal‐Organic Frameworks (MOFs) Derived from Flexible Ligands, 1,4‐bis(3‐pyridyl)‐2,3‐diaza‐1,3‐butadiene (3‐bpd) and/or 1,2‐bis(4‐pyridyl)ethane (dpe)

Three coordination polymers, {[Cd(3‐bpd)₂(NCS)₂]×C₂H₅OH}_n ( 1 ), {[Cd(3‐bpd)(dpe)(NO₃)₂]×(3‐bpd)}₂ ( 2 ), {[Cd(dpe)₂(NCS)₂]×3‐bpd×2H₂O}_n ( 3 ) (3‐bpd = 1,4‐bis(3‐pyridyl)‐2,3‐diaza‐1,3‐butadiene; dpe = 1,2‐bis(4‐pyridyl)ethane), were prepared and structurally characterized by a single‐crystal X‐ray diffraction method. In compound 1 , each Cd(II) ion is six‐coordinate bonded to six nitrogen atoms from four 3‐bpd and two NCS^? ligands. The 3‐bpd acts as a bridging ligand connecting the Cd(II) ion to generate a 2D layered metal‐organic framework (MOF) by using a rhomboidal‐grid as the basic building units with the 4⁴ topology. In compound 2 , the Cd(II) ion is also six‐coordinate bonded to four nitrogen atoms of two 3‐bpd, two dpe and two oxygen atoms of two NO₃^? ligands. The 3‐bpd and dpe ligands both adopt bis‐monodentate coordination mode connecting the Cd(II) ions to generate a 2D layered MOF by using a rectangle‐grid as the basic building units with the 4⁴ topology. In compound 3 , two crystallographically independent Cd(II) ions are both coordinated by four nitrogen atoms of dpe ligands in the basal plane and two nitrogen atom of NCS^? in the axial sites. The dpe acts as a bridging ligand to connect the Cd(II) ions forming a 2D interpenetrating MOFs by using a square‐grid as the basic unit with the 4⁴ topology. All of their 2D layered MOFs in compounds 1 ‐ 3 are then arranged in a parallel non‐interpenetrating ABAB—packing manner in 1 and 2 , and mutually interpenetrating manner in 3 , respectively, to extend their 3D supramolecular architectures with their 1D pores intercalated with solvent (ethanol in 1 or H₂O in 3 ) or free 3‐bpd molecules in 2 and 3 , respectively. The photoluminescence measurements of 1 ‐ 3 reveal that the emission is tentatively assigned to originate from π‐π* transition for 1 and 2 and probably due to ligand‐center luminescence for compounds 3 , respectively.     

Cyclotris(paraquat‐p‐phenylenes)

Reported here is the synthesis, solid‐state characterization, and redox properties of new triangular, threefold symmetric, viologen‐containing macrocycles. Cyclotris(paraquat‐p‐phenylene) ( CTPQT⁶⁺ ) and cyclotris(paraquat‐p‐1,4‐dimethoxyphenylene) ( MCTPQT⁶⁺ ) were prepared and their X‐ray single‐crystal (super)structures reveal intricate three‐dimensional packing. MCTPQT⁶⁺ results in nanometer‐sized channels, in contrast with its parent counterpart CTPQT⁶⁺ which crystallizes as a couple of polymorphs in the form of intercalated assemblies. In the solid state, MCTPQT^3(.+) exhibits stacks between the 1,4‐dimethoxyphenylene and bipyridinium radical cations, providing new opportunities for the manipulation and control of the recognition motif associated with viologen radical cations. These redox‐active cyclophanes demonstrate that geometry‐matching and weak intermolecular interactions are of paramount importance in dictating the formation of their intricate solid‐state superstructures.     

Synthesis of star‐shaped poly(D,L‐lactic acid‐alt‐glycolic acid)‐b‐poly(L‐lactic acid) with the poly(D,L‐lactic acid‐alt‐glycolic acid) macroinitiator and stannous octoate catalyst

Two types of three‐arm and four‐arm, star‐shaped poly(D,L ‐lactic acid‐alt‐glycolic acid)‐b‐poly(L ‐lactic acid) (D,L ‐PLGA50‐b‐PLLA) were successfully synthesized via the sequential ring‐opening polymerization of D,L ‐3‐methylglycolide (MG) and L ‐lactide (L ‐LA) with a multifunctional initiator, such as trimethylolpropane and pentaerythritol, and stannous octoate (SnOct₂) as a catalyst. Star‐shaped, hydroxy‐terminated poly(D,L ‐lactic acid‐alt‐glycolic acid) (D,L ‐PLGA50) obtained from the polymerization of MG was used as a macroinitiator to initiate the block polymerization of L ‐LA with the SnOct₂ catalyst in bulk at 130 °C. For the polymerization of L ‐LA with the three‐arm, star‐shaped D,L ‐PLGA50 macroinitiator (number‐average molecular weight = 6800) and the SnOct₂ catalyst, the molecular weight of the resulting D,L ‐PLGA50‐b‐PLLA polymer linearly increased from 12,600 to 27,400 with the increasing molar ratio (1:1 to 3:1) of L ‐LA to MG, and the molecular weight distribution was rather narrow (weight‐average molecular weight/number‐average molecular weight = 1.09–1.15). The ¹H NMR spectrum of the D,L ‐PLGA50‐b‐PLLA block copolymer showed that the molecular weight and unit composition of the block copolymer were controlled by the molar ratio of L ‐LA to the macroinitiator. The ¹³C NMR spectrum of the block copolymer clearly showed its diblock structures, that is, D,L ‐PLGA50 as the first block and poly(L ‐lactic acid) as the second block. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 409–415, 2002     

Melt spinning of propylene carbonate‐plasticized poly(acrylonitrile)‐co‐poly(methyl acrylate)

The primary use of poly(acrylonitrile) (PAN) fibers, commonly referred to as acrylic fibers, is in textile applications like clothing, furniture, carpets, and awnings. All commercially available PAN fibers are processed by solution spinning; however, alternative, more cost‐effective processes like melt spinning are still highly desired. Here, the melt spinning of PAN‐co‐poly(methyl acrylate) (PMA) plasticized with propylene carbonate (PC) at 175°C is reported. The use of methyl acrylate (MA) as comonomer and PC as an external plasticizer renders the approach a combination of internal and external plasticization. Various mixtures of PAN and PC used in this work were examined by rheology, subjected to melt spinning, followed by discontinuous and continuous washing, respectively. The best fibers were derived from a PAN‐co‐PMA copolymer containing 8.1 mol‐% of MA having a number‐average molecular weight M _n of 34 000 g/mol, spun in the presence of 22.5 wt.‐% of PC. The resulting fibers were analyzed by scanning electron microscopy and wide‐angle X‐ray scattering (WAXS), and were subjected to mechanical testing.     

Synthesis of three‐armed poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L‐proline)‐block‐poly(ε‐caprolactone) copolymers

A series of novel types of three‐armed poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline)‐block‐poly(ε‐caprolactone) (PHpr‐b‐PCL) copolymers were successfully synthesized via melt block copolymerization of trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline (N‐CBz‐Hpr) and ε‐caprolactone (ε‐CL) with a trifunctional initiator trimethylolpropane (TMP) and stannous octoate (SnOct₂) as a catalyst. For the homopolycondensation of N‐CBz‐Hpr with TMP initiator and SnOct₂ catalyst, the number‐average molecular weight (M_n) of prepolymer increases from 530 to 3540 g mol^?1 with the molar ratio of monomer to initiator (3–30), and the molecular weight distribution (M_w/M_n) is between 1.25 to 1.32. These three‐armed prepolymer PHpr were subsequently block copolymerized with ε‐caprolactone (ε‐CL) in the presence of SnOct₂ as a catalyst. The M_n of the copolymer increased from 2240 to 18,840 g mol^?1 with the molar ratio (0–60) of ε‐CL to PHpr. These products were characterized by differential scanning calorimetry (DSC), ¹H NMR, and gel permeation chromatography. According to DSC, the glass‐transition temperature (T_g) of the three‐armed polymers depended on the molar ratio of monomer/initiator that were added. In vitro degradation of these copolymers was evaluated from weight‐loss measurements and the change of M_n and M_w/M_n. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1708–1717, 2005     

Syntheses and Crystal Structures of 2,7‐Di(trimethylsilyl)thieno[3,2‐e]benzothiophene, 1,2,5,6(5)‐Tetra(trimethylsilyl)‐1,2,5,6(2,3)‐tetrathiophenacyclooctaphan‐3(z),7(z)‐diene,and 2,7‐Di(trimethylsilyl)thieno[3,2‐e]benzothiophene‐4‐ol

With 5,5′‐di(trimethylsilanyl)‐3,3′‐bithiophenyl‐2,2′‐dicarbaldehyde as precusor, 2,7‐di(trimethylsilyl)‐thieno[3,2‐e]benzothiophene was obtained effiently via intramolecular McMurry reaction. At the same time, another two unexpected compounds, 1,2,5,6(5)‐tetra‐(trimethylsilyl)‐1,2,5,6(2,3)‐tetrathiophena‐cyclooctaphan‐3(Z),7(Z)‐diene and 2,7‐di(trimethylsilyl)thieno[3,2‐e]‐benzothiophene‐4‐ol were generated as side products. The crystal structures of all three title compounds are described.     

Carbon fibers prepared from tailored reversible‐addition‐fragmentation transfer copolymerization‐derived poly(acrylonitrile)‐co‐poly(methylmethacrylate)

Reversible‐addition fragmentation‐transfer (RAFT) polymerization of acrylonitrile (AN) was performed with 2‐(2‐cyano‐2‐propyl‐dodecyl)trithiocarbonate as RAFT agent and azobis(isobutyronitrile) as initiator. Linear polyacrylonitrile (M_n = 133,000 g/mol, PDI = 1.34) was prepared within 7 h in 86% isolated yield. High‐yield copolymerization with methyl methacrylate (MMA) was performed and copolymerization parameters were determined according to Kelen and Tüdös at 90 °C in ethylene carbonate yielding r_AN = 0.2 and r_MMA = 0.42. The molecular weights, polydispersity indices (PDIs), and MMA content of the copolymer were adjusted in a way that precursor fibers could be prepared via wet spinning. These precursor fibers had round cross‐sections and a dense morphology, showing tenacities of 40–50 cN/tex and elastic moduli of 900–1000 cN/tex at a fineness of 1 dtex and an elongation of 13–17%. Precursor fibers were oxidatively stabilized and then carbonized at different temperatures. A maximum tensile strength of 2.5 GPa was reached at 1350 °C. Thermal analysis, infrared and Raman spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and tensile testing were used to characterize the resulting carbon fibers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1322–1333     

Synthesis and properties of biomimetic poly(L‐glutamate)‐b‐poly(2‐acryloyloxyethyllactoside)‐b‐poly(L‐glutamate) triblock copolymers

A novel class of biomimetic glycopolymer–polypeptide triblock copolymers [poly(L ‐glutamate)–poly(2‐acryloyloxyethyllactoside)–poly(L ‐glutamate)] was synthesized by the sequential atom transfer radical polymerization of a protected lactose‐based glycomonomer and the ring‐opening polymerization of β‐benzyl‐L ‐glutamate N‐carboxyanhydride. Gel permeation chromatography and nuclear magnetic resonance analyses demonstrated that triblock copolymers with defined architectures, controlled molecular weights, and low polydispersities were successfully obtained. Fourier transform infrared spectroscopy of the triblock copolymers revealed that the α‐helix/β‐sheet ratio increased with the poly(benzyl‐L ‐glutamate) block length. Furthermore, the water‐soluble triblock copolymers self‐assembled into lactose‐installed polymeric aggregates; this was investigated with the hydrophobic dye solubilization method and ultraviolet–visible analysis. Notably, this kind of aggregate may be useful as an artificial polyvalent ligand in the investigation of carbohydrate–protein recognition and for the design of site‐specific drug‐delivery systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5754–5765, 2004     

meso‐(2‐Pyridyl)‐boron(III)‐subporphyrin: Perimeter Iridium(III) Coordination

Peripherally metalated porphyrinoids are promising functional π‐systems displaying characteristic optical, electronic, and catalytic properties. In this work, 5‐(2‐pyridyl)‐ and 5,10,15‐tri(2‐pyridyl)‐B^III‐subporphyrins were prepared and used to produce cyclometalated subporphyrins by reactions with [Cp*IrCl₂]₂, which proceeded through an efficient C?H activation to give the corresponding mono‐ and tri‐Ir^III complexes, respectively. While the mono‐Ir^III complex was obtained as a diastereomeric mixture, a C₃‐symmetric tri‐Ir^III complex with the three Cp*‐units all at the concave side was predominantly obtained in a high yield of 90 %, which displays weak NIR phosphorescence even at room temperature in degassed CH₂Cl₂, differently from the mono‐Ir^III complexes.     

Spectroscopic,DFT and antimicrobial activity of Zn(II), Zr(IV), Ce(IV) and U(VI) complexes of N,N‐ chelated 4,6‐bis (4‐chlorophenyl)‐2‐amino‐1,2‐dihydropyridine‐3‐carbinitrile

Four novel metal complexes of 4,6‐bis (4‐chlorophenyl)‐2‐amino‐1,2‐dihydropyridine‐3‐carbinitrile (H₂L) with Zn(II), Zr(IV), Ce(IV) and U(VI) were synthesized. The structure was elucidated using elemental analysis, melting point, molar conductivity; spectroscopic techniques (IR, ¹H NMR, UV–Vis., mass spectra) as well as thermo gravimetric analysis. The spectroscopic data proved that H₂L chelated with the metal ions as a bidentate ligand through N_amino and N_carbinitrile atoms. The molecular structure of the complexes was determined using density functional theory (DFT). The central metal ion in each complex is six‐coordinate and the angles around it vary from 62.74° to 166.46°; these values agree with distorted octahedral geometry. The calculated total energy of the complexes found in the region – 406.342 to ?459.717 au and the dipole moment change from 4.675 to 13.171D. The antibacterial and antifungal activities of the ligand, metal salts and complexes were estimated on some microorganisms. The complexes showed significant antibacterial profile in comparison to the free ligand.     

RGD peptide grafted biodegradable amphiphilic triblock copolymer poly(glutamic acid)‐b‐poly(L‐lactide)‐b‐poly(glutamic acid): Synthesis and self‐assembly

A novel amphiphilic biodegradable triblock copolymer (PGL‐PLA‐PGL) with polylactide (PLA) as hydrophobic middle block and poly(glutamic acid) (PGL) as hydrophilic lateral blocks was successfully synthesized by ring‐opening polymerization (ROP) of L ‐lactide (LA) and N‐carboxy anhydride (NCA) consecutively and by subsequent catalytic hydrogenation. The results of cell experiment of PGL‐PLA‐PGL suggested that PGL could improve biocompatibility of polyester obviously. The copolymer could form micelles of spindly shape easily in aqueous solution. The pendant carboxyl groups of the triblock copolymer were further activated with N‐hydroxysuccinimide and combined with a cell‐adhesive peptide GRGDSY. Incorporation of the oligopeptide further enhanced the hydrophilicity and led to formation of spherical micelles. PGL‐PLA‐PGL showed better cell adhesion and spreading ability than pure PLA and the GRGDSY‐containing copolymer exhibited even further improvement in cell adhesion and spreading ability, indicating that the copolymer could find a promising application in drug delivery or tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3218–3230, 2007     

Synthesis of 2,2,5,5‐Tetrasubstituted 1,4‐Dioxa‐2,5‐disilacyclohexanes via Organotin(IV)‐Catalyzed Transesterification of (Acetoxymethyl)alkoxysilanes

(Acetoxymethyl)silanes 2 , 7 a – c , and 10 a – c with at least one alkoxy group, of the general formula (AcOCH₂)Si(OR)_3?n(CH₃)_n (R: Me, Et, iPr; n=0, 1, 2), were synthesized from the corresponding (chloromethyl)silanes 1 , 6 a – c , and 9 a – c by treatment with potassium acetate under phase‐transfer‐catalysis conditions. These compounds were found to provide 2,2,5,5‐organo‐substituted 1,4‐dioxa‐2,5‐disilacyclohexanes 3 , 8 a – c , and 11 a – c if treated with organotin(IV) catalysts such as dioctyltin oxide. The reaction proceeds through transesterification of the acetoxy and alkoxy units followed by ring‐closure to form a dimeric six‐membered ring. The corresponding alkyl acetates are formed as the reaction by‐products. With these mild conditions, the method overcomes the drawbacks of previously reported synthetic routes to furnish 2,2,5,5‐tetramethyl‐1,4‐dioxa‐2,5‐disilacyclohexane ( 3 ) and even allows the synthesis of 1,4‐dioxa‐2,5‐disilacyclohexanes bearing hydrolytically labile alkoxy substituents at the silicon atom in good yields and high purity. These new materials were fully characterized by NMR spectroscopy, elemental analysis, mass spectrometry, and X‐ray analysis (trans‐ 8 a ).     

Poly(N‐vinyl pyrrolidone)‐block‐Poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) triblock copolymers: Synthesis via RAFT/MADIX process,self‐assembly behavior,and photophysical properties

Poly(N‐vinyl pyrrolidone)‐block‐poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) (PVP‐b‐PVK‐b‐PVP) triblock copolymers were synthesized via sequential reversible addition‐fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) process. First, 1,4‐phenylenebis(methylene)bis(ethyl xanthate) was used as a chain transfer agent to mediate the radical polymerization of N‐vinyl carbazole (NVK). It was found that the polymerization was in a controlled and living manner. Second, one of α,ω‐dixanthate‐terminated PVKs was used as the macromolecular chain transfer agent to mediate the radical polymerization of N‐vinyl pyrrolidone (NVP) to obtain the triblock copolymers with various lengths of PVP blocks. Transmission electron microscopy (TEM) showed that the triblock copolymers in bulks were microphase‐separated and that PVK blocks were self‐organized into cylindrical microdomains, depending on the lengths of PVP blocks. In aqueous solutions, all these triblock copolymers can self‐assemble into the spherical micelles. The critical micelle concentrations of the triblock copolymers were determined without external adding fluorescence probe. By analyzing the change in fluorescence intensity as functions of the concentration, it was judged that the onset of micellization occurred at the concentration while the FL intensity began negatively to deviate from the initial linear increase with the concentration. Fluorescence spectroscopy indicates that the self‐assembled nanoobjects of the PVP‐b‐PVK‐b‐PVP triblock copolymers in water were capable of emitting blue/or purple fluorescence under the irradiation of ultraviolet light. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1852–1863     

Synthesis and Investigation of 2,6‐Bis(picrylamino)‐3,5‐dinitro‐pyridine (PYX) and Its Salts

2,6‐Bis(picrylamino)pyridine ( 1 ; pre‐PYX) and 2,6‐bis(picrylamino)‐3,5‐dinitropyridine ( 2 ; PYX) were synthesized using an improved literature method. Compounds 1 and 2 were reinvestigated in detail and the X‐ray structures ( 1 : ρ=1.698 g cm^?3 at 173 K; 2 : ρ=1.757 g cm^?3 at 298 K) are given. The reactions of 2 with different bases, such as alkali metal hydroxides (sodium, potassium, rubidium, cesium), and N‐bases (ammonia, hydrazine, hydroxylamine, guanidinium carbonate, aminoguanidine bicarbonate) are reported, as well as metathesis reactions producing energetic salts. Several energetic compounds were synthesized and characterized for the first time using vibrational (IR, Raman) and multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and DSC. The crystal structures of four energetic salts were determined using low temperature single‐crystal X‐ray diffraction. Heats of formation for the metal‐free species were calculated using the Gaussian 09 software. Detonation parameters were estimated using the EXPLO5 program. The sensitivities towards impact, friction, and electrostatic discharge were also determined.     

Hydrophilic surface modification of polydimetylsiloxane‐co‐2‐hydroxyethylmethacrylate (PDMS‐HEMA) by Silwet L‐77 (heptamethyltrisiloxane) surface treatment

Biomaterials and their host organism's quintessential place of interaction are the surfaces of materials, as transportation of liquids within microchannels requires hydrophilic surfaces. Modifying the hydrophobic surface of polydimethylsiloxane (PDMS) into a hydrophilic one which can be used in biomaterials remains a big challenge. Herein, PDMS‐hydroxyethylmethacrylate (HEMA) films were prepared by the condensation of PDMS using isophorone diisocyanate as a cross‐linker, followed by the incorporation of HEMA via radical copolymerization. The as‐prepared PDMS‐HEMA films were thereafter hydrophilized via physical treatment with heptamethyltrisiloxane. The surface properties of the obtained PDMS‐HEMA films were characterized in wettability, morphology, topography, swelling, mechanical properties, and protein adsorption. Compared to pristine PDMS‐HEMA as control, the surface wettability, roughness, and protein adsorption of the hydrophilized PDMS‐HEMA films were significantly improved while the films also exhibited excellent optical properties. However, the improvement of the swelling properties remains insignificant, indicating that the interior morphology was still based on the hydrophobic siloxane PDMS. The long‐term hydrophilicity was considered good as no significant hydrophobic recovery was noticeable in a period of 5 months after treatment.