Diels–Alder reactions of carbonyl-containing dienophiles catalyzed by tungstophosphoric acid supported on silica gel

Tungstophosphoric acid (H₃PW₁₂O₄₀) supported on silica gel proved to be an active heterogeneous catalyst for Diels–Alder reactions of enones with various dienes. The Diels–Alder adducts were formed in high regio- and/or stereoselectivity. In some cases the Diels–Alder reactions were accompanied by competing polymerization of the starting compounds. We also found that trifluoromethanesulfonic acid (triflic acid) is an effective homogeneous catalyst for the reaction of unprotected but-3-en-2-one (methyl vinyl ketone) with 1,3-cyclohexadiene, albeit with a lower activity than tungstophosphoric acid. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non‐covalent interactions of pyrene end‐labeled star poly(ɛ‐caprolactone)s with fullerene

Pyrene end‐labeled star poly(?‐caprolactone)s (PCLs) with polyhedral oligomeric silsesquioxane (POSS) core were prepared by combination of copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) click chemistry and ring‐opening polymerization techniques. First, ?‐caprolactone (?‐CL) is polymerized by using 1‐pyrene methanol as initiator and stannous octoate as catalyst to obtain α‐pyrene‐ω‐hydroxyl telechelic PCL with different chain lengths. Then, its hydroxyl group is converted to acetylene functionality by esterification reaction with propargyl chloroformate. Finally, the CuAAC click reaction of α‐pyrene‐ω‐acetylene telechelic PCL with POSS‐(N₃)₈ leads to corresponding pyrene end‐labeled star‐shaped PCLs. The successful synthesis of pyrene end‐labeled star polymers is clearly confirmed by ¹H‐nuclear magnetic resonance, Fourier transform infrared, gel permeation chromatograph, differential scanning calorimeter, and thermogravimetric analysis. Furthermore, non‐covalent interactions of obtained star polymers with fullerene are investigated in liquid media. Based on Raman spectroscopy and visual investigations, the star polymer having shorter chain length exhibited better and more stable dispersion with fullerene. The amount of pyrene units present per polymer chains can directly influence the dispersion stability of fullerene. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46520.     

Self-healing bio-based furan polymers cross-linked with various bis-maleimides

A series of bio-based self-healing polymers was prepared by cross-linking a furan polymer, poly(2,5-furandimethylene succinate), with bis-maleimide compounds by means of Diels–Alder reactions. In addition to the amount of the bis-maleimide linker, the molecular structure of the bis-maleimide played a key role in determining the extent of the Diels–Alder reaction and the mechanical and healing properties of the polymers. Bis-maleimides with phenylene rings markedly enhanced the tensile strength of the network polymers but hindered healing. In contrast, bis-maleimides with a flexible molecular structure tended to improve the polymer elongation, affording polymers with excellent healing ability. The efficiencies of self-healing (=healing without any external stimulus) and healing with an assistance of solvent (CHCl₃) were over 70% and 80%, respectively, for the network polymer crosslinked by bis-maleimide with flexible long-alkyl segment. Thus, our results indicate that the choice of bis-maleimide linker is an important factor for designing furan-maleimide–based self-healing polymers.     

Synthesis of UV-curable tung oil and UV-curable tung oil based alkyd

Two UV-curable tung oil-based resins were synthesized via a Diels–Alder cycloaddition. An UV-curable tung oil (UVTO) was prepared from bodied tung oil and trimethylolpropane trimethacrylate (TMPTMA). An inhibitor, phenothiazine, was added to avoid homopolymerization of TMPTMA. The UV-curable tung oil alkyd (UVTA) was prepared from the monoglyceride process and then reacted with TMPTMA via the Diels–Alder reaction similar to the UVTO. The UVTO and UVTA were characterized by ¹H NMR, ¹³C NMR, and MALDI-TOF mass spectroscopy. The UVTO and UVTA were formulated with a free radical reactive diluent, tripropylene glycol diacrylate (TPGDA) and photoinitiator Irgacure 2100. Photo differential scanning calorimeter (Photo-DSC) was used to investigate curing kinetics of the UVTO and the UVTA. Both the UVTO and UVTA were photocurable with the UVTA formula exhibiting a faster curing speed than the UVTO.     

Diels–Alder Reaction of Cyclopentadiene and Alkyl Acrylates in the Presence of Pyrrolidinium Ionic Liquids with Various Anions

Abstract  

The conversion and stereoselectivity of transformation to endo and exo norbornene derivatives was determined in the Diels–Alder reaction of cyclopentadiene with alkyl acrylates. The reactions were carried out in the pyrrolidinium ionic liquids in the presence of metal chlorides and trifluoromethanesulfonates as the catalysts. Shorter reaction times and higher conversions of dienophile were observed in a comparison with analogous cycloadditions carried out in the presence of conventional organic solvents. A higher stereoselectivity to the endo isomer was found in the majority of cases. The ionic liquids composed of 1-butyl-1-methylpyrrolidinium cation (Pyrr_1.4) and various anions were used. The influence of ionic liquid anion and several metal chlorides and metal triflates used as the catalysts on the conversion was determined.     

Synthesis and characterization of ferrocene end-capped poly(ε-caprolactone)s by a combination of ring-opening polymerization and “click” chemistry techniques

Ferrocene (Fc) end-capped linear and star-shaped poly(ε-caprolactone)s (PCLs) with different numbers of arms were synthesized by a combination of ring-opening polymerization (ROP) and “click” chemistry techniques in a four-step reaction procedure. In the first step, the polymer backbones were prepared via ROP of the ε-caprolactone (ε-CL) monomer in bulk by employing the compounds with different numbers of hydroxyl groups as the multisite initiators and stannous octoate (Sn(Oct)₂) as the coordination-insertion catalyst. The hydroxyl end-groups of the obtained PCLs were then converted into a bromides and azides consecutively. In the final step, the Fc moiety was attached to the termini of the PCLs using a Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction between the azide end-groups of the PCLs and the acetylene group of ethynylferrocene under ambient conditions. In all cases, the FT-IR and ¹H NMR spectra indicated a successful and quantitative transformation of the desired end-functional groups. The electrochemical properties of the Fc end-capped PCLs were also investigated via cyclic voltammetry (CV).     

Telechelic polymers by living and controlled/living polymerization methods

Telechelic polymers, defined as macromolecules that contain two reactive end groups, are used as cross-linkers, chain extenders, and important building blocks for various macromolecular structures, including block and graft copolymers, star, hyperbranched or dendritic polymers. This review article describes the general techniques for the preparation of telechelic polymers by living and controlled/living polymerization methods; namely atom transfer radical polymerization, nitroxide mediated radical polymerization, reversible addition-fragmentation chain transfer polymerization, iniferters, iodine transfer polymerization, cobalt mediated radical polymerization, organotellurium-, organostibine-, organobismuthine-mediated living radical polymerization, living anionic polymerization, living cationic polymerization, and ring opening metathesis polymerization. The efficient click reactions for the synthesis of telechelic polymers are also presented.     

Water-soluble starlike poly(acrylic acid) graft polymer: preparation and application as templates for silver nanoclusters

Water-soluble starlike polymers containing concentrated carboxyl groups were conveniently synthesized via the combination of “click” chemistry and atom transfer radical polymerization. The starlike polymer was composed of a shorter polyacrylate main chain and longer poly(acrylic acid) side chains. Alkyne and azide groups were introduced to the structure units of the main chain by esterification and the chain end of the side chain by substitution reaction of NaN₃ to bromine, respectively. By click chemistry between alkyne and azide group, well-defined starlike polymers were obtained. FT-IR, gel permeation chromatography, and ¹H NMR were used to characterize the resulting polymers. Aggregation behavior demonstrated by transmission electron microscopy was observed when the starlike polymers were dispersed in water at pH 7.0–7.5. Using the starlike polymers as templates, water-soluble silver nanoclusters mainly consisting of Ag₂ supported by the generated nanoparticles and carboxyl groups were successfully synthesized. Also, their optical properties and morphology were characterized by UV–vis absorption spectra and TEM.     

Synthesis of A<Subscript>2</Subscript>B<Subscript>2</Subscript> miktoarm star copolymers from a new heterobifunctional initiator by combination of ROP and ATRP

Abstract  

A new heterobifunctional initiator, 2,3-bis(2-bromo-2-methylpropionyloxy) succinic acid, was synthesized and used in preparation of A₂B₂ miktoarm star copolymers, (polystyrene)₂(poly(ε-caprolactone))₂, by combination of atom transfer radical polymerization (ATRP) and Controlled ring-opening polymerization (ROP). The structures of products were confirmed by the ¹H NMR, ¹³C NMR, FT–IR, elemental analysis, differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). GPC traces show that the obtained polymers have a relatively narrow molecular weight distribution. The compositions of resulting miktoarm star copolymers were very close to theoretical.     

p-benzoquinone diimines and thiophene based alternating copolymers: organometallic catalyzed syntheses and elementary characterization

A series of alternating polymers, which were prepared by coupling of N, N’-dichloro-benzoquinonediimine (a) or 2, 5-dimethyl-N, N’-dichloro-benzoquinonediimine (b) with Grignard reagents of thiophene, were successfully prepared using Ni(II) complexes as catalyst with moderate yields (54–88%) and molecular weights (4.3–7.0 × 10³). The basic properties of the obtained copolymers were characterized by FT-IR, ¹H NMR, UV-vis absorption, cyclic voltammetry, thermal analysis and Gel permeation chromatography (GPC). The maximum UV–vis absorption of these polymers appears in the range of 410–430 nm and 437–494 nm in DMF and CF₃COOH, respectively. XRD patterns of these polymers suggest the low crystallinty. After doped by iodine, conductivity of obtained polymers was improved five-eight orders of magnitude relative to their corresponding neutral precursors (the conductivity of them was <10⁻¹³ S/cm). The electrochemical activity of iodine-doped polymers was greatly improved as compared to un-doped ones. The reduction of pristine benzoquinone polymers was also studied in order to tune their properties conveniently.     

Macromolecular Carriers for Methotrexate and Ferrocene in Cancer Chemotherapy

Several drug-carrier polymers were synthesized in this program, including polyaspartamides, ester-amine condensation polymers, and polyamidoamines (PAAs). Functionalized polyaspartamides were obtained in 46–73% yield by an aminolytic ring-opening process resulting from the nucleophilic attack of a number of selected amines on polysuccinimide, which in turn was obtained by a high-temperature polycondensation reaction in the presence of phosphoric acid. These polyaspartamides were characterized by inherent viscosities in the range of 8–26 mL g⁻¹. The ester-amine polymers were obtained in 42–71% yield by base-catalyzed polycondensation reactions under controlled conditions of temperature, in DMSO, so as to ensure the incorporation and integrity of unprotected hydroxyl functional groups in the polymer’s main chain. These polymers were characterized by inherent viscosities in the range of 10–13 mL g⁻¹. PAAs were synthesized by the addition of amine nucleophiles across the double bonds of methylene bisacrylamide (Michael-type addition), under carefully controlled experimental conditions to obtain both amide and secondary amine functions in the water-soluble polymeric main chain. They were obtained in 16–29% yield and characterized by inherent viscosities in the range of 20–26 mL g⁻¹. These three types of polymers are perfectly water-soluble polymeric products which are purified by dialysis (12,000 molecular mass cut-off) and freeze-drying. They are of interest as macromolecular carriers for pharmaceuticals and biologically active agents.     

Polymerization of Triazolinediones with trans-3,3-Dichloro-1-phenyl-1-propene

The reaction of 4-phenyl-1,2,4-triazoline-3,5-dione (PhTD) ( 2 ) with trans-3,3-dichloro-1-phenyl-1-propene ( 4 ) was investigated at room and reflux temperatures in methylene chloride solution. Although the reaction is slow, it gives quantitative yield. This reaction leads to the formation of two 2:1 adducts via double Diels–Alder and Diels–Alder-Ene reactions in a ratio of about 1: 7. The major product was isolated by means of fractional crystallization as a pure compound and was characterized by infra-red (IR), ¹H nuclear magnetic resonance (NMR), ¹³C NMR, mass spectra and elemental analysis. The structure of the minor product was determined by IR and ¹H NMR. These compounds were used as models for the polymerization reactions. The reaction of bistriazolinediones (1,6-bis-(3,5-dioxo-1,2,4-triazoline-4-yl)hexane and bis-(p-3,5-dioxo-1,2,4-triazoline-4-ylphenyl)methane) with ( 4 ) was carried out in dimethylformamide (DMF). The reactions gave novel polymers via repetitive double Diels–Alder and Diels–Alder-Ene polyaddition reactions, with the major component being a Diels–Alder-Ene structure. These polymers have intrinsic viscosities in a range from 0·08 to 0·18dlg^-1 in DMF. The physical properties and structural characterization of these polymers have been studied and are reported. © of SCI.     

Synthesis of 2-Propanoyl-5-Norbornene in Pyridinium Ionic Liquids Catalyzed by Yttrium Salts

Abstract  

The use of pyridinium ionic liquids as solvent and catalytic systems based on yttrium salts dissolved in pyridinium ionic liquids for the synthetically important Diels–Alder reaction between cyclopentadiene and ethyl-vinyl ketone was studied. Both chloride and triflate were active catalysts in cycloaddition, strongly improving the reaction rate and stereoselectivity. The catalytic system—1 mol% YCl₃/[C₄-3-C₁py][OTf] (N-butyl-3-methylpyridinium trifluoromethanesulfonate) proved to be stable under recycling conditions.     

Multifunctional Initiator with Platinum-Acetylide Dendritic Core for Living Polymerization of Isocyanides

A novel multifunctional initiator has been developed by peripheral modification of a Pt-acetylide dendrimer. Pd–Pt μ-ethynediyl units were introduced to the first-generation dendrimer by a divergent method. The dendritic initiator was applicable to the living polymerization of aryl isocyanides, producing high molecular weight polymers with a narrow polydispersity index in quantitative yields. The ³¹P NMR spectrum of the resulting polymer suggested that all Pd–Pt μ-ethynediyl units in the dendritic molecule actually functioned as an initiator.     

Synthesis of Multiple Bispecific Antibody Formats with Only One Single Enzyme Based on Enhanced Trypsiligase

Bispecific antibodies (bsAbs) were first developed in the 1960s and are now emerging as a leading class of immunotherapies for cancer treatment with the potential to further improve clinical efficacy and safety. Many different formats of bsAbs have been established in the last few years, mainly generated genetically. Here we report on a novel, flexible, and fast chemo–enzymatic, as well as purely enzymatic strategies, for generating bispecific antibody fragments by covalent fusion of two functional antibody Fab fragments (Fabs). For the chemo–enzymatic approach, we first modified the single Fabs site-specifically with click anchors using an enhanced Trypsiligase variant (eTl) and afterward converted the modified Fabs into the final heterodimers via click chemistry. Regarding the latter, we used the strain-promoted alkyne-azide cycloaddition (SPAAC) and inverse electron-demand Diels–Alder reaction (IEDDA) click approaches well known for their fast reaction kinetics and fewer side reactions. For applications where the non-natural linkages or hydrophobic click chemistry products might interfere, we developed two purely enzymatic alternatives enabling C- to C- and C- to N-terminal coupling of the two Fabs via a native peptide bond. This simple system could be expanded into a modular system, eliminating the need for extensive genetic engineering. The bispecific Fab fragments (bsFabs) produced here to bind the growth factors ErbB2 and ErbB3 with similar K_D values, such as the sole Fabs. Tested in breast cancer cell lines, we obtained biologically active bsFabs with improved properties compared to its single Fab counterparts.     

Synthesis and characterization of poly(arylene ether ketone)s containing triazole units through click chemistry

In order to develop a novel process for poly(arylene ether ketone)s with high thermal and chemical stability, a series of poly(aylene ether ketone)s containing triazloe moieties were synthesized via the click chemistry of 4,4′-bis(azidomethyl) diphenyl ketone (BADPK) and bisethynyl compounds (BEAE1-5). The resulting polymers were characterized by using IR and ¹H NMR techniques. The solubility data showed that samples possessed good solubility in highly polar solvents. Molecular mass of these samples was determined by GPC which indicated they exhibited reasonable molecules weights and relatively small polydispersity. Furthermore, thermal stability of the samples was evaluated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), which indicated that they possessed good thermal stability and high T _g (100–140 °C). All the polymers were amorphous confirmed by DSC and X-ray diffraction (WAXD).     

Coupling and linking reactions of living polyisobutylene by allylsilanes

The reactions of living polyisobutylene (PIB⁺) with different allylsilanes, as potential linking and coupling agents, have been studied. Quantitative monoaddition of 2-Phenylallyltrimethylsilane to living PIB⁺ yielded macromonomer (I), however coupling was absent. Rapid and quantitative coupling has been observed with 1,3-bis[2-(3-trimethylsilyl)-propenyl]benzene (bTPB). Using 1-(2-propenyl)-3-[2-(3-trimethylsilyl)-propenyl]benzene (PTPB) star polymers with an average of four arms have been prepared with high efficiency. The study of this linking reaction revealed that star formation takes place in two well separated steps. In the first step a macromonomer is formed in situ by the rapid reaction of PIB⁺ with the allyltrimethylsilyl functionality. Subsequent reaction of this macromonomer with the remaining electrophilic PIB⁺ ends followed by interchain reactions results in the formation of star polymers. Received: 16 May 1999/Revised version: 1 September 1999/Accepted: 1 September 1999     

The Synthesis and Characterization of a Novel Ternary Polymer Bisphenol A-4,4’-Difluorobenzophenone-bis(p-hydroxylphenyl)-1,4,5,8-naphthalenetetracarboxylic Diimide Monomer

Summary A novel bis(p-hydroxylphenyl)-1,4,5,8-naphthalenetetracarboxylic diimide (NTDA–OH) monomer was prepared through the condensations of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) with p-aminophenol. A series of ternary copolymers derived from NTDA–OH were further synthesized by the nucleophilic substitution reactions. Both the monomer and the ternary copolymers were characterized by FT–IR, ¹H NMR, and inductively coupled plasma (ICP). The characterization results showed that, the imide groups were successfully introduced into the prepared monomer. The differential scanning calorimetry (DSC) and the thermal gravimetry analysis (TGA) were further performed on the produced polymers. The thermal stability of the polymer increased with the content of the NTDA–OH increasing.     

Preparation of hydrophobic poly(isobutylene) star polymers with hydrophilic poly(propylene imine) dendritic cores

Summary Poly(propylene imine) dendrimers with amino chain ends have been used for the preparation of hydrophobic star polymers with hydrophilic dendritic cores. The unsaturated end groups of polyisobutylene (PIB) were transformed into reactive anhydride end groups by an “ene” reaction with maleic anhydride, and the resulting functionalized PIB was then reacted with dendrimers to afford dendrimer-PIB star copolymers. Received: 20 May 1999/Accepted: 17 June 1999     

Preparation and properties of azobenzene-containing amphiphilic miktoarm star polymers

Summary A series of novel miktoarm star polymers composed of a poly(ethylene oxide) (PEO) and two side-chain liquid crystalline azobenzene-containing polymethacrylate (PEO-(PMMAZO)₂) were prepared using atom transfer radical polymerization (ATRP). Bifunctional macroinitiator PEO-Br₂ was synthesized by condensation reaction in two steps and characterized by ¹H NMR, ¹³C NMR and IR. Kinetic study showed that it was a first order reaction referred to the monomer MMAZO, namely, 6-(4-methoxy-4’-oxy-azobenzene)hexyl methacrylate. The liquid crystalline behaviors of the miktoarm star polymers were studied by differential scanning calorimetry (DSC) and polarized optical microscope (POM). They exhibited smectic and nematic mesophases when Mn was beyond 9.4×10³ g/mol. The phase transition temperatures of the smectic and nematic phases increased while the melting temperature of PEO decreased with increasing molecular weight of the LC block. Compared with diblock polymer PEO-PMMAZO, the melting temperature of PEO in miktoarm star polymer decreased more rapidly.