MgCl2‐supported TiCl4 catalysts containing diethyl norbornene‐2,3‐dicarboxylate internal electron donor for 1‐butene polymerization: Effects of internal electron donor configuration

Three isomeric 5‐norbornene‐2,3‐dicarboxylic acid diethyl ester (NDDE) with endo‐, exo‐, and trans‐configuration have been synthesized and employed as internal electron donors (IED) in 1‐butene polymerization over magnesium chloride supported Ziegler–Natta catalysts. It was found that the configuration of NDDE plays a key role in tuning the catalyst activity, stereospecificity, molecular weight (MW), and polydispersity index (PDI) of resulting poly(1‐butene). The type of catalyst with cis‐5‐norbornene‐endo‐2,3‐dicarboxylic acid diethyl ester as IED shows the highest catalyst activity, while catalyst with trans‐NDDE as IED yields the poly(1‐butene) with the highest MW and the most broad PDI. IR results showed that the NDDE with endo‐, exo‐, and trans‐configuration have different coordination way to MgCl₂, subsequently affecting the catalysts performance. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40758.     

Rheokinetics of ring‐opening metathesis polymerization of norbornene‐based monomers intended for self‐healing applications

Constant shear rate rheokinetics was used to evaluate the polymerization of four norbornene‐based monomer systems as candidate healing agents in self‐healing composites: endo‐dicyclopentadiene (endo‐DCPD), exo‐DCPD, 5‐ethylidene‐2‐norbornene (ENB), and a 1:1 volume mixture of endo‐DCPD:ENB. The ruthenium catalyst induced ring‐opening metathesis polymerization of the healing agent candidates were measured experimentally under isothermal conditions while the influences of several different variables were considered (e.g., test temperature, catalyst concentration, catalyst form). Analyzing the increase in viscosity during the polymerization, comparisons of the reaction kinetics of the different monomers were quantified by defining two parameters, t_t and Δt, which correspond to the polymerization initiation and propagation rates respectively. Generally, ENB shows the fastest polymerization kinetics, and endo‐DCPD the slowest. POLYM. ENG. SCI. 46:1804–1811, 2006. © 2006 Society of Plastics Engineers     

Two‐Step Protein Labeling by Using Lipoic Acid Ligase with Norbornene Substrates and Subsequent Inverse‐Electron Demand Diels–Alder Reaction

Inverse‐electron‐demand Diels–Alder cycloaddition (DA_inv) between strained alkenes and tetrazines is a highly bio‐orthogonal reaction that has been applied in the specific labeling of biomolecules. In this work we present a two‐step labeling protocol for the site‐specific labeling of proteins based on attachment of a highly stable norbornene derivative to a specific peptide sequence by using a mutant of the enzyme lipoic acid ligase A (LplA^W37V), followed by the covalent attachment of tetrazine‐modified fluorophores to the norbornene moiety through the bio‐orthogonal DA_inv . We investigated 15 different norbornene derivatives for their selective enzymatic attachment to a 13‐residue lipoic acid acceptor peptide (LAP) by using a standardized HPLC protocol. Finally, we used this two‐step labeling strategy to label proteins in cell lysates in a site‐specific manner and performed cell‐surface labeling on living cells.     

Specificity of Donor Structures for endo‐β‐N‐Acetylglucosaminidase‐Catalyzed Transglycosylation Reactions

To demonstrate the structural specificity of the glycosyl donor for the transglycosylation reaction by using endo‐β‐N‐acetylglucosaminidase from Mucor hiemalis (endo‐M), a series of tetrasaccharide oxazoline derivatives was synthesized. These derivatives correspond to the core structure of an asparagine‐linked glycoprotein glycan with a β‐mannose unit of a non‐natural‐type monosaccharide, including β‐glucose, β‐galactose, and β‐talose in place of the β‐mannose moiety. The transglycosylation activity of wildtype (WT) endo‐M and two mutants, N175Q and N175A, was examined by using these tetrasaccharide donors with p‐nitrophenyl N‐acetylglucosaminide (GlcNAc‐pNp). The essential configuration of the hydroxy group for the transglycosylation reaction was determined. On the basis of these results, the transglycosylation reaction was investigated by using chemically modified donors, and transglycosylated products were successfully obtained.     

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 of novel polymeric HALS stabilizers and chain transfer effect of hindered amine norbornene derivatives on ring-opening metathesis polymerization

Cyclooctadiene (COD) was polymerized via ring-opening metathesis polymerization (ROMP) in the presence of 5-norbornene-exo, endo-2-carboxylic acid 2,2,6,6-tetramethyl-4-piperidinyl ester (PN) or 5-norbornene-2-exo-3-endo-dicarboxylic acid bis(2,2,6,6-tetramethyl-4-piperidinyl) ester (2,3-PN) to prepare a new kind of polymeric hindered amine (HALS) stabilizers. Unexpectedly, hindered amine norbornene derivatives PN and 2,3-PN did not act as comonomer but acted as chain transfer agent (CTA). The resulting polymers were characterized by gel permeation chromatography (GPC) and ¹H-NMR. Investigation of polymerization behavior showed that hindered amine groups were introduced into polymer chain by virtue of chain degradation resulted from chain transfer. The molecular weight (M _n) and HALS content of the resulting polymeric HALS stabilizer could be regulated by varying molar ratio of initial monomer to catalyst.     

Synthesis and functionalization of poly(ethylene‐co‐dicyclopentadiene)

Copolymerizations of ethylene with endo‐dicyclopentadiene (DCP) were performed by using Cp₂ZrCl₂ (Cp = Cyclopentadienyl), Et(Ind)₂ZrCl₂ (Ind = Indenyl), and Ph₂C(Cp)(Flu)ZrCl₂ (Flu = Fluorenyl) combined with MAO as cocatalyst. Among these three metallocenes, Et(Ind)₂ZrCl₂ showed the highest catalyst performance for the copolymerization. From ¹H‐NMR analysis, it was found that DCP was copolymerized through enchainment of norbornene rings. The copolymer was then epoxidated by reacting with m‐chloroperbenzoic acid. ¹³C‐NMR spectrum of the resulting copolymer indicated the quantitative conversion of olefinic to epoxy groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 103–108, 1999     

Thiol–norbornene photoclick hydrogels for tissue engineering applications

Thiol–norbornene (thiol–ene) photoclick hydrogels have emerged as a diverse material system for tissue engineering applications. These hydrogels are crosslinked through light‐mediated orthogonal reactions between multifunctional norbornene‐modified macromers [e.g., poly(ethylene glycol) (PEG), hyaluronic acid, gelatin] and sulfhydryl‐containing linkers (e.g., dithiothreitol, PEG–dithiol, biscysteine peptides) with a low concentration of photoinitiator. The gelation of thiol–norbornene hydrogels can be initiated by long‐wave UV light or visible light without an additional coinitiator or comonomer. The crosslinking and degradation behaviors of thiol–norbornene hydrogels are controlled through material selections, whereas the biophysical and biochemical properties of the gels are easily and independently tuned because of the orthogonal reactivity between norbornene and the thiol moieties. Uniquely, the crosslinking of step‐growth thiol–norbornene hydrogels is not oxygen‐inhibited; therefore, gelation is much faster and highly cytocompatible compared with chain‐growth polymerized hydrogels with similar gelation conditions. These hydrogels have been prepared as tunable substrates for two‐dimensional cell cultures as microgels and bulk gels for affinity‐based or protease‐sensitive drug delivery, and as scaffolds for three‐dimensional cell encapsulation. Reports from different laboratories have demonstrated the broad utility of thiol–norbornene hydrogels in tissue engineering and regenerative medicine applications, including valvular and vascular tissue engineering, liver and pancreas‐related tissue engineering, neural regeneration, musculoskeletal (bone and cartilage) tissue regeneration, stem cell culture and differentiation, and cancer cell biology. This article provides an up‐to‐date overview on thiol–norbornene hydrogel crosslinking and degradation mechanisms, tunable material properties, and the use of thiol–norbornene hydrogels in drug‐delivery and tissue engineering applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41563.     

Synthesis and Analysis of Specific Covalent Inhibitors of endo‐Xyloglucanases

A series of N‐bromoacetylglycosylamines and bromoketone C‐glycosides were synthesised from complex xyloglucan oligosaccharide (XyGO) scaffolds as specific active‐site affinity labels for endo‐xyloglucanases. Compounds based on XXXG (Xyl₃Glc₄) and XLLG (Xyl₃Glc₄Gal₂) oligosaccharides exhibited strikingly higher affinities and higher rates of irreversible inhibition than known cellobiosyl and new lactosyl disaccharide congeners when tested with endo‐xyloglucanases from two distinct glycoside hydrolase (GH) families. Intact‐protein mass spectrometry indicated that inactivation with XyGO derivatives generally resulted in a 1:1 labelling stoichiometry. Together, these results indicate that XyGO‐based affinity reagents have significant potential as inhibitors and proteomic reagents for the identification and analysis of diverse xyloglucan‐active enzymes in nature, to facilitate industrial enzyme applications.     

Evaluation of Norbornene‐Based Adhesives to Amine‐Cured Epoxy for Self‐Healing Applications

High adhesive strengths are essential in self‐healing polymers. In these novel materials, healing is triggered by crack propagation through embedded microcapsules in an epoxy matrix, which then release the liquid healing agent into the crack plane. Subsequent exposure of the healing agent to an embedded chemical initiator triggers ring‐opening metathesis polymerization (ROMP), bonding the crack faces closed. In order to improve self‐healing efficiencies in these systems, it is necessary to improve the adhesion of the polymerized healing agent with the epoxy matrix. In this study, the adhesive shear strength between different norbornene‐based healing agents and an amine‐cured epoxy resin was evaluated using single lap shear specimens. The healing agents tested include endo‐dicyclopentadiene (DCPD), 5‐ethylidene‐2‐norbornene (ENB) and DCPD/ENB blends. 5‐Norbornene‐2‐methanol (NBM) and 5‐norbornene‐2‐exo,3‐exo‐dimethanol (NBDM) were used as adhesion promoters because they contain hydroxyl groups which can form hydrogen bonds with the amine‐cured epoxy adherend. A custom synthesized norbornene‐based crosslinking agent was also added to improve the adhesion of the polymerized ENB by increasing its crosslink density after ROMP. The effects of catalyst loading, polymerization time and cure temperature on the adhesive bond strength are studied in detail.

     

A New Class of Enantioselective Catalytic 2‐Pyrone Diels–Alder Cycloadditions

A highly enantioselective catalytic Diels–Alder (DA) cycloaddition of 2H‐pyran‐2,5‐diones (synthon of 5‐hydroxy‐2‐pyrones) has been developed with a Cinchona‐derived thiourea as the catalyst. The conditions were optimized by using 0.2 equiv. of the catalyst and 0.1 equiv. of formic acid in 2‐propanol at room temperature, which afforded the DA products in yields of up to 90% (exo/endo=5.5:1, 98% ee) with trans‐β‐nitrostyrene derivatives as the dienophiles. The structure/activity relationships of the bifunctional catalyst and the effects of the steric, electronic and hydrogen‐bonding properties of the dienophiles have been studied.     

A New Fluorogenic Probe for the Detection of endo‐β‐N‐Acetylglucosaminidase

We developed a fluorescence‐quenching‐based assay system to determine the hydrolysis activity of endo‐β‐N‐acetylglucosaminidases (ENGases). The pentasaccharide derivative 1 was labeled with an N‐methylanthraniloyl group as a reporter dye at the non‐reducing end and with a 2,4‐dinitrophenyl group as a quencher molecule at the reducing end. This derivative is hydrolyzed by ENGase, resulting in an increase in fluorescence intensity. Thus, the fluorescence signal is directly proportional to the amount of the tetrasaccharide derivative, hence allowing ENGase activity to be evaluated easily and quantitatively. Using this system, we succeeded in measuring the hydrolysis activities of ENGases and thus the inhibitory activities of known inhibitors. We confirmed that this assay system is suitable for high‐throughput screening for potential inhibitors of human ENGase that might serve as therapeutic agents for the treatment of N‐glycanase 1 (NGLY1) deficiency.     

Biocidal polymers: Synthesis,antimicrobial activity,and possible toxicity of poly (hydroxystyrene‐co‐methylmethacrylate) derivatives

Functionalized polymers have gained much interest in the last decades. This is due to their functional group and their polymer nature that give them unique properties and more advantages than the corresponding small molecules. In this trend, polyhydroxystyrene‐co‐MMA was modified to introduce amino group in the side chain of the polymer. The amine modified polymer was reacted with two classes of active compounds. The first class is aldehydes such as vanilline, p‐hydroxybenzaldehyde, p‐chlorobenzaldehyde, and anisaldehyde. The second class is phenolic esters such as p‐hydroxymethylbenzoate, 2,4‐dihydroxymethyl benzoate, and methyl salicylate. The antimicrobial activities of the polymer and modified polymer with these two classes were explored with Gram‐negative bacteria (Escherichia coli), Gram‐positive bacteria (Bacillus subtilus), fugus like yeast (Candida albicans SC5314), and pathogenic molds (Aspergillus flavus, Trycophyton rubrum, and F. oxysporium). In vitro studies indicated that the start polymer did not affect on the test microorganisms, in contrary to its derivatives. The diameter of inhibition zone varied according to the active group in the modified polymer, polymer microstructure, and the test microorganism. Derivatives I, II, and III were selected among the most effective antimicrobial compounds. Their inhibitory effects on the ratio of surviving cell number (M/C) increased by increasing derivatives concentrations. Derivatives I and II were inhibitorier to C. albicans and molds than to bacteria while derivative III was only antibacterial. These derivatives seemed toxic to Brine shrimp by increasing their concentrations above 10 ppm, with derivative III being the less toxic, compared to others. To clarify this toxic effect and to decrease the toxicity of these derivatives, more detailed studies are necessary, and this will be focused in the nearest future. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Addition polymerization of norbornene, 5-vinyl-2-norbornene and 2-methoxycarbonyl-5-norbornene with a catalyst based on a palladium(0) precursor complex

Pd(dibenzylideneacetone)₂, when activated in situ with 1 equiv of [CPh₃][B(C₆F₅)₄] in the presence of 1 equiv of P(C₆H₁₁)₃, efficiently catalyzed the addition polymerization and copolymerization of norbornene and its derivatives. Homopolymerization of 5-vinyl-2-norbornene took place regio-selectively with the endo-cyclic double bond to give high-molecular weight polymers, while the exocyclic double bond remained intact so that the resulting polymer had pendent vinyl groups along the polymer chain. In the polymerization of a mixture of the endo-/exo- isomers of 2-methoxycarbonyl-5-norbornene, the endo-isomer was consumed prior to consumption of the exo-isomer, contrary to the well-known tendency in Pd(II)-based catalyst systems. Another notable feature of the present catalytic system was the strong dependency of the molecular weight on the reaction temperature, which was studied in detail for the copolymerization of 2-methoxycarbonyl-5-norbornene with norbornene: we could control the molecular weight without the use of a chain transfer agent. The extracted oligomeric fraction of poly(norbornene) showed the presence of a terminal CC double bond as well as a C₆F₅ unit that was bound to the first norbornane unit in the polymer chain.     

Synthesis of a new siloxane‐containing alicyclic dianhydride and the derived polyimides with improved solubility and hydrophobicity

The structural transformation strategy of cis‐5‐norbornene‐endo‐2,3‐dicarboxylic anhydride (NA) was performed by esterification. The double bond on the diester of NA showed adequate hydrosilylation reactivity with Si? H bonds of phenyl‐containing disiloxane. Thereby, a new siloxane‐containing alicyclic dianhydride, 5,5′‐exo‐(1,3‐dimethyl‐1,3‐diphenyl‐disiloxane‐1,5‐diyl)bisbicyclo[2,2,1]heptane‐2,3‐endo‐dicarboxylic anhydride 6 was successfully synthesized starting from NA, 1,3‐dimethyl‐1,3‐diphenyldisiloxane and platinum complex catalyst. The whole synthetic route of dianhydride 6 consisted of esterification, hydrosilylation, saponification, acidification, and dehydration. A series of polyimides (PIs) were prepared from dianhydride comonomers of 6 and 4,4′‐biphenyltetracarboxylic dianhydride (BPDA) in different molar ratio together with the diamine 4,4′‐oxydianiline (ODA). The thermal and mechanical properties of PIs showed somewhat decrease with increasing content of dianhydride 6. The solubility of PIs increased with the increasing content of dianhydride 6, and further calculation from Bragg's equation indicated that average interchain distance (d‐spacing value) increased with increasing content of siloxane and alicyclic segments in the backbone of PIs. It was revealed that the hydrophobicity of PIs increased with the increasing content of dianhydride 6 . Polyimide 7g , which was prepared from 100% 6 and ODA, showed water adsorption of less than 0.7% and contact angle against water of 101.1°. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci., 2013     

Imidazolium‐functionalized norbornene ionic liquid block copolymer and silica composite electrolyte membranes for lithium‐ion batteries

Imidazolium‐functionalized norbornene and benzene‐functionalized norbornene were synthesized and copolymerized via ring‐opening metathesis polymerization to afford a polymeric ionic liquid (PIL) block copolymers {5‐norbornene‐2‐methyl benzoate‐block ‐5‐norbornene‐2‐carboxylate‐1‐hexyl‐3‐methyl imidazolium bis[(trifluoromethyl)sulfonyl]amide [P(NPh‐b ‐NIm‐TFSI)]} with good thermal stability. On this basis, the solid electrolyte, P(NPh‐b ‐NIm‐TFSI)–lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), through blending with LiTFSI, and the nanosilica composite electrolyte, P(NPh‐b ‐NIm‐TFSI)–LiTFSI–SiO₂, through blending with LiTFSI and nanosilica, were prepared. The effects of the PILs and silica compositions on the properties, morphology, and ionic conductivity were investigated. The ionic conductivity was enhanced by an order of magnitude compared to that of polyelectrolytes with lower PIL compositions. In addition, the ionic conductivity of the nanosilica composite polyelectrolyte was obviously improved compared with that of the P(NPh‐b ‐NIm‐TFSI)–LiTFSI polyelectrolyte and increased progressively up to a maximum with increasing silica content when SiO₂ was 10 wt % or lower. The best conductivity of the P(NPh‐b ‐NIm‐TFSI)–20 wt % LiTFSI–10 wt % SiO₂ composite electrolyte with 7.7 × 10^?5 S/cm at 25 °C and 1.3 × 10^?3 S/cm at 100 °C were obtained, respectively. All of the polyelectrolytes exhibited suitable electrochemical stability windows. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44884.     

Catalytic Dicyanative 5‐exo‐ and 6‐endo‐Cyclization Triggered by Cyanopalladation of Alkynes

A stereoselective dicyanative 5‐exo‐ and 6‐endo‐cyclization using various enynes has been investigated. The mode of cyclization is critically controlled by the structure of the substrates. For example, N‐allyl derivatives prefer 5‐exo‐cyclization, while methacryloyl amides are transformed to the corresponding lactams with tetra‐substituted carbons at the alpha‐position via 6‐endo‐cyclization. Both reactions include syn‐cyanopalladation to carboncarbon triple bonds in the initial step, and sequential cyclization followed by reductive elimination in one operation enables the construction of the highly functionalized nitrogen heterocycles. The scope of suitable substrates and a proposed mechanism are also described.     

Structures and properties of closed‐cell polyimide rigid foams

Closed‐cell polyimide rigid foams with different Calculated Molecular Weight (Calc'd M_n) and foam density (ρ) have been prepared by thermal foaming of nadimide‐endcapped imideoligomers (NAIO) powder. The NAIO powder was obtained by thermally treating of a PMR poly(amide ester) solution derived from the reaction of diethyl ester of 2,3,3′,4′‐biphenyltetracarboxylic dianhydride (α‐BPDE) and p‐phenylenediamine (p‐PDA) using monoethyl ester of cis‐5‐norbornene‐ endo‐2,3‐dicarboxylic acid (NE) as reactive endcapping agent in ethyl alcohol. Effect of Calc'd M_n and foam density (ρ) on mechanical and thermal properties of the polyimide rigid foams have been systematically investigated. It was found that the thermal foaming properties of NAIO powders were affected by the Calc'd M_n. The appreciate Calc'd M_n could yield polyimide foams with both high closed‐cell content (C_c) (>80%) and outstanding mechanical properties. Moreover, the thermal properties were reduced by increasing of Calc'd M_n and the mechanical properties improved gradually by increasing foam densities. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3282–3291, 2013     

Polymeric coatings for photostability enhancement of poly(p‐phenylene vinylene) derivative films

Poly(p‐phenylene vinylene) (PPV) derivatives are an important class of conjugated polymers, known for their applications as electroluminescent materials for light‐emitting devices and sensors. These derivatives are highly susceptible to photodegradation by the combined action of oxygen and light. Here, the use of various commercial polymers as protective coatings against the photodegradation of PPV derivatives was explored. Cast films of two similar PPV derivatives, poly[(2‐methoxy‐5‐n‐hexyloxy)‐p‐phenylene vinylene] and poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐p‐phenylene vinylene], were submitted to photodegradation by exposure to white light under atmospheric conditions in order to verify if the type of side chain (linear or branched) had an effect on the photodegradation. No significant differences in the photodegradation behaviour between the two polymers were noticed. The following commercial polymers were tested as protective coatings for the PPV derivative cast films: 99 and 80% hydrolysed poly(vinyl alcohol) (PVA) and starch. The best results were achieved using coatings of 99% hydrolysed PVA, which increased about 700 times the time necessary for complete degradation of the PPV derivative films. The results show the effectiveness of this coating in minimizing and, possibly, controlling the effects of the photodegradation of PPV derivative films, which can be useful in many applications, e.g. oxygen sensors. Copyright © 2009 Society of Chemical Industry     

Remarkable improvement of thermal stability of main‐chain benzoxazine oligomer by incorporating o‐norbornene as terminal functionality

A new main‐chain benzoxazine oligomer with o‐norbornene functionality as end groups has been designed and synthesized. As compared to traditional main‐chain type benzoxazine polymers, this benzoxazine oligomer with o‐norbornene terminal functionality can undergo further crosslinking polymerization after general ring‐opening polymerization of oxazine rings. Another main‐chain benzoxazine oligomer has also been designed based on the reaction of bisphenol‐A, 4,4′‐diaminodiphenylmethane, paraformaldehyde, and phenol for comparison. The structure of the synthesized oligomers is confirmed by ¹H nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy (FTIR). The molecular weight has been determined by using gel permeation chromatography (GPC). The benzoxazine oligomer containing o‐norbornene functionality can polymerize with multiple polymerization mechanisms rather than the single mechanism common to traditional 1,3‐benzoxazine resins. The polymerization mechanisms are monitored by in situ FTIR and differential scanning calorimetry (DSC). Moreover, the thermoset derived from the benzoxazine oligomer containing o‐norbornene functionality exhibits high thermal stability with the transition temperature of 360 °C and a high T_d5 of 404 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45408.