Synthesis and diels–alder polymerization of furfurylidene and furfuryl-substituted maleamic acids

The reactions of monomaleamic acid derived from an aromatic diamine with furfural afforded a novel class of furfurylidene-substituted maleamic acids 2a–2d . The latter were cyclodehydrated to yield maleimides 3a–3d which are AB-monomers for a Diels–Alder polymerization. In addition, N-furfurylmaleamic acid ( 4 ) was synthesized by reacting furfurylamine with maleic anhydride at ambient temperature. Cyclodehydration of 4 afforded N-furfurylmaleimide ( 5 ). The polymer precursors were characterized by IR and ¹H-NMR spectroscopy. Their curing behavior was investigated by DTA and correlated with chemical structures. Diels–Alder polymerization of monomers occurred at the temperature range of 113–210°C. Thermal stability of monomers was evaluated by TGA and isothermal gravimetric analysis (IGA). It was shown that thermal stability of the polymer derived from maleamic acid 4 was dramatically improved upon curing at high temperatures due to the formation by dehydration of a stable aromatic structure.     

A tailor‐made polymethacrylate bearing a reactive diene in reversible diels–alder reaction

A tailor‐made polymethacrylate bearing a pendant furfuryl group was prepared by atom transfer radical polymerization (ATRP), an important method of recent advances in controlled radical polymerization. It was otherwise difficult to prepare via conventional radical polymerization, because of several side reactions involving the reactive diene functionality of the furfuryl group. Successful Diels–Alder (DA) chemistry was carried out using this reactive furfuryl group of the tailor‐made polymer as diene and a bismaleimide as a dienophile. Interestingly, the resultant material was observed to be thermoreversible as evidenced by FT‐IR and DSC studies. This example of application of a tailor‐made polymer having controlled molecular architecture and with reactive diene functionality in DA chemistry will open new possibilities to prepare newer tailor‐made reversible materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4441–4449, 2007     

Radical copolymerization of N‐phenylmaleimide and diene monomers in competition with diels–alder reaction

Radical copolymerization of N‐phenylmaleimide (PhMI) is carried out with various diene monomers including naturally occurring compounds and the copolymers are efficiently produced by the suppression of Diels–Alder reaction as the competitive side reaction. Diene monomers with an exomethylene moiety and a fixed s‐trans diene structure, such as 3‐methylenecyclopentene and 4‐isopropyl‐1‐methyl‐3‐methylenecyclohexene, exhibit high copolymerization reactivity to produce a high‐molecular‐weight copolymer in a high yield. The copolymerization of sterically hindered noncyclic diene monomers, such as 2,4‐dimethyl‐1,3‐pentadiene and 2,4‐hexadiene, also results in the formation of a high‐molecular‐weight copolymer in a moderate yield. The NMR spectroscopy reveals that the obtained copolymers consist of predominant 1,4‐repeating structures for the corresponding diene unit. The copolymers have excellent thermal stability, that is, an onset temperature of decomposition over 330 °C and a glass transition temperature over 130 °C. The copolymerization reactivity of these diene monomers is discussed based on the results of the DFT calculations. The efficient copolymer formation in competition with Diels–Alder addition is investigated under various conditions of the temperature, solvents, and initiators used for the copolymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3616–3625.     

Preparation of polyimides utilizing the diels–alder reaction. I. Bis(3,4-dimethylenepyrrolidyl) arylenes with bismaleimides

Bis(exocyclic)dienes were prepared by the reaction of 2,3-dibromomethyl-1,3-butadiene with aromatic diamines. The diamines were 4,4′-methylene dianiline, 4,4′-oxy dianiline, benzidine, and α, α′-bis(4-aminophenyl)-p-isopropyl benzene (EPON HPT 1061). Polymers were synthesized by the Diels–Alder reaction of these bisdienes with bis(4-maleimidylphenyl) methane. Flexible films were obtained for diene: dienophile ratios ranging from 0.7 : 1 to 0.8 : 1. Films were found to be insoluble in organic solvents and those cured above 120°C were insoluble in concentrated sulfuric acid. The polymers were characterized by IR, TGA, and elemental analysis.     

Benzocyclobutene in polymer synthesis. III. Heat-resistant thermosets based on Diels–Alder polymerization of a bisbenzocyclobutene and a bismaleimide

Several compatible mixtures of 2,2-bis[4-(N-4-benzocyclobutenyl) phthalimid-4-phenyl]hexafluoropropane (BCB) and 1,1′-(methylene di-4,1-phenylene)bismaleimide (BMI) were prepared according to the molar ratios (BCB : BMI): 1 : 1; 1 : 1.5; 1 : 3; 1.5 : 1. Complete compatibility of the mixtures was evidenced by a single initial T_g. All mixtures showed relatively low initial T_g's (61–70°C) and characteristic polymerization exotherms of benzocyclobutene-based systems (onset: 221–225°C; maximum: 257–259°C), providing an excellent processing window (ca. 155°C). The cured sample of the mixtures, pure BCB and BMI (250°C; N₂; 8 h) were subjected to comparative isothermal gravimetric analysis (ITGA). After 200 h at 650°F (343°C) in circulating air, the cured BMI sample retained only 3% of its original weight, whereas the mixtures of BCB and BMI exhibited thermo-oxidative stabilities similar to BCB (13–15% weight loss). A model compound was synthesized from the intimate mixture of N-phenylmaleimide and N-benzocyclobutenyl phthalimide in 63% yield. The ITGA results and isolation of the model Diels–Alder adduct render strong support to the conviction that Diels–Alder polymerization is indeed the predominant curing process in the BCB/BMI system.     

Synthesis of tadpole polymers via triple click reactions: Copper‐catalyzed azide–alkyne cycloaddition,diels–alder,and nitroxide radical coupling reactions

We designed a trifunctional initiator ( 3 ) containing anthracene, bromide, and OH functionalities and subsequently used as an initiator in atom transfer radical Polymerization (ATRP) of styrene to yield linear polystyrene (PS) with α‐anthracene, OH, and ω‐bromide terminal groups, of which bromide is later transformed into azide to result in the linear anthracene‐, OH‐, and azide‐terminated PS (l‐α‐anthracene‐OH‐ω‐azide‐PS). The copper‐catalyzed azide–alkyne cycloaddition reaction between l‐α‐anthracene‐OH‐ω‐azide‐PS and α‐furan‐protected‐maleimide‐ω‐alkyne linkage, 4 afforded the linear anthracene‐, OH‐, and maleimide‐terminated PS. The cyclization via intramolecular Diels–Alder click reaction of this linear PS and the subsequent conversion of the hydroxyl into bromide resulted in the cyclic PS with one bromide located on the ring, (c‐PS)‐Br. Finally, the c‐PS‐Br was clicked with either well‐defined tetramethylpiperidine‐1‐oxyl‐terminated poly(ethylene glycol) (PEG) or poly(ε‐caprolactone) (PCL) yielding the tadpole polymer, (c‐PS)‐b‐PEG or (c‐PS)‐b‐PCL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Linear tetrablock quaterpolymers via triple click reactions,azide‐alkyne,diels–alder,and nitroxide radical coupling in a one‐pot fashion

Azide‐alkyne and Diels–Alder click reactions together with a click‐like nitroxide radical coupling reaction were used in a one‐pot fashion to generate tetrablock quaterpolymer. The various living polymerization generated linear polymers with orthogonal end‐functionalities, maleimide‐terminated poly(ethylene glycol) (PEG‐MI), anthracene‐ and azide‐terminated polystyrene, alkyne‐ and bromide‐terminated poly(tert‐butyl acrylate) or alkyne‐poly(n‐butyl acrylate), and tetramethylpiperidine‐1‐oxyl (TEMPO)‐terminated poly(ε‐caprolactone) (PCL‐TEMPO) were clicked together in a one‐pot fashion to generate PEG‐b‐PS‐b‐PtBA‐b‐PCL or PEG‐b‐PS‐b‐PnBA‐b‐PCL quaterpolymer using Cu(0), CuBr, and N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalyst in dimethyl formamide at 80 °C for 36 h. Linear precursors and target quaterpolymers were analyzed via ¹H NMR and gel permeation chromatography. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Hydrogen transfer in the retro diels–alder fragmentation of oxygen-containing heterocyclic compounds. II—Chromones

Mass Spectra of unsubstituted, 2-methyl-, 3-methyl and 2,3-dimethylchromones were examined. These compounds showed [RDA]⁺˙ and [RDA + H]⁺ ions as characteristc ions, together with [M? H]⁺,[M? CO]⁺˙,[M? CHO]⁺ and [RDA? CO]⁺˙ ions. Based on deuterium labelling experiments and measurement of metastable peaks by the ion kinetic energy defocusing technique, the origin of transferred hydrogen in the [RDA + H]⁺ ion was clarified. The mechanism of the [RDA + H]⁺ ion formation is discussed.     

Microwave‐assisted synthesis and diels–alder reactions of 1,3‐azaphospholo[5,1‐a]isoquinolines

The application of microwave technique has been extended successfully for the first time to the synthesis of a representative class of azaphospholes, viz. 1,3‐bis(alkoxycarbonyl)‐1,3‐azaphospholo[5,1‐a]isoquinolines ( 2 ), which occurs rapidly giving higher yields. Stereoselectivity is observed in the reaction with 2,3‐dimethyl‐1,3‐butadiene, and isoprene reacts regioselectively as well. 1‐Methyl‐3‐ethoxycarbonyl‐1,3‐azaphospholo[1,5‐a]pyridine ( 4 ) remains inert toward [2+4] cycloaddition. The nonoccurrence of the Diels–Alder reaction in the latter case has been supported by semiempirical PM3 calculations. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:560–563, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10193     

Liquid–liquid phase separation in multicomponent polymer solutions. II. The critical state

Theoretical and experimental evidence is put forward to prove that the determination of the phase-volume ratio as a function of temperature and concentration is a sensitive and simple means of determining the liquid–liquid critical state. Knowledge of the critical conditions permits very accurate calculations of the interaction parameter g in the free-energy function. In experiments with polystyrene–cyclohexane, g was found to depend on the concentration. The value of g and its concentration dependence agree very well with the results of osmotic measurements by Rehage and Palmen. In experiments with polyethylene–diphenyl ether, g proved to be independent of concentration in the range of measurement. The temperature function was found to be: g = ?0.6086 + 482.2/T (at 137–148°C.). Gibbs' expressions for the critical conditions were worked out for a free-energy relation in the form of an extended Flory-Huggins function.     

Click chemistry in materials synthesis. II. Acid‐swellable crosslinked polymers made by copper‐catalyzed azide–alkyne cycloaddition

A highly crosslinked hyperbranched polymer that rapidly swells and shrinks in a halogenated solvent in response to the addition of an acid or base has been prepared by Cu(I) catalysis of the reaction between a diazide and an amine‐containing trialkyne. The triazole linkages in the polymer are highly stable and may also play a role in the swelling behavior. The swelling–deswelling process is reversible. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5513–5518, 2006     

Kinetics of the diels–alder addition of ethene to cyclohexa-1,3-diene and its reverse reaction in the gas phase

The addition of ethene to cyclohexa-1,3-diene has been studied between 466 and 591 K at pressures ranging from 27 to 119 torr for ethene and 10 to 74 torr for cyclohexa-1,3-diene. The reaction is of the “Diels–Alder” type and leads to the formation of bicyclo[2.2.2]oct-2-ene. It is homogeneous and first order with respect to each reagent. The rate constant (in l./mol sec) is given by The retron-Diels–Alder pyrolysis of bicyclo[2.2.2]oct-2-ene has also been studied. In the ranges of 548–632 K and 4–21 torr the reaction is first order, and its rate constant (in sec^?1) is given by The reaction mechanism is discussed. The heat of formation and the entropy of bicyclo[2.2.2]oct-2-ene are estimated.     

A rheological and spectroscopic study on the kinetics of self‐healing in a single‐component diels–alder copolymer and its underlying chemical reaction

In this work, pendant groups with both furan and maleimide moieties were incorporated into a polymethacrylate copolymer with lauryl methacrylate as comonomer to yield a one‐system Diels–Alder (DA) polymer. A combined Fourier transform infrared (FTIR) spectroscopy and rheological study was performed to quantify the extent of the reversible DA reaction and the resulting changes in mechanical properties of the polymer. The kinetics of the retro‐Diels–Alder (rDA) reaction was studied at different temperatures to determine an enthalpy of activation. Control polymers with only one functional moiety, that is, the furan or maleimide, were also synthesized to study the differences in viscoelastic behavior and the absence of self‐healing. Microscratch tests were performed to obtain information about the disappearance of well‐defined intentional surface scratches under different healing conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1669–1675     

Magnesium chloride supported high mileage catalyst for olefin polymerization. VII. Determinations of concentrations of titanium–polymer and aluminum–polymer bonds

Two methods were used in an attempt to determine by radioquenching the active site concentration, [Ti*], in a MgCl₂ supported high activity catalyst. For the reactions of tritium labelled methanol, the kinetic isotope effects were first determined: k_H/k_T = 1.63 for the total polymer and 1.67 for the isotactic polypropylene fraction. Polymerizations were quenched with an excess of isotopic CH₃OH after various lengths of time, at different A/T (amount of AlEt₃ with 0.33 equivalent of methyl-p-toluate to amount of Ti in the catalyst) ratios, and temperatures. From the known specific activity of tritium in CH₃OH and radioassay of the polymer, value of the total metal polymer bond, [MPB], can be obtained. [MPB] increases linearly with polymerization time. Extrapolation to t = 0 gives [MPB]₀, which should be close to [Ti*] because chain transfer with aluminum alkyls to produce Al–P bonds is negligible during very early stage of the polymerization. The values of [MPB]₀ range from 7–30% of the total Ti; the number of MPB is nearly equally distributed in the amorphous and isotactic fractions of polypropylene in most runs. The rate of incorporation of radioactive CO into polymers produced by the MgCl₂ supported high mileage catalyst is far slower than that claimed by some investigators for TiCl₃ type catalysts. There is an initial rapid phase of incorporation of CO which lasts for about 1 hr of contact time. The subsequent rate of CO incorporation steadily declines, yet there is no constant maximum value of radioactivity even after 48 h of reaction in the absence of monomer. Radioquenching of polymerizations with CO was also performed at several temperatures and A/T ratios. In all cases, the maximum [Ti–P] was reached after 30–40 min of polymerization, whereas the maximum rates of polymerization, R_p,m, occurred within 3–10 min. In fact, the rate of polymerization decays to a small fraction of R_p,m after 30–40 min. Furthermore, this maximum value of [Ti–P] remains constant until the end of polymerization (t = 90 min). Therefore, isotopic CO is not reacting with the initially formed active sites Ti₁*, but only with those sites, Ti₂*, which predominate during the later stage of polymerization.     

Reversible addition–fragmentation chain‐transfer graft polymerization of styrene: Solid phases for organic and peptide synthesis

The γ‐initiated reversible addition–fragmentation chain‐transfer (RAFT)‐agent‐mediated free‐radical graft polymerization of styrene onto a polypropylene solid phase has been performed with cumyl phenyldithioacetate (CPDA). The initial CPDA concentrations range between 1 × 10^?2 and 2 × 10^?3 mol L^?1 with dose rates of 0.18, 0.08, 0.07, 0.05, and 0.03 kGy h^?1. The RAFT graft polymerization is compared with the conventional free‐radical graft polymerization of styrene onto polypropylene. Both processes show two distinct regimes of grafting: (1) the grafting layer regime, in which the surface is not yet totally covered with polymer chains, and (2) a regime in which a second polymer layer is formed. Here, we hypothesize that the surface is totally covered with polymer chains and that new polymer chains are started by polystyrene radicals from already grafted chains. The grafting ratio of the RAFT‐agent‐mediated process is controlled via the initial CPDA concentration. The molecular weight of the polystyrene from the solution (PS_free) shows a linear behavior with conversion and has a low polydispersity index. Furthermore, the loading of the grafted solid phase shows a linear relationship with the molecular weight of PS_free for both regimes. Regime 2 has a higher loading capacity per molecular weight than regime 1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4180–4192, 2002     

Synthesis,characterization, and diels–alder extension of cyclopentadiene telechelic polyisobutylene. IV. α,ω-Di(3-cyclopentadienylpropyldimethylsilyl)polyisobutylene

The synthesis and chain extension of polyisobutylene having nonfluxional terminal cyclopentadiene groups is described. The fluxional behavior of silylcyclopentadiene end groups was previously found to prevent Diels–Alder dimerization of the end groups. The incorporation of a propyl moiety between the silicon atom and the cyclopentadiene ring was found to prevent this fluxional isomerization. Polyisobutylene was synthesized having 3-cyclopentadienylpropyldimethylsilyl end groups with a functionality near 2.0. While thermal extension at 80°C resulted in threefold molecular weight increase, coupling with bisdienophiles yielded greater than tenfold molecular weight increases. The retro-Diels–Alder reaction of coupled end groups prevents the attainment of high-molecular-weight polymers at equilibrium.     

In situ polymerization and morphology of polypyrrole obtained in water‐soluble polymer templates

Several water‐soluble polymers were used as templates for the in situ polymerization of pyrrole to determine their effect on the generation of nanosized polypyrrole (PPy) particles. The polymers used include: polyvinyl alcohol (PVA), polyethylene oxide (PEO), poly(vinyl butyral), polystyrene sulfonic acid, poly(ethylene‐alt‐maleic anhydride) (PEMA), poly(octadecene‐alt‐maleic anhydride), poly(N‐vinyl pyrrolidone), poly(vinyl butyral‐co‐vinyl alcohol‐co‐vinyl acetate), poly(N‐isopropyl acrylamide), poly(ethylene oxide‐block‐propylene oxide), hydroxypropyl methyl cellulose, and guar gum. The oxidative polymerization of pyrrole was carried out with FeCl₃ as an oxidant. The morphology of PPy particles obtained after drying the resulting aqueous dispersions was examined by optical microscopy, and selected samples were further analyzed via atomic force microscopy. Among the template polymers, PVA was the most efficient in generating stable dispersions of PPy nanospheres in water, followed by PEO and PEMA. The average size of PPy nanospheres was in the range of 160 nm and found to depend on the molecular weight and concentration of PVA. Model reactions and kinetics of the polymerization reaction of pyrrole in PVA were carried out by hydrogen ¹H NMR spectroscopy using ammonium persulfate as an oxidant. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ethylene polymerization reactions with Ziegler–Natta catalysts. II. Ethylene polymerization reactions in the presence of deuterium

Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit several features which differentiate them from polymerization reactions of α-olefins: a relatively low ethylene reactivity, higher polymerization rates in the presence of α-olefins, a high reaction order with respect to ethylene concentration, and strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions (see ref. 1 ) provided the basis for a new reaction scheme which explains all these features by postulating the equilibrium formation of a Ti C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts that the β-agostically stabilized Ti C₂H₅ groups can decompose in the β-hydride elimination reaction with expulsion of ethylene and the formation of a Ti H bond even in the absence of hydrogen in the reaction medium. If D₂ is used as a chain transfer agent instead of H₂, the mechanism predicts the formation of deuterated ethylene molecules, which copolymerize with protioethylene. To prove this prediction, several ethylene homopolymerization reactions were carried out with a supported Ziegler–Natta titanium-based catalyst in the presence of large amounts of D₂. Analysis of gaseous reaction products and polymers confirmed the formation of several types of deuterated ethylene molecules and protio/deuterioethylene copolymers, respectively. In contrast, a metallocene catalyst, Cp₂ZrCl₂ MAO, does not exhibit these kinetic features. In the presence of deuterium, it produces only DCH₂ CH₂ (CH₂ CH₂)_x CH₂ CH₂D molecules. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4273–4280, 1999     

Heterogeneous azide–alkyne cycloaddition in the presence of a copper catalyst supported on an ionic liquid polymer/silica hybrid material

Heterogeneous copper catalysts were prepared by the deposition of CuI on a hybrid material consisting of silica and a polymer with imidazolium moieties. The solid materials were characterised using solid‐phase NMR, Fourier transform infrared, Raman and X‐ray photoelectron spectroscopies and Brunauer–Emmett–Teller measurements. The formation of copper–carbene complexes was proved from Raman spectra and the results were supported by density functional theory calculations. The catalyst could be recycled efficiently with low loss of copper. Metal leaching was proved to be facilitated by the use of conditions typical for a homogeneous system (the presence of a polar solvent or the addition of a tertiary amine). Besides simple model reactions, the best catalyst was found to be suitable for the synthesis of triazoles of more elaborate structure, such as ferrocene or steroid derivatives.     

Solid state NMR characterization of formation of poly(ϵ‐caprolactone)/maghnite nanocomposites by in situ polymerization

Results of multinuclear MAS NMR spectroscopy are reported for poly (ε‐caprolactone)/maghnite nanocomposite formation, with ε‐caprolactone in situ polymerized in the presence of maghnite, a proton exchanged montmorillonite clay. Exfoliated and intercalated materials with different maghnite loading in the range 3–15 wt % were investigated. ¹H NMR evidences Brønsted acid hydroxyl groups in the silicate layers and shows that their broad signal at 7.6 ppm present in the parent clay disappears in the nanocomposite material. ²⁷Al MAS NMR results show that beside the hexacoordinated aluminum signal, two additional peaks corresponding to two different tetrahedral Al sites are present in the clay framework. The NMR signal intensity of only one of them was found to be affected in the nanocomposites compared with the parent maghnite, suggesting that these specific aluminum sites are the reactive ones at the initial stages of the polymerization. However almost no changes occurred in the ²⁹Si NMR spectra, confirming that the polymer grafting, as indicated earlier by atomic force microscopy, took place on the aluminum tetracoordinated sites rather than on the silicon sites. A mechanism of maghnite surface catalyzed polymerization of ε‐caprolactone was proposed, involving Brønsted and Lewis acid sites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3060–3068, 2007