Cyclopentadiene‐functionalized polyketone as self‐cross‐linking thermo‐reversible thermoset with increased softening temperature

Self‐cross‐linkable thermo‐reversible thermosets were obtained by a two‐steps post‐functionalization of aliphatic alternating polyketones yielding two different cyclopentadiene functionalization degree of 9 and 22% (with the respect of initial 1,4‐dicarbonyl units). Thermo‐reversibility was verified by gelation experiments and differential scanning calorimetry (DSC) scans displayed a broad transition varying from 75–100°C till 160°C that can be related to retro‐Diels Alder de‐bonding of the dicyclopentadienyl moieties. The dynamic mechanical thermal (DMTA) analysis showed the complete thermo‐mechanical recovery of the material up to six thermal cycles with a softening temperature around 210°C, thereby ensuring a suitable application window for high‐temperature resistant thermosets. Independently of the exact mechanism at the molecular level and in addition to previous studies which used the same Diels‐Alder diene‐dienophile system, it must be noticed that all prepared materials retained their mechanical behavior during at least six consecutive thermal cycles, thus indicating the re‐workability of the system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42924.     

Diels–Alder reaction in water for the straightforward preparation of thermoresponsive hydrogels

Because the properties and applications of hydrogels are determined by the formation principle and conditions of the hydrogels, novel methods for preparing hydrogels have increasingly triggered scientists' interest. Here the Diels–Alder reaction was applied to the preparation of hydrogels. For the resultant polymeric diene and dienophile, the Diels–Alder reaction could be performed in water. The gelation time was found to be closely related to the temperature. The gelation time decreased with the temperature increasing. Moreover, the hydrogels were stable in water, and the retro‐Diels–Alder reaction could be performed in N,N‐dimethylformamide easily. A study of the swelling ratio indicated that the hydrogels were responsive to the temperature. The hydrogel formation method described here provides several advantages, such as mild reaction conditions, no initiator or catalyst, a tunable gelation rate, and thermal reversibility, and it has great potential for the preparation of biomaterials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and polymerization of anthracene‐based itaconimides

Two new anthracene‐based itaconimides, ie N‐(1‐ and 2‐anthryl) itaconimides, were synthesized by the reaction of aromatic amines with itaconic anhydride, followed by itaconamic acid imidization. The same reaction failed in the case of anthracene‐ring substitution at the position 9′. Radical and thermal polymerization of N‐(1‐ and 2‐anthryl) itaconimides led to polymers with anthracene pendant groups. No self‐polymerization by Diels–Alder cycloaddition of the itaconic function (dienophile) and anthracene nucleus (diene) was observed, as is the case for N‐(anthryl) maleimides and citraconimides. Copyright © 2004 Society of Chemical Industry     

Epoxy‐amine based thermoresponsive networks designed by Diels–Alder reactions

The synthesis of Diels–Alder (DA) adducts from stoichiometric quantities of a new multi‐maleimide dienophile and epoxy‐amine type oligomers bearing furan group units on their side chains was investigated. Precursors of the DA reaction were first synthesized and their functionalities were determined by ¹H NMR and gel permeation chromatography/SEC analysis. TGA and DSC were used to characterize their thermal properties. In this study, the effect of the multi‐furan diene functionality on the network density was analyzed. Rheological analysis was used to highlight the thermal reversibility of the DA reaction and to calculate the average molar weight between crosslinks. The results showed that network density could be regulated or modulated by varying the functionality of the diene. Copyright © 2012 Society of Chemical Industry     

Two‐Step Labeling of Endogenous Enzymatic Activities by Diels–Alder Ligation

A ligation strategy based on the Diels–Alder [4+2] cycloaddition for the two‐step activity‐based labeling of endogenously expressed enzymes in complex biological samples has been developed. A panel of four diene‐derivatized proteasome probes was synthesized, along with a dienophile‐functionalized BODIPY(TMR) tag. These probes were applied in a Diels–Alder labeling procedure that enabled us to label active proteasome β‐subunits selectively in cellular extracts and in living cells. We were also able to label the activity of cysteine proteases in cell extracts by utilizing a diene‐derivatized cathepsin probe. Importantly, the Diels–Alder strategy described here is fully orthogonal with respect to the Staudinger–Bertozzi ligation, as demonstrated by the independent labeling of different proteolytic activities by the two methods in a single experiment.     

Retro‐Diels–Alder Reactions of Masked Cyclopentadienones Catalyzed by Heterogeneous Brønsted Acids

The zeolite H‐Beta catalyzes the retro‐Diels–Alder reaction of a range of cyclopentadiene cyclo‐adducts at moderate temperatures and ambient pressure, in the presence of an active dienophile. The active catalyst was identified and optimum reaction conditions established after screening a range of zeolites in the retro‐Diels–Alder reaction of the cyclopentadiene adduct of cyclopentenone. Our results suggest that retro‐Diels–Alder reactions of tricyclodecadienones are catalyzed by Brønsted acids and the high catalytic performance of H‐Beta catalysts can be ascribed to the optimal balance between the number of acid sites and their strength as well as to the accessibility of these sites. The methodology was then applied to a series of alkyl derivatives of cyclopentadienylcyclopentenones to provide a viable alternative synthetic route to 4‐alkylcyclopentenones and the versatility of the approach was demonstrated by the successful cycloreversion of N‐cyclohexyl‐2‐azanorborn‐5‐ene.     

High‐performance bio‐based thermosetting resins composed of dehydrated castor oil and bismaleimide

The reaction of dehydrated castor oil (DCO) and 1,1′‐(methylenedi‐4,1‐phenylene)bismaleimide (BMI) in 1,3‐dimethyl‐2‐imidazolidinone (DMI) at 130°C for 6 h and subsequent precipitation gave DCO/BMI prepolymer, which was cured at 200°C for 2 h gave DCO/BMI cured product. The FE‐SEM analysis revealed that the cured products with C?C ratio 2/1 and 1/1 are homogeneous, whereas phase separation occurs for the 1/2 product. The glass transition temperature, 5% weight loss temperature, and tensile modulus of the cured DCO/BMI increased with increasing BMI content. Regarding the tensile strength, the cured DCO/BMI 1/1 product showed the highest value. To evaluate the reaction of DCO and BMI, the model reaction products of DCO and N‐phenylmaleimide (PMI) in DMI were analyzed by ¹H NMR spectroscopy. The ¹H NMR data of DCO revealed that DCO has about 4.8 CH?CH bonds per triglyceride and that the ratio of conjugated and nonconjugated diene moieties is about 41/59. The NMR data of the reaction products of DCO/PMI with the C?C ratio 2/1 and 1/1 at 200°C for 24 h revealed that both Diels–Alder and ene reactions occurs in addition to radical polymerization. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

No Evidence Found for Diels–Alder Reaction Products in Soybean Oil Oxidized at the Frying Temperature by NMR Study

It has been generally accepted that the Diels–Alder reaction mechanism is one of the major reaction mechanisms to produce dimers and polymers during heating process of vegetable oil. Soybean oil oxidized at 180 °C for 24 h with 1.45 surface area-to-volume ratio showed 36 % polymer peak area in gel permeation chromatogram. However, the NMR DEPT (Distortionless Enhancement by Polarization Transfer) 135 spectrum did not show any signals of possible Diels–Alder products. A fraction separated from the oxidized soybean oil by column chromatography contained 98 % polymers, but again, showed no signals of proposed Diels–Alder products in the DEPT 135 spectrum. Methyl oleate and triolein without a diene required for the Diels–Alder reaction produced 27 and 63 % of total polymers, respectively, under the same condition. This indicates that the polymers must be produced by reactions other than the Diels–Alder reaction for these oils. This study shows that the Diels–Alder reaction is not the major reaction to produce polymers during oxidation of soybean oil, within the DEPT 135 spectroscopy sensitivity level, about 5 mol %.     

Synthesis of novel polyimides containing side‐chain azo‐2‐naphthol moieties

An amine‐ester derivative of isoeugenol was prepared in three steps. This amine‐ester was converted to diazonium salt and subsequently was reacted with 2‐naphthol and a novel isoeugenol ester‐azo derivative as a new monomer was obtained in quantitative yield. This monomer was characterized by high‐field ¹H‐NMR, IR, and elemental analysis and then was used for the preparation of model compound and polymerization reactions. 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione was allowed to react with this new monomer. The reaction was very fast and gave only one double adduct by Diels–Alder and ene pathways in excellent yield. The polymerization reactions of novel monomer with bistriazolinediones [bis(p‐3,5‐dioxo‐1,2,4‐triazolin‐4‐ylphenyl)methane and 1,6‐bis(3,5‐dioxo‐1,2,4‐triazolin‐4‐yl)hexane] were carried out in N,N‐dimethylacetamide at room temperature. The reactions were exothermic, fast, and gave novel heterocyclic polyimides by repetitive Diels–Alder‐ene polyaddition reactions. Some structural characterization and physical properties of these novel heterocyclic polyimides are reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1942–1951, 2003     

Superbase‐Catalyzed [4+2] Cycloaddition of Acetylenes to 3,6‐Di(pyrrol‐2‐yl)‐1,2,4,5‐tetrazine: A Facile Synthesis of 3,6‐Di(pyrrol‐2‐yl)pyridazines

Acetylenes undergo the [4+2] cycloaddition to 3,6‐di(pyrrol‐2‐yl)‐1,2,4,5‐tetrazine in the potassium hydroxide/dimethyl sulfoxide or potassium tert‐butoxide/dimethyl sulfoxide systems (80 °C, 2.5–4 h) to afford (after extrusion of the nitrogen molecule from the intermediate) 3,6‐di(pyrrol‐2‐yl)pyridazines in up to 73% yield, while under non‐catalytic conditions this reaction does not take place. This unusual result substantially extends the scope of synthetic application and mechanistic diversity of the Diels–Alder reaction. The step‐wise mechanisms involving the formation of [OH/tetrazine]⁻ or [t‐BuO/tetrazine]⁻ anionic intermediate complexes or cycloaddition of tetrazine to the acetylide anion are considered.     

Reversibly crosslinked self‐healing PCL‐based networks

Poly(ε‐caprolactone) (PCL)‐based thermoreversible networks with self‐healing properties were prepared through Diels–Alder (DA) and retro‐DA reactions. Bis‐ or Tris‐maleimide compounds and a series of copolymer(caprolactone‐diene) PCL_XF_Y (X: degree of polymerization and Y: furan‐average functionality) with Y between 2.4 and 4.9 were used. The successive sequences of formation and dissociation of polycaprolactone networks via DA and retro‐DA reactions were observed repeatedly by dynamic mechanical analyses (DMA) and their gel‐temperatures determined. The cross‐linking densities, thermal properties, and thermal reversibility of the PCL_XF_Y/multimaleimide polymers have been modulated by the structure and functionalities of the used diene and dienophile moieties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polymerization of propylene using the high‐activity Ziegler–Natta catalyst system SiO2/MgCl2 (ethoxide type)/TiCl4/Di‐n‐butyl phthalate/triethylaluminum/dimethoxy methyl cyclohexyl silane

The bisupported Ziegler–Natta catalyst system SiO₂/MgCl₂ (ethoxide type)/TiCl₄/di‐n‐butyl phthalate/triethylaluminum (TEA)/dimethoxy methyl cyclohexyl silane (DMMCHS) was prepared. TEA and di‐n‐butyl phthalate were used as a cocatalyst and an internal donor, respectively. DMMCHS was used as an external donor. The slurry polymerization of propylene was studied with the catalyst system in n‐heptane from 45 to 70°C. The effects of the TEA and H₂ concentrations, temperature, and monomer pressure on the polymerization were investigated. The optimum productivity was obtained at [Al]/[DMMCHS]/[Ti] = 61.7:6.2:1 (mol/mol/mol). The highest activity of the catalyst was obtained at 60°C. Increasing the H₂ concentration to 100 mL/L increased the productivity of the catalyst, but a further increase in H₂ reduced the activity of the catalyst. Increasing the propylene pressure from 1 to 7 bar significantly increased the polymer yield. The isotacticity index (II) decreased with increasing TEA, but the H₂ concentration, temperature, and monomer pressure did not have a significant effect on the II value. The viscosity‐average molecular weight decreased with increasing temperature and with the addition of H₂. Three catalysts with different Mg/Si molar ratios were studied under the optimum conditions. The catalyst with a Mg/Si molar ratio of approximately 0.93 showed the highest activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1177–1181, 2003     

Polymerization of acrylated epoxidized soybean oil with phenol furfural resins via repeated forward and retro diels–alder reactions

In this work, the Diels–Alder reaction between the acrylate groups of acrylated epoxidized soybean oil and the furan rings of p‐tertiary butyl phenol furfural resin (TBPF) is described. The reaction was carried out at 110°C in presence of FeCl₃ catalyst, and tough polymers were obtained in 1 h. Surprisingly, samples that were heated and cooled 5, 10, and 20 times to 140°C and room temperature had better mechanical properties than samples that were kept at 140°C for the same total duration. This unexpected behavior is attributed to a series of forward and retro Diels–Alder reactions between the functional groups. To prove this hypothesis, a model reaction between TBPF and n‐butyl acrylate was studied. At 100°C, ¹H‐nuclear magnetic resonance signals of the furan ring protons disappeared, only to reappear at 140°C. Thermogravimetric analysis of the adduct showed a weight loss at 140–150°C, which was in quantitative agreement with the amount of butyl acrylate. Infrared analysis showed that furan rings were not completely consumed by extended heating at 110°C. After five heating and cooling cycles of much shorter duration at 140°C, the furan absorption in the infrared disappeared. The storage modulus of acrylated epoxidized soybean oil‐TBPF samples after 20 heating cycles was 1.15 GPa. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermally reversible crosslinked polyethylene using Diels–Alder reaction in molten state

Thermally reversible crosslinked polyethylene was prepared by Diels–Alder (DA) and retro Diels–Alder (rDA) reaction. Maleimide/furan adduct was used as crosslinking agent. Dienophile named 11-maleimido-undecanoic acid was first synthesized and between this dienophile and commercial 3-(2-furyl) propanoic acid, the DA reaction was studied to determine DA and rDA reactions temperatures in the solid state. Then, an original modification method was employed to graft the two molecules onto the Lotader® poly(ethylene-co-glycidyl methacrylate) in one step procedure. The DA and rDA reactions between diene and dienophile grafted moieties are followed by FT-IR analysis on a thin film. Readily polymer network is synthesized and the cycle of DA and retro-DA reactions is repeatable with no significant polymer degradation.     

Preparation of copolymer of L‐aspartic acid and L‐glutamic acid

In this article, a new copolymer of L ‐aspartic acid and L ‐glutamic acid, which may be a biodegradable high molecular polymer and can be used more widely in many areas, was synthesized. The conditions of preparation, such as catalyst, reaction time, reaction temperature, the amount of catalyst, the times of adding catalyst, and the molar ratio of L ‐aspartic acid to L ‐glutamic acid, were optimized. The copolymer was characterized by ¹³C NMR, infrared spectroscopy, and X‐ray diffractometer. The molecular weight was determined by GPC. The result indicated that production yield, purity of product, and molecular weight of product increased with amount of catalyst and molar ratio of L ‐aspartic acid to L ‐glutamic acid increasing. The best condition of preparation was the following: reacting 2–4 h at the temperature of 180–200°C. The product yield with the molecular weight 13,000.00 reached 63.2% and the purity of product was 96.33% when the copolymerization was carried out at the temperature of 200°C under vacuum for 2 h. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3626–3633, 2006     

OPTIMIZATION OF LIPASE-CATALYZED SYNTHESIS OF N-trans-FERULOYLTYRAMINE USING RESPONSE SURFACE METHODOLOGY (RSM)

Enzymatic synthesis of N-trans-feruloyltyramine amide was optimized by response surface methodology (RSM) using 4-hydroxy-3-methoxycinnamic acid and tyramine hydrochloride in a one-step lipase catalyzed reaction using Lipozyme TL IM. Response surface methodology (RSM) based on five-level, four-variable central composite rotatable design (CCRD) was used to evaluate the interaction of synthesis, reaction time (24–96 h), temperature (30°–50°C), amount of enzyme (50–500 mg, 12.5–125.0 IUN), and substrate molar ratio (cinnamic acid:tyramine HCl) 1:1–8:1 mmol on the percentage yield of N-trans-feruloyltyramine amide. The optimum conditions derived via RSM were: reaction time 52 h, temperature 43°C, amount of enzyme 260 mg (65.0 IUN), and substrate molar ratio (cinnamic acid:tyramine HCl) 6.2:1. The actual experimental yield was 96.3% under optimum conditions, which compared well to the maximum predicted value of 97.2%.     

Some observations on the copolymerization of styrene with furfuryl methacrylate

The tendency for crosslinking to occur either during free radical polymerization in solution or to develop subsequently in air after precipitation of linear polymer has been observed for both polymerization of furfuryl methacrylate (FM) and copolymerization of FM with styrene (ST). Reactivity ratios r_FM=0.33±0.08 and r_ST=0.44±0.02 have been determined. Thermo-oxidative stability is lowered by incorporation of FM moieties into poly-ST. Glass transition temperatures (T_g) of copolymers accord with the Fox equation and extrapolation affords a value of 64°C for the T_g of linear poly-FM. After admixture of solutions of poly(FM-co-ST) and bismaleimide (BM) at ambient temperature crosslinked gel is produced slowly by intermolecular Diels–Alder reaction between diene units (FM) and the dienophile (BM). The retro Diels–Alder reaction occurs rapidly on heating, regenerating linear copolymer and BM. The crosslinked gels exhibit considerable swelling in chloroform and toluene.     

New Bismaleimide-Silica Hybrid Materials: A Critical Assessment of Properties in Correlation with the Method of Synthesis

New hybrid materials have been prepared by sol–gel technique. They have been obtained from bismaleimide monomers either in reaction with N-(3-triethoxysilylpropyl)furan-2-carboxamide monomer, by a Diels–Alder reaction, or in reaction with (3-aminopropyl)triethoxysilane following a Michael addition reaction. The sol–gel process was conducted with or without adding different amounts of tetraethyl orthosilicate. The structures of the obtained compounds have been confirmed by proton nuclear magnetic resonance and Fourier transform infrared spectroscopy. A comparative study between Diels–Alder- and Michael addition-type products regarding their thermal and mechanical properties was also conducted for samples as obtained from synthesis. The thermoreversible character of the Diels–Alder hybrid materials has been demonstrated with the aids of differential scanning calorimetry and attenuated total reflectance Fourier transform infrared spectroscopy, the results from both methods being in good agreement with each other, and with literature data. The morphology of hybrid materials was studied by the atomic force microscopy, optical microscopy for three different stages: initial (24°C), at heating (150°C), and after cooling at 24°C, and scanning electron microscopy. All data confirmed the driving force for the dispersion of the Si-containing aggregates in the Michael addition series is the dynamic evolution of the sol–gel process, whereas the Diels–Alder series behavior is ruled by the thermoreversible character of the Diels–Alder cycloaddition.     

High-temperature thermoplastic elastomers via the grafting reaction of polyarylate onto EPDM rubber

Polyarylate monofunctionally terminated with a 1,2-dihydrobenzocyclobutene group undergoes thermally initiated grafting reactions onto ethylene/propylene/nonconjugated diene rubber via the Diels—Alder reaction between the diene (benzocyclobutene) and the dienophile (pendant unsaturation on the EPDM). Characterization of the graft copolymer(s) is presented as is the resultant thermoplastic elastomeric mechanical performance exhibited by the graft copolymers. © 1993 John Wiley & Sons, Inc.     

Preparation of SBS/poly(styrene–methyl methacrylate) thermoplastic interpenetrating polymer network

SBS as polymer I, poly(styrene–methyl methacrylate) polymerized by atom transfer radical polymerization as polymer II, and a thermoplastic interpenetrating polymer network of SBS/poly(styrene–methyl methacrylate) were prepared by the sequential method. The effects of the polymerization temperature, the composition of the catalyst, the ratio of the monomers studied, and the kinetics at 90°C were also investigated. It was shown that when polymerization was initiated by a BPO/CuCl/bpy (BPO:CuCl:bpy = 1:1:3) system at 90°C, the mass averaged molecular weight of the poly(styrene–methyl methacrylate) increased with monomer conversion, and the polydispersities were kept very low. Fourier transform infrared spectroscopy and gel permeation chromatogram showed that poly(styrene–methyl methacrylate) with low polydispersities had been synthesized. Thus, a thermoplastic interpenetrating polymer network comprised of both narrow molecular‐weight‐distribution components was successfully prepared. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2007–2011, 2003